[C2y] Implement WG14 N3344 (#115313)

https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3344.pdf

This paper disallows a single `void` parameter from having qualifiers or
storage class specifiers. Clang has diagnosed most of these as an error
for a long time, but `register void` was previously accepted in all C
language modes and is now being rejected in all C language modes.

1 files changed, 15 insertions, 3 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index aba6b55..c9cd81a 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -15002,6 +15002,12 @@ Decl *Sema::ActOnParamDeclarator(Scope *S, Declarator &D,
   const DeclSpec &DS = D.getDeclSpec();
 
   // Verify C99 6.7.5.3p2: The only SCS allowed is 'register'.
+  // C2y 6.7.7.4p4: A parameter declaration shall not specify a void type,
+  // except for the special case of a single unnamed parameter of type void
+  // with no storage class specifier, no type qualifier, and no following
+  // ellipsis terminator.
+  // Clang applies the C2y rules for 'register void' in all C language modes,
+  // same as GCC, because it's questionable what that could possibly mean.
 
   // C++03 [dcl.stc]p2 also permits 'auto'.
   StorageClass SC = SC_None;
@@ -15010,10 +15016,16 @@ Decl *Sema::ActOnParamDeclarator(Scope *S, Declarator &D,
     // In C++11, the 'register' storage class specifier is deprecated.
     // In C++17, it is not allowed, but we tolerate it as an extension.
     if (getLangOpts().CPlusPlus11) {
+      Diag(DS.getStorageClassSpecLoc(), getLangOpts().CPlusPlus17
+                                            ? diag::ext_register_storage_class
+                                            : diag::warn_deprecated_register)
+          << FixItHint::CreateRemoval(DS.getStorageClassSpecLoc());
+    } else if (!getLangOpts().CPlusPlus &&
+               DS.getTypeSpecType() == DeclSpec::TST_void) {
       Diag(DS.getStorageClassSpecLoc(),
-           getLangOpts().CPlusPlus17 ? diag::ext_register_storage_class
-                                     : diag::warn_deprecated_register)
-        << FixItHint::CreateRemoval(DS.getStorageClassSpecLoc());
+           diag::err_invalid_storage_class_in_func_decl)
+          << FixItHint::CreateRemoval(DS.getStorageClassSpecLoc());
+      D.getMutableDeclSpec().ClearStorageClassSpecs();
     }
   } else if (getLangOpts().CPlusPlus &&
              DS.getStorageClassSpec() == DeclSpec::SCS_auto) {