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.

(cherry picked from commit f07778f6f92111aa0abfd0f669b148a0bda537a9)

4 files changed, 84 insertions, 12 deletions

diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 94f6222b436..ab238dbb4cb 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -3179,9 +3179,15 @@ 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.  */
@@ -3243,9 +3249,13 @@ 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;
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 2db847868b6..72f4398a8f9 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7317,6 +7317,7 @@ extern tree lookup_template_function		(tree, tree);
 extern tree lookup_template_variable		(tree, tree);
 extern int uses_template_parms			(tree);
 extern bool uses_template_parms_level		(tree, int);
+extern bool uses_outer_template_parms_in_constraints (tree);
 extern bool in_template_function		(void);
 extern bool need_generic_capture		(void);
 extern tree instantiate_class_template		(tree);
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 38c138bd835..cf4ae7775da 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -389,7 +389,9 @@ template_class_depth (tree type)
     {
       tree tinfo = get_template_info (type);
 
-      if (tinfo && PRIMARY_TEMPLATE_P (TI_TEMPLATE (tinfo))
+      if (tinfo
+	  && TREE_CODE (TI_TEMPLATE (tinfo)) == TEMPLATE_DECL
+	  && PRIMARY_TEMPLATE_P (TI_TEMPLATE (tinfo))
 	  && uses_template_parms (INNERMOST_TEMPLATE_ARGS (TI_ARGS (tinfo))))
 	++depth;
 
@@ -10953,7 +10955,7 @@ uses_template_parms_level (tree t, int level)
 /* Returns true if the signature of DECL depends on any template parameter from
    its enclosing class.  */
 
-bool
+static bool
 uses_outer_template_parms (tree decl)
 {
   int depth = template_class_depth (CP_DECL_CONTEXT (decl));
@@ -10984,13 +10986,27 @@ uses_outer_template_parms (tree decl)
 	    return true;
 	}
     }
+  if (uses_outer_template_parms_in_constraints (decl))
+    return true;
+  return false;
+}
+
+/* Returns true if the constraints of DECL depend on any template parameters
+   from its enclosing scope.  */
+
+bool
+uses_outer_template_parms_in_constraints (tree decl)
+{
   tree ci = get_constraints (decl);
   if (ci)
     ci = CI_ASSOCIATED_CONSTRAINTS (ci);
-  if (ci && for_each_template_parm (ci, template_parm_outer_level,
-				    &depth, NULL, /*nondeduced*/true))
-    return true;
-  return false;
+  if (!ci)
+    return false;
+  int depth = template_class_depth (CP_DECL_CONTEXT (decl));
+  if (depth == 0)
+    return false;
+  return for_each_template_parm (ci, template_parm_outer_level,
+				 &depth, NULL, /*nondeduced*/true);
 }
 
 /* Returns TRUE iff INST is an instantiation we don't need to do in an
@@ -27982,6 +27998,17 @@ type_dependent_expression_p (tree expression)
       return false;
     }
 
+  /* Otherwise, its constraints could still depend on outer template parameters
+     from its (dependent) scope.  */
+  if (TREE_CODE (expression) == FUNCTION_DECL
+      /* As an optimization, check this cheaper sufficient condition first.
+	 (At this point we've established that we're looking at a member of
+	 a dependent class, so it makes sense to start treating say undeduced
+	 auto as dependent.)  */
+      && !dependent_type_p (TREE_TYPE (expression))
+      && uses_outer_template_parms_in_constraints (expression))
+    return true;
+
   /* Always dependent, on the number of arguments if nothing else.  */
   if (TREE_CODE (expression) == EXPR_PACK_EXPANSION)
     return true;
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-memtmpl6.C b/gcc/testsuite/g++.dg/cpp2a/concepts-memtmpl6.C
new file mode 100644
index 00000000000..0e09ae6ed4c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-memtmpl6.C
@@ -0,0 +1,34 @@
+// PR c++/105842
+// { dg-do compile { target c++20 } }
+
+template<class T>
+struct S {
+  static void func1() requires __is_same(T, int);
+  static void func1() requires (!__is_same(T, int));
+
+  static void func2() requires false && false;
+  static void func2() requires false;
+
+  template<class...> static void tmpl1() requires __is_same(T, int);
+  template<class...> static void tmpl1() requires (!__is_same(T, int));
+
+  template<class... Us> static void tmpl2() requires (sizeof...(Us) == 1);
+  template<class... Us> static void tmpl2() requires (sizeof...(Us) == 2);
+
+  static void foo() {
+    // Both calls resolve to the first overload at instantiation time.
+    func1();
+    tmpl1();
+  }
+
+  static void bar() {
+    // We can check and reject both calls ahead of time since the functions'
+    // constraints don't depend on outer template parameters.
+    func2(); // { dg-error "no match" }
+    tmpl2(); // { dg-error "no match" }
+  }
+};
+
+int main() {
+  S<int>::foo();
+}