Revert "[C23] Disable diagnostic on struct defn in prototype (llvm#138516)"

This reverts commit 15f7e02.

Author: cyndyishida

clang/lib/Sema/SemaDecl.cpp

@@ -19526,10 +19526,7 @@ Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
 
   // If we're declaring or defining a tag in function prototype scope in C,
   // note that this type can only be used within the function and add it to
-  // the list of decls to inject into the function definition scope. However,
-  // in C23 and later, while the type is only visible within the function, the
-  // function can be called with a compatible type defined in the same TU, so
-  // we silence the diagnostic in C23 and up. This matches the behavior of GCC.
+  // the list of decls to inject into the function definition scope.
   if ((Name || Kind == TagTypeKind::Enum) &&
       getNonFieldDeclScope(S)->isFunctionPrototypeScope()) {
     if (getLangOpts().CPlusPlus) {
@@ -19543,10 +19540,7 @@ Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
       if (TUK == TagUseKind::Declaration)
         Invalid = true;
     } else if (!PrevDecl) {
-      // In C23 mode, if the declaration is complete, we do not want to
-      // diagnose.
-      if (!getLangOpts().C23 || TUK != TagUseKind::Definition)
-        Diag(Loc, diag::warn_decl_in_param_list) << Context.getTagDeclType(New);
+      Diag(Loc, diag::warn_decl_in_param_list) << Context.getTagDeclType(New);
     }
   }
 

clang/test/C/C23/n3030.c

@@ -61,7 +61,7 @@ static_assert(b == 1);
 
 void f1(enum a : long b); // expected-error {{non-defining declaration of enumeration with a fixed underlying type is only permitted as a standalone declaration; missing list of enumerators?}}
                           // expected-warning@-1 {{declaration of 'enum a' will not be visible outside of this function}}
-void f2(enum c : long{x} d);
+void f2(enum c : long{x} d); // expected-warning {{declaration of 'enum c' will not be visible outside of this function}}
 enum e : int f3(); // expected-error {{non-defining declaration of enumeration with a fixed underlying type is only permitted as a standalone declaration; missing list of enumerators?}}
 
 typedef enum t u; // expected-warning {{ISO C forbids forward references to 'enum' types}}

clang/test/C/drs/dr0xx.c

@@ -1,9 +1,9 @@
-/* RUN: %clang_cc1 -std=c89 -fsyntax-only -verify=expected,c89only,c17andearlier -pedantic -Wno-declaration-after-statement -Wno-c11-extensions %s
-   RUN: %clang_cc1 -std=c89 -fsyntax-only -verify=expected,c89only,c17andearlier -pedantic -Wno-declaration-after-statement -Wno-c11-extensions -fno-signed-char %s
-   RUN: %clang_cc1 -std=c99 -fsyntax-only -verify=expected,c99untilc2x,c17andearlier -pedantic -Wno-c11-extensions %s
-   RUN: %clang_cc1 -std=c11 -fsyntax-only -verify=expected,c99untilc2x,c17andearlier -pedantic %s
-   RUN: %clang_cc1 -std=c17 -fsyntax-only -verify=expected,c99untilc2x,c17andearlier -pedantic %s
-   RUN: %clang_cc1 -std=c23 -fsyntax-only -verify=expected,c2xandup -pedantic %s
+/* RUN: %clang_cc1 -std=c89 -fsyntax-only -verify=expected,c89only -pedantic -Wno-declaration-after-statement -Wno-c11-extensions %s
+   RUN: %clang_cc1 -std=c89 -fsyntax-only -verify=expected,c89only -pedantic -Wno-declaration-after-statement -Wno-c11-extensions -fno-signed-char %s
+   RUN: %clang_cc1 -std=c99 -fsyntax-only -verify=expected,c99untilc2x -pedantic -Wno-c11-extensions %s
+   RUN: %clang_cc1 -std=c11 -fsyntax-only -verify=expected,c99untilc2x -pedantic %s
+   RUN: %clang_cc1 -std=c17 -fsyntax-only -verify=expected,c99untilc2x -pedantic %s
+   RUN: %clang_cc1 -std=c2x -fsyntax-only -verify=expected,c2xandup -pedantic %s
  */
 
 /* The following are DRs which do not require tests to demonstrate
@@ -245,13 +245,13 @@ int dr032 = (1, 2); /* expected-warning {{left operand of comma operator has no
  * Questions about definition of functions without a prototype
  */
 void dr035_1(a, b) /* expected-warning {{a function definition without a prototype is deprecated in all versions of C and is not supported in C23}} */
-  int a(enum b {x, y}); /* c17andearlier-warning {{declaration of 'enum b' will not be visible outside of this function}} */
+  int a(enum b {x, y}); /* expected-warning {{declaration of 'enum b' will not be visible outside of this function}} */
   int b; {
   int test = x; /* expected-error {{use of undeclared identifier 'x'}} */
 }
 
 void dr035_2(c) /* expected-warning {{a function definition without a prototype is deprecated in all versions of C and is not supported in C23}} */
-  enum m{q, r} c; { /* c17andearlier-warning {{declaration of 'enum m' will not be visible outside of this function}} */
+  enum m{q, r} c; { /* expected-warning {{declaration of 'enum m' will not be visible outside of this function}} */
   /* FIXME: This should be accepted because the scope of m, q, and r ends at
    * the closing brace of the function per C89 6.1.2.1.
    */

clang/test/C/drs/dr1xx.c

@@ -107,7 +107,7 @@ void dr103_2(struct S s) {} /* expected-warning {{declaration of 'struct S' will
                                expected-note {{forward declaration of 'struct S'}} */
 void dr103_3(struct S s);               /* expected-warning {{declaration of 'struct S' will not be visible outside of this function}}
                                            expected-note {{previous declaration is here}} */
-void dr103_3(struct S { int a; } s) { } /* untilc23-warning {{declaration of 'struct S' will not be visible outside of this function}}
+void dr103_3(struct S { int a; } s) { } /* expected-warning {{declaration of 'struct S' will not be visible outside of this function}}
                                            expected-error {{conflicting types for 'dr103_3'}} */
 void dr103_4(struct S s1, struct S { int a; } s2); /* expected-warning {{declaration of 'struct S' will not be visible outside of this function}} */
 

clang/test/Sema/c23-decl-in-prototype.c

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsyntax-only -verify -std=c17 %s
+// RUN: %clang_cc1 -fsyntax-only -verify %s
 
 #define SA(n, c) int arr##n[(c) ? 1 : -1] = {}
 

clang/test/Sema/decl-in-prototype.c

@@ -108,7 +108,7 @@ void PR8694(int* e) // expected-note {{passing argument to parameter 'e' here}}
 {
 }
 
-void crash(enum E *e) // expected-warning {{declaration of 'enum E' will not be visible outside of this function}} \
+void crash(enum E* e) // expected-warning {{declaration of 'enum E' will not be visible outside of this function}} \
                       // expected-warning {{ISO C forbids forward references to 'enum' types}}
 {
         PR8694(e); // expected-warning {{incompatible pointer types passing 'enum E *' to parameter of type 'int *'}}