YouCompleteMe: a code-completion engine for Vim

Early Warning: Dropping support for Python 2 in 2020

In early 2020, YCM will drop support for Python 2. But we will maintain criticial fixes on a branch (name TBA) of YCM for a period of 1 year.

Why?

Over the past decade, YouCompleteMe has had an at times fractious, but ultimately very successful relationship with Python 2. However, more recently it has been carrying on a simultaneous relationship with Python 3. Indeed all of YCM and ycmd code is Python 3 code, with a lot of gubbins to make it work also on Python 2. This makes the code more complex, requires double testing of everything, and restricts the developers from using certain new langauge features, ultimately restricting the features we can deliver to users.

On 1st January 2020, Python 2 will be officially end of life. And therefore, so will its relationship with YouCompleteMe and ycmd.

Help, Advice, Support

Looking for help, advice or support? Having problems getting YCM to work?

First carefully read the installation instructions for your OS. We recommend you use the supplied install.py.

Next check the User Guide section on the semantic completer that you are using. For C/C++/Objective-C/Objective-C++/CUDA, you must read this section.

Finally, check the FAQ.

If, after reading the installation and user guides, and checking the FAQ, you're still having trouble, check the contacts section below for how to get in touch.

Please do NOT go to #vim on freenode for support. Please contact the YouCompleteMe maintainers directly using the contact details below.

Intro

YouCompleteMe is a fast, as-you-type, fuzzy-search code completion engine for Vim. It has several completion engines:

an identifier-based engine that works with every programming language,
a Clang-based engine that provides native semantic code completion for C/C++/Objective-C/Objective-C++/CUDA (from now on referred to as "the C-family languages"),
a powerful clangd-based completion engine for the C-family languages.
a Jedi-based completion engine for Python 2 and 3,
an OmniSharp-Roslyn-based completion engine for C#,
a Gopls-based completion engine for Go,
a TSServer-based completion engine for JavaScript and TypeScript,
a rls-based completion engine for Rust,
a jdt.ls-based experimental completion engine for Java.
a generic Language Server Protocol implementation for any language
and an omnifunc-based completer that uses data from Vim's omnicomplete system to provide semantic completions for many other languages (Ruby, PHP etc.).

Here's an explanation of what happens in the short GIF demo above.

First, realize that no keyboard shortcuts had to be pressed to get the list of completion candidates at any point in the demo. The user just types and the suggestions pop up by themselves. If the user doesn't find the completion suggestions relevant and/or just wants to type, they can do so; the completion engine will not interfere.

When the user sees a useful completion string being offered, they press the TAB key to accept it. This inserts the completion string. Repeated presses of the TAB key cycle through the offered completions.

If the offered completions are not relevant enough, the user can continue typing to further filter out unwanted completions.

A critical thing to notice is that the completion filtering is NOT based on the input being a string prefix of the completion (but that works too). The input needs to be a subsequence match of a completion. This is a fancy way of saying that any input characters need to be present in a completion string in the order in which they appear in the input. So abc is a subsequence of xaybgc, but not of xbyxaxxc. After the filter, a complicated sorting system ranks the completion strings so that the most relevant ones rise to the top of the menu (so you usually need to press TAB just once).

All of the above works with any programming language because of the identifier-based completion engine. It collects all of the identifiers in the current file and other files you visit (and your tags files) and searches them when you type (identifiers are put into per-filetype groups).

The demo also shows the semantic engine in use. When the user presses ., -> or :: while typing in insert mode (for C++; different triggers are used for other languages), the semantic engine is triggered (it can also be triggered with a keyboard shortcut; see the rest of the docs).

The last thing that you can see in the demo is YCM's diagnostic display features (the little red X that shows up in the left gutter; inspired by Syntastic) if you are editing a C-family file. As the completer engine compiles your file and detects warnings or errors, they will be presented in various ways. You don't need to save your file or press any keyboard shortcut to trigger this, it "just happens" in the background.

In essence, YCM obsoletes the following Vim plugins because it has all of their features plus extra:

clang_complete
AutoComplPop
Supertab
neocomplcache

And that's not all...

YCM also provides semantic IDE-like features in a number of languages, including:

displaying signature help (argument hints) when entering the arguments to a function call
finding declarations, definitions, usages, etc. of identifiers,
displaying type information for classes, variables, functions etc.,
displaying documentation for methods, members, etc. in the preview window,
fixing common coding errors, like missing semi-colons, typos, etc.,
semantic renaming of variables across files,
formatting code,
removing unused imports, sorting imports, etc.

For example, here's a demo of signature help:

Features vary by file type, so make sure to check out the file type feature summary and the full list of completer subcommands to find out what's available for your favourite languages.

You'll also find that YCM has filepath completers (try typing ./ in a file) and a completer that integrates with UltiSnips.

Installation

macOS

These instructions (using install.py) are the quickest way to install YouCompleteMe, however they may not work for everyone. If the following instructions don't work for you, check out the full installation guide.

MacVim is required. YCM won't work with the pre-installed Vim from Apple as its Python support is broken. If you don't already use MacVim, install it with Homebrew. Install CMake as well:

brew install cmake macvim

Install YouCompleteMe with Vundle.

Remember: YCM is a plugin with a compiled component. If you update YCM using Vundle and the ycm_core library APIs have changed (happens rarely), YCM will notify you to recompile it. You should then rerun the install process.

NOTE: If you want C-family completion, you MUST have the latest Xcode installed along with the latest Command Line Tools (they are installed automatically when you run clang for the first time, or manually by running xcode-select --install)

Compiling YCM with semantic support for C-family languages through libclang:

cd ~/.vim/bundle/YouCompleteMe
./install.py --clang-completer

Compiling YCM with semantic support for C-family languages through clangd:

cd ~/.vim/bundle/YouCompleteMe
./install.py --clangd-completer

Note that you can install YCM with both libclang and clangd enabled. In that case clangd will be preferred unless you have the following in your vimrc:

let g:ycm_use_clangd = 0

Compiling YCM without semantic support for C-family languages:

cd ~/.vim/bundle/YouCompleteMe
./install.py

The following additional language support options are available:

C# support: install Mono with Homebrew or by downloading the Mono macOS package and add --cs-completer when calling install.py.
Go support: install Go and add --go-completer when calling install.py.
JavaScript and TypeScript support: install Node.js and npm and add --ts-completer when calling install.py.
Rust support: add --rust-completer when calling install.py.
- If your Python interpreter is older than 2.7.9, you will also need rustup in your PATH.
Java support: install JDK8 (version 8 required) and add --java-completer when calling install.py.

To simply compile with everything enabled, there's a --all flag. Note that this flag does not install clangd. You need to specify it manually by adding --clangd-completer. So, to install with all language features, ensure xbuild, go, tsserver, node and npm tools are installed and in your PATH, then simply run:

cd ~/.vim/bundle/YouCompleteMe
./install.py --all

That's it. You're done. Refer to the User Guide section on how to use YCM. Don't forget that if you want the C-family semantic completion engine to work, you will need to provide the compilation flags for your project to YCM. It's all in the User Guide.

YCM comes with sane defaults for its options, but you still may want to take a look at what's available for configuration. There are a few interesting options that are conservatively turned off by default that you may want to turn on.

Linux 64-bit

These instructions (using install.py) are the quickest way to install YouCompleteMe, however they may not work for everyone. If the following instructions don't work for you, check out the full installation guide.

Make sure you have Vim 7.4.1578 with Python 2 or Python 3 support. The Vim package on Fedora 27 and later and the pre-installed Vim on Ubuntu 16.04 and later are recent enough. You can see the version of Vim installed by running vim --version. If the version is too old, you may need to compile Vim from source (don't worry, it's easy).

NOTE: For all features, such as signature help, use Vim 8.1.1875 or later.

Install YouCompleteMe with Vundle.

Remember: YCM is a plugin with a compiled component. If you update YCM using Vundle and the ycm_core library APIs have changed (happens rarely), YCM will notify you to recompile it. You should then rerun the install process.

Install development tools, CMake, and Python headers:

Fedora 27 and later:

sudo dnf install cmake gcc-c++ make python3-devel

Ubuntu 14.04:

sudo apt install build-essential cmake3 python3-dev

Ubuntu 16.04 and later:

sudo apt install build-essential cmake python3-dev

Compiling YCM with semantic support for C-family languages through libclang:

cd ~/.vim/bundle/YouCompleteMe
python3 install.py --clang-completer

Compiling YCM with semantic support for C-family languages through clangd:

cd ~/.vim/bundle/YouCompleteMe
python3 install.py --clangd-completer

Note that you can install YCM with both libclang and clangd enabled. In that case clangd will be preferred unless you have the following in your vimrc:

let g:ycm_use_clangd = 0

Compiling YCM without semantic support for C-family languages:

cd ~/.vim/bundle/YouCompleteMe
python3 install.py

The following additional language support options are available:

C# support: install Mono and add --cs-completer when calling install.py.
Go support: install Go and add --go-completer when calling install.py.
JavaScript and TypeScript support: install Node.js and npm and add --ts-completer when calling install.py.
Rust support: add --rust-completer when calling install.py.
- If your Python interpreter is older than 2.7.9, you will also need rustup in your PATH.
Java support: install JDK8 (version 8 required) and add --java-completer when calling install.py.

To simply compile with everything enabled, there's a --all flag. Note that this flag does not install clangd. You need to specify it manually by adding --clangd-completer. So, to install with all language features, ensure xbuild, go, tsserver, node, npm and tools are installed and in your PATH, then simply run:

cd ~/.vim/bundle/YouCompleteMe
python3 install.py --all

That's it. You're done. Refer to the User Guide section on how to use YCM. Don't forget that if you want the C-family semantic completion engine to work, you will need to provide the compilation flags for your project to YCM. It's all in the User Guide.

YCM comes with sane defaults for its options, but you still may want to take a look at what's available for configuration. There are a few interesting options that are conservatively turned off by default that you may want to turn on.

Windows

These instructions (using install.py) are the quickest way to install YouCompleteMe, however they may not work for everyone. If the following instructions don't work for you, check out the full installation guide.

Important: we assume that you are using the cmd.exe command prompt and that you know how to add an executable to the PATH environment variable.

Make sure you have at least Vim 7.4.1578 with Python 2 or Python 3 support. You can check the version and which Python is supported by typing :version inside Vim. Look at the features included: +python/dyn for Python 2 and +python3/dyn for Python 3. Take note of the Vim architecture, i.e. 32 or 64-bit. It will be important when choosing the Python installer. We recommend using a 64-bit client. Daily updated installers of 32-bit and 64-bit Vim with Python 2 and Python 3 support are available.

NOTE: For all features, such as signature help, use Vim 8.1.1875 or later.

Add the line:

set encoding=utf-8

to your vimrc if not already present. This option is required by YCM. Note that it does not prevent you from editing a file in another encoding than UTF-8. You can do that by specifying the ++enc argument to the :e command.

Install YouCompleteMe with Vundle.

Remember: YCM is a plugin with a compiled component. If you update YCM using Vundle and the ycm_core library APIs have changed (happens rarely), YCM will notify you to recompile it. You should then rerun the install process.

Download and install the following software:

Python 2 or Python 3. Be sure to pick the version corresponding to your Vim architecture. It is Windows x86 for a 32-bit Vim and Windows x86-64 for a 64-bit Vim. We recommend installing Python 3. Additionally, the version of Python you install must match up exactly with the version of Python that Vim is looking for. Type :version and look at the bottom of the page at the list of compiler flags. Look for flags that look similar to -DDYNAMIC_PYTHON_DLL=\"python27.dll\" and -DDYNAMIC_PYTHON3_DLL=\"python35.dll\". The former indicates that Vim is looking for Python 2.7 and the latter indicates that Vim is looking for Python 3.5. You'll need one or the other installed, matching the version number exactly.
CMake. Add CMake executable to the PATH environment variable.
Visual Studio Build Tools 2017. During setup, select Visual C++ build tools in Workloads.

Compiling YCM with semantic support for C-family languages through libclang:

cd %USERPROFILE%/vimfiles/bundle/YouCompleteMe
python install.py --clang-completer

Compiling YCM with semantic support for C-family languages through clangd:

cd %USERPROFILE%/vimfiles/bundle/YouCompleteMe
python install.py --clangd-completer

Note that you can install YCM with both libclang and clangd enabled. In that case clangd will be preferred unless you have the following in your vimrc:

let g:ycm_use_clangd = 0

Compiling YCM without semantic support for C-family languages:

cd %USERPROFILE%/vimfiles/bundle/YouCompleteMe
python install.py

The following additional language support options are available:

C# support: add --cs-completer when calling install.py. Be sure that the build utility msbuild is in your PATH.
Go support: install Go and add --go-completer when calling install.py.
JavaScript and TypeScript support: install Node.js and npm and add --ts-completer when calling install.py.
Rust support: add --rust-completer when calling install.py.
- If your Python interpreter is older than 2.7.9, you will also need rustup in your PATH.
Java support: install JDK8 (version 8 required) and add --java-completer when calling install.py.

To simply compile with everything enabled, there's a --all flag. Note that this flag does not install clangd. You need to specify it manually by adding --clangd-completer. So, to install with all language features, ensure msbuild, go, tsserver, node and npm tools are installed and in your PATH, then simply run:

cd %USERPROFILE%/vimfiles/bundle/YouCompleteMe
python install.py --all

You can specify the Microsoft Visual C++ (MSVC) version using the --msvc option. YCM officially supports MSVC 14 (Visual Studio 2015) and 15 (2017).

That's it. You're done. Refer to the User Guide section on how to use YCM. Don't forget that if you want the C-family semantic completion engine to work, you will need to provide the compilation flags for your project to YCM. It's all in the User Guide.

YCM comes with sane defaults for its options, but you still may want to take a look at what's available for configuration. There are a few interesting options that are conservatively turned off by default that you may want to turn on.

FreeBSD/OpenBSD

These instructions (using install.py) are the quickest way to install YouCompleteMe, however they may not work for everyone. If the following instructions don't work for you, check out the full installation guide.

NOTE: OpenBSD / FreeBSD are not officially supported platforms by YCM.

Make sure you have Vim 7.4.1578 with Python 2 or Python 3 support.

NOTE: For all features, such as signature help, use Vim 8.1.1875 or later.

OpenBSD 5.5 and later have a Vim that's recent enough. You can see the version of Vim installed by running vim --version.

For FreeBSD 11.x, the requirement is cmake:

pkg install cmake

Install YouCompleteMe with Vundle.

Remember: YCM is a plugin with a compiled component. If you update YCM using Vundle and the ycm_core library APIs have changed (happens rarely), YCM will notify you to recompile it. You should then rerun the install process.

