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

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Fangrui Song (MaskRay)

<details>
<summary>Changes</summary>

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 -
&lt;stdin&gt;: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 -
&lt;stdin&gt;: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.

```
% echo 'long long x = 0;' | myclang -std=c89 -pedantic-errors 
-Wno-error=long-long -x c -fsyntax-only -
&lt;stdin&gt;: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


---
Full diff: https://github.com/llvm/llvm-project/pull/184756.diff


2 Files Affected:

- (modified) clang/lib/Basic/DiagnosticIDs.cpp (+7-2) 
- (modified) clang/test/Misc/diag-mapping.c (+5) 


``````````diff
diff --git a/clang/lib/Basic/DiagnosticIDs.cpp 
b/clang/lib/Basic/DiagnosticIDs.cpp
index fcd2d9f34414e..36ed9dbbe8dab 100644
--- a/clang/lib/Basic/DiagnosticIDs.cpp
+++ b/clang/lib/Basic/DiagnosticIDs.cpp
@@ -501,8 +501,13 @@ DiagnosticIDs::getDiagnosticSeverity(unsigned DiagID, 
SourceLocation Loc,
 
   // For extension diagnostics that haven't been explicitly mapped, check if we
   // should upgrade the diagnostic.
-  if (IsExtensionDiag && !Mapping.isUser())
-    Result = std::max(Result, State->ExtBehavior);
+  if (IsExtensionDiag && !Mapping.isUser()) {
+    if (Mapping.hasNoWarningAsError())
+      Result = std::max(Result,
+                        std::min(State->ExtBehavior, diag::Severity::Warning));
+    else
+      Result = std::max(Result, State->ExtBehavior);
+  }
 
   // At this point, ignored errors can no longer be upgraded.
   if (Result == diag::Severity::Ignored)
diff --git a/clang/test/Misc/diag-mapping.c b/clang/test/Misc/diag-mapping.c
index edc137ec68fef..b17561b098343 100644
--- a/clang/test/Misc/diag-mapping.c
+++ b/clang/test/Misc/diag-mapping.c
@@ -18,12 +18,17 @@
 // This should emit an error with -pedantic-errors.
 // RUN: not %clang_cc1 %s -pedantic-errors 2>&1 | grep "error:"
 
+// RUN: %clang_cc1 %s -pedantic -Wno-error=extra-tokens 2>&1 | grep "warning:"
+
 // This should emit a warning, because -Wfoo overrides -pedantic*.
 // RUN: %clang_cc1 %s -pedantic-errors -Wextra-tokens 2>&1 | grep "warning:"
 
 // This should emit nothing, because -Wno-extra-tokens overrides -pedantic*
 // RUN: %clang_cc1 %s -pedantic-errors -Wno-extra-tokens 2>&1 | not grep 
diagnostic
 
+// -Wno-error=extra-tokens should downgrade -pedantic-errors to warning.
+// RUN: %clang_cc1 %s -pedantic-errors -Wno-error=extra-tokens 2>&1 | grep 
"warning:"
+
 #ifdef foo
 #endif bad // extension!
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/184756
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