[clang] Fix designated initializers inside templates (llvm#69712)

Skip anonymous members when rebuilding `DesignatedInitExpr` since
designated inits for them are meant to be created during
`InitListChecker::CheckDesignatedInitializer` routine.

Fixes llvm#65143

clang/docs/ReleaseNotes.rst

@@ -732,6 +732,9 @@ Bug Fixes in This Version
   ``thread_local`` instead of ``_Thread_local``.
   Fixes (`#70068 <https://github.com/llvm/llvm-project/issues/70068>`_) and
   (`#69167 <https://github.com/llvm/llvm-project/issues/69167>`_)
+- Clang now accepts anonymous members initialized with designated initializers
+  inside templates.
+  Fixes (`#65143 <https://github.com/llvm/llvm-project/issues/65143>`_)
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/TreeTransform.h

@@ -11722,21 +11722,23 @@ TreeTransform<Derived>::TransformDesignatedInitExpr(DesignatedInitExpr *E) {
   bool ExprChanged = false;
   for (const DesignatedInitExpr::Designator &D : E->designators()) {
     if (D.isFieldDesignator()) {
-      Desig.AddDesignator(Designator::CreateFieldDesignator(
-          D.getFieldName(), D.getDotLoc(), D.getFieldLoc()));
       if (D.getFieldDecl()) {
         FieldDecl *Field = cast_or_null<FieldDecl>(
             getDerived().TransformDecl(D.getFieldLoc(), D.getFieldDecl()));
         if (Field != D.getFieldDecl())
           // Rebuild the expression when the transformed FieldDecl is
           // different to the already assigned FieldDecl.
           ExprChanged = true;
+        if (Field->isAnonymousStructOrUnion())
+          continue;
       } else {
         // Ensure that the designator expression is rebuilt when there isn't
         // a resolved FieldDecl in the designator as we don't want to assign
         // a FieldDecl to a pattern designator that will be instantiated again.
         ExprChanged = true;
       }
+      Desig.AddDesignator(Designator::CreateFieldDesignator(
+          D.getFieldName(), D.getDotLoc(), D.getFieldLoc()));
       continue;
     }
 

clang/test/SemaCXX/cxx2b-designated-initializers.cpp

@@ -9,17 +9,36 @@ union S {
 };
 
 void f(int x, auto) {
-  const S result { // expected-error {{field designator (null) does not refer to any field in type 'const S'}}
+  const S result {
     .a = x
   };
 }
 
 void g(void) {
-  f(0, 0); // expected-note {{in instantiation of function template specialization 'PR61118::f<int>' requested here}}
+  f(0, 0);
 }
 
 } // end namespace PR61118
 
+namespace GH65143 {
+struct Inner {
+  int a;
+};
+
+struct Outer {
+  struct {
+    Inner inner;
+  };
+};
+
+template <int val> void f() {
+  constexpr Outer x{.inner = {val}};
+  static_assert(x.inner.a == val);
+}
+
+void bar() { f<4>(); }
+}
+
 namespace GH62156 {
 union U1 {
    int x;