c++: dependence of constrained memfn from current inst [PR105842]

Here we incorrectly deem the calls to func1, func2 and tmpl2 as
ambiguous ahead of time ultimately because we mishandle dependence
of a constrained member function from the current instantiation.

In type_dependent_expression_p, we already consider dependence of a
TEMPLATE_DECL's constraints (via uses_outer_template_parms), but
neglect to do the same for a FUNCTION_DECL (such as that for func1).

And in satisfy_declaration_constraints, we give up if _any_ template
argument is dependent, but for non-dependent member functions from
the current instantiation (such as func2 and tmpl2), we can and must
check constraints as long as the innermost arguments aren't dependent.

	PR c++/105842

gcc/cp/ChangeLog:

	* constraint.cc (satisfy_declaration_constraints): Refine early
	exit test for argument dependence.
	* cp-tree.h (uses_outer_template_parms_in_constraints): Declare.
	* pt.cc (template_class_depth): Handle TI_TEMPLATE being a
	FIELD_DECL.
	(usse_outer_template_parms): Factor out constraint dependence
	test into ...
	(uses_outer_template_parms_in_constraints): ... here.
	(type_dependent_expression_p): Use it for FUNCTION_DECL.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-memtmpl6.C: New test.

1 files changed, 16 insertions, 6 deletions

diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 591155c..f2137eb 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -3176,9 +3176,15 @@ satisfy_declaration_constraints (tree t, sat_info info)
 	args = regen_args;
     }
 
-  /* If any arguments depend on template parameters, we can't
-     check constraints. Pretend they're satisfied for now.  */
-  if (uses_template_parms (args))
+  /* If the innermost arguments are dependent, or if the outer arguments
+     are dependent and are needed by the constraints, we can't check
+     satisfaction yet so pretend they're satisfied for now.  */
+  if (uses_template_parms (args)
+      && ((DECL_TEMPLATE_INFO (t)
+	   && PRIMARY_TEMPLATE_P (DECL_TI_TEMPLATE (t))
+	   && (TMPL_ARGS_DEPTH (args) == 1
+	       || uses_template_parms (INNERMOST_TEMPLATE_ARGS (args))))
+	  || uses_outer_template_parms_in_constraints (t)))
     return boolean_true_node;
 
   /* Get the normalized constraints.  */
@@ -3240,9 +3246,13 @@ satisfy_declaration_constraints (tree t, tree args, sat_info info)
   else
     args = add_outermost_template_args (t, args);
 
-  /* If any arguments depend on template parameters, we can't
-     check constraints. Pretend they're satisfied for now.  */
-  if (uses_template_parms (args))
+  /* If the innermost arguments are dependent, or if the outer arguments
+     are dependent and are needed by the constraints, we can't check
+     satisfaction yet so pretend they're satisfied for now.  */
+  if (uses_template_parms (args)
+      && (TMPL_ARGS_DEPTH (args) == 1
+	  || uses_template_parms (INNERMOST_TEMPLATE_ARGS (args))
+	  || uses_outer_template_parms_in_constraints (t)))
     return boolean_true_node;
 
   tree result = boolean_true_node;