[Clang] Fix an inadvertent overwrite of sub-initializers (llvm#140714)

When using InitChecker with VerifyOnly, we create a new designated
initializer to handle anonymous fields. However in the last call to
CheckDesignatedInitializer, the subinitializer isn't properly preserved
but it gets overwritten by the cloned one. Which causes the initializer
to reference the dependent field, breaking assumptions when we
initialize the instantiated specialization.

Fixes llvm#67173

Author: zyn0217

clang/docs/ReleaseNotes.rst

@@ -703,6 +703,7 @@ Bug Fixes to C++ Support
   certain differences in qualifiers (this could happen during template argument
   deduction or when building a ternary operator). (#GH97005)
 - Fixed type alias CTAD issues involving default template arguments. (#GH134471)
+- Fixed CTAD issues when initializing anonymous fields with designated initializers. (#GH67173)
 - The initialization kind of elements of structured bindings
   direct-list-initialized from an array is corrected to direct-initialization.
 - Clang no longer crashes when a coroutine is declared ``[[noreturn]]``. (#GH127327)

clang/lib/Sema/SemaInit.cpp

@@ -2791,16 +2791,20 @@ InitListChecker::CheckDesignatedInitializer(const InitializedEntity &Entity,
     // initializer list that the child calls see, so that we don't try
     // to re-process the designator.
     unsigned OldIndex = Index;
-    IList->setInit(OldIndex, DIE->getInit());
+    auto *OldDIE =
+        dyn_cast_if_present<DesignatedInitExpr>(IList->getInit(OldIndex));
+    if (!OldDIE)
+      OldDIE = DIE;
+    IList->setInit(OldIndex, OldDIE->getInit());
 
     CheckSubElementType(Entity, IList, CurrentObjectType, Index, StructuredList,
                         StructuredIndex, /*DirectlyDesignated=*/true);
 
     // Restore the designated initializer expression in the syntactic
     // form of the initializer list.
-    if (IList->getInit(OldIndex) != DIE->getInit())
-      DIE->setInit(IList->getInit(OldIndex));
-    IList->setInit(OldIndex, DIE);
+    if (IList->getInit(OldIndex) != OldDIE->getInit())
+      OldDIE->setInit(IList->getInit(OldIndex));
+    IList->setInit(OldIndex, OldDIE);
 
     return hadError && !prevHadError;
   }

clang/test/SemaTemplate/deduction-guide.cpp

@@ -886,3 +886,30 @@ CC c{};
 // CHECK-NEXT:        `-ClassTemplateSpecialization {{.+}} 'A'
 
 }
+
+namespace GH67173 {
+
+template <class T> struct Vec2d {
+  struct {
+    T x;
+    T y;
+  };
+};
+
+void f() {
+  Vec2d v{.x = 1, .y = 2};
+}
+
+// CHECK-LABEL: Dumping GH67173::<deduction guide for Vec2d>:
+// CHECK-NEXT: FunctionTemplateDecl {{.+}} implicit <deduction guide for Vec2d>
+// CHECK-NEXT: |-TemplateTypeParmDecl {{.+}} referenced class depth 0 index 0 T
+// CHECK:      |-CXXDeductionGuideDecl {{.+}} implicit <deduction guide for Vec2d> 'auto (T, T) -> Vec2d<T>' aggregate
+// CHECK-NEXT: | |-ParmVarDecl {{.+}} col:27 'T'
+// CHECK-NEXT: | `-ParmVarDecl {{.+}} col:27 'T'
+// CHECK-NEXT: `-CXXDeductionGuideDecl {{.+}} implicit used <deduction guide for Vec2d> 'auto (int, int) -> GH67173::Vec2d<int>' implicit_instantiation aggregate
+// CHECK-NEXT:   |-TemplateArgument type 'int'
+// CHECK-NEXT:   | `-BuiltinType {{.+}} 'int'
+// CHECK-NEXT:   |-ParmVarDecl {{.+}} 'int'
+// CHECK-NEXT:   `-ParmVarDecl {{.+}} 'int'
+
+}