[all-commits] [llvm/llvm-project] 180f80: [clang] Fix ASTWriter crash after merging named en...

[Michael Jabbour via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 180f8032f0f67faf2a73791ee37a87cb8560135c
      https://github.com/llvm/llvm-project/commit/180f8032f0f67faf2a73791ee37a87cb8560135c
  Author: Michael Jabbour <117195239+michael-jabbour-sonarsource at users.noreply.github.com>
  Date:   2025-03-07 (Fri, 07 Mar 2025)

  Changed paths:
    M clang/docs/ReleaseNotes.rst
    M clang/include/clang/Sema/Sema.h
    M clang/lib/Parse/ParseDecl.cpp
    M clang/lib/Parse/ParseDeclCXX.cpp
    M clang/lib/Sema/SemaDecl.cpp
    A clang/test/Modules/modules-merge-enum.m

  Log Message:
  -----------
  [clang] Fix ASTWriter crash after merging named enums (#114240)

Clang already removes parsed enumerators when merging typedefs to
anonymous enums. This is why the following example decl used to be
handled correctly while merging, and ASTWriter behaves as expected:

```c
typedef enum { Val } AnonEnum;
```
However, the mentioned mechanism didn't handle named enums. This leads
to stale declarations in `IdResolver`, causing an assertion violation in
ASTWriter ``Assertion `DeclIDs.contains(D) && "Declaration not
emitted!"' failed`` when a module is being serialized with the following
example merged enums:

```c
typedef enum Enum1 { Val_A } Enum1;
enum Enum2 { Val_B };
```

The PR applies the same mechanism in the named enums case.

Additionally, I dropped the call to
`getLexicalDeclContext()->removeDecl` as it was causing a wrong
odr-violation diagnostic with anonymous enums.

Might be easier to to review commit by commit. Any feedback is
appreciated.

### Context

This fixes frontend crashes that were encountered when certain
Objective-C modules are included on Xcode 16. For example, by running
`CC=/path/to/clang-19 xcodebuild clean build` on a project that contains
the following Objective-C file:

```c
#include <os/atomic.h>

int main() {
  return memory_order_relaxed;
}
```
This crashes the parser in release, when ASTReader tries to load the
enumerator declaration.



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