c++: designated init with anonymous union [PR100489]

My patch for PR98463 added an assert that tripped on this testcase, because
we ended up with a U CONSTRUCTOR with an initializer for a, which is not a
member of U.  We need to wrap the a initializer in another CONSTRUCTOR for
the anonymous union.

There was already support for this in process_init_constructor_record, but
not in process_init_constructor_union.  But since this is about brace
elision, it really belongs under reshape_init rather than digest_init, so
this patch moves the handling to reshape_init_class, which also handles
unions.

	PR c++/100489

gcc/cp/ChangeLog:

	* decl.c (reshape_init_class): Handle designator for
	member of anonymous aggregate here.
	* typeck2.c (process_init_constructor_record): Not here.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/desig18.C: New test.

1 files changed, 29 insertions, 4 deletions

diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 7c32f09..6107b55 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -6418,10 +6418,9 @@ reshape_init_class (tree type, reshape_iter *d, bool first_initializer_p,
 	      /* We already reshaped this.  */
 	      if (field != d->cur->index)
 		{
-		  tree id = DECL_NAME (d->cur->index);
-		  gcc_assert (id);
-		  gcc_checking_assert (d->cur->index
-				       == get_class_binding (type, id));
+		  if (tree id = DECL_NAME (d->cur->index))
+		    gcc_checking_assert (d->cur->index
+					 == get_class_binding (type, id));
 		  field = d->cur->index;
 		}
 	    }
@@ -6442,6 +6441,32 @@ reshape_init_class (tree type, reshape_iter *d, bool first_initializer_p,
 		       d->cur->index);
 	      return error_mark_node;
 	    }
+
+	  /* If the element is an anonymous union object and the initializer
+	     list is a designated-initializer-list, the anonymous union object
+	     is initialized by the designated-initializer-list { D }, where D
+	     is the designated-initializer-clause naming a member of the
+	     anonymous union object.  */
+	  tree ictx = DECL_CONTEXT (field);
+	  if (!same_type_ignoring_top_level_qualifiers_p (ictx, type))
+	    {
+	      gcc_assert (ANON_AGGR_TYPE_P (ictx));
+	      /* Find the anon aggr that is a direct member of TYPE.  */
+	      while (true)
+		{
+		  tree cctx = TYPE_CONTEXT (ictx);
+		  if (same_type_ignoring_top_level_qualifiers_p (cctx, type))
+		    break;
+		  ictx = cctx;
+		}
+	      /* And then the TYPE member with that anon aggr type.  */
+	      tree aafield = TYPE_FIELDS (type);
+	      for (; aafield; aafield = TREE_CHAIN (aafield))
+		if (TREE_TYPE (aafield) == ictx)
+		  break;
+	      gcc_assert (aafield);
+	      field = aafield;
+	    }
 	}
 
       /* If we processed all the member of the class, we are done.  */