Compiling YCM with semantic support for C-family languages through libclang:

cd ~/.vim/bundle/YouCompleteMe
./install.py --clang-completer

Compiling YCM with semantic support for C-family languages through clangd:

cd ~/.vim/bundle/YouCompleteMe
./install.py --clangd-completer

Note that you can install YCM with both libclang and clangd enabled. In that case clangd will be preferred unless you have the following in your vimrc:

let g:ycm_use_clangd = 0

Compiling YCM without semantic support for C-family languages:

cd ~/.vim/bundle/YouCompleteMe
./install.py

If the python executable is not present, or the default python is not the one that should be compiled against, specify the python interpreter explicitly:

python3 install.py --clang-completer

The following additional language support options are available:

C# support: install Mono and add --cs-completer when calling ./install.py.
Go support: install Go and add --go-completer when calling ./install.py.
JavaScript and TypeScript support: install Node.js and npm and add --ts-completer when calling install.py.
Rust support: add --rust-completer when calling ./install.py.
- If your Python interpreter is older than 2.7.9, you will also need rustup in your PATH.
Java support: install JDK8 (version 8 required) and add --java-completer when calling ./install.py.

To simply compile with everything enabled, there's a --all flag. Note that this flag does not install clangd. You need to specify it manually by adding --clangd-completer. So, to install with all language features, ensure xbuild, go, tsserver, node, npm and tools are installed and in your PATH, then simply run:

cd ~/.vim/bundle/YouCompleteMe
./install.py --all

That's it. You're done. Refer to the User Guide section on how to use YCM. Don't forget that if you want the C-family semantic completion engine to work, you will need to provide the compilation flags for your project to YCM. It's all in the User Guide.

YCM comes with sane defaults for its options, but you still may want to take a look at what's available for configuration. There are a few interesting options that are conservatively turned off by default that you may want to turn on.

Full Installation Guide

These are the steps necessary to get YCM working on a Unix OS and on Windows.

Note to Windows users: we assume that you are running the cmd.exe command prompt and that the needed executables are in the PATH environment variable. Do not just copy the shell commands. Replace ~ by %USERPROFILE% in them and use the right Vim home directory. It should be vimfiles by default instead of .vim.

See the FAQ if you have any issues.

Remember: YCM is a plugin with a compiled component. If you update YCM using Vundle and the ycm_core library APIs have changed (happens rarely), YCM will notify you to recompile it. You should then rerun the install process.

Please follow the instructions carefully. Read EVERY WORD.

Ensure that your version of Vim is at least 7.4.1578 and that it has support for Python 2 or Python 3 scripting.

Inside Vim, type :version. Look at the first two to three lines of output; it should say Vi IMproved X.Y, where X.Y is the major version of vim. If your version is greater than 7.4, then you're all set. If your version is 7.4 then look below that where it says, Included patches: 1-Z, where Z will be some number. That number needs to be 1578 or higher.

If your version of Vim is not recent enough, you may need to compile Vim from source (don't worry, it's easy).

After you have made sure that you have Vim 7.4.1578+, type the following in Vim: :echo has('python') || has('python3'). The output should be 1. If it's 0, then get a version of Vim with Python support.

NOTE: For all features, such as signature help, use Vim 8.1.1875 or later.

On Windows, check also if your Vim architecture is 32 or 64-bit. This is critical because it must match the Python and the YCM libraries architectures. We recommend using a 64-bit Vim.
Install YCM with Vundle (or Pathogen, but Vundle is a better idea). With Vundle, this would mean adding a Plugin 'Valloric/YouCompleteMe' line to your vimrc.

If you don't install YCM with Vundle, make sure you have run git submodule update --init --recursive after checking out the YCM repository (Vundle will do this for you) to fetch YCM's dependencies.
Complete this step ONLY if you care about semantic completion support for C-family languages. Otherwise it's not necessary.

Download the latest version of libclang. Clang is an open-source compiler that can compile C-family languages. The libclang library it provides is used to power the YCM semantic completion engine for those languages. YCM is designed to work with libclang version 9.0.0 or higher.

In addition to libclang, YCM also supports a clangd-based completer. You can download the latest version of clangd from llvm.org releases. Follow Step 4 to learn how to tell YCM where to find clangd binary. Please note that YCM is designed to work with clangd version 9.0.0 or higher.

You can use the system libclang or clangd only if you are sure it is version 9.0.0 or higher, otherwise don't. Even if it is, we recommend using the official binaries from llvm.org if at all possible. Make sure you download the correct archive file for your OS.

We STRONGLY recommend AGAINST use of the system libclang or clangd instead of the upstream compiled binaries. Random things may break. Save yourself the hassle and use the upstream pre-built libclang or clangd.
Compile the ycm_core library that YCM needs. This library is the C++ engine that YCM uses to get fast completions.

You will need to have cmake installed in order to generate the required makefiles. Linux users can install cmake with their package manager (sudo apt-get install cmake for Ubuntu) whereas other users can download and install cmake from its project site. macOS users can also get it through Homebrew with brew install cmake.

On a Unix OS, you need to make sure you have Python headers installed. On a Debian-like Linux distro, this would be sudo apt-get install python-dev python3-dev. On macOS they should already be present.

On Windows, you need to download and install Python 2 or Python 3. Pick the version corresponding to your Vim architecture. You will also need Microsoft Visual C++ (MSVC) to build YCM. You can obtain it by installing Visual Studio Build Tools. MSVC 14 (Visual Studio 2015) and 15 (2017) are officially supported.

Here we'll assume you installed YCM with Vundle. That means that the top-level YCM directory is in ~/.vim/bundle/YouCompleteMe.

We'll create a new folder where build files will be placed. Run the following:
```
cd ~
mkdir ycm_build
cd ycm_build
```
Now we need to generate the makefiles. If you DON'T care about semantic support for C-family languages or plan to use experimental clangd based completer, run the following command in the ycm_build directory:
```
cmake -G "<generator>" . ~/.vim/bundle/YouCompleteMe/third_party/ycmd/cpp
```
where <generator> is Unix Makefiles on Unix systems and one of the following Visual Studio generators on Windows:
- Visual Studio 14 Win64
- Visual Studio 15 Win64
Remove the Win64 part in these generators if your Vim architecture is 32-bit.

For those who want to use the system version of boost, you would pass -DUSE_SYSTEM_BOOST=ON to cmake. This may be necessary on some systems where the bundled version of boost doesn't compile out of the box.

NOTE: We STRONGLY recommend AGAINST use of the system boost instead of the bundled version of boost. Random things may break. Save yourself the hassle and use the bundled version of boost.

If you DO care about semantic support for C-family languages, and want to use libclang as the provider instead of experimental clangd-based completer then your cmake call will be a bit more complicated. We'll assume you downloaded a binary distribution of LLVM+Clang from llvm.org in step 3 and that you extracted the archive file to folder ~/ycm_temp/llvm_root_dir (with bin, lib, include etc. folders right inside that folder). On Windows, you can extract the files from the LLVM+Clang installer using 7-zip.

NOTE: This only works with a downloaded LLVM binary package, not a custom-built LLVM! See docs below for EXTERNAL_LIBCLANG_PATH when using a custom LLVM build.

With that in mind, run the following command in the ycm_build directory:
```
cmake -G "<generator>" -DPATH_TO_LLVM_ROOT=~/ycm_temp/llvm_root_dir . ~/.vim/bundle/YouCompleteMe/third_party/ycmd/cpp
```
where <generator> is replaced like above.

Now that configuration files have been generated, compile the libraries using this command:
```
cmake --build . --target ycm_core --config Release
```
The --config Release part is specific to Windows and will be ignored on a Unix OS.

For those who want to use the system version of libclang, you would pass -DUSE_SYSTEM_LIBCLANG=ON to cmake instead of the -DPATH_TO_LLVM_ROOT=... flag.

NOTE: We STRONGLY recommend AGAINST use of the system libclang instead of the upstream compiled binaries. Random things may break. Save yourself the hassle and use the upstream pre-built libclang.

You could also force the use of a custom libclang library with -DEXTERNAL_LIBCLANG_PATH=/path/to/libclang.so flag (the library would end with .dylib on macOS). Again, this flag would be used instead of the other flags. If you compiled LLVM from source, this is the flag you should be using.

Running the cmake command will also place the libclang.[so|dylib|dll] in the YouCompleteMe/third_party/ycmd folder for you if you compiled with clang support (it needs to be there for YCM to work).

If you DO care about semantic support for C-family languages, and want to use experimental clangd-based completer then you need to add following line to your vimrc:
```
let g:ycm_clangd_binary_path = "/path/to/clangd"
```
You need to change /path/to/clangd with the path of binary you downloaded in step 3.
This step is optional.

Build the regex module for improved Unicode support and better performance with regular expressions. The procedure is similar to compiling the ycm_core library:
```
cd ~
mkdir regex_build
cd regex_build
cmake -G "<generator>" . ~/.vim/bundle/YouCompleteMe/third_party/ycmd/third_party/cregex
cmake --build . --target _regex --config Release
```
where <generator> is the same generator used in the previous step.
Set up support for additional languages, as desired:
- C# support: install Mono on non-Windows platforms. Navigate to YouCompleteMe/third_party/ycmd/third_party/omnisharp-roslyn. Download an Omnisharp-Roslyn release archive and extract the archive to YouCompleteMe/third_party/ycmd/third_party/omnisharp-roslyn.
  
  On Windows, be sure that the build utility msbuild is in your PATH.
- Go support: install Go and add it to your path. Navigate to YouCompleteMe/third_party/ycmd/third_party/go/src/golang.org/x/tools/cmd/gopls and run
```
go build
```
- JavaScript and TypeScript support: install Node.js and npm, navigate to YouCompleteMe/third_party/ycmd and run npm install -g --prefix third_party/tsserver typescript.
- Rust support: install rustup. Export RUSTUP_HOME environment variable and point it to an empty temporary directory. Run the following commands:
```
rustup toolchain install nightly
rustup default nightly
rustup component add rls rust-analysis rust-src
```
  Ensure that YouCompleteMe/third_party/ycmd/third_party/rls directory exists and is empty. Go into the temporary directory and then into toolchains/<toolchain>. Finally, move everything from that directory to YouCompleteMe/third_party/ycmd/third_party/rls.
- Java support: install JDK8 (version 8 required). Download a binary release of eclipse.jdt.ls and extract it to YouCompleteMe/third_party/ycmd/third_party/eclipse.jdt.ls/target/repository. Note: this approach is not recommended for most users and is supported only for advanced users and developers of YCM on a best-efforts basis. Please use install.py to enable java support.

That's it. You're done. Refer to the User Guide section on how to use YCM. Don't forget that if you want the C-family semantic completion engine to work, you will need to provide the compilation flags for your project to YCM. It's all in the User Guide.

YCM comes with sane defaults for its options, but you still may want to take a look at what's available for configuration. There are a few interesting options that are conservatively turned off by default that you may want to turn on.

Quick Feature Summary

General (all languages)

Super-fast identifier completer including tags files and syntax elements
Intelligent suggestion ranking and filtering
File and path suggestions
Suggestions from Vim's OmniFunc
UltiSnips snippet suggestions

C-family languages (C, C++, Objective C, Objective C++, CUDA)

Semantic auto-completion with automatic fixes
Signature help (when using clangd)
Real-time diagnostic display
Go to include/declaration/definition (GoTo, etc.)
View documentation comments for identifiers (GetDoc)
Type information for identifiers (GetType)
Automatically fix certain errors (FixIt)

C♯

Semantic auto-completion
Real-time diagnostic display
Go to declaration/definition (GoTo, etc.)
Go to implementation (GoToImplementation)
View documentation comments for identifiers (GetDoc)
Type information for identifiers (GetType)
Automatically fix certain errors (FixIt)
Management of OmniSharp-Roslyn server instance

Python

Semantic auto-completion
Signature help
Go to definition (GoTo)
Reference finding (GoToReferences)
View documentation comments for identifiers (GetDoc)
Type information for identifiers (GetType)

Go

Semantic auto-completion
Signature help
Real-time diagnostic display
Go to declaration/definition (GoTo, etc.)
Go to type definition (GoToType)
Automatically fix certain errors (FixIt)
Type information for identifiers (GetType)
Code formatting (Format)
Management of gopls server instance

JavaScript and TypeScript

Semantic auto-completion with automatic import insertion
Real-time diagnostic display
Go to definition (GoTo, GoToDefinition, and GoToDeclaration are identical)
Go to type definition (GoToType)
Reference finding (GoToReferences)
View documentation comments for identifiers (GetDoc)
Type information for identifiers (GetType)
Automatically fix certain errors (FixIt)
Renaming symbols (RefactorRename <new name>)
Code formatting (Format)
Organize imports (OrganizeImports)
Management of TSServer server instance

Rust

Semantic auto-completion
Real-time diagnostic display
Go to declaration/definition (GoTo, etc.)
Go to implementation (GoToImplementation)
Reference finding (GoToReferences)
View documentation comments for identifiers (GetDoc)
Automatically fix certain errors (FixIt)
Type information for identifiers (GetType)
Renaming symbols (RefactorRename <new name>)
Code formatting (Format)
Execute custom server command (ExecuteCommand <args>)
Management of rls server instance

Java

Semantic auto-completion with automatic import insertion
Signature help
Real-time diagnostic display
Go to definition (GoTo, GoToDefinition, and GoToDeclaration are identical)
Go to type definition (GoToType)
Go to implementation (GoToImplementation)
Reference finding (GoToReferences)
View documentation comments for identifiers (GetDoc)
Type information for identifiers (GetType)
Automatically fix certain errors including code generation (FixIt)
Renaming symbols (RefactorRename <new name>)
Code formatting (Format)
Organize imports (OrganizeImports)
Detection of java projects
Execute custom server command (ExecuteCommand <args>)
Management of jdt.ls server instance

User Guide

General Usage

If the offered completions are too broad, keep typing characters; YCM will continue refining the offered completions based on your input.

Filtering is "smart-case" and "smart-diacritic" sensitive; if you are typing only lowercase letters, then it's case-insensitive. If your input contains uppercase letters, then the uppercase letters in your query must match uppercase letters in the completion strings (the lowercase letters still match both). On top of that, a letter with no diacritic marks will match that letter with or without marks:

matches	foo	fôo	fOo	fÔo
foo	✔️	✔️	✔️	✔️
fôo	❌	✔️	❌	✔️
fOo	❌	❌	✔️	✔️
fÔo	❌	❌	❌	✔️

Use the TAB key to accept a completion and continue pressing TAB to cycle through the completions. Use Shift-TAB to cycle backwards. Note that if you're using console Vim (that is, not Gvim or MacVim) then it's likely that the Shift-TAB binding will not work because the console will not pass it to Vim. You can remap the keys; see the Options section below.

Knowing a little bit about how YCM works internally will prevent confusion. YCM has several completion engines: an identifier-based completer that collects all of the identifiers in the current file and other files you visit (and your tags files) and searches them when you type (identifiers are put into per-filetype groups).

