[all-commits] [llvm/llvm-project] b59ab7: [C] Handle comma operator for implicit int->enum c...

[Aaron Ballman via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: b59ab701e94cce455a53358cbe5082a3efb58fbf
      https://github.com/llvm/llvm-project/commit/b59ab701e94cce455a53358cbe5082a3efb58fbf
  Author: Aaron Ballman <aaron at aaronballman.com>
  Date:   2025-05-07 (Wed, 07 May 2025)

  Changed paths:
    M clang/lib/Sema/SemaChecking.cpp
    M clang/test/Sema/implicit-cast.c
    M clang/test/Sema/implicit-int-enum-conversion.c

  Log Message:
  -----------
  [C] Handle comma operator for implicit int->enum conversions (#138752)

In C++, the type of an enumerator is the type of the enumeration,
whereas in C, the type of the enumerator is 'int'. The type of a comma
operator is the type of the right-hand operand, which means you can get
an implicit conversion with this code in C but not in C++:
```
  enum E { Zero };
  enum E foo() {
    return ((void)0, Zero);
  }
```
We were previously incorrectly diagnosing this code as being
incompatible with C++ because the type of the paren expression would be
'int' there, whereas in C++ the type is 'E'.

So now we handle the comma operator with special logic when analyzing
implicit conversions in C. When analyzing the left-hand operand of a
comma operator, we do not need to check for that operand causing an
implicit conversion for the entire comma expression. So we only check
for that case with the right-hand operand.

This addresses a concern brought up post-commit:
https://github.com/llvm/llvm-project/pull/137658#issuecomment-2854525259



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