Allow use of an elaborated type specifier in a _Generic association in C++

Currently, Clang accepts this code in C mode (where the tag is required
to be used) but rejects it in C++ mode thinking that the association is
defining a new type.

void foo(void) {
  struct S { int a; };
  _Generic(something, struct S : 1);
}
Clang thinks this in C++ because it sees struct S : when parsing the
class specifier and decides that must be a type definition (because the
colon signifies the presence of a base class type). This patch adds a
new declarator context to represent a _Generic association so that we
can distinguish these situations properly.

Fixes #55562

Differential Revision: https://reviews.llvm.org/D126969

1 files changed, 3 insertions, 1 deletions

diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index 18f4f12..0cdf915 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -2870,6 +2870,8 @@ Parser::getDeclSpecContextFromDeclaratorContext(DeclaratorContext Context) {
   if (Context == DeclaratorContext::AliasDecl ||
       Context == DeclaratorContext::AliasTemplate)
     return DeclSpecContext::DSC_alias_declaration;
+  if (Context == DeclaratorContext::Association)
+    return DeclSpecContext::DSC_association;
   return DeclSpecContext::DSC_normal;
 }
 
@@ -4573,7 +4575,7 @@ void Parser::ParseEnumSpecifier(SourceLocation StartLoc, DeclSpec &DS,
 
   // Determine whether this declaration is permitted to have an enum-base.
   AllowDefiningTypeSpec AllowEnumSpecifier =
-      isDefiningTypeSpecifierContext(DSC);
+      isDefiningTypeSpecifierContext(DSC, getLangOpts().CPlusPlus);
   bool CanBeOpaqueEnumDeclaration =
       DS.isEmpty() && isOpaqueEnumDeclarationContext(DSC);
   bool CanHaveEnumBase = (getLangOpts().CPlusPlus11 || getLangOpts().ObjC ||