There are also several semantic engines in YCM. There are libclang-based and clangd-based completers that provide semantic completion for C-family languages. There's a Jedi-based completer for semantic completion for Python. There's also an omnifunc-based completer that uses data from Vim's omnicomplete system to provide semantic completions when no native completer exists for that language in YCM.

There are also other completion engines, like the UltiSnips completer and the filepath completer.

YCM automatically detects which completion engine would be the best in any situation. On occasion, it queries several of them at once, merges the outputs and presents the results to you.

Client-Server Architecture

YCM has a client-server architecture; the Vim part of YCM is only a thin client that talks to the ycmd HTTP+JSON server that has the vast majority of YCM logic and functionality. The server is started and stopped automatically as you start and stop Vim.

Completion String Ranking

The subsequence filter removes any completions that do not match the input, but then the sorting system kicks in. It's actually very complicated and uses lots of factors, but suffice it to say that "word boundary" (WB) subsequence character matches are "worth" more than non-WB matches. In effect, this means given an input of "gua", the completion "getUserAccount" would be ranked higher in the list than the "Fooguxa" completion (both of which are subsequence matches). A word-boundary character are all capital characters, characters preceded by an underscore and the first letter character in the completion string.

Signature Help

Signature help is an experimental feature for which we value your feedback. Valid signatures are displayed in a second popup menu and the current signature is highlighed along with the current arguemnt.

Signature help is triggered in insert mode automatically when g:ycm_auto_trigger is enabled and is not supported when it is not enabled.

The signatures popup is hidden when there are no matching signatures or when you leave insert mode. There is no key binding to clear the popup.

For more details on this feature and a few demos, check out the PR that proposed it.

General Semantic Completion

You can use Ctrl+Space to trigger the completion suggestions anywhere, even without a string prefix. This is useful to see which top-level functions are available for use.

C-family Semantic Completion

In order to perform semantic analysis such as code completion, GoTo and diagnostics, YouCompleteMe uses libclang or clangd. Both of them make use of clang compiler, sometimes also referred to as llvm. Like any compiler, clang also requires a set of compile flags in order to parse your code. Simply put: If clang can't parse your code, YouCompleteMe can't provide semantic analysis.

There are 2 methods which can be used to provide compile flags to clang:

Option 1: Use a compilation database

The easiest way to get YCM to compile your code is to use a compilation database. A compilation database is usually generated by your build system (e.g. CMake) and contains the compiler invocation for each compilation unit in your project.

For information on how to generate a compilation database, see the clang documentation. In short:

If using CMake, add -DCMAKE_EXPORT_COMPILE_COMMANDS=ON when configuring (or add set( CMAKE_EXPORT_COMPILE_COMMANDS ON ) to CMakeLists.txt) and copy or symlink the generated database to the root of your project.
If using Ninja, check out the compdb tool (-t compdb) in its docs.
If using GNU make, check out compiledb or Bear.
For other build systems, check out .ycm_extra_conf.py below.

If no .ycm_extra_conf.py is found, YouCompleteMe automatically tries to load a compilation database if there is one.

YCM looks for a file named compile_commands.json in the directory of the opened file or in any directory above it in the hierarchy (recursively); when the file is found, it is loaded. YouCompleteMe performs the following lookups when extracting flags for a particular file:

If the database contains an entry for the file, the flags for that file are used.
If the file is a header file and a source file with the same root exists in the database, the flags for the source file are used. For example, if the file is /home/Test/project/src/lib/something.h and the database contains an entry for /home/Test/project/src/lib/something.cc, then the flags for /home/Test/project/src/lib/something.cc are used.
Otherwise, if any flags have been returned from the directory containing the requested file, those flags are used. This heuristic is intended to provide potentially working flags for newly created files.

Finally, YCM converts any relative paths in the extracted flags to absolute paths. This ensures that compilation can be performed from any Vim working directory.

Option 2: Provide the flags manually

If you don't have a compilation database, or aren't able to generate one, you have to tell YouCompleteMe how to compile your code some other way.

Every C-family project is different. It is not possible for YCM to guess what compiler flags to supply for your project. Fortunately, YCM provides a mechanism for you to generate the flags for a particular file with arbitrary complexity. This is achieved by requiring you to provide a Python module which implements a trivial function which, given the file name as argument, returns a list of compiler flags to use to compile that file.

YCM looks for a .ycm_extra_conf.py file in the directory of the opened file or in any directory above it in the hierarchy (recursively); when the file is found, it is loaded (only once!) as a Python module. YCM calls a Settings method in that module which should provide it with the information necessary to compile the current file. You can also provide a path to a global configuration file with the g:ycm_global_ycm_extra_conf option, which will be used as a fallback. To prevent the execution of malicious code from a file you didn't write YCM will ask you once per .ycm_extra_conf.py if it is safe to load. This can be disabled and you can white-/blacklist files. See the g:ycm_confirm_extra_conf and g:ycm_extra_conf_globlist options respectively.

This system was designed this way so that the user can perform any arbitrary sequence of operations to produce a list of compilation flags YCM should hand to Clang.

NOTE: It is highly recommended to include -x <language> flag to libclang. This is so that the correct language is detected, particularly for header files. Common values are -x c for C, -x c++ for C++, -x objc for Objective-C, and -x cuda for CUDA.

To give you an impression, if your C++ project is trivial, and your usual compilation command is: g++ -Wall -Wextra -Werror -o FILE.o FILE.cc, then the following .ycm_extra_conf.py is enough to get semantic analysis from YouCompleteMe:

def Settings( **kwargs ):
  return {
    'flags': [ '-x', 'c++', '-Wall', '-Wextra', '-Werror' ],
  }

As you can see from the trivial example, YCM calls the Settings method which returns a dictionary with a single element 'flags'. This element is a list of compiler flags to pass to libclang for the current file. The absolute path of that file is accessible under the filename key of the kwargs dictionary. That's it! This is actually enough for most projects, but for complex projects it is not uncommon to integrate directly with an existing build system using the full power of the Python language.

For a more elaborate example, see ycmd's own .ycm_extra_conf.py. You should be able to use it as a starting point. Don't just copy/paste that file somewhere and expect things to magically work; your project needs different flags. Hint: just replace the strings in the flags variable with compilation flags necessary for your project. That should be enough for 99% of projects.

You could also consider using YCM-Generator to generate the ycm_extra_conf.py file.

Errors during compilation

If Clang encounters errors when compiling the header files that your file includes, then it's probably going to take a long time to get completions. When the completion menu finally appears, it's going to have a large number of unrelated completion strings (type/function names that are not actually members). This is because Clang fails to build a precompiled preamble for your file if there are any errors in the included headers and that preamble is key to getting fast completions.

Call the :YcmDiags command to see if any errors or warnings were detected in your file.

Selecting a C-family completion engine

Currently YCM supports two completion engines for C-family semantic completion. One libclang-based and an clangd-based completer. When in doubt we recommend using the libclang-based engine. Here is a quick comparison of the two completer engines:

Project wide indexing: Clangd has both dynamic and static index support. The dynamic index stores up-to-date symbols coming from any files you are currently editing, whereas static index contains project-wide symbol information. This symbol information is used for code completion and code navigation. Whereas libclang is limited to the current translation unit(TU).
Code navigation: Clangd provides all the GoTo requests libclang provides and it improves those using the above mentioned index information to contain project-wide information rather than just the current TU.
Rename: Clangd can perform semantic rename operations on the current file, whereas libclang doesn’t support such functionality.
Code Completion: Clangd can perform code completions at a lower latency than libclang; also, it has information about all the symbols in your project so it can suggest items outside your current TU and also provides proper #include insertions for those items.
Signature help: Clangd provides signature help so that you can see the names and types of arguments when calling functions.
Format Code: Clangd provides code formatting either for the selected lines or the whole file, whereas libclang doesn’t have such functionality.
Performance: Clangd has faster reparse and code completion times compared to libclang.

To enable:

libclang-based completer pass --clang-completer
clangd-based completer pass --clangd-completer

to install.py while following the installation guide. As mentioned before, pass --clang-completer when in doubt, since the clangd-based completer is still in heavy development.

Java Semantic Completion

Java quick Start

Ensure that you have enabled the Java completer. See the installation guide for details.
Create a project file (gradle or maven) file in the root directory of your Java project, by following the instructions below.
(Optional) Configure the LSP server. The jdt.ls configuration options can be found in their codebase.
If you previously used Eclim or Syntastic for Java, disable them for Java.
Edit a Java file from your project.

For the best experience, we highly recommend at least Vim 8.1.1875 when using Java support with YouCompleteMe.

Java Project Files

In order to provide semantic analysis, the Java completion engine requires knowledge of your project structure. In particular it needs to know the class path to use, when compiling your code. Fortunately jdt.ls supports eclipse project files, maven projects and gradle projects.

NOTE: Our recommendation is to use either maven or gradle projects.

Diagnostic display - Syntastic

The native support for Java includes YCM's native realtime diagnostics display. This can conflict with other diagnostics plugins like Syntastic, so when enabling Java support, please manually disable Syntastic Java diagnostics.

Add the following to your vimrc:

let g:syntastic_java_checkers = []

Diagnostic display - Eclim

The native support for Java includes YCM's native realtime diagnostics display. This can conflict with other diagnostics plugins like Eclim, so when enabling Java support, please manually disable Eclim Java diagnostics.

Add the following to your vimrc:

let g:EclimFileTypeValidate = 0

NOTE: We recommend disabling Eclim entirely when editing Java with YCM's native Java support. This can be done temporarily with :EclimDisable.

Eclipse Projects

Eclipse style projects require two files: .project and .classpath.

If your project already has these files due to previously being set up within eclipse, then no setup is required. jdt.ls should load the project just fine (it's basically eclipse after all).

However, if not, it is possible (easy in fact) to craft them manually, though it is not recommended. You're better off using gradle or maven (see below).

A simple eclipse style project example can be found in the ycmd test directory. Normally all that is required is to copy these files to the root of your project and to edit the .classpath to add additional libraries, such as:

  <classpathentry kind="lib" path="/path/to/external/jar" />
  <classpathentry kind="lib" path="/path/to/external/java/source" />

It may also be necessary to change the directory in which your source files are located (paths are relative to the .project file itself):

  <classpathentry kind="src" output="target/classes" path="path/to/src/" />

NOTE: The eclipse project and classpath files are not a public interface and it is highly recommended to use Maven or Gradle project definitions if you don't already use eclipse to manage your projects.

Maven Projects

Maven needs a file named pom.xml in the root of the project. Once again a simple pom.xml can be found in ycmd source.

The format of pom.xml files is way beyond the scope of this document, but we do recommend using the various tools that can generate them for you, if you're not familiar with them already.

Gradle Projects

Gradle projects require a build.gradle. Again, there is a trivial example in ycmd's tests.

The format of build.gradle files is way beyond the scope of this document, but we do recommend using the various tools that can generate them for you, if you're not familiar with them already.

Troubleshooting

If you're not getting completions or diagnostics, check the server health:

The Java completion engine takes a while to start up and parse your project. You should be able to see its progress in the command line, and :YcmDebugInfo. Ensure that the following lines are present:

--   jdt.ls Java Language Server running
--   jdt.ls Java Language Server Startup Status: Ready

If the above lines don't appear after a few minutes, check the jdt.ls and ycmd log files using :YcmToggleLogs . The jdt.ls log file is called .log (for some reason).

If you get a message about "classpath is incomplete", then make sure you have correctly configured the project files.

If you get messages about unresolved imports, then make sure you have correctly configured the project files, in particular check that the classpath is set correctly.

For anything else, contact us. Java support is experimental at present so we'd love to hear your feedback! Please do remember to check CONTRIBUTING.md for the list of diagnostics we'll need.

C# Semantic Completion

YCM relies on OmniSharp-Roslyn to provide completion and code navigation. OmniSharp-Roslyn needs a solution file for a C# project and there are two ways of letting YCM know about your solution files.

Automaticly discovered solution files

YCM will scan all parent directories of the file currently being edited and look for file with .sln extension.

Manually specified solution files

If YCM loads .ycm_extra_conf.py which contains CSharpSolutionFile function, YCM will try to use that to determine the solution file. This is useful when one wants to override the default behaviour and specify a solution file that is not in any of the parent directories of the currently edited file. Example:

def CSharpSolutionFile( filepath ):
  # `filepath` is the path of the file user is editing
  return '/path/to/solution/file' # Can be relative to the `.ycm_extra_conf.py`

If the path returned by CSharpSolutionFile is not an actual file, YCM will fall back to the other way of finding the file.

Python Semantic Completion

YCM relies on the Jedi engine to provide completion and code navigation. By default, it will pick the version of Python running the ycmd server and use its sys.path. While this is fine for simple projects, this needs to be configurable when working with virtual environments or in a project with third-party packages. The next sections explain how to do that.

Working with virtual environments

A common practice when working on a Python project is to install its dependencies in a virtual environment and develop the project inside that environment. To support this, YCM needs to know the interpreter path of the virtual environment. You can specify it by creating a .ycm_extra_conf.py file at the root of your project with the following contents:

def Settings( **kwargs ):
  return {
    'interpreter_path': '/path/to/virtual/environment/python'
  }

where /path/to/virtual/environment/python is the path to the Python used by the virtual environment you are working in. Typically, the executable can be found in the Scripts folder of the virtual environment directory on Windows and in the bin folder on other platforms.

If you don't like having to create a .ycm_extra_conf.py file at the root of your project and would prefer to specify the interpreter path with a Vim option, read the Configuring through Vim options section.

Working with third-party packages

Another common practice is to put the dependencies directly into the project and add their paths to sys.path at runtime in order to import them. YCM needs to be told about this path manipulation to support those dependencies. This can be done by creating a .ycm_extra_conf.py file at the root of the project. This file must define a Settings( **kwargs ) function returning a dictionary with the list of paths to prepend to sys.path under the sys_path key. For instance, the following .ycm_extra_conf.py

def Settings( **kwargs ):
  return {
    'sys_path': [
      '/path/to/some/third_party/package',
      '/path/to/another/third_party/package'
    ]
  }

adds the paths /path/to/some/third_party/package and /path/to/another/third_party/package at the start of sys.path.

If you would rather prepend paths to sys.path with a Vim option, read the Configuring through Vim options section.

If you need further control on how to add paths to sys.path, you should define the PythonSysPath( **kwargs ) function in the .ycm_extra_conf.py file. Its keyword arguments are sys_path which contains the default sys.path, and interpreter_path which is the path to the Python interpreter. Here's a trivial example that insert the /path/to/third_party/package path at the second position of sys.path:

def PythonSysPath( **kwargs ):
  sys_path = kwargs[ 'sys_path' ]
  sys_path.insert( 1, '/path/to/third_party/package' )
  return sys_path

A more advanced example can be found in YCM's own .ycm_extra_conf.py.

