c++: non-dependent variable template-id [PR108848]

Here we're treating deeming the non-dependent variable template-id
tag<int> as dependent ever since r226642 gave variable TEMPLATE_ID_EXPR
an empty type, which causes the call to finish_template_variable from
finish_id_expression_1 to be unreachable at template parse time.  Thus
we're led into thinking tag<int>.var<void> refers to a dependent name.

This patch fixes this by making finish_id_expression_1 instantiate a
variable template-id as long as it's not dependent according to the
dependence test in lookup_and_finish_template_variable rather than
according to type_dependent_expression_p.

	PR c++/108848

gcc/cp/ChangeLog:

	* pt.cc (finish_template_variable): Move dependence check
	to here from ...
	(lookup_and_finish_template_variable): ... here.
	* semantics.cc (finish_id_expression_1): Call
	finish_template_variable sooner, before (and regardless of) the
	type_dependent_expression_p test.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1y/noexcept1.C: Don't expect a bogus "different
	exception specifier" error.  Expect a separate "not usable
	in a constant expression" error.
	* g++.dg/cpp1y/var-templ75.C: New test.
	* g++.dg/cpp1y/var-templ76.C: New test.

1 files changed, 16 insertions, 14 deletions

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index f636bac..03958da 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -10317,7 +10317,8 @@ lookup_template_variable (tree templ, tree arglist)
   return build2 (TEMPLATE_ID_EXPR, NULL_TREE, templ, arglist);
 }
 
-/* Instantiate a variable declaration from a TEMPLATE_ID_EXPR for use. */
+/* Instantiate a variable declaration from a TEMPLATE_ID_EXPR if it's
+   not dependent.  */
 
 tree
 finish_template_variable (tree var, tsubst_flags_t complain)
@@ -10325,6 +10326,12 @@ finish_template_variable (tree var, tsubst_flags_t complain)
   tree templ = TREE_OPERAND (var, 0);
   tree arglist = TREE_OPERAND (var, 1);
 
+  /* If the template or arguments are dependent, then we
+     can't resolve the TEMPLATE_ID_EXPR yet.  */
+  if (TMPL_PARMS_DEPTH (DECL_TEMPLATE_PARMS (templ)) != 1
+      || any_dependent_template_arguments_p (arglist))
+    return var;
+
   tree parms = DECL_TEMPLATE_PARMS (templ);
   arglist = coerce_template_parms (parms, arglist, templ, complain);
   if (arglist == error_mark_node)
@@ -10352,19 +10359,14 @@ lookup_and_finish_template_variable (tree templ, tree targs,
 				     tsubst_flags_t complain)
 {
   tree var = lookup_template_variable (templ, targs);
-  if (TMPL_PARMS_DEPTH (DECL_TEMPLATE_PARMS (templ)) == 1
-      && !any_dependent_template_arguments_p (targs))
-    {
-      /* We may be called while doing a partial substitution, but the
-	 type of the variable template may be auto, in which case we
-	 will call do_auto_deduction in mark_used (which clears tf_partial)
-	 and the auto must be properly reduced at that time for the
-	 deduction to work.  */
-      complain &= ~tf_partial;
-      var = finish_template_variable (var, complain);
-      mark_used (var);
-    }
-
+  /* We may be called while doing a partial substitution, but the
+     type of the variable template may be auto, in which case we
+     will call do_auto_deduction in mark_used (which clears tf_partial)
+     and the auto must be properly reduced at that time for the
+     deduction to work.  */
+  complain &= ~tf_partial;
+  var = finish_template_variable (var, complain);
+  mark_used (var);
   return convert_from_reference (var);
 }