[all-commits] [llvm/llvm-project] 10be0a: [clang] Allow -Wno-error=X to downgrade -pedantic-...

[Fangrui Song via All-commits]

  Branch: refs/heads/release/22.x
  Home:   https://github.com/llvm/llvm-project
  Commit: 10be0a2552059450b02e3a293e39cab034882ba6
      https://github.com/llvm/llvm-project/commit/10be0a2552059450b02e3a293e39cab034882ba6
  Author: Fangrui Song <i at maskray.me>
  Date:   2026-04-17 (Fri, 17 Apr 2026)

  Changed paths:
    M clang/docs/ReleaseNotes.rst
    M clang/lib/Basic/DiagnosticIDs.cpp
    M clang/test/Misc/diag-mapping.c

  Log Message:
  -----------
  [clang] Allow -Wno-error=X to downgrade -pedantic-errors diagnostics to warnings (#184756)

While -Wno-long-long suppresses -pedantic-errors diagnostics in both GCC
and Clang, GCC -Wno-error=long-long emits warnings while Clang still
emits errors.

```
% echo 'long long x = 0;' | gcc -std=c89 -pedantic-errors -Wno-error=long-long -x c -fsyntax-only -
<stdin>:1:6: warning: ISO C90 does not support 'long long' [-Wlong-long]
% echo 'long long x = 0;' | clang -std=c89 -pedantic-errors -Wno-error=long-long -x c -fsyntax-only -
<stdin>:1:1: error: 'long long' is an extension when C99 mode is not enabled [-Werror,-Wlong-long]
    1 | long long x = 0;
      | ^
1 error generated.
```

The order of -pedantic-errors and -Wno-error=long-long does not matter.

Change Clang -Wno-error=long-long to match GCC behavior and be more
consistent with -Wno-long-long. setDiagnosticGroupWarningAsError() sets
HasNoWarningAsError but not IsUser, so the ExtBehavior upgrade would
re-promote to error. When HasNoWarningAsError is set, cap the
ExtBehavior upgrade at Warning.

```
% echo 'long long x = 0;' | myclang -std=c89 -pedantic-errors -Wno-error=long-long -x c -fsyntax-only -
<stdin>:1:1: warning: 'long long' is an extension when C99 mode is not enabled [-Wlong-long]
    1 | long long x = 0;
      | ^
1 warning generated.
```

Fixes https://github.com/llvm/llvm-project/issues/184250

(cherry picked from commit a195c719aa96c491ea52bbb8b9e496d2cd6c8445)



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