Configuring through Vim options

You may find inconvenient to have to create a .ycm_extra_conf.py file at the root of each one of your projects in order to set the path to the Python interpreter and/or add paths to sys.path and would prefer to be able to configure those through Vim options. Don't worry, this is possible by using the g:ycm_extra_conf_vim_data option and creating a global extra configuration file. Let's take an example. Suppose that you want to set the interpreter path with the g:ycm_python_interpreter_path option and prepend paths to sys.path with the g:ycm_python_sys_path option. Suppose also that you want to name the global extra configuration file global_extra_conf.py and that you want to put it in your HOME folder. You should then add the following lines to your vimrc:

let g:ycm_python_interpreter_path = ''
let g:ycm_python_sys_path = []
let g:ycm_extra_conf_vim_data = [
  \  'g:ycm_python_interpreter_path',
  \  'g:ycm_python_sys_path'
  \]
let g:ycm_global_ycm_extra_conf = '~/global_extra_conf.py'

and create the ~/global_extra_conf.py file with the following contents:

def Settings( **kwargs ):
  client_data = kwargs[ 'client_data' ]
  return {
    'interpreter_path': client_data[ 'g:ycm_python_interpreter_path' ],
    'sys_path': client_data[ 'g:ycm_python_sys_path' ]
  }

That's it. You are done. Note that you don't need to restart the server when setting one of the options. YCM will automatically pick the new values.

Rust Semantic Completion

Completions and GoTo commands within the current crate and its dependencies should work out of the box with no additional configuration (provided that you built YCM with the --rust-completer flag; see the Installation section for details). The install script takes care of installing the Rust source code, so no configuration is necessary. In case you are running Python 2.7.8 and older, you will need to manually install rustup.

To configure RLS look up rls configuration options

Go Semantic Completion

Completions and GoTo commands should work out of the box (provided that you built YCM with the --go-completer flag; see the Installation section for details). The server only works for projects with the "canonical" layout.

While YCM can configure a LSP server, currently gopls doesn't implement the required notification.

JavaScript and TypeScript Semantic Completion

NOTE: YCM originally used the Tern engine for JavaScript but due to Tern not being maintained anymore by its main author and the TSServer engine offering more features, YCM is moving to TSServer. This won't affect you if you were already using Tern but you are encouraged to do the switch by deleting the third_party/ycmd/third_party/tern_runtime/node_modules directory in YCM folder. If you are a new user but still want to use Tern, you should pass the --js-completer option to the install.py script during installation. Further instructions on how to setup YCM with Tern are available on the wiki.

All JavaScript and TypeScript features are provided by the TSServer engine, which is included in the TypeScript SDK. To enable these features, install Node.js and npm and call the install.py script with the --ts-completer flag.

TSServer relies on the jsconfig.json file for JavaScript and the tsconfig.json file for TypeScript to analyze your project. Ensure the file exists at the root of your project.

To get diagnostics in JavaScript, set the checkJs option to true in your jsconfig.json file:

{
    "compilerOptions": {
        "checkJs": true
    }
}

Semantic Completion for Other Languages

C-family, C#, Go, Java, Python, Rust, and JavaScript/TypeScript languages are supported natively by YouCompleteMe using the Clang, OmniSharp-Roslyn, Gopls, jdt.ls, Jedi, rls, and TSServer engines, respectively. Check the installation section for instructions to enable these features if desired.

Plugging an arbitrary LSP server

Similar to other LSP clients, YCM can use an arbitrary LSP server with the help of g:ycm_language_server option. An example of a value of this option would be:

let g:ycm_language_server = 
  \ [ 
  \   {
  \     'name': 'yaml',
  \     'cmdline': [ '/path/to/yaml/server/yaml-language-server', '--stdio' ],
  \     'filetypes': [ 'yaml' ]
  \   },
  \   {
  \     'name': 'rust',
  \     'cmdline': [ 'ra_lsp_server' ],
  \     'filetypes': [ 'rust' ],
  \     'project_root_files': [ 'Cargo.toml' ]
  \   }
  \ ]

project_root_files is an optional key, since not all servers need it.

When configuring a LSP server the value of the name key will be used as the kwargs[ 'language' ].

See the LSP Examples project for more examples of configuring the likes of PHP, Ruby, Kotlin, and D.

Using `omnifunc` for semantic completion

YCM will use your omnifunc (see :h omnifunc in Vim) as a source for semantic completions if it does not have a native semantic completion engine for your file's filetype. Vim comes with okayish omnifuncs for various languages like Ruby, PHP, etc. It depends on the language.

You can get a stellar omnifunc for Ruby with Eclim. Just make sure you have the latest Eclim installed and configured (this means Eclim >= 2.2.* and Eclipse >= 4.2.*).

After installing Eclim remember to create a new Eclipse project within your application by typing :ProjectCreate <path-to-your-project> -n ruby inside vim and don't forget to have let g:EclimCompletionMethod = 'omnifunc' in your vimrc. This will make YCM and Eclim play nice; YCM will use Eclim's omnifuncs as the data source for semantic completions and provide the auto-triggering and subsequence-based matching (and other YCM features) on top of it.

LSP Configuration

Many LSP servers allow some level of user configuration. YCM enables this with the help of .ycm_extra_conf.py files. Here's an example of jdt.ls user configuration.

def Settings( **kwargs ):
  if kwargs[ 'language' ] == 'java':
    return { 'ls': { 'java.format.onType.enabled': True } }

The ls key tells YCM that the dictionary should be passed to thet LSP server. For each of the LSP server's configuration you should look up the respective server's documentation.

Writing New Semantic Completers

You have two options here: writing an omnifunc for Vim's omnicomplete system that YCM will then use through its omni-completer, or a custom completer for YCM using the Completer API.

Here are the differences between the two approaches:

You have to use VimScript to write the omnifunc, but get to use Python to write for the Completer API; this by itself should make you want to use the API.
The Completer API is a much more powerful way to integrate with YCM and it provides a wider set of features. For instance, you can make your Completer query your semantic back-end in an asynchronous fashion, thus not blocking Vim's GUI thread while your completion system is processing stuff. This is impossible with VimScript. All of YCM's completers use the Completer API.
Performance with the Completer API is better since Python executes faster than VimScript.

If you want to use the omnifunc system, see the relevant Vim docs with :h complete-functions. For the Completer API, see the API docs.

If you want to upstream your completer into YCM's source, you should use the Completer API.

Diagnostic Display

YCM will display diagnostic notifications for the C-family, C#, Go, Java, JavaScript, Rust and TypeScript languages. Since YCM continuously recompiles your file as you type, you'll get notified of errors and warnings in your file as fast as possible.

Here are the various pieces of the diagnostic UI:

Icons show up in the Vim gutter on lines that have a diagnostic.
Regions of text related to diagnostics are highlighted (by default, a red wavy underline in gvim and a red background in vim).
Moving the cursor to a line with a diagnostic echoes the diagnostic text.
Vim's location list is automatically populated with diagnostic data (off by default, see options).

The new diagnostics (if any) will be displayed the next time you press any key on the keyboard. So if you stop typing and just wait for the new diagnostics to come in, that will not work. You need to press some key for the GUI to update.

Having to press a key to get the updates is unfortunate, but cannot be changed due to the way Vim internals operate; there is no way that a background task can update Vim's GUI after it has finished running. You have to press a key. This will make YCM check for any pending diagnostics updates.

You can force a full, blocking compilation cycle with the :YcmForceCompileAndDiagnostics command (you may want to map that command to a key; try putting nnoremap <F5> :YcmForceCompileAndDiagnostics<CR> in your vimrc). Calling this command will force YCM to immediately recompile your file and display any new diagnostics it encounters. Do note that recompilation with this command may take a while and during this time the Vim GUI will be blocked.

YCM will display a short diagnostic message when you move your cursor to the line with the error. You can get a detailed diagnostic message with the <leader>d key mapping (can be changed in the options) YCM provides when your cursor is on the line with the diagnostic.

You can also see the full diagnostic message for all the diagnostics in the current file in Vim's locationlist, which can be opened with the :lopen and :lclose commands (make sure you have set let g:ycm_always_populate_location_list = 1 in your vimrc). A good way to toggle the display of the locationlist with a single key mapping is provided by another (very small) Vim plugin called ListToggle (which also makes it possible to change the height of the locationlist window), also written by yours truly.

Diagnostic Highlighting Groups

You can change the styling for the highlighting groups YCM uses. For the signs in the Vim gutter, the relevant groups are:

YcmErrorSign, which falls back to group SyntasticErrorSign and then error if they exist
YcmWarningSign, which falls back to group SyntasticWarningSign and then todo if they exist

You can also style the line that has the warning/error with these groups:

YcmErrorLine, which falls back to group SyntasticErrorLine if it exists
YcmWarningLine, which falls back to group SyntasticWarningLine if it exists

Note that the line highlighting groups only work when the g:ycm_enable_diagnostic_signs option is set. If you want highlighted lines but no signs in the Vim gutter, ensure that your Vim version is 7.4.2201 or later and set the signcolumn option to off in your vimrc:

set signcolumn=off

The syntax groups used to highlight regions of text with errors/warnings:

YcmErrorSection, which falls back to group SyntasticError if it exists and then SpellBad
YcmWarningSection, which falls back to group SyntasticWarning if it exists and then SpellCap

Here's how you'd change the style for a group:

highlight YcmErrorLine guibg=#3f0000

Commands

The `:YcmRestartServer` command

If the ycmd completion server suddenly stops for some reason, you can restart it with this command.

The `:YcmForceCompileAndDiagnostics` command

Calling this command will force YCM to immediately recompile your file and display any new diagnostics it encounters. Do note that recompilation with this command may take a while and during this time the Vim GUI will be blocked.

You may want to map this command to a key; try putting nnoremap <F5> :YcmForceCompileAndDiagnostics<CR> in your vimrc.

The `:YcmDiags` command

Calling this command will fill Vim's locationlist with errors or warnings if any were detected in your file and then open it. If a given error or warning can be fixed by a call to :YcmCompleter FixIt, then (FixIt available) is appended to the error or warning text. See the FixIt completer subcommand for more information.

NOTE: The absence of (FixIt available) does not strictly imply a fix-it is not available as not all completers are able to provide this indication. For example, the c-sharp completer provides many fix-its but does not add this additional indication.

The g:ycm_open_loclist_on_ycm_diags option can be used to prevent the location list from opening, but still have it filled with new diagnostic data. See the Options section for details.

The `:YcmShowDetailedDiagnostic` command

This command shows the full diagnostic text when the user's cursor is on the line with the diagnostic.

The `:YcmDebugInfo` command

This will print out various debug information for the current file. Useful to see what compile commands will be used for the file if you're using the semantic completion engine.

The `:YcmToggleLogs` command

This command presents the list of logfiles created by YCM, the ycmd server, and the semantic engine server for the current filetype, if any. One of these logfiles can be opened in the editor (or closed if already open) by entering the corresponding number or by clicking on it with the mouse. Additionally, this command can take the logfile names as arguments. Use the <TAB> key (or any other key defined by the wildchar option) to complete the arguments or to cycle through them (depending on the value of the wildmode option). Each logfile given as an argument is directly opened (or closed if already open) in the editor. Only for debugging purposes.

The `:YcmCompleter` command

This command gives access to a number of additional IDE-like features in YCM, for things like semantic GoTo, type information, FixIt and refactoring.

This command accepts a range that can either be specified through a selection in one of Vim's visual modes (see :h visual-use) or on the command line. For instance, :2,5YcmCompleter will apply the command from line 2 to line 5. This is useful for the Format subcommand.

Call YcmCompleter without further arguments for a list of the commands you can call for the current completer.

See the file type feature summary for an overview of the features available for each file type. See the YcmCompleter subcommands section for more information on the available subcommands and their usage.

YcmCompleter Subcommands

NOTE: See the docs for the YcmCompleter command before tackling this section.

The invoked subcommand is automatically routed to the currently active semantic completer, so :YcmCompleter GoToDefinition will invoke the GoToDefinition subcommand on the Python semantic completer if the currently active file is a Python one and on the Clang completer if the currently active file is a C-family language one.

You may also want to map the subcommands to something less verbose; for instance, nnoremap <leader>jd :YcmCompleter GoTo<CR> maps the <leader>jd sequence to the longer subcommand invocation.

GoTo Commands

These commands are useful for jumping around and exploring code. When moving the cursor, the subcommands add entries to Vim's jumplist so you can use CTRL-O to jump back to where you were before invoking the command (and CTRL-I to jump forward; see :h jumplist for details). If there is more than one destination, the quickfix list (see :h quickfix) is populated with the available locations and opened to full width at the bottom of the screen. You can change this behavior by using the YcmQuickFixOpened autocommand.

The `GoToInclude` subcommand

Looks up the current line for a header and jumps to it.

Supported in filetypes: c, cpp, objc, objcpp, cuda

The `GoToDeclaration` subcommand

Looks up the symbol under the cursor and jumps to its declaration.

Supported in filetypes: c, cpp, objc, objcpp, cuda, cs, go, java, javascript, python, rust, typescript

The `GoToDefinition` subcommand

Looks up the symbol under the cursor and jumps to its definition.

NOTE: For C-family languages this only works in certain situations, namely when the definition of the symbol is in the current translation unit. A translation unit consists of the file you are editing and all the files you are including with #include directives (directly or indirectly) in that file.

Supported in filetypes: c, cpp, objc, objcpp, cuda, cs, go, java, javascript, python, rust, typescript

The `GoTo` subcommand

This command tries to perform the "most sensible" GoTo operation it can. Currently, this means that it tries to look up the symbol under the cursor and jumps to its definition if possible; if the definition is not accessible from the current translation unit, jumps to the symbol's declaration. For C-family languages, it first tries to look up the current line for a header and jump to it. For C#, implementations are also considered and preferred.

Supported in filetypes: c, cpp, objc, objcpp, cuda, cs, go, java, javascript, python, rust, typescript

The `GoToImprecise` subcommand

WARNING: This command trades correctness for speed!

Same as the GoTo command except that it doesn't recompile the file with libclang before looking up nodes in the AST. This can be very useful when you're editing files that take long to compile but you know that you haven't made any changes since the last parse that would lead to incorrect jumps. When you're just browsing around your codebase, this command can spare you quite a bit of latency.

Supported in filetypes: c, cpp, objc, objcpp, cuda

The `GoToReferences` subcommand

This command attempts to find all of the references within the project to the identifier under the cursor and populates the quickfix list with those locations.

Supported in filetypes: java, javascript, python, typescript, rust

The `GoToImplementation` subcommand

Looks up the symbol under the cursor and jumps to its implementation (i.e. non-interface). If there are multiple implementations, instead provides a list of implementations to choose from.

Supported in filetypes: cs, java, rust

The `GoToImplementationElseDeclaration` subcommand

Looks up the symbol under the cursor and jumps to its implementation if one, else jump to its declaration. If there are multiple implementations, instead provides a list of implementations to choose from.

