From 2c3309e3d0f5cb8f298f7604848d115f0992e04f Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Thu, 10 Feb 2022 17:57:38 -0500
Subject: [PATCH] c++: TTP in member alias template [PR104107]

In the first testcase, coerce_template_template_parms was adding too much of
outer_args when coercing to match P's template parameters, so that when
substituting into the 'const T&' parameter we got an unrelated template
argument for T.  We should only add outer_args when the argument template is
a nested template.

	PR c++/104107
	PR c++/95036

gcc/cp/ChangeLog:

	* pt.cc (coerce_template_template_parms): Take full parms.
	Avoid adding too much of outer_args.
	(coerce_template_template_parm): Adjust.
	(template_template_parm_bindings_ok_p): Adjust.
	(convert_template_argument): Adjust.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/alias-decl-ttp2.C: New test.
	* g++.dg/cpp1z/ttp2.C: New test.
---
 gcc/cp/pt.cc                                 | 41 +++++++++++++++++++++-------
 gcc/testsuite/g++.dg/cpp0x/alias-decl-ttp2.C | 25 +++++++++++++++++
 gcc/testsuite/g++.dg/cpp1z/ttp2.C            | 21 ++++++++++++++
 3 files changed, 77 insertions(+), 10 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/alias-decl-ttp2.C
 create mode 100644 gcc/testsuite/g++.dg/cpp1z/ttp2.C

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 1b18e2a..6dda660 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -7731,8 +7731,8 @@ coerce_template_template_parm (tree parm,
 	 template <template <template <class> class> class TT>
 	 class C;  */
       {
-	tree parmparm = DECL_INNERMOST_TEMPLATE_PARMS (parm);
-	tree argparm = DECL_INNERMOST_TEMPLATE_PARMS (arg);
+	tree parmparm = DECL_TEMPLATE_PARMS (parm);
+	tree argparm = DECL_TEMPLATE_PARMS (arg);
 
 	if (!coerce_template_template_parms
 	    (parmparm, argparm, complain, in_decl, outer_args))
@@ -8001,8 +8001,8 @@ unify_bound_ttp_args (tree tparms, tree targs, tree parm, tree& arg,
    the parameters to A, and OUTER_ARGS contains A.  */
 
 static int
-coerce_template_template_parms (tree parm_parms,
-				tree arg_parms,
+coerce_template_template_parms (tree parm_parms_full,
+				tree arg_parms_full,
 				tsubst_flags_t complain,
 				tree in_decl,
 				tree outer_args)
@@ -8011,6 +8011,9 @@ coerce_template_template_parms (tree parm_parms,
   tree parm, arg;
   int variadic_p = 0;
 
+  tree parm_parms = INNERMOST_TEMPLATE_PARMS (parm_parms_full);
+  tree arg_parms = INNERMOST_TEMPLATE_PARMS (arg_parms_full);
+
   gcc_assert (TREE_CODE (parm_parms) == TREE_VEC);
   gcc_assert (TREE_CODE (arg_parms) == TREE_VEC);
 
@@ -8046,8 +8049,26 @@ coerce_template_template_parms (tree parm_parms,
 	 specialized as P, so they match.*/
       processing_template_decl_sentinel ptds (/*reset*/false);
       ++processing_template_decl;
+
       tree pargs = template_parms_level_to_args (parm_parms);
-      pargs = add_outermost_template_args (outer_args, pargs);
+
+      /* PARM, and thus the context in which we are passing ARG to it, may be
+	 at a deeper level than ARG; when trying to coerce to ARG_PARMS, we
+	 want to provide the right number of levels, so we reduce the number of
+	 levels in OUTER_ARGS before prepending them.  This is most important
+	 when ARG is a namespace-scope template, as in alias-decl-ttp2.C.
+
+	 ARG might also be deeper than PARM (ttp23).  In that case, we include
+	 all of OUTER_ARGS.  The missing levels seem potentially problematic,
+	 but I can't come up with a testcase that breaks.  */
+      if (int arg_outer_levs = TMPL_PARMS_DEPTH (arg_parms_full) - 1)
+	{
+	  auto x = make_temp_override (TREE_VEC_LENGTH (outer_args));
+	  if (TMPL_ARGS_DEPTH (outer_args) > arg_outer_levs)
+	    TREE_VEC_LENGTH (outer_args) = arg_outer_levs;
+	  pargs = add_to_template_args (outer_args, pargs);
+	}
+
       pargs = coerce_template_parms (arg_parms, pargs, NULL_TREE, tf_none,
 				     /*require_all*/true, /*use_default*/true);
       if (pargs != error_mark_node)
@@ -8186,16 +8207,16 @@ template_template_parm_bindings_ok_p (tree tparms, tree targs)
 	      /* Extract the template parameters from the template
 		 argument.  */
 	      if (TREE_CODE (targ) == TEMPLATE_DECL)
-		targ_parms = DECL_INNERMOST_TEMPLATE_PARMS (targ);
+		targ_parms = DECL_TEMPLATE_PARMS (targ);
 	      else if (TREE_CODE (targ) == TEMPLATE_TEMPLATE_PARM)
-		targ_parms = DECL_INNERMOST_TEMPLATE_PARMS (TYPE_NAME (targ));
+		targ_parms = DECL_TEMPLATE_PARMS (TYPE_NAME (targ));
 
