[clang] cb50d78 - [C] static_assert in a for loop is not an extension (#151955)

[via cfe-commits]

Author: Aaron Ballman
Date: 2025-08-04T12:46:53-04:00
New Revision: cb50d78a0063244434d883d89ddda7f74abbffc9

URL: https://github.com/llvm/llvm-project/commit/cb50d78a0063244434d883d89ddda7f74abbffc9
DIFF: https://github.com/llvm/llvm-project/commit/cb50d78a0063244434d883d89ddda7f74abbffc9.diff

LOG: [C] static_assert in a for loop is not an extension (#151955)

The original wording can be squinted at to pretend this was always
allowed. GCC squints at it that way, so we're doing the same and no
longer issuing an extension diagnostic for use of static_assert in the
condition-1 of a for loop in C.

Fixes #149633

Added: 
    

Modified: 
    clang/lib/Sema/SemaStmt.cpp
    clang/test/Sema/for.c

Removed: 
    


################################################################################
diff  --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index 3f89843a9081a..a5f92020f49f8 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -2284,7 +2284,11 @@ StmtResult Sema::ActOnForStmt(SourceLocation ForLoc, SourceLocation LParenLoc,
           // we can diagnose if we don't see any variable declarations. This
           // covers a case like declaring a typedef, function, or structure
           // type rather than a variable.
-          NonVarSeen = DI;
+          //
+          // Note, _Static_assert is acceptable because it does not declare an
+          // identifier at all, so "for object having" does not apply.
+          if (!isa<StaticAssertDecl>(DI))
+            NonVarSeen = DI;
         }
       }
       // Diagnose if we saw a non-variable declaration but no variable

diff  --git a/clang/test/Sema/for.c b/clang/test/Sema/for.c
index e16169aac0c4c..35c4720ef3305 100644
--- a/clang/test/Sema/for.c
+++ b/clang/test/Sema/for.c
@@ -26,6 +26,5 @@ void b11 (void) { for (static _Thread_local struct { int i; } s;s.i;); } /* c11-
 #endif
 
 void b12(void) {
-  for(_Static_assert(1, "");;) {} /* c11-warning {{non-variable declaration in 'for' loop is a C23 extension}}
-                                     c23-warning {{non-variable declaration in 'for' loop is incompatible with C standards before C23}} */
+  for(_Static_assert(1, "");;) {} /* okay, _Static_assert declares *no* identifiers */
 }