Supported in filetypes: cs

The `GoToType` subcommand

Looks up the symbol under the cursor and jumps to the definition of its type e.g. if the symbol is an object, go to the definition of its class.

Supported in filetypes: go, java, javascript, typescript

Semantic Information Commands

These commands are useful for finding static information about the code, such as the types of variables, viewing declarations and documentation strings.

The `GetType` subcommand

Echos the type of the variable or method under the cursor, and where it differs, the derived type.

For example:

    std::string s;

Invoking this command on s returns std::string => std::basic_string<char>

NOTE: Causes re-parsing of the current translation unit.

Supported in filetypes: c, cpp, objc, objcpp, cuda, java, javascript, go, python, typescript, rust

The `GetTypeImprecise` subcommand

WARNING: This command trades correctness for speed!

Same as the GetType command except that it doesn't recompile the file with libclang before looking up nodes in the AST. This can be very useful when you're editing files that take long to compile but you know that you haven't made any changes since the last parse that would lead to incorrect type. When you're just browsing around your codebase, this command can spare you quite a bit of latency.

Supported in filetypes: c, cpp, objc, objcpp, cuda

The `GetParent` subcommand

Echos the semantic parent of the point under the cursor.

The semantic parent is the item that semantically contains the given position.

For example:

class C {
    void f();
};

void C::f() {

}

In the out-of-line definition of C::f, the semantic parent is the class C, of which this function is a member.

In the example above, both declarations of C::f have C as their semantic context, while the lexical context of the first C::f is C and the lexical context of the second C::f is the translation unit.

For global declarations, the semantic parent is the translation unit.

NOTE: Causes re-parsing of the current translation unit.

Supported in filetypes: c, cpp, objc, objcpp, cuda

The `GetDoc` subcommand

Displays the preview window populated with quick info about the identifier under the cursor. Depending on the file type, this includes things like:

The type or declaration of identifier,
Doxygen/javadoc comments,
Python docstrings,
etc.

Supported in filetypes: c, cpp, objc, objcpp, cuda, cs, java, javascript, python, typescript, rust

The `GetDocImprecise` subcommand

WARNING: This command trades correctness for speed!

Same as the GetDoc command except that it doesn't recompile the file with libclang before looking up nodes in the AST. This can be very useful when you're editing files that take long to compile but you know that you haven't made any changes since the last parse that would lead to incorrect docs. When you're just browsing around your codebase, this command can spare you quite a bit of latency.

Supported in filetypes: c, cpp, objc, objcpp, cuda

Refactoring Commands

These commands make changes to your source code in order to perform refactoring or code correction. YouCompleteMe does not perform any action which cannot be undone, and never saves or writes files to the disk.

The `FixIt` subcommand

Where available, attempts to make changes to the buffer to correct diagnostics on the current line. Where multiple suggestions are available (such as when there are multiple ways to resolve a given warning, or where multiple diagnostics are reported for the current line), the options are presented and one can be selected.

Completers which provide diagnostics may also provide trivial modifications to the source in order to correct the diagnostic. Examples include syntax errors such as missing trailing semi-colons, spurious characters, or other errors which the semantic engine can deterministically suggest corrections.

If no fix-it is available for the current line, or there is no diagnostic on the current line, this command has no effect on the current buffer. If any modifications are made, the number of changes made to the buffer is echo'd and the user may use the editor's undo command to revert.

When a diagnostic is available, and g:ycm_echo_current_diagnostic is set to 1, then the text (FixIt) is appended to the echo'd diagnostic when the completer is able to add this indication. The text (FixIt available) is also appended to the diagnostic text in the output of the :YcmDiags command for any diagnostics with available fix-its (where the completer can provide this indication).

NOTE: Causes re-parsing of the current translation unit.

Supported in filetypes: c, cpp, objc, objcpp, cuda, cs, go, java, javascript, rust, typescript

The `RefactorRename <new name>` subcommand

In supported file types, this command attempts to perform a semantic rename of the identifier under the cursor. This includes renaming declarations, definitions and usages of the identifier, or any other language-appropriate action. The specific behavior is defined by the semantic engine in use.

Similar to FixIt, this command applies automatic modifications to your source files. Rename operations may involve changes to multiple files, which may or may not be open in Vim buffers at the time. YouCompleteMe handles all of this for you. The behavior is described in the following section.

Supported in filetypes: java, javascript, typescript, rust

Multi-file Refactor

When a Refactor or FixIt command touches multiple files, YouCompleteMe attempts to apply those modifications to any existing open, visible buffer in the current tab. If no such buffer can be found, YouCompleteMe opens the file in a new small horizontal split at the top of the current window, applies the change, and then hides the window. NOTE: The buffer remains open, and must be manually saved. A confirmation dialog is opened prior to doing this to remind you that this is about to happen.

Once the modifications have been made, the quickfix list (see :help quickfix) is populated with the locations of all modifications. This can be used to review all automatic changes made by using :copen. Typically, use the CTRL-W <enter> combination to open the selected file in a new split. It is possible to customize how the quickfix window is opened by using the YcmQuickFixOpened autocommand.

The buffers are not saved automatically. That is, you must save the modified buffers manually after reviewing the changes from the quickfix list. Changes can be undone using Vim's powerful undo features (see :help undo). Note that Vim's undo is per-buffer, so to undo all changes, the undo commands must be applied in each modified buffer separately.

NOTE: While applying modifications, Vim may find files which are already open and have a swap file. The command is aborted if you select Abort or Quit in any such prompts. This leaves the Refactor operation partially complete and must be manually corrected using Vim's undo features. The quickfix list is not populated in this case. Inspect :buffers or equivalent (see :help buffers) to see the buffers that were opened by the command.

The `Format` subcommand

This command formats the whole buffer or some part of it according to the value of the Vim options shiftwidth and expandtab (see :h 'sw' and :h et respectively). To format a specific part of your document, you can either select it in one of Vim's visual modes (see :h visual-use) and run the command or directly enter the range on the command line, e.g. :2,5YcmCompleter Format to format it from line 2 to line 5.

Supported in filetypes: java, javascript, go, typescript, rust

The `OrganizeImports` subcommand

This command removes unused imports and sorts imports in the current file. It can also group imports from the same module in TypeScript and resolves imports in Java.

Supported in filetypes: java, javascript, typescript

Miscellaneous Commands

These commands are for general administration, rather than IDE-like features. They cover things like the semantic engine server instance and compilation flags.

The `ExecuteCommand <args>` subcommand

Some LSP completers (currently Rust and Java completers) support executing server specific commands. Consult the rls and jdt.ls respective documentations to find out what commands are supported and which arguments are expected.

The support for ExecuteCommand was implemented to support plugins like vimspector to debug java, but isn't limited to that specific use case.

The `RestartServer` subcommand

Restarts the semantic-engine-as-localhost-server for those semantic engines that work as separate servers that YCM talks to.

Supported in filetypes: cs, go, java, javascript, rust, typescript

The `ClearCompilationFlagCache` subcommand

YCM caches the flags it gets from the Settings function in your .ycm_extra_conf.py file unless you return them with the do_cache parameter set to False. It also caches the flags extracted from the compilation database. The cache is in memory and is never invalidated (unless you restart the server with the :YcmRestartServer command).

This command clears that cache entirely. YCM will then re-query your Settings function or your compilation database as needed in the future.

Supported in filetypes: c, cpp, objc, objcpp, cuda, rust

The `ReloadSolution` subcommand

Instruct the Omnisharp-Roslyn server to clear its cache and reload all files from disk. This is useful when files are added, removed, or renamed in the solution, files are changed outside of Vim, or whenever Omnisharp-Roslyn cache is out-of-sync.

Supported in filetypes: cs

Functions

The `youcompleteme#GetErrorCount` function

Get the number of YCM Diagnostic errors. If no errors are present, this function returns 0.

For example:

  call youcompleteme#GetErrorCount()

Both this function and youcompleteme#GetWarningCount can be useful when integrating YCM with other Vim plugins. For example, a lightline user could add a diagnostics section to their statusline which would display the number of errors and warnings.

The `youcompleteme#GetWarningCount` function

Get the number of YCM Diagnostic warnings. If no warnings are present, this function returns 0.

For example:

  call youcompleteme#GetWarningCount()

Autocommands

The `YcmLocationOpened` autocommand

This User autocommand is fired when YCM opens the location list window in response to the YcmDiags command. By default, the location list window is opened to the bottom of the current window and its height is set to fit all entries. This behavior can be overridden by using the YcmLocationOpened autocommand which is triggered while the cursor is in the location list window. For instance:

function! s:CustomizeYcmLocationWindow()
  " Move the window to the top of the screen.
  wincmd K
  " Set the window height to 5.
  5wincmd _
  " Switch back to working window.
  wincmd p
endfunction

autocmd User YcmLocationOpened call s:CustomizeYcmLocationWindow()

The `YcmQuickFixOpened` autocommand

This User autocommand is fired when YCM opens the quickfix window in response to the GoTo* and RefactorRename subcommands. By default, the quickfix window is opened to full width at the bottom of the screen and its height is set to fit all entries. This behavior can be overridden by using the YcmQuickFixOpened autocommand which is triggered while the cursor is in the quickfix window. For instance:

function! s:CustomizeYcmQuickFixWindow()
  " Move the window to the top of the screen.
  wincmd K
  " Set the window height to 5.
  5wincmd _
endfunction

autocmd User YcmQuickFixOpened call s:CustomizeYcmQuickFixWindow()

Options

All options have reasonable defaults so if the plug-in works after installation you don't need to change any options. These options can be configured in your vimrc script by including a line like this:

let g:ycm_min_num_of_chars_for_completion = 1

Note that after changing an option in your vimrc script you have to restart ycmd with the :YcmRestartServer command for the changes to take effect.

The `g:ycm_min_num_of_chars_for_completion` option

This option controls the number of characters the user needs to type before identifier-based completion suggestions are triggered. For example, if the option is set to 2, then when the user types a second alphanumeric character after a whitespace character, completion suggestions will be triggered. This option is NOT used for semantic completion.

Setting this option to a high number like 99 effectively turns off the identifier completion engine and just leaves the semantic engine.

Default: 2

let g:ycm_min_num_of_chars_for_completion = 2

The `g:ycm_min_num_identifier_candidate_chars` option

This option controls the minimum number of characters that a completion candidate coming from the identifier completer must have to be shown in the popup menu.

A special value of 0 means there is no limit.

NOTE: This option only applies to the identifier completer; it has no effect on the various semantic completers.

Default: 0

let g:ycm_min_num_identifier_candidate_chars = 0

The `g:ycm_max_num_candidates` option

This option controls the maximum number of semantic completion suggestions shown in the completion menu. This only applies to suggestions from semantic completion engines; see the g:ycm_max_identifier_candidates option to limit the number of suggestions from the identifier-based engine.

A special value of 0 means there is no limit.

NOTE: Setting this option to 0 or to a value greater than 100 is not recommended as it will slow down completion when there are a very large number of suggestions.

Default: 50

let g:ycm_max_num_candidates = 50

The `g:ycm_max_num_identifier_candidates` option

This option controls the maximum number of completion suggestions from the identifier-based engine shown in the completion menu.

A special value of 0 means there is no limit.

NOTE: Setting this option to 0 or to a value greater than 100 is not recommended as it will slow down completion when there are a very large number of suggestions.

Default: 10

let g:ycm_max_num_identifier_candidates = 10

The `g:ycm_auto_trigger` option

When set to 0, this option turns off YCM's identifier completer (the as-you-type popup) and the semantic triggers (the popup you'd get after typing . or -> in say C++). You can still force semantic completion with the <C-Space> shortcut.

If you want to just turn off the identifier completer but keep the semantic triggers, you should set g:ycm_min_num_of_chars_for_completion to a high number like 99.

Default: 1

let g:ycm_auto_trigger = 1

The `g:ycm_filetype_whitelist` option

This option controls for which Vim filetypes (see :h filetype) should YCM be turned on. The option value should be a Vim dictionary with keys being filetype strings (like python, cpp, etc.) and values being unimportant (the dictionary is used like a hash set, meaning that only the keys matter).

The * key is special and matches all filetypes. By default, the whitelist contains only this * key.

YCM also has a g:ycm_filetype_blacklist option that lists filetypes for which YCM shouldn't be turned on. YCM will work only in filetypes that both the whitelist and the blacklist allow (the blacklist "allows" a filetype by not having it as a key).

For example, let's assume you want YCM to work in files with the cpp filetype. The filetype should then be present in the whitelist either directly (cpp key in the whitelist) or indirectly through the special * key. It should not be present in the blacklist.

Filetypes that are blocked by the either of the lists will be completely ignored by YCM, meaning that neither the identifier-based completion engine nor the semantic engine will operate in them.

You can get the filetype of the current file in Vim with :set ft?.

Default: {'*': 1}

let g:ycm_filetype_whitelist = {'*': 1}

The `g:ycm_filetype_blacklist` option

This option controls for which Vim filetypes (see :h filetype) should YCM be turned off. The option value should be a Vim dictionary with keys being filetype strings (like python, cpp, etc.) and values being unimportant (the dictionary is used like a hash set, meaning that only the keys matter).

See the g:ycm_filetype_whitelist option for more details on how this works.

Default: [see next line]

let g:ycm_filetype_blacklist = {
      \ 'tagbar': 1,
      \ 'notes': 1,
      \ 'markdown': 1,
      \ 'netrw': 1,
      \ 'unite': 1,
      \ 'text': 1,
      \ 'vimwiki': 1,
      \ 'pandoc': 1,
      \ 'infolog': 1,
      \ 'mail': 1
      \}

The `g:ycm_filetype_specific_completion_to_disable` option

This option controls for which Vim filetypes (see :h filetype) should the YCM semantic completion engine be turned off. The option value should be a Vim dictionary with keys being filetype strings (like python, cpp, etc.) and values being unimportant (the dictionary is used like a hash set, meaning that only the keys matter). The listed filetypes will be ignored by the YCM semantic completion engine, but the identifier-based completion engine will still trigger in files of those filetypes.

Note that even if semantic completion is not turned off for a specific filetype, you will not get semantic completion if the semantic engine does not support that filetype.

You can get the filetype of the current file in Vim with :set ft?.

Default: [see next line]

let g:ycm_filetype_specific_completion_to_disable = {
      \ 'gitcommit': 1
      \}

The `g:ycm_filepath_blacklist` option

This option controls for which Vim filetypes (see :h filetype) should filepath completion be disabled. The option value should be a Vim dictionary with keys being filetype strings (like python, cpp, etc.) and values being unimportant (the dictionary is used like a hash set, meaning that only the keys matter).

The * key is special and matches all filetypes. Use this key if you want to completely disable filepath completion:

let g:ycm_filepath_blacklist = {'*': 1}

You can get the filetype of the current file in Vim with :set ft?.