 	      /* Verify that we can coerce the template template
 		 parameters from the template argument to the template
 		 parameter.  This requires an exact match.  */
 	      if (targ_parms
 		  && !coerce_template_template_parms
-		       (DECL_INNERMOST_TEMPLATE_PARMS (tparm),
+		       (DECL_TEMPLATE_PARMS (tparm),
 			targ_parms,
 			tf_none,
 			tparm,
@@ -8489,13 +8510,13 @@ convert_template_argument (tree parm,
 	    val = orig_arg;
 	  else
 	    {
-	      tree parmparm = DECL_INNERMOST_TEMPLATE_PARMS (parm);
+	      tree parmparm = DECL_TEMPLATE_PARMS (parm);
 	      tree argparm;
 
 	      /* Strip alias templates that are equivalent to another
 		 template.  */
 	      arg = get_underlying_template (arg);
-              argparm = DECL_INNERMOST_TEMPLATE_PARMS (arg);
+	      argparm = DECL_TEMPLATE_PARMS (arg);
 
 	      if (coerce_template_template_parms (parmparm, argparm,
 						  complain, in_decl,
diff --git a/gcc/testsuite/g++.dg/cpp0x/alias-decl-ttp2.C b/gcc/testsuite/g++.dg/cpp0x/alias-decl-ttp2.C
new file mode 100644
index 0000000..230b277
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/alias-decl-ttp2.C
@@ -0,0 +1,25 @@
+// PR c++/104107
+// { dg-do compile { target c++11 } }
+
+template<int targ_id, typename t_parameter,
+	 template<typename T, const T&> class tt_w_data>
+struct tt_main {
+  static t_parameter m_parameter;
+  template<template<typename T, const T&> class t_data>
+    using t_make = t_data<t_parameter, m_parameter>;
+  using t_data = t_make<tt_w_data>;
+};
+
+template<int targ_id, typename t_parameter,
+	 template<typename T, const T&> class tt_w_data>
+t_parameter tt_main<targ_id, t_parameter, tt_w_data>::m_parameter;
+
+template<typename T, const T&> struct P {};
+struct t_parameter {};
+
+using toto = tt_main<0, t_parameter, P>;
+
+int main() {
+  toto t;
+  return 0;
+}
diff --git a/gcc/testsuite/g++.dg/cpp1z/ttp2.C b/gcc/testsuite/g++.dg/cpp1z/ttp2.C
new file mode 100644
index 0000000..1f161e5
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/ttp2.C
@@ -0,0 +1,21 @@
+// PR c++/95036
+// { dg-do compile { target c++17 } }
+
+namespace a {
+template <int b> struct c { static constexpr int d = b; };
+template <bool, typename e = void> using f = e;
+template <typename e, e...> struct g;
+template <typename> struct array;
+} // namespace a
+template <template <class> class h> struct i {
+  template <template <class, auto...> class, class = void> struct n;
+  template <class j> struct n<h, j> : a::c<true> {};
+  template <template <class> class k, class = a::f<n<k>::d>> void function();
+};
+template <template <class> class... l> struct derived : i<l>... {
+  using i<l>::function...;
+};
+int main() {
+  derived<a::array, a::g> m;
+  m.function<a::array>();
+}
-- 
2.7.4