Address feedback.

Author: shafik

clang/docs/ReleaseNotes.rst

@@ -402,7 +402,6 @@ Bug Fixes to Attribute Support
 
 Bug Fixes to C++ Support
 ^^^^^^^^^^^^^^^^^^^^^^^^
-
 - Diagnose binding a reference to ``*nullptr`` during constant evaluation. (#GH48665)
 - Suppress ``-Wdeprecated-declarations`` in implicitly generated functions. (#GH147293)
 - Fix a crash when deleting a pointer to an incomplete array (#GH150359).
@@ -439,6 +438,8 @@ Bug Fixes to C++ Support
 - Correctly deduce return types in ``decltype`` expressions. (#GH160497) (#GH56652) (#GH116319) (#GH161196)
 - Fixed a crash in the pre-C++23 warning for attributes before a lambda declarator (#GH161070).
 - Fix a crash when attempting to deduce a deduction guide from a non deducible template template parameter. (#130604)
+- Fix for clang incorrectly rejecting the default construction of a union with
+  nontrivial member when another member has an initializer. (#GH81774)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaDeclCXX.cpp

@@ -9546,26 +9546,32 @@ bool SpecialMemberDeletionInfo::shouldDeleteForSubobjectCall(
   CXXMethodDecl *Decl = SMOR.getMethod();
   FieldDecl *Field = Subobj.dyn_cast<FieldDecl*>();
 
-  int DiagKind = -1;
+  enum {
+    NotSet = -1,
+    NoDecl,
+    DeletedDecl,
+    MultipleDecl,
+    InaccessibleDecl,
+    NonTrivialDecl
+  } DiagKind = NotSet;
 
   if (SMOR.getKind() == Sema::SpecialMemberOverloadResult::NoMemberOrDeleted) {
-    if (CSM == Sema::CXXDefaultConstructor && Field &&
+    if (CSM == CXXSpecialMemberKind::DefaultConstructor && Field &&
         Field->getParent()->isUnion()) {
       // [class.default.ctor]p2:
       //   A defaulted default constructor for class X is defined as deleted if
       //   - X is a union that has a variant member with a non-trivial default
       //     constructor and no variant member of X has a default member
       //     initializer
       const auto *RD = cast<CXXRecordDecl>(Field->getParent());
-      if (!RD->hasInClassInitializer())
-        DiagKind = !Decl ? 0 : 1;
-    } else {
-      DiagKind = !Decl ? 0 : 1;
+      if (RD->hasInClassInitializer())
+        return false;
     }
+    DiagKind = !Decl ? NoDecl : DeletedDecl;
   } else if (SMOR.getKind() == Sema::SpecialMemberOverloadResult::Ambiguous)
-    DiagKind = 2;
+    DiagKind = MultipleDecl;
   else if (!isAccessible(Subobj, Decl))
-    DiagKind = 3;
+    DiagKind = InaccessibleDecl;
   else if (!IsDtorCallInCtor && Field && Field->getParent()->isUnion() &&
            !Decl->isTrivial()) {
     // A member of a union must have a trivial corresponding special member.
@@ -9581,13 +9587,13 @@ bool SpecialMemberDeletionInfo::shouldDeleteForSubobjectCall(
       //     initializer
       const auto *RD = cast<CXXRecordDecl>(Field->getParent());
       if (!RD->hasInClassInitializer())
-        DiagKind = 4;
+        DiagKind = NonTrivialDecl;
     } else {
-      DiagKind = 4;
+      DiagKind = NonTrivialDecl;
     }
   }
 
-  if (DiagKind == -1)
+  if (DiagKind == NotSet)
     return false;
 
   if (Diagnose) {
@@ -9605,9 +9611,9 @@ bool SpecialMemberDeletionInfo::shouldDeleteForSubobjectCall(
           << /*IsObjCPtr*/ false;
     }
 
-    if (DiagKind == 1)
+    if (DiagKind == DeletedDecl)
       S.NoteDeletedFunction(Decl);
-    // FIXME: Explain inaccessibility if DiagKind == 3.
+    // FIXME: Explain inaccessibility if DiagKind == InaccessibleDecl.
   }
 
   return true;