[Clang][Sema] Fix type of enumerators in incomplete enumerations

Enumerators dont have the type of their enumeration before the
closing brace. In these cases Expr::getEnumCoercedType()
incorrectly returned the enumeration type.

Introduced in PR #81418

Author: martinkupa

clang/lib/AST/Expr.cpp

@@ -264,10 +264,13 @@ namespace {
 }
 
 QualType Expr::getEnumCoercedType(const ASTContext &Ctx) const {
-  if (isa<EnumType>(this->getType()))
+  if (isa<EnumType>(this->getType())) {
     return this->getType();
-  else if (const auto *ECD = this->getEnumConstantDecl())
-    return Ctx.getTypeDeclType(cast<EnumDecl>(ECD->getDeclContext()));
+  } else if (const auto *ECD = this->getEnumConstantDecl()) {
+    const auto *ED = cast<EnumDecl>(ECD->getDeclContext());
+    if (ED->isCompleteDefinition())
+      return Ctx.getTypeDeclType(ED);
+  }
   return this->getType();
 }
 

clang/test/Sema/warn-compare-enum-types-mismatch.c

@@ -6,7 +6,9 @@ typedef enum EnumA {
 } EnumA;
 
 enum EnumB {
-  B
+  B,
+  B1 = 1,
+  B2 = A == B1
 };
 
 enum {