Implement replace_segment attribute (#197)

* Implement `replace_segment` attribute

This implements the `replace_segment` attribute. This attribute can be
used to rename one or multiple segments returned by `TypeInfo::path`. It
could be for example be used to rename a changed crate name. For more
info see the examples and the docs in this pr.

* Update trybuild

* Directly pass the ident str.

* Update changelog

CHANGELOG.md

@@ -5,6 +5,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [2.10.0] - 2023-10-20
+
+### Added
+- Implement `replace_segment` attribute [(#197)](https://github.com/paritytech/scale-info/pull/197)
+
 ## [2.9.0] - 2023-07-03
 
 ### Changed

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "scale-info"
-version = "2.9.0"
+version = "2.10.0"
 authors = ["Parity Technologies <[email protected]>"]
 edition = "2021"
 rust-version = "1.60.0"
@@ -17,7 +17,7 @@ include = ["Cargo.toml", "src/**/*.rs", "README.md", "LICENSE"]
 [dependencies]
 bitvec = { version = "1", default-features = false, features = ["alloc"], optional = true }
 cfg-if = "1.0"
-scale-info-derive = { version = "2.9.0", path = "derive", default-features = false, optional = true }
+scale-info-derive = { version = "2.10.0", path = "derive", default-features = false, optional = true }
 serde = { version = "1", default-features = false, optional = true, features = ["derive", "alloc"] }
 derive_more = { version = "0.99.1", default-features = false, features = ["from"] }
 scale = { package = "parity-scale-codec", version = "3", default-features = false, features = ["derive"] }

derive/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "scale-info-derive"
-version = "2.9.0"
+version = "2.10.0"
 authors = [
     "Parity Technologies <[email protected]>",
     "Centrality Developers <[email protected]>",

derive/src/attr.rs

@@ -16,7 +16,7 @@ use syn::{
     parse::{Parse, ParseBuffer},
     punctuated::Punctuated,
     spanned::Spanned,
-    Token,
+    LitStr, Token,
 };
 
 const SCALE_INFO: &str = "scale_info";
@@ -26,6 +26,7 @@ mod keywords {
     syn::custom_keyword!(bounds);
     syn::custom_keyword!(skip_type_params);
     syn::custom_keyword!(capture_docs);
+    syn::custom_keyword!(replace_segment);
 }
 
 /// Parsed and validated set of `#[scale_info(...)]` attributes for an item.
@@ -34,6 +35,7 @@ pub struct Attributes {
     skip_type_params: Option<SkipTypeParamsAttr>,
     capture_docs: Option<CaptureDocsAttr>,
     crate_path: Option<CratePathAttr>,
+    replace_segments: Vec<ReplaceSegment>,
 }
 
 impl Attributes {
@@ -43,6 +45,7 @@ impl Attributes {
         let mut skip_type_params = None;
         let mut capture_docs = None;
         let mut crate_path = None;
+        let mut replace_segments = Vec::new();
 
         let attributes_parser = |input: &ParseBuffer| {
             let attrs: Punctuated<ScaleInfoAttr, Token![,]> =
@@ -86,7 +89,6 @@ impl Attributes {
                         }
                         capture_docs = Some(parsed_capture_docs);
                     }
-
                     ScaleInfoAttr::CratePath(parsed_crate_path) => {
                         if crate_path.is_some() {
                             return Err(syn::Error::new(
@@ -97,6 +99,9 @@ impl Attributes {
 
                         crate_path = Some(parsed_crate_path);
                     }
+                    ScaleInfoAttr::ReplaceSegment(replace_segment) => {
+                        replace_segments.push(replace_segment);
+                    }
                 }
             }
         }
@@ -127,6 +132,7 @@ impl Attributes {
             skip_type_params,
             capture_docs,
             crate_path,
+            replace_segments,
         })
     }
 
@@ -153,6 +159,11 @@ impl Attributes {
     pub fn crate_path(&self) -> Option<&CratePathAttr> {
         self.crate_path.as_ref()
     }
+
+    /// Returns an iterator over the `#[scale_info(replace_segment("Hello", "world"))]` attributes.
+    pub fn replace_segments(&self) -> impl Iterator<Item = &ReplaceSegment> {
+        self.replace_segments.iter()
+    }
 }
 
 /// Parsed representation of the `#[scale_info(bounds(...))]` attribute.
@@ -266,29 +277,59 @@ impl Parse for CratePathAttr {
     }
 }
 