Default: [see next line]

let g:ycm_filepath_blacklist = {
      \ 'html': 1,
      \ 'jsx': 1,
      \ 'xml': 1,
      \}

The `g:ycm_show_diagnostics_ui` option

When set, this option turns on YCM's diagnostic display features. See the Diagnostic display section in the User Manual for more details.

Specific parts of the diagnostics UI (like the gutter signs, text highlighting, diagnostic echo and auto location list population) can be individually turned on or off. See the other options below for details.

Note that YCM's diagnostics UI is only supported for C-family languages.

When set, this option also makes YCM remove all Syntastic checkers set for the c, cpp, objc, objcpp, and cuda filetypes since this would conflict with YCM's own diagnostics UI.

If you're using YCM's identifier completer in C-family languages but cannot use the clang-based semantic completer for those languages and want to use the GCC Syntastic checkers, unset this option.

Default: 1

let g:ycm_show_diagnostics_ui = 1

The `g:ycm_error_symbol` option

YCM will use the value of this option as the symbol for errors in the Vim gutter.

This option is part of the Syntastic compatibility layer; if the option is not set, YCM will fall back to the value of the g:syntastic_error_symbol option before using this option's default.

Default: >>

let g:ycm_error_symbol = '>>'

The `g:ycm_warning_symbol` option

YCM will use the value of this option as the symbol for warnings in the Vim gutter.

This option is part of the Syntastic compatibility layer; if the option is not set, YCM will fall back to the value of the g:syntastic_warning_symbol option before using this option's default.

Default: >>

let g:ycm_warning_symbol = '>>'

The `g:ycm_enable_diagnostic_signs` option

When this option is set, YCM will put icons in Vim's gutter on lines that have a diagnostic set. Turning this off will also turn off the YcmErrorLine and YcmWarningLine highlighting.

This option is part of the Syntastic compatibility layer; if the option is not set, YCM will fall back to the value of the g:syntastic_enable_signs option before using this option's default.

Default: 1

let g:ycm_enable_diagnostic_signs = 1

The `g:ycm_enable_diagnostic_highlighting` option

When this option is set, YCM will highlight regions of text that are related to the diagnostic that is present on a line, if any.

This option is part of the Syntastic compatibility layer; if the option is not set, YCM will fall back to the value of the g:syntastic_enable_highlighting option before using this option's default.

Default: 1

let g:ycm_enable_diagnostic_highlighting = 1

The `g:ycm_echo_current_diagnostic` option

When this option is set, YCM will echo the text of the diagnostic present on the current line when you move your cursor to that line. If a FixIt is available for the current diagnostic, then (FixIt) is appended.

This option is part of the Syntastic compatibility layer; if the option is not set, YCM will fall back to the value of the g:syntastic_echo_current_error option before using this option's default.

Default: 1

let g:ycm_echo_current_diagnostic = 1

The `g:ycm_filter_diagnostics` option

This option controls which diagnostics will be rendered by YCM. This option holds a dictionary of key-values, where the keys are Vim's filetype strings delimited by commas and values are dictionaries describing the filter.

A filter is a dictionary of key-values, where the keys are the type of filter, and the value is a list of arguments to that filter. In the case of just a single item in the list, you may omit the brackets and just provide the argument directly. If any filter matches a diagnostic, it will be dropped and YCM will not render it.

The following filter types are supported:

"regex": Accepts a string regular expression. This type matches when the regex (treated as case-insensitive) is found in the diagnostic text.
"level": Accepts a string level, either "warning" or "error." This type matches when the diagnostic has the same level.

NOTE: The regex syntax is NOT Vim's, it's Python's.

Default: {}

let g:ycm_filter_diagnostics = {
  \ "java": {
  \      "regex": [ ".*taco.*", ... ],
  \      "level": "error",
  \      ...
  \    }
  \ }

The `g:ycm_always_populate_location_list` option

When this option is set, YCM will populate the location list automatically every time it gets new diagnostic data. This option is off by default so as not to interfere with other data you might have placed in the location list.

See :help location-list in Vim to learn more about the location list.

This option is part of the Syntastic compatibility layer; if the option is not set, YCM will fall back to the value of the g:syntastic_always_populate_loc_list option before using this option's default.

Default: 0

let g:ycm_always_populate_location_list = 0

The `g:ycm_open_loclist_on_ycm_diags` option

When this option is set, :YcmDiags will automatically open the location list after forcing a compilation and filling the list with diagnostic data.

See :help location-list in Vim to learn more about the location list.

Default: 1

let g:ycm_open_loclist_on_ycm_diags = 1

The `g:ycm_complete_in_comments` option

When this option is set to 1, YCM will show the completion menu even when typing inside comments.

Default: 0

let g:ycm_complete_in_comments = 0

The `g:ycm_complete_in_strings` option

When this option is set to 1, YCM will show the completion menu even when typing inside strings.

Note that this is turned on by default so that you can use the filename completion inside strings. This is very useful for instance in C-family files where typing #include " will trigger the start of filename completion. If you turn off this option, you will turn off filename completion in such situations as well.

Default: 1

let g:ycm_complete_in_strings = 1

The `g:ycm_collect_identifiers_from_comments_and_strings` option

When this option is set to 1, YCM's identifier completer will also collect identifiers from strings and comments. Otherwise, the text in comments and strings will be ignored.

Default: 0

let g:ycm_collect_identifiers_from_comments_and_strings = 0

The `g:ycm_collect_identifiers_from_tags_files` option

When this option is set to 1, YCM's identifier completer will also collect identifiers from tags files. The list of tags files to examine is retrieved from the tagfiles() Vim function which examines the tags Vim option. See :h 'tags' for details.

YCM will re-index your tags files if it detects that they have been modified.

The only supported tag format is the Exuberant Ctags format. The format from "plain" ctags is NOT supported. Ctags needs to be called with the --fields=+l option (that's a lowercase L, not a one) because YCM needs the language:<lang> field in the tags output.

See the FAQ for pointers if YCM does not appear to read your tag files.

This option is off by default because it makes Vim slower if your tags are on a network directory.

Default: 0

let g:ycm_collect_identifiers_from_tags_files = 0

The `g:ycm_seed_identifiers_with_syntax` option

When this option is set to 1, YCM's identifier completer will seed its identifier database with the keywords of the programming language you're writing.

Since the keywords are extracted from the Vim syntax file for the filetype, all keywords may not be collected, depending on how the syntax file was written. Usually at least 95% of the keywords are successfully extracted.

Default: 0

let g:ycm_seed_identifiers_with_syntax = 0

The `g:ycm_extra_conf_vim_data` option

If you're using semantic completion for C-family files, this option might come handy; it's a way of sending data from Vim to your Settings function in your .ycm_extra_conf.py file.

This option is supposed to be a list of VimScript expression strings that are evaluated for every request to the ycmd server and then passed to your Settings function as a client_data keyword argument.

For instance, if you set this option to ['v:version'], your Settings function will be called like this:

# The '801' value is of course contingent on Vim 8.1; in 8.0 it would be '800'
Settings( ..., client_data = { 'v:version': 801 } )

So the client_data parameter is a dictionary mapping Vim expression strings to their values at the time of the request.

The correct way to define parameters for your Settings function:

def Settings( **kwargs ):

You can then get to client_data with kwargs['client_data'].

Default: []

let g:ycm_extra_conf_vim_data = []

The `g:ycm_server_python_interpreter` option

YCM will by default search for an appropriate Python interpreter on your system. You can use this option to override that behavior and force the use of a specific interpreter of your choosing.

NOTE: This interpreter is only used for the ycmd server. The YCM client running inside Vim always uses the Python interpreter that's embedded inside Vim.

Default: ''

let g:ycm_server_python_interpreter = ''

The `g:ycm_keep_logfiles` option

When this option is set to 1, YCM and the ycmd completion server will keep the logfiles around after shutting down (they are deleted on shutdown by default).

To see where the logfiles are, call :YcmDebugInfo.

Default: 0

let g:ycm_keep_logfiles = 0

The `g:ycm_log_level` option

The logging level that YCM and the ycmd completion server use. Valid values are the following, from most verbose to least verbose:

debug
info
warning
error
critical

Note that debug is very verbose.

Default: info

let g:ycm_log_level = 'info'

The `g:ycm_auto_start_csharp_server` option

When set to 1, the OmniSharp-Roslyn server will be automatically started (once per Vim session) when you open a C# file.

Default: 1

let g:ycm_auto_start_csharp_server = 1

The `g:ycm_auto_stop_csharp_server` option

When set to 1, the OmniSharp-Roslyn server will be automatically stopped upon closing Vim.

Default: 1

let g:ycm_auto_stop_csharp_server = 1

The `g:ycm_csharp_server_port` option

When g:ycm_auto_start_csharp_server is set to 1, specifies the port for the OmniSharp-Roslyn server to listen on. When set to 0 uses an unused port provided by the OS.

Default: 0

let g:ycm_csharp_server_port = 0

The `g:ycm_csharp_insert_namespace_expr` option

By default, when YCM inserts a namespace, it will insert the using statement under the nearest using statement. You may prefer that the using statement is inserted somewhere, for example, to preserve sorting. If so, you can set this option to override this behavior.

When this option is set, instead of inserting the using statement itself, YCM will set the global variable g:ycm_namespace_to_insert to the namespace to insert, and then evaluate this option's value as an expression. The option's expression is responsible for inserting the namespace - the default insertion will not occur.

Default: ''

let g:ycm_csharp_insert_namespace_expr = ''

The `g:ycm_add_preview_to_completeopt` option

When this option is set to 1, YCM will add the preview string to Vim's completeopt option (see :h completeopt). If your completeopt option already has preview set, there will be no effect. You can see the current state of your completeopt setting with :set completeopt? (yes, the question mark is important).

When preview is present in completeopt, YCM will use the preview window at the top of the file to store detailed information about the current completion candidate (but only if the candidate came from the semantic engine). For instance, it would show the full function prototype and all the function overloads in the window if the current completion is a function name.

Default: 0

let g:ycm_add_preview_to_completeopt = 0

The `g:ycm_autoclose_preview_window_after_completion` option

When this option is set to 1, YCM will auto-close the preview window after the user accepts the offered completion string. If there is no preview window triggered because there is no preview string in completeopt, this option is irrelevant. See the g:ycm_add_preview_to_completeopt option for more details.

Default: 0

let g:ycm_autoclose_preview_window_after_completion = 0

The `g:ycm_autoclose_preview_window_after_insertion` option

When this option is set to 1, YCM will auto-close the preview window after the user leaves insert mode. This option is irrelevant if g:ycm_autoclose_preview_window_after_completion is set or if no preview window is triggered. See the g:ycm_add_preview_to_completeopt option for more details.

Default: 0

let g:ycm_autoclose_preview_window_after_insertion = 0

The `g:ycm_max_diagnostics_to_display` option

This option controls the maximum number of diagnostics shown to the user when errors or warnings are detected in the file. This option is only relevant for the C-family, C#, Java, JavaScript, and TypeScript languages.

A special value of 0 means there is no limit.

Default: 30

let g:ycm_max_diagnostics_to_display = 30

The `g:ycm_key_list_select_completion` option

This option controls the key mappings used to select the first completion string. Invoking any of them repeatedly cycles forward through the completion list.

Some users like adding <Enter> to this list.

Default: ['<TAB>', '<Down>']

let g:ycm_key_list_select_completion = ['<TAB>', '<Down>']

The `g:ycm_key_list_previous_completion` option

This option controls the key mappings used to select the previous completion string. Invoking any of them repeatedly cycles backwards through the completion list.

Note that one of the defaults is <S-TAB> which means Shift-TAB. That mapping will probably only work in GUI Vim (Gvim or MacVim) and not in plain console Vim because the terminal usually does not forward modifier key combinations to Vim.

Default: ['<S-TAB>', '<Up>']

let g:ycm_key_list_previous_completion = ['<S-TAB>', '<Up>']

The `g:ycm_key_list_stop_completion` option

This option controls the key mappings used to close the completion menu. This is useful when the menu is blocking the view, when you need to insert the <TAB> character, or when you want to expand a snippet from UltiSnips and navigate through it.

Default: ['<C-y>']

let g:ycm_key_list_stop_completion = ['<C-y>']

The `g:ycm_key_invoke_completion` option

This option controls the key mapping used to invoke the completion menu for semantic completion. By default, semantic completion is triggered automatically after typing ., -> and :: in insert mode (if semantic completion support has been compiled in). This key mapping can be used to trigger semantic completion anywhere. Useful for searching for top-level functions and classes.

Console Vim (not Gvim or MacVim) passes <Nul> to Vim when the user types <C-Space> so YCM will make sure that <Nul> is used in the map command when you're editing in console Vim, and <C-Space> in GUI Vim. This means that you can just press <C-Space> in both console and GUI Vim and YCM will do the right thing.

Setting this option to an empty string will make sure no mapping is created.

Default: <C-Space>

let g:ycm_key_invoke_completion = '<C-Space>'

The `g:ycm_key_detailed_diagnostics` option

This option controls the key mapping used to show the full diagnostic text when the user's cursor is on the line with the diagnostic. It basically calls :YcmShowDetailedDiagnostic.

Setting this option to an empty string will make sure no mapping is created.

Default: <leader>d

let g:ycm_key_detailed_diagnostics = '<leader>d'

The `g:ycm_global_ycm_extra_conf` option

Normally, YCM searches for a .ycm_extra_conf.py file for compilation flags (see the User Guide for more details on how this works). This option specifies a fallback path to a config file which is used if no .ycm_extra_conf.py is found.

You can place such a global file anywhere in your filesystem.

Default: ''

let g:ycm_global_ycm_extra_conf = ''

The `g:ycm_confirm_extra_conf` option

When this option is set to 1 YCM will ask once per .ycm_extra_conf.py file if it is safe to be loaded. This is to prevent execution of malicious code from a .ycm_extra_conf.py file you didn't write.

To selectively get YCM to ask/not ask about loading certain .ycm_extra_conf.py files, see the g:ycm_extra_conf_globlist option.

Default: 1

let g:ycm_confirm_extra_conf = 1

The `g:ycm_extra_conf_globlist` option

This option is a list that may contain several globbing patterns. If a pattern starts with a ! all .ycm_extra_conf.py files matching that pattern will be blacklisted, that is they won't be loaded and no confirmation dialog will be shown. If a pattern does not start with a ! all files matching that pattern will be whitelisted. Note that this option is not used when confirmation is disabled using g:ycm_confirm_extra_conf and that items earlier in the list will take precedence over the later ones.

Rules:

* matches everything
? matches any single character
[seq] matches any character in seq
[!seq] matches any char not in seq

Example:

let g:ycm_extra_conf_globlist = ['~/dev/*','!~/*']

The first rule will match everything contained in the ~/dev directory so .ycm_extra_conf.py files from there will be loaded.
The second rule will match everything in the home directory so a .ycm_extra_conf.py file from there won't be loaded.
As the first rule takes precedence everything in the home directory excluding the ~/dev directory will be blacklisted.

