[clang] Fix a crash issue that caused by handling of fields with initializers in nested anonymous unions

clang/include/clang/Sema/Sema.h

@@ -5287,7 +5287,7 @@ class Sema final : public SemaBase {
   /// is complete.
   void ActOnFinishCXXInClassMemberInitializer(Decl *VarDecl,
                                               SourceLocation EqualLoc,
-                                              Expr *Init);
+                                              ExprResult Init);
 
   /// Handle a C++ member initializer using parentheses syntax.
   MemInitResult

clang/lib/Parse/ParseCXXInlineMethods.cpp

@@ -722,8 +722,7 @@ void Parser::ParseLexedMemberInitializer(LateParsedMemberInitializer &MI) {
   ExprResult Init = ParseCXXMemberInitializer(MI.Field, /*IsFunction=*/false,
                                               EqualLoc);
 
-  Actions.ActOnFinishCXXInClassMemberInitializer(MI.Field, EqualLoc,
-                                                 Init.get());
+  Actions.ActOnFinishCXXInClassMemberInitializer(MI.Field, EqualLoc, Init);
 
   // The next token should be our artificial terminating EOF token.
   if (Tok.isNot(tok::eof)) {

clang/lib/Sema/SemaDeclCXX.cpp

@@ -4080,24 +4080,28 @@ ExprResult Sema::ConvertMemberDefaultInitExpression(FieldDecl *FD,
 
 void Sema::ActOnFinishCXXInClassMemberInitializer(Decl *D,
                                                   SourceLocation InitLoc,
-                                                  Expr *InitExpr) {
+                                                  ExprResult InitExpr) {
   // Pop the notional constructor scope we created earlier.
   PopFunctionScopeInfo(nullptr, D);
 
-  FieldDecl *FD = dyn_cast<FieldDecl>(D);
-  assert((isa<MSPropertyDecl>(D) || FD->getInClassInitStyle() != ICIS_NoInit) &&
-         "must set init style when field is created");
-
-  if (!InitExpr) {
+  // Microsoft C++'s property declaration cannot have a default member
+  // initializer.
+  if (isa<MSPropertyDecl>(D)) {
     D->setInvalidDecl();
-    if (FD)
-      FD->removeInClassInitializer();
     return;
   }
 
-  if (DiagnoseUnexpandedParameterPack(InitExpr, UPPC_Initializer)) {
+  FieldDecl *FD = dyn_cast<FieldDecl>(D);
+  assert((FD && FD->getInClassInitStyle() != ICIS_NoInit) &&
+         "must set init style when field is created");
+
+  if (!InitExpr.isUsable() ||
+      DiagnoseUnexpandedParameterPack(InitExpr.get(), UPPC_Initializer)) {
     FD->setInvalidDecl();
-    FD->removeInClassInitializer();
+    ExprResult RecoveryInit =
+        CreateRecoveryExpr(InitLoc, InitLoc, {}, FD->getType());
+    if (RecoveryInit.isUsable())
+      FD->setInClassInitializer(RecoveryInit.get());
     return;
   }
 

clang/lib/Sema/SemaInit.cpp

@@ -750,6 +750,18 @@ void InitListChecker::FillInEmptyInitForField(unsigned Init, FieldDecl *Field,
     if (Field->hasInClassInitializer()) {
       if (VerifyOnly)
         return;
+
+      // We do not want to aggressively set the hadError flag and cutoff
+      // parsing. Try to recover when in-class-initializer is a RecoveryExpr.
+      if (isa_and_nonnull<RecoveryExpr>(Field->getInClassInitializer())) {
+        if (Init < NumInits)
+          ILE->setInit(Init, Field->getInClassInitializer());
+        else
+          ILE->updateInit(SemaRef.Context, Init,
+                          Field->getInClassInitializer());
+        return;
+      }
+
       ExprResult DIE;
       {
         // Enter a default initializer rebuild context, then we can support

clang/test/SemaCXX/cxx1y-initializer-aggregates.cpp

@@ -115,3 +115,14 @@ namespace nested_union {
   // of Test3, or we should exclude f(Test3) as a candidate.
   static_assert(f({1}) == 2, ""); // expected-error {{call to 'f' is ambiguous}}
 }
+
+// Fix crash issue https://github.com/llvm/llvm-project/issues/112560.
+// Make sure clang compiles the following code without crashing:
+namespace GH112560 {
+union U {
+  int f = ; // expected-error {{expected expression}}
+};
+void foo() {
+  U g{};
+}
+} // namespace GH112560