+/// Parsed representation of the `#[scale_info(replace_segment("Hello", "world"))]` attribute.
+#[derive(Clone)]
+pub struct ReplaceSegment {
+    search: LitStr,
+    replace: LitStr,
+}
+
+impl ReplaceSegment {
+    pub fn search(&self) -> &LitStr {
+        &self.search
+    }
+
+    pub fn replace(&self) -> &LitStr {
+        &self.replace
+    }
+}
+
+impl Parse for ReplaceSegment {
+    fn parse(input: &ParseBuffer) -> syn::Result<Self> {
+        input.parse::<keywords::replace_segment>()?;
+        let content;
+        syn::parenthesized!(content in input);
+
+        let search = content.parse::<LitStr>()?;
+        content.parse::<Token![,]>()?;
+        let replace = content.parse::<LitStr>()?;
+
+        Ok(Self { search, replace })
+    }
+}
+
 /// Parsed representation of one of the `#[scale_info(..)]` attributes.
 pub enum ScaleInfoAttr {
     Bounds(BoundsAttr),
     SkipTypeParams(SkipTypeParamsAttr),
     CaptureDocs(CaptureDocsAttr),
     CratePath(CratePathAttr),
+    ReplaceSegment(ReplaceSegment),
 }
 
 impl Parse for ScaleInfoAttr {
     fn parse(input: &ParseBuffer) -> syn::Result<Self> {
         let lookahead = input.lookahead1();
         if lookahead.peek(keywords::bounds) {
-            let bounds = input.parse()?;
-            Ok(Self::Bounds(bounds))
+            Ok(Self::Bounds(input.parse()?))
         } else if lookahead.peek(keywords::skip_type_params) {
-            let skip_type_params = input.parse()?;
-            Ok(Self::SkipTypeParams(skip_type_params))
+            Ok(Self::SkipTypeParams(input.parse()?))
         } else if lookahead.peek(keywords::capture_docs) {
-            let capture_docs = input.parse()?;
-            Ok(Self::CaptureDocs(capture_docs))
+            Ok(Self::CaptureDocs(input.parse()?))
         } else if lookahead.peek(Token![crate]) {
-            let crate_path = input.parse()?;
-            Ok(Self::CratePath(crate_path))
+            Ok(Self::CratePath(input.parse()?))
+        } else if lookahead.peek(keywords::replace_segment) {
+            Ok(Self::ReplaceSegment(input.parse()?))
         } else {
             Err(lookahead.error())
         }

derive/src/lib.rs

@@ -66,6 +66,7 @@ impl TypeInfoImpl {
 
     fn expand(&self) -> Result<TokenStream2> {
         let ident = &self.ast.ident;
+        let ident_str = ident.to_string();
         let scale_info = crate_path(self.attrs.crate_path())?;
 
         let where_clause = trait_bounds::make_where_clause(
@@ -101,12 +102,23 @@ impl TypeInfoImpl {
         };
         let docs = self.generate_docs(&self.ast.attrs);
 
+        let replaces = self.attrs.replace_segments().map(|r| {
+            let search = r.search();
+            let replace = r.replace();
+
+            quote!(( #search, #replace ))
+        });
+
         Ok(quote! {
             impl #impl_generics #scale_info::TypeInfo for #ident #ty_generics #where_clause {
                 type Identity = Self;
                 fn type_info() -> #scale_info::Type {
                     #scale_info::Type::builder()
-                        .path(#scale_info::Path::new(::core::stringify!(#ident), ::core::module_path!()))
+                        .path(#scale_info::Path::new_with_replace(
+                            #ident_str,
+                            ::core::module_path!(),
+                            &[ #( #replaces ),* ]
+                        ))
                         .type_params(#scale_info::prelude::vec![ #( #type_params ),* ])
                         #docs
                         .#build_type

src/lib.rs

@@ -224,6 +224,30 @@
 //! }
 //! ```
 //!
+//! #### `#[scale_info(replace_segment("search", "replace"))]`
+//!
+//! Specify to rename a segment in the `path` returned by the [`TypeInfo::path`] function.
+//! Normally the path is generated by using the `module_path!` macro. This path includes
+//! the crate name and all the modules up to the declaration of the type. Sometimes it
+//! is useful to replace one of these segments to ensure that for example a renaming
+//! of the crate isn't propagated to downstream users. Be aware that if a `crate-name`
+//! contains an hypen, the actual segment is `crate_name`. The `replace` name needs
+//! to be a valid Rust identifier. The attribute is allowed to be passed multiple
+//! times to replace multiple segments.
+//!
+//! Example:
+//! ```ignore
+//! use scale_info_reexport::info::TypeInfo;
+//!
+//! #[derive(TypeInfo)]
+//! #[scale_info(replace_segment("something", "better_name"))]
+//! #[scale_info(replace_segment("TestEnum", "BetterEnumName"))]
+//! enum TestEnum {
+//!     FirstVariant,
+//!     SecondVariant,
+//! }
+//! ```
+//!
 //! # Forms
 //!
 //! To bridge between compile-time type information and runtime the

src/prelude.rs

@@ -40,7 +40,8 @@ cfg_if! {
             sync,
             time,
             vec,
-            rc
+            rc,
+            iter,
         };
     } else {
         pub use alloc::{
@@ -64,6 +65,7 @@ cfg_if! {
             num,
             ops,
             time,
+            iter,
         };
     }
 }

src/ty/path.rs

@@ -14,6 +14,7 @@
 
 use crate::prelude::{
     fmt::{Display, Error as FmtError, Formatter},
+    iter,
     vec::Vec,
 };
 