NOTE: The glob pattern is first expanded with Python's os.path.expanduser() and then resolved with os.path.abspath() before being matched against the filename.

Default: []

let g:ycm_extra_conf_globlist = []

The `g:ycm_filepath_completion_use_working_dir` option

By default, YCM's filepath completion will interpret relative paths like ../ as being relative to the folder of the file of the currently active buffer. Setting this option will force YCM to always interpret relative paths as being relative to Vim's current working directory.

Default: 0

let g:ycm_filepath_completion_use_working_dir = 0

The `g:ycm_semantic_triggers` option

This option controls the character-based triggers for the various semantic completion engines. The option holds a dictionary of key-values, where the keys are Vim's filetype strings delimited by commas and values are lists of strings, where the strings are the triggers.

Setting key-value pairs on the dictionary adds semantic triggers to the internal default set (listed below). You cannot remove the default triggers, only add new ones.

A "trigger" is a sequence of one or more characters that trigger semantic completion when typed. For instance, C++ (cpp filetype) has . listed as a trigger. So when the user types foo., the semantic engine will trigger and serve foo's list of member functions and variables. Since C++ also has -> listed as a trigger, the same thing would happen when the user typed foo->.

It's also possible to use a regular expression as a trigger. You have to prefix your trigger with re! to signify it's a regex trigger. For instance, re!\w+\. would only trigger after the \w+\. regex matches.

NOTE: The regex syntax is NOT Vim's, it's Python's.

Default: [see next line]

let g:ycm_semantic_triggers =  {
  \   'c': ['->', '.'],
  \   'objc': ['->', '.', 're!\[[_a-zA-Z]+\w*\s', 're!^\s*[^\W\d]\w*\s',
  \            're!\[.*\]\s'],
  \   'ocaml': ['.', '#'],
  \   'cpp,cuda,objcpp': ['->', '.', '::'],
  \   'perl': ['->'],
  \   'php': ['->', '::'],
  \   'cs,d,elixir,go,groovy,java,javascript,julia,perl6,python,scala,typescript,vb': ['.'],
  \   'ruby,rust': ['.', '::'],
  \   'lua': ['.', ':'],
  \   'erlang': [':'],
  \ }

The `g:ycm_cache_omnifunc` option

Some omnicompletion engines do not work well with the YCM cache—in particular, they might not produce all possible results for a given prefix. By unsetting this option you can ensure that the omnicompletion engine is re-queried on every keypress. That will ensure all completions will be presented, but might cause stuttering and lagginess if the omnifunc is slow.

Default: 1

let g:ycm_cache_omnifunc = 1

The `g:ycm_use_ultisnips_completer` option

By default, YCM will query the UltiSnips plugin for possible completions of snippet triggers. This option can turn that behavior off.

Default: 1

let g:ycm_use_ultisnips_completer = 1

The `g:ycm_goto_buffer_command` option

Defines where GoTo* commands result should be opened. Can take one of the following values: 'same-buffer', 'split', or 'split-or-existing-window'. If this option is set to the 'same-buffer' but current buffer can not be switched (when buffer is modified and nohidden option is set), then result will be opened in a split. When the option is set to 'split-or-existing-window', if the result is already open in a window of the current tab page (or any tab pages with the :tab modifier; see below), it will jump to that window. Otherwise, the result will be opened in a split as if the option was set to 'split'.

To customize the way a new window is split, prefix the GoTo* command with one of the following modifiers: :aboveleft, :belowright, :botright, :leftabove, :rightbelow, :topleft, and :vertical. For instance, to split vertically to the right of the current window, run the command:

:rightbelow vertical YcmCompleter GoTo

To open in a new tab page, use the :tab modifier with the 'split' or 'split-or-existing-window' options e.g.:

:tab YcmCompleter GoTo

NOTE: command modifiers were added in Vim 7.4.1898. If you are using an older version, you can still configure this by setting the option to one of the deprecated values: 'vertical-split', 'new-tab', or 'new-or-existing-tab'.

Default: 'same-buffer'

let g:ycm_goto_buffer_command = 'same-buffer'

The `g:ycm_disable_for_files_larger_than_kb` option

Defines the max size (in Kb) for a file to be considered for completion. If this option is set to 0 then no check is made on the size of the file you're opening.

Default: 1000

let g:ycm_disable_for_files_larger_than_kb = 1000

The `g:ycm_use_clangd` option

This option controls whether clangd should be used as completion engine for C-family languages. Can take one of the following values: 1, 0, with meanings:

1: YCM will use clangd if clangd binary exists in third party or it was provided with ycm_clangd_binary_path option.
0: YCM will never use clangd completer.

Default: 1

let g:ycm_use_clangd = 1

The `g:ycm_clangd_binary_path` option

When ycm_use_clangd option is set to 1, this option sets the path to clangd binary.

Default: ''

let g:ycm_clangd_binary_path = ''

The `g:ycm_clangd_args` option

This option controls the command line arguments passed to the clangd binary. It appends new options and overrides the existing ones.

Default: []

let g:ycm_clangd_args = []

The `g:ycm_clangd_uses_ycmd_caching` option

This option controls which ranking and filtering algorithm to use for completion items. It can take values:

1: Uses ycmd's caching and filtering logic.
0: Uses clangd's caching and filtering logic.

Default: 1

let g:ycm_clangd_uses_ycmd_caching = 1

The `g:ycm_language_server` option

This option lets YCM use an arbitrary LSP server, not unlike coc.nvim and others. However, the officially supported completers are favoured over custom LSP ones, so overriding an existing completer means first making sure YCM won't choose that existing completer in the first place.

A simple working example of this option can be found in the section called "Semantic Completion for Other Languages".

Default: []

let g:ycm_language_server = []

The `g:ycm_disable_signature_help` option

This option allows you to disable all signature help for all completion engines. There is no way to disable it per-completer. This option is reserved, meaning that while signature help support remains experimental, its values and meaning may change and it may be removed in a future version.

Default: 0

" Disable signature help
let g:ycm_disable_signature_help = 1

FAQ

I used to be able to `import vim` in `.ycm_extra_conf.py`, but now can't

YCM was rewritten to use a client-server architecture where most of the logic is in the ycmd server. So the magic vim module you could have previously imported in your .ycm_extra_conf.py files doesn't exist anymore.

To be fair, importing the magic vim module in extra conf files was never supported in the first place; it only ever worked by accident and was never a part of the extra conf API.

But fear not, you should be able to tweak your extra conf files to continue working by using the g:ycm_extra_conf_vim_data option. See the docs on that option for details.

I get `ImportError` exceptions that mention `PyInit_ycm_core` or `initycm_core`

These errors are caused by building the YCM native libraries for Python 2 and trying to load them into a Python 3 process (or the other way around).

For instance, if building for Python 2 but loading in Python 3:

ImportError: dynamic module does not define init function (PyInit_ycm_core)

If building for Python 3 but loading in Python 2:

ImportError: dynamic module does not define init function (initycm_core)

Setting the g:ycm_server_python_interpreter option to force the use of a specific Python interpreter for ycmd is usually the easiest way to solve the problem. Common values for that option are /usr/bin/python and /usr/bin/python3.

I get a linker warning regarding `libpython` on macOS when compiling YCM

If the warning is ld: warning: path '/usr/lib/libpython2.7.dylib' following -L not a directory, then feel free to ignore it; it's caused by a limitation of CMake and is not an issue. Everything should still work fine.

I get a weird window at the top of my file when I use the semantic engine

This is Vim's preview window. Vim uses it to show you extra information about something if such information is available. YCM provides Vim with such extra information. For instance, when you select a function in the completion list, the preview window will hold that function's prototype and the prototypes of any overloads of the function. It will stay there after you select the completion so that you can use the information about the parameters and their types to write the function call.

If you would like this window to auto-close after you select a completion string, set the g:ycm_autoclose_preview_window_after_completion option to 1 in your vimrc file. Similarly, the g:ycm_autoclose_preview_window_after_insertion option can be set to close the preview window after leaving insert mode.

If you don't want this window to ever show up, add set completeopt-=preview to your vimrc. Also make sure that the g:ycm_add_preview_to_completeopt option is set to 0.

It appears that YCM is not working

In Vim, run :messages and carefully read the output. YCM will echo messages to the message log if it encounters problems. It's likely you misconfigured something and YCM is complaining about it.

Also, you may want to run the :YcmDebugInfo command; it will make YCM spew out various debugging information, including the YCM and ycmd logfile paths and the compile flags for the current file if the file is a C-family language file and you have compiled in Clang support. Logfiles can be opened in the editor using the :YcmToggleLogs command.

Sometimes it takes much longer to get semantic completions than normal

This means that libclang (which YCM uses for C-family semantic completion) failed to pre-compile your file's preamble. In other words, there was an error compiling some of the source code you pulled in through your header files. I suggest calling the :YcmDiags command to see what they were.

Bottom line, if libclang can't pre-compile your file's preamble because there were errors in it, you're going to get slow completions because there's no AST cache.

YCM auto-inserts completion strings I don't want!

If this happens when Vim automatically wraps text then it's a Vim bug that has been fixed in version 8.0.0127. Update your Vim to this version or later.

This could also be some mappings that interfere with YCM's internal ones. Make sure you don't have something mapped to <C-p>, <C-x> or <C-u> (in insert mode).

YCM never selects something for you; it just shows you a menu and the user has to explicitly select something. If something is being selected automatically, this means there's a bug or a misconfiguration somewhere.

I get a `E227: mapping already exists for <blah>` error when I start Vim

This means that YCM tried to set up a key mapping but failed because you already had something mapped to that key combination. The <blah> part of the message will tell you what was the key combination that failed.

Look in the Options section and see if any of the default mappings conflict with your own. Then change that option value to something else so that the conflict goes away.

I get `'GLIBC_2.XX' not found (required by libclang.so)` when starting Vim

Your system is too old for the precompiled binaries from llvm.org. Compile Clang on your machine and then link against the libclang.so you just produced. See the full installation guide for help.

I get `LONG_BIT definition appears wrong for platform` when compiling

Look at the output of your CMake call. There should be a line in it like the following (with .dylib in place of .so on macOS):

-- Found PythonLibs: /usr/lib/libpython2.7.so (Required is at least version "2.5")

That would be the correct output. An example of incorrect output would be the following:

-- Found PythonLibs: /usr/lib/libpython2.7.so (found suitable version "2.5.1", minimum required is "2.5")

Notice how there's an extra bit of output there, the found suitable version "<version>" part, where <version> is not the same as the version of the dynamic library. In the example shown, the library is version 2.7 but the second string is version 2.5.1.

This means that CMake found one version of Python headers and a different version for the library. This is wrong. It can happen when you have multiple versions of Python installed on your machine.

You should probably add the following flags to your cmake call (again, dylib instead of so on macOS):

-DPYTHON_INCLUDE_DIR=/usr/include/python2.7 -DPYTHON_LIBRARY=/usr/lib/libpython2.7.so

This will force the paths to the Python include directory and the Python library to use. You may need to set these flags to something else, but you need to make sure you use the same version of Python that your Vim binary is built against, which is highly likely to be the system's default Python.

I get `libpython2.7.a [...] relocation R_X86_64_32` when compiling

The error is usually encountered when compiling YCM on Centos or RHEL. The full error looks something like the following:

/usr/bin/ld: /usr/local/lib/libpython2.7.a(abstract.o): relocation R_X86_64_32 against `a local symbol' can not be used when making a shared object; recompile with -fPIC

It's possible to get a slightly different error that's similar to the one above. Here's the problem and how you solve it:

Your libpython2.7.a was not compiled with -fPIC so it can't be linked into ycm_core.so. Use the -DPYTHON_LIBRARY= CMake flag to point it to a .so version of libpython on your machine (for instance, -DPYTHON_LIBRARY=/usr/lib/libpython2.7.so). Naturally, this means you'll have to go through the full installation guide by hand.

I see `undefined symbol: clang_getCompletionFixIt` in the server logs.

This means that the server is trying to load a version of libclang that is too old. You need at least libclang 9.0.0. We recommend running the install.py script without --system-libclang or downloading the latest prebuilt binaries from llvm.org when going through the full installation guide.

I get `Fatal Python error: PyThreadState_Get: no current thread` on startup

This is caused by linking a static version of libpython into ycmd's ycm_core.so. This leads to multiple copies of the python interpreter loaded when python loads ycmd_core.so and this messes up python's global state. The details aren't important.

The solution is that the version of Python linked and run against must be built with either --enable-shared or --enable-framework (on OS X). This is achieved as follows (NOTE: for macOS, replace --enable-shared with --enable-framework):

When building python from source: ./configure --enable-shared {options}
When building python from pyenv: PYTHON_CONFIGURE_OPTS="--enable-shared" pyenv install {version}

`install.py` says python must be compiled with `--enable-framework`. Wat?

See the previous answer for how to ensure your python is built to support dynamic modules.

YCM does not read identifiers from my tags files

First, put let g:ycm_collect_identifiers_from_tags_files = 1 in your vimrc.

Make sure you are using Exuberant Ctags to produce your tags files since the only supported tag format is the Exuberant Ctags format. The format from "plain" ctags is NOT supported. The output of ctags --version should list "Exuberant Ctags". See Universal Ctags for a maintained version.

Ctags needs to be called with the --fields=+l (that's a lowercase L, not a one) option because YCM needs the language:<lang> field in the tags output.

NOTE: Exuberant Ctags by default sets language tag for *.h files as C++. If you have C (not C++) project, consider giving parameter --langmap=c:.c.h to ctags to see tags from *.h files.

NOTE: macOS comes with "plain" ctags installed by default. brew install ctags will get you the Exuberant Ctags version.

Also make sure that your Vim tags option is set correctly. See :h 'tags' for details. If you want to see which tag files YCM will read for a given buffer, run :echo tagfiles() with the relevant buffer active. Note that that function will only list tag files that already exist.

`CTRL-U` in insert mode does not work while the completion menu is visible

YCM uses completefunc completion mode to show suggestions and Vim disables <C-U> in that mode as a "feature." Sadly there's nothing I can do about this.

My `CTRL-R` mapping does not work while the completion menu is visible

Vim prevents remapping of the <C-R> key in all <C-X> completion modes (except the <C-X><C-N>/<C-X><C-P> mode which operates in the same mode as <C-N>/<C-P>) and YCM uses the <C-X><C-U> (completefunc) mode for completions. This means that adding <C-R> to any of the g:ycm_key_list_* options has no effect. You need to use another key.

