c++: Fix ({ ... }) array mem-initializer.

Here, we were going down the wrong path in perform_member_init because of
the incorrect parens around the mem-initializer for the array.  And then
cxx_eval_vec_init_1 didn't know what to do with a CONSTRUCTOR as the
initializer.  The latter issue was a straightforward fix, but I also wanted
to fix us silently accepting the parens, which led to factoring out handling
of TREE_LIST and flexarrays.  The latter led to adjusting the expected
behavior on flexary29.C: we should complain about the initializer, but not
complain about a missing initializer.

As I commented on PR 92812, in this process I noticed that we weren't
handling C++20 parenthesized aggregate initialization as a mem-initializer.
So my TREE_LIST handling includes a commented out section that should
probably be part of a future fix for that issue; with it uncommented we
continue to crash on the testcase in C++20 mode, but should instead complain
about the braced-init-list not being a valid initializer for an A.

	PR c++/86917
	* init.c (perform_member_init): Simplify.
	* constexpr.c (cx_check_missing_mem_inits): Allow uninitialized
	flexarray.
	(cxx_eval_vec_init_1): Handle CONSTRUCTOR.

1 files changed, 10 insertions, 1 deletions

diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 3962763..c35ec5a 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -826,7 +826,12 @@ cx_check_missing_mem_inits (tree ctype, tree body, bool complain)
 		return true;
 	      continue;
 	    }
-	  ftype = strip_array_types (TREE_TYPE (field));
+	  ftype = TREE_TYPE (field);
+	  if (!ftype || !TYPE_P (ftype) || !COMPLETE_TYPE_P (ftype))
+	    /* A flexible array can't be intialized here, so don't complain
+	       that it isn't.  */
+	    continue;
+	  ftype = strip_array_types (ftype);
 	  if (type_has_constexpr_default_constructor (ftype))
 	    {
 	      /* It's OK to skip a member with a trivial constexpr ctor.
@@ -3784,6 +3789,10 @@ cxx_eval_vec_init_1 (const constexpr_ctx *ctx, tree atype, tree init,
   unsigned HOST_WIDE_INT i;
   tsubst_flags_t complain = ctx->quiet ? tf_none : tf_warning_or_error;
 
+  if (init && TREE_CODE (init) == CONSTRUCTOR)
+    return cxx_eval_bare_aggregate (ctx, init, lval,
+				    non_constant_p, overflow_p);
+
   /* For the default constructor, build up a call to the default
      constructor of the element type.  We only need to handle class types
      here, as for a constructor to be constexpr, all members must be