@@ -84,9 +85,33 @@ impl Path<MetaForm> {
     ///
     /// - If the type identifier or module path contain invalid Rust identifiers
     pub fn new(ident: &'static str, module_path: &'static str) -> Path {
-        let mut segments = module_path.split("::").collect::<Vec<_>>();
-        segments.push(ident);
-        Self::from_segments(segments).expect("All path segments should be valid Rust identifiers")
+        let segments = module_path.split("::");
+        Self::from_segments(segments.chain(iter::once(ident)))
+            .expect("All path segments should be valid Rust identifiers")
+    }
+
+    /// Create a new Path
+    ///
+    /// The `segment_replace` is a list of `(search, replace)` items. Every
+    /// `search` item that appears in the `module_path` is replaced by the
+    /// `replace` item. This can be used for example to replace the crate name
+    /// or even the name of the type in the final [`Path`].
+    ///
+    /// # Panics
+    ///
+    /// - If the type identifier, module path or replace contain invalid Rust identifiers
+    pub fn new_with_replace(
+        ident: &'static str,
+        module_path: &'static str,
+        segment_replace: &[(&'static str, &'static str)],
+    ) -> Path {
+        let segments = module_path.split("::");
+        Self::from_segments(
+            segments
+                .chain(iter::once(ident))
+                .map(|s| segment_replace.iter().find(|r| s == r.0).map_or(s, |r| r.1)),
+        )
+        .expect("All path segments should be valid Rust identifiers")
     }
 
     /// Create a Path from the given segments

test_suite/tests/derive.rs

@@ -857,3 +857,53 @@ fn strips_invisible_delimiters_from_type_name() {
 
     assert_type!(S, expected);
 }
+
+#[test]
+fn replace_segments_works() {
+    #[allow(unused)]
+    #[derive(TypeInfo)]
+    #[scale_info(replace_segment("derive", "hey"))]
+    pub struct S;
+
+    let ty = Type::builder()
+        .path(Path::new("S", "hey"))
+        .composite(Fields::unit());
+
+    assert_type!(S, ty);
+
+    mod nested {
+        #[allow(unused)]
+        #[derive(info::TypeInfo)]
+        #[scale_info(replace_segment("derive", "hey"))]
+        #[scale_info(replace_segment("nested", "what"))]
+        pub struct S;
+
+        #[allow(unused)]
+        #[derive(info::TypeInfo)]
+        #[scale_info(replace_segment("nested", "what"))]
+        pub struct R;
+    }
+
+    let ty = Type::builder()
+        .path(Path::new("S", "hey::what"))
+        .composite(Fields::unit());
+
+    assert_type!(nested::S, ty);
+
+    let ty = Type::builder()
+        .path(Path::new("R", "derive::what"))
+        .composite(Fields::unit());
+
+    assert_type!(nested::R, ty);
+
+    #[allow(unused)]
+    #[derive(info::TypeInfo)]
+    #[scale_info(replace_segment("R", "AWESOME"))]
+    pub struct R;
+
+    let ty = Type::builder()
+        .path(Path::new("AWESOME", "derive"))
+        .composite(Fields::unit());
+
+    assert_type!(R, ty);
+}

test_suite/tests/ui/fail_missing_derive.stderr

@@ -5,14 +5,14 @@ error[E0277]: the trait bound `PawType<u16>: TypeInfo` is not satisfied
    |                        ^^^^^^^^^^^^^^^^^^ the trait `TypeInfo` is not implemented for `PawType<u16>`
    |
    = help: the following other types implement trait `TypeInfo`:
-             &T
-             &mut T
-             ()
-             (A, B)
-             (A, B, C)
-             (A, B, C, D)
-             (A, B, C, D, E)
-             (A, B, C, D, E, F)
+             bool
+             char
+             i8
+             i16
+             i32
+             i64
+             i128
+             u8
            and $N others
 note: required for `Cat<bool, u8, u16>` to implement `TypeInfo`
   --> tests/ui/fail_missing_derive.rs:8:10