Create target "format" by default only if yaml-cpp is main cmake project

[OlivierLDff]

Use Case

I included yaml-cpp with FetchContent.
I don't want to have in my targets, a format target that do not format my main project.

Fix

I introduce cmake option YAML_CPP_ENABLE_FORMAT that is ON by default when yaml-cpp is root project, and OFF otherwise.
Then target format is created if (YAML_CPP_ENABLE_FORMAT AND YAML_CPP_CLANG_FORMAT_EXE)

[jbeder]

Solved by 0e6e98e?

[OlivierLDff]

Yes but don't you think

cmake_dependent_option(YAML_CPP_FORMAT_SOURCE 
  "Enable format target" ON
  "CMAKE_SOURCE_DIR STREQUAL PROJECT_SOURCE_DIR" OFF)

would make more sense?

It would ease integration with FetchContent, CPM, etc...

[jbeder]

Is that right? There are some other PRs (e.g. #1007) that seem to prefer option instead of cmake_dependent_option.

[OlivierLDff]

Oh yes I didn't know cmake_dependent_option couldn't be overridable.

Then following code is the best option:

option(YAML_CPP_FORMAT_SOURCE "Format source" ${YAML_CPP_MAIN_PROJECT})

That would also be consistent with what have been done for: YAML_CPP_INSTALL.

To push it a little bit further even

cmake_dependent_option(YAML_CPP_BUILD_TESTS
  "Enable yaml-cpp tests" ON
  "BUILD_TESTING;CMAKE_SOURCE_DIR STREQUAL PROJECT_SOURCE_DIR" OFF)

should behave that way. Let's say if you want to run yaml-cpp tests along with your project unit test using ctest for example

---

And don't you think YAML_CPP_ENABLE_FORMAT should become dependent on YAML_CPP_CLANG_FORMAT_EXE

cmake_dependent_option(YAML_CPP_ENABLE_FORMAT 
  "Format source" ${YAML_CPP_MAIN_PROJECT}
  "YAML_CPP_CLANG_FORMAT_EXE" OFF)

or something similar? I'm not sure this would work, I haven't tested this code