YCM conflicts with UltiSnips TAB key usage

YCM comes with support for UltiSnips (snippet suggestions in the popup menu), but you'll have to change the UltiSnips mappings. See :h UltiSnips-triggers in Vim for details. You'll probably want to change some/all of the following options:

g:UltiSnipsExpandTrigger
g:UltiSnipsJumpForwardTrigger
g:UltiSnipsJumpBackwardTrigger

Snippets added with `:UltiSnipsAddFiletypes` do not appear in the popup menu

For efficiency, YCM only fetches UltiSnips snippets in specific scenarios like visiting a buffer or setting its filetype. You can force YCM to retrieve them by manually triggering the FileType autocommand:

:doautocmd FileType

Why isn't YCM just written in plain VimScript, FFS?

Because of the identifier completion engine and subsequence-based filtering. Let's say you have many dozens of files open in a single Vim instance (I often do); the identifier-based engine then needs to store thousands (if not tens of thousands) of identifiers in its internal data-structures. When the user types, YCM needs to perform subsequence-based filtering on all of those identifiers (every single one!) in less than 10 milliseconds.

I'm sorry, but that level of performance is just plain impossible to achieve with VimScript. I've tried, and the language is just too slow. No, you can't get acceptable performance even if you limit yourself to just the identifiers in the current file and simple prefix-based filtering.

Why does YCM demand such a recent version of Vim?

YCM needs a version of Vim with the timers feature to achieve full asynchronicity. This feature is available since Vim 7.4.1578.

YCM provides powerful new functionality like signature help by using new features in Vim such as popup windows, and new APIs such as pum_getpos. This requires Vim 8.1.1875 and we strongly recommend using this version or later.

Nasty bugs happen if I have the `vim-autoclose` plugin installed

Use the delimitMate plugin instead. It does the same thing without conflicting with YCM.

Is there some sort of YCM mailing list? I have questions

If you have questions about the plugin or need help, please use the ycm-users mailing list, don't create issues on the tracker. The tracker is for bug reports and feature requests.

I get an internal compiler error when installing

This can be a problem on virtual servers with limited memory. A possible solution is to add more swap memory. A more practical solution would be to force the build script to run only one compile job at a time. You can do this by setting the YCM_CORES environment variable to 1. Example:

YCM_CORES=1 ./install.py --clang-completer

I get weird errors when I press `Ctrl-C` in Vim

Never use Ctrl-C in Vim.

Using Ctrl-C to exit insert mode in Vim is a bad idea. The main issue here is that Ctrl-C in Vim doesn't just leave insert mode, it leaves it without triggering InsertLeave autocommands (as per Vim docs). This is a bad idea and is likely to break many other things and not just YCM.

Bottom line, if you use Ctrl-C to exit insert mode in Vim, you're gonna have a bad time.

If pressing <esc> is too annoying (agreed, it is), we suggest mapping it to something more convenient. On a QWERTY keyboard, a good pick for the <esc> map is inoremap jk <Esc>. This is right on the home row, it's an incredibly rare digraph in English and if you ever need to type those two chars in sequence in insert mode, you just type j, then wait 500ms, then type k.

Why did YCM stop using Syntastic for diagnostics display?

Previously, YCM would send any diagnostics it would receive from the libclang semantic engine to Syntastic for display as signs in the gutter, red squiggles etc. Today, YCM uses its own code to do that.

Using Syntastic for this was always a kludge. Syntastic assumes its "checker" plugins behave in a certain way; those assumptions have never fit YCM. For instance, YCM continuously recompiles your code in the background for C-family languages and tries to push new diagnostics to the user as fast as possible, even while the user types.

Syntastic assumes that a checker only runs on file save ("active" mode) or even less frequently, when the user explicitly invokes it ("passive" mode). This mismatch in assumptions causes performance problems since Syntastic code isn't optimized for this use case of constant diagnostic refreshing.

Poor support for this use case also led to crash bugs in Vim caused by Syntastic-Vim interactions (issue #593) and other problems, like random Vim flickering. Attempts were made to resolve these issues in Syntastic, but ultimately some of them failed (for various reasons).

Implementing diagnostic display code directly in YCM resolves all of these problems. Performance also improved substantially since the relevant code is now written in Python instead of VimScript (which is very slow) and is tailored only for YCM's use-cases. We were also able to introduce new features in this area since we're now not limited to the Syntastic checker API.

We've tried to implement this in the most backwards-compatible way possible; YCM options that control diagnostic display fall back to Syntastic options that control the same concepts if the user has those set.

Still, some Syntastic-specific configuration you might have had might not be supported by the new code. Please file issues on the tracker in such cases; if we find the request to be reasonable, we'll find a way to address it.

Completion doesn't work with the C++ standard library headers

This is caused by an issue with libclang that only affects some operating systems. Compiling with clang the binary will use the correct default header search paths but compiling with libclang.so (which YCM uses) does not.

macOS is normally affected, but there's a workaround in YCM for that specific OS. If you're not running that OS but still have the same problem, continue reading.

The workaround is to call echo | clang -v -E -x c++ - and look at the paths under the #include <...> search starts here: heading. You should take those paths, prepend -isystem to each individual path and append them all to the list of flags you return from your Settings function in your .ycm_extra_conf.py file.

See issue #303 for details.

When I start vim I get a runtime error saying `R6034 An application has made an attempt to load the C runtime library incorrectly.`

CMake and other things seem to screw up the PATH with their own msvcrXX.dll versions. Add the following to the very top of your vimrc to remove these entries from the path.

python << EOF
import os
import re
path = os.environ['PATH'].split(';')

def contains_msvcr_lib(folder):
    try:
        for item in os.listdir(folder):
            if re.match(r'msvcr\d+\.dll', item):
                return True
    except:
        pass
    return False

path = [folder for folder in path if not contains_msvcr_lib(folder)]
os.environ['PATH'] = ';'.join(path)
EOF

I hear that YCM only supports Python 2, is that true?

No. Both the Vim client and the ycmd server run on Python 2 or 3. If you are talking about code completion in a project, you can configure the Python used for your project through a .ycm_extra_conf.py file. See the Python Semantic Completion section for more details.

On Windows I get `E887: Sorry, this command is disabled, the Python's site module could not be loaded`

If you are running vim on Windows with Python 2.7.11, this is likely caused by a bug. Follow this workaround or use a different version (Python 2.7.12 does not suffer from the bug).

I can't complete Python packages in a virtual environment.

This means that the Python used to run Jedi is not the Python of the virtual environment you're in. To resolve this you should create a .ycm_extra_conf.py file at the root of your project that sets the interpreter_path option to the Python of your virtual environment, e.g.

def Settings(**kwargs):
  return {
    'interpreter_path': '/path/to/virtual/env/bin/python'
  }

See the Python Semantic Completion section for more details.

I want to defer loading of YouCompleteMe until after Vim finishes booting

In recent versions of Vim, you can install YCM in a folder under ~/.vim/pack/*/opt and then load it once the user is idle via an autocommand:

augroup load_ycm
  autocmd!
  autocmd CursorHold, CursorHoldI * :packadd YouCompleteMe
                                \ | autocmd! load_ycm
augroup END

YCM does not shut down when I quit Vim

YCM relies on the VimLeave event to shut down the ycmd server. Some plugins prevent this event from triggering by exiting Vim through an autocommand without using the nested keyword (see :h autocmd-nested). You should identify which plugin is responsible for the issue and report it to the plugin author. Note that when this happens, ycmd will automatically shut itself down after 30 minutes.

YCM does not work with my Anaconda Python setup

Anaconda is often incompatible with the pre-built libclang used by YCM and therefore is not supported. The recommended way to solve this is to run /path/to/real/python install.py (for example /usr/bin/python install.py).

If you want completion in Anaconda projects, point the interpreter_path option in your .ycm_extra_conf.py file to the path of your Anaconda Python e.g.

def Settings(**kwargs):
  return {
    'interpreter_path': '/path/to/anaconda/python'
  }

See the Python Semantic Completion section for more details.

Automatic import insertion after selecting a completion breaks undo

This is a Vim bug fixed in version 8.1.0256. Update your Vim to this version or later.

`TAB` is already mapped to trigger completion in the command-line window

Vim automatically maps the key set by the wildchar option, which is TAB by default, to complete commands in the command-line window. If you would prefer using this key to cycle through YCM's suggestions without changing the value of wildchar, add the following to your vimrc:

autocmd CmdwinEnter * inoremap <expr><buffer> <TAB>
      \ pumvisible() ? "\<C-n>" : "\<TAB>"

Contributor Code of Conduct

Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms.

Contact

If you have questions about the plugin or need help, please join the Gitter room or use the ycm-users mailing list.

If you have bug reports or feature suggestions, please use the issue tracker. Before you do, please carefully read CONTRIBUTING.md as this asks for important diagnostics which the team will use to help get you going.

The latest version of the plugin is available at http://ycm-core.github.io/YouCompleteMe/.

The author's homepage is http://val.markovic.io.

Please do NOT go to #vim on freenode for support. Please contact the YouCompleteMe maintainers directly using the contact details.

Name		Name	Last commit message	Last commit date
Latest commit History 2,569 Commits
.github		.github
autoload		autoload
azure		azure
doc		doc
plugin		plugin
python		python
test		test
third_party		third_party
.coveragerc		.coveragerc
.gitignore		.gitignore
.gitmodules		.gitmodules
.mergify.yml		.mergify.yml
.ycm_extra_conf.py		.ycm_extra_conf.py
CODE_OF_CONDUCT.md		CODE_OF_CONDUCT.md
CONTRIBUTING.md		CONTRIBUTING.md
COPYING.txt		COPYING.txt
README.md		README.md
azure-pipelines.yml		azure-pipelines.yml
codecov.yml		codecov.yml
install.py		install.py
install.sh		install.sh
print_todos.sh		print_todos.sh
run_tests.py		run_tests.py
tox.ini		tox.ini

License

ariel-miculas/YouCompleteMe

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YouCompleteMe: a code-completion engine for Vim

Early Warning: Dropping support for Python 2 in 2020

Help, Advice, Support

Contents

Intro

Installation

macOS

Linux 64-bit

Windows

FreeBSD/OpenBSD

Full Installation Guide

Quick Feature Summary

General (all languages)

C-family languages (C, C++, Objective C, Objective C++, CUDA)

C♯

Python

Go

JavaScript and TypeScript

Rust

Java

User Guide

General Usage

Client-Server Architecture

Completion String Ranking

Signature Help

General Semantic Completion

C-family Semantic Completion

Option 1: Use a compilation database

Option 2: Provide the flags manually

Errors during compilation

Selecting a C-family completion engine

Java Semantic Completion

Java quick Start

Java Project Files

Diagnostic display - Syntastic

Diagnostic display - Eclim

Eclipse Projects

Maven Projects

Gradle Projects

Troubleshooting

C# Semantic Completion

Automaticly discovered solution files

Manually specified solution files

Python Semantic Completion

Working with virtual environments

Working with third-party packages

Configuring through Vim options

Rust Semantic Completion

Go Semantic Completion

JavaScript and TypeScript Semantic Completion

Semantic Completion for Other Languages

Plugging an arbitrary LSP server

Using omnifunc for semantic completion

LSP Configuration

Writing New Semantic Completers

Diagnostic Display

Diagnostic Highlighting Groups

Commands

The :YcmRestartServer command

The :YcmForceCompileAndDiagnostics command

The :YcmDiags command

The :YcmShowDetailedDiagnostic command

The :YcmDebugInfo command

The :YcmToggleLogs command

The :YcmCompleter command

YcmCompleter Subcommands

GoTo Commands

The GoToInclude subcommand

The GoToDeclaration subcommand

The GoToDefinition subcommand

The GoTo subcommand

The GoToImprecise subcommand

The GoToReferences subcommand

The GoToImplementation subcommand

Using `omnifunc` for semantic completion

The `:YcmRestartServer` command

The `:YcmForceCompileAndDiagnostics` command

The `:YcmDiags` command

The `:YcmShowDetailedDiagnostic` command

The `:YcmDebugInfo` command

The `:YcmToggleLogs` command

The `:YcmCompleter` command

The `GoToInclude` subcommand

The `GoToDeclaration` subcommand

The `GoToDefinition` subcommand

The `GoTo` subcommand

The `GoToImprecise` subcommand

The `GoToReferences` subcommand

The `GoToImplementation` subcommand

The `GoToImplementationElseDeclaration` subcommand

The `GoToType` subcommand

The `GetType` subcommand

The `GetTypeImprecise` subcommand

The `GetParent` subcommand

The `GetDoc` subcommand

The `GetDocImprecise` subcommand

The `FixIt` subcommand

The `RefactorRename <new name>` subcommand

The `Format` subcommand

The `OrganizeImports` subcommand

The `ExecuteCommand <args>` subcommand

The `RestartServer` subcommand

The `ClearCompilationFlagCache` subcommand

The `ReloadSolution` subcommand

The `youcompleteme#GetErrorCount` function

The `youcompleteme#GetWarningCount` function

The `YcmLocationOpened` autocommand

The `YcmQuickFixOpened` autocommand

The `g:ycm_min_num_of_chars_for_completion` option

The `g:ycm_min_num_identifier_candidate_chars` option

The `g:ycm_max_num_candidates` option

The `g:ycm_max_num_identifier_candidates` option

The `g:ycm_auto_trigger` option

The `g:ycm_filetype_whitelist` option

The `g:ycm_filetype_blacklist` option

The `g:ycm_filetype_specific_completion_to_disable` option

The `g:ycm_filepath_blacklist` option

The `g:ycm_show_diagnostics_ui` option

The `g:ycm_error_symbol` option

The `g:ycm_warning_symbol` option

The `g:ycm_enable_diagnostic_signs` option

The `g:ycm_enable_diagnostic_highlighting` option

The `g:ycm_echo_current_diagnostic` option

The `g:ycm_filter_diagnostics` option

The `g:ycm_always_populate_location_list` option

The `g:ycm_open_loclist_on_ycm_diags` option

The `g:ycm_complete_in_comments` option

The `g:ycm_complete_in_strings` option

The `g:ycm_collect_identifiers_from_comments_and_strings` option

The `g:ycm_collect_identifiers_from_tags_files` option

The `g:ycm_seed_identifiers_with_syntax` option

The `g:ycm_extra_conf_vim_data` option

The `g:ycm_server_python_interpreter` option

The `g:ycm_keep_logfiles` option

The `g:ycm_log_level` option

The `g:ycm_auto_start_csharp_server` option

The `g:ycm_auto_stop_csharp_server` option

The `g:ycm_csharp_server_port` option

The `g:ycm_csharp_insert_namespace_expr` option

The `g:ycm_add_preview_to_completeopt` option

The `g:ycm_autoclose_preview_window_after_completion` option

The `g:ycm_autoclose_preview_window_after_insertion` option

The `g:ycm_max_diagnostics_to_display` option

The `g:ycm_key_list_select_completion` option

The `g:ycm_key_list_previous_completion` option

The `g:ycm_key_list_stop_completion` option

The `g:ycm_key_invoke_completion` option