[PATCH] D99861: [Clang] Record tokens in attribute arguments for user-defined C++/C2x attributes

[Josh Junon via Phabricator via cfe-commits]

Qix- created this revision.
Qix- added a reviewer: aaron.ballman.
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Currently, user-defined attributes (e.g. those registered via Clang plugins) don't hold much information or allow for much to be done with them, as their argument tokens are discarded entirely in almost all cases.

However, since they are quite flexible with their syntax (pretty much anything can go in there), it would be massively helpful if plugins could be handed the pre-processed and parsed tokens as a listed to be consumed by third-party plugins and the like.

This diff creates a trailing data list for `ParsedAttr` objects and places the "recorded" tokens there from the lexer. I would have piggy-backed off of the normal backtrack system but unfortunately it doesn't call the handler for tokens being replayed from the backtrack cache, which in many cases we *do* care about. So I had to create a second recording callback.

The new plugin directory shows how this would be used from a plugin.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D99861

Files:
  clang/examples/CMakeLists.txt
  clang/examples/PrintAttributeTokens/CMakeLists.txt
  clang/examples/PrintAttributeTokens/PrintAttributeTokens.cpp
  clang/examples/PrintAttributeTokens/PrintAttributeTokens.exports
  clang/examples/PrintAttributeTokens/README.txt
  clang/include/clang/Lex/Preprocessor.h
  clang/include/clang/Sema/ParsedAttr.h
  clang/lib/Lex/Preprocessor.cpp
  clang/lib/Parse/ParseDecl.cpp
  clang/lib/Parse/ParseDeclCXX.cpp
  clang/lib/Sema/ParsedAttr.cpp
  clang/test/Frontend/plugin-print-attr-tokens.cpp

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