https://bugs.gentoo.org/788829
https://gcc.gnu.org/PR100489

From 0a1010428b3861464eb319c629c68cb13b9ca01e Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Wed, 19 May 2021 21:12:45 -0400
Subject: [PATCH] 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.
---
 gcc/cp/decl.c                        | 33 ++++++++++++++++++++++++----
 gcc/cp/typeck2.c                     | 26 ----------------------
 gcc/testsuite/g++.dg/cpp2a/desig18.C | 17 ++++++++++++++
 3 files changed, 46 insertions(+), 30 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/desig18.C

--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -6388,10 +6388,9 @@ 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;
 		}
 	    }
@@ -6412,6 +6411,32 @@ 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.  */
diff --git a/gcc/cp/typeck2.c b/gcc/cp/typeck2.c
index 4e9632f6a7d..142c6fd8e75 100644
--- a/gcc/cp/typeck2.c
+++ b/gcc/cp/typeck2.c
@@ -1511,19 +1511,6 @@ process_init_constructor_record (tree type, tree init, int nested, int flags,
 			  || identifier_p (ce->index));
 	      if (ce->index == field || ce->index == DECL_NAME (field))
 		next = ce->value;
-	      else if (ANON_AGGR_TYPE_P (fldtype)
-		       && search_anon_aggr (fldtype,
-					    TREE_CODE (ce->index) == FIELD_DECL
-					    ? DECL_NAME (ce->index)
-					    : ce->index))
-		/* 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.  */
-		next = build_constructor_single (init_list_type_node,
-						 ce->index, ce->value);
 	      else
 		{
 		  ce = NULL;
@@ -1669,19 +1656,6 @@ process_init_constructor_record (tree type, tree init, int nested, int flags,
 
 		  if (ce->index == field || ce->index == DECL_NAME (field))
 		    break;
-		  if (ANON_AGGR_TYPE_P (TREE_TYPE (field)))
-		    {
-		      tree t
-			= search_anon_aggr (TREE_TYPE (field),
-					    TREE_CODE (ce->index) == FIELD_DECL
-					    ? DECL_NAME (ce->index)
-					    : ce->index);
-		      if (t)
-			{
-			  field = t;
-			  break;
-			}
-		    }
 		}
 	    }
 	  if (field)
diff --git a/gcc/testsuite/g++.dg/cpp2a/desig18.C b/gcc/testsuite/g++.dg/cpp2a/desig18.C
new file mode 100644
index 00000000000..4851579b7c7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/desig18.C
@@ -0,0 +1,17 @@
+// PR c++/100489
+// { dg-options "" }
+
+union U
+{
+  union
+  {
+    unsigned char a;
+  };
+
+  unsigned char b[1];
+};
+
+void f(unsigned char a)
+{
+  union U u = { .a = a };
+}
-- 
2.31.1