[SemaCXX] Set promotion type for enum if its type is promotable to integer type even if it has no definition.

[zequanwu]

Summary

EnumDecl's promotion type is set either to the parsed type or calculated type
after completing its definition. When it's bool type and has no definition,
its promotion type is bool which is not allowed by clang.

This fixes https://github.com/llvm/llvm-project/issues/56560.

[shafik]

Thank you for working on this.

We seem to have a few tests with enums that bool as a specified type. Maybe this belongs better in one of those under the namespace GH56560

I am curious that this does not change the test results of clang/test/CXX/conv/conv.prom/p4.cpp

[aaron.ballman]

clang/lib/Sema/SemaDecl.cpp

16198–16201

16824–16828

Same here as above

[zequanwu]

• Address comment.
• Move test to clang/test/CXX/conv/conv.prom/p4.cpp.

[zequanwu]

I am curious that this does not change the test results of clang/test/CXX/conv/conv.prom/p4.cpp

The crash only happens when the enum is bool and has no definition.

[aaron.ballman]

LGTM, though you should add a release note to clang/docs/ReleaseNotes.rst for the bug fix. Thank you!

[zequanwu]

In D130210#3669464, @aaron.ballman wrote:

LGTM, though you should add a release note to clang/docs/ReleaseNotes.rst for the bug fix. Thank you!

Added a release note.

clang/lib/Sema/SemaDecl.cpp

if (Kind == TTK_Enum) {
       if (TUK != TUK_Definition && !Invalid)
         return nullptr;
       if (EnumUnderlying) {
         EnumDecl *ED = cast<EnumDecl>(New);
         if (TypeSourceInfo *TI = EnumUnderlying.dyn_cast<TypeSourceInfo *>())
           ED->setIntegerTypeSourceInfo(TI);
         else
           ED->setIntegerType(QualType(EnumUnderlying.get<const Type *>(), 0));
-        ED->setPromotionType(ED->getIntegerType());
+        QualType EnumTy = ED->getIntegerType();
+        if (EnumTy->isPromotableIntegerType())
+          ED->setPromotionType(Context.getPromotedIntegerType(EnumTy));
+        else
+          ED->setPromotionType(EnumTy);
       }
     } else { // struct/union
       New = RecordDecl::Create(Context, Kind, SearchDC, KWLoc, Loc, Name,
                                nullptr);
     }
 
     if (RecordDecl *RD = dyn_cast<RecordDecl>(New)) {
       // Add alignment attributes if necessary; these attributes are checked
if (TUK != TUK_Definition && !Invalid) {
       }
     }
 
     if (EnumUnderlying) {
       EnumDecl *ED = cast<EnumDecl>(New);
       if (TypeSourceInfo *TI = EnumUnderlying.dyn_cast<TypeSourceInfo*>())
         ED->setIntegerTypeSourceInfo(TI);
       else
-        ED->setIntegerType(QualType(EnumUnderlying.get<const Type*>(), 0));
-      ED->setPromotionType(ED->getIntegerType());
+        ED->setIntegerType(QualType(EnumUnderlying.get<const Type *>(), 0));
+      QualType EnumTy = ED->getIntegerType();
+      if (EnumTy->isPromotableIntegerType())
+        ED->setPromotionType(Context.getPromotedIntegerType(EnumTy));
+      else
+        ED->setPromotionType(EnumTy);
       assert(ED->isComplete() && "enum with type should be complete");
     }
   } else {
     // struct/union/class
 
     // FIXME: Tag decls should be chained to any simultaneous vardecls, e.g.:
     // struct X { int A; } D;    D should chain to X.
     if (getLangOpts().CPlusPlus) {

clang/test/SemaCXX/enum-bool.cpp

+// RUN: %clang_cc1  -fsyntax-only %s
+
+// This shouldn't crash.
+
+enum GH56560_1 : bool;
+bool GH56560_2(GH56560_1 a, GH56560_1 b) {
+    return a == b;
+}