[all-commits] [llvm/llvm-project] 4295ae: [clang][modules] Use extensible RTTI for ModuleFil...

[Jan Svoboda via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 4295ae96cdf275cdda8bded9271960a4cac11fb2
      https://github.com/llvm/llvm-project/commit/4295ae96cdf275cdda8bded9271960a4cac11fb2
  Author: Jan Svoboda <jan_svoboda at apple.com>
  Date:   2021-03-05 (Fri, 05 Mar 2021)

  Changed paths:
    M clang/include/clang/Serialization/ModuleFileExtension.h
    M clang/lib/Frontend/TestModuleFileExtension.cpp
    M clang/lib/Frontend/TestModuleFileExtension.h
    M clang/lib/Serialization/ModuleFileExtension.cpp
    M clang/unittests/Frontend/CompilerInvocationTest.cpp

  Log Message:
  -----------
  [clang][modules] Use extensible RTTI for ModuleFileExtension

Clang exposes an interface for extending the PCM/PCH file format: `ModuleFileExtension`.

Clang itself has only a single implementation of the interface: `TestModuleFileExtension` that can be instantiated via the `-ftest-module-file_extension=` command line argument (and is stored in `FrontendOptions::ModuleFileExtensions`).

Clients of the Clang library can extend the PCM/PCH file format by pushing an instance of their extension class to the `FrontendOptions::ModuleFileExtensions` vector.

When generating the `-ftest-module-file_extension=` command line argument from `FrontendOptions`, a downcast is used to distinguish between the Clang's testing extension and other (client) extensions.

This functionality is enabled by LLVM-style RTTI. However, this style of RTTI is hard to extend, as it requires patching Clang (adding new case to the `ModuleFileExtensionKind` enum).

This patch switches to the LLVM RTTI for open class hierarchies, which allows libClang users (e.g. Swift) to create implementations of `ModuleFileExtension` without patching Clang. (Documentation of the feature: https://llvm.org/docs/HowToSetUpLLVMStyleRTTI.html#rtti-for-open-class-hierarchies)

Reviewed By: artemcm

Differential Revision: https://reviews.llvm.org/D97702