[clang] 468d2e7 - [Clang] Document when to use ExtWarn and Extension (#223440)

[via cfe-commits]

Author: Nikolas Klauser
Date: 2026-09-21T12:29:33+02:00
New Revision: 468d2e73112a8e9f5fae4e21ad53526a7dc03262

URL: https://github.com/llvm/llvm-project/commit/468d2e73112a8e9f5fae4e21ad53526a7dc03262
DIFF: https://github.com/llvm/llvm-project/commit/468d2e73112a8e9f5fae4e21ad53526a7dc03262.diff

LOG: [Clang] Document when to use ExtWarn and Extension (#223440)

Added: 
    

Modified: 
    clang/docs/InternalsManual.md

Removed: 
    


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diff  --git a/clang/docs/InternalsManual.md b/clang/docs/InternalsManual.md
index 0d9ee745927aa..c2925563aa388 100644
--- a/clang/docs/InternalsManual.md
+++ b/clang/docs/InternalsManual.md
@@ -114,6 +114,17 @@ severe that error recovery won't be able to recover sensibly from them (thus
 spewing a ton of bogus errors). One example of this class of error is failure
 to `#include` a file.
 
+##### Extension vs ExtWarn
+
+Deciding whether to use `Extension` or `ExtWarn` can be 
diff icult. 
+`ExtWarn` should be used if one of the following applies (or another good reason is stated):
+- the extension is likely to be used incorrectly (e.g. `-Wvla`);
+- the diagnosed code is likely wrong (e.g. `-Wmain`);
+- the extension is likely surprising in some cases (e.g. `SFINAEFailure`);
+- the extension is deprecated (e.g. `-Wauto-storage-class`).
+
+`Extension` should be used in all other circumstances.
+
 #### Diagnostic Wording
 
 The wording used for a diagnostic is critical because it is the only way for a