c++: designator and anon struct [PR101767]

We found .x in the anonymous struct, but then didn't find .y there; we
should decide that means we're done with the struct rather than that the
code is wrong.

	PR c++/101767

gcc/cp/ChangeLog:

	* decl.cc (reshape_init_class): Back out of anon struct
	if a designator doesn't match.

gcc/testsuite/ChangeLog:

	* g++.dg/ext/anon-struct10.C: New test.

gcc/cp/decl.cc

@@ -6626,6 +6626,11 @@ reshape_init_class (tree type, reshape_iter *d, bool first_initializer_p,
 	      return error_mark_node;
 	    }
 
+	  if (!field && ANON_AGGR_TYPE_P (type))
+	    /* Apparently the designator isn't for a member of this anonymous
+	       struct, so head back to the enclosing class.  */
+	    break;
+
 	  if (!field || TREE_CODE (field) != FIELD_DECL)
 	    {
 	      if (complain & tf_error)

gcc/testsuite/g++.dg/ext/anon-struct10.C

@@ -0,0 +1,21 @@
+// PR c++/101767
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-Wno-pedantic" }
+
+typedef struct {
+  struct {
+    int x;
+  };
+  union {
+    int y;
+    float z;
+  };
+} S;
+
+void foo(void)
+{
+  [[maybe_unused]] S a = {
+    .x = 1,
+    .y = 0
+  };
+}