[clang] handle extended integer constant expressions in _Static_asser…

…t (PR llvm#57687)

Automated commit created by applying diff 461610

Phabricator-ID: PHID-HMBT-5xgffhiglu2gf7cydmvf
Review-ID: D134311

clang/lib/Sema/SemaDeclCXX.cpp

@@ -16731,10 +16731,22 @@ Decl *Sema::BuildStaticAssertDeclaration(SourceLocation StaticAssertLoc,
       AssertExpr = FullAssertExpr.get();
 
     llvm::APSInt Cond;
+    Expr *BaseExpr = AssertExpr;
+    AllowFoldKind FoldKind = NoFold;
+
+    if (!getLangOpts().CPlusPlus) {
+      // In C mode only allow folding and strip the implicit conversion
+      // to the type of the first _Static_assert argument that would
+      // otherwise suppress diagnostics for arguments that convert to int.
+      FoldKind = AllowFold;
+      while (auto *BaseCast = dyn_cast<ImplicitCastExpr>(BaseExpr))
+        BaseExpr = BaseCast->getSubExpr();
+    }
+
     if (!Failed && VerifyIntegerConstantExpression(
-                       AssertExpr, &Cond,
-                       diag::err_static_assert_expression_is_not_constant)
-                       .isInvalid())
+                       BaseExpr, &Cond,
+                       diag::err_static_assert_expression_is_not_constant,
+                       FoldKind).isInvalid())
       Failed = true;
 
     if (!Failed && !Cond) {

clang/test/Sema/static-assert.c

@@ -5,7 +5,7 @@
 
 _Static_assert("foo", "string is nonzero"); // ext-warning {{'_Static_assert' is a C11 extension}}
 #ifndef __cplusplus
-// expected-error@-2 {{static assertion expression is not an integral constant expression}}
+// ext-warning@-2 {{expression is not an integer constant}}
 #endif
 
 _Static_assert(1, "1 is nonzero"); // ext-warning {{'_Static_assert' is a C11 extension}}