[PATCH] c++: passing partially inst tmpl as ttp [PR110566]

[Patrick Palka <ppalka@redhat.com>]

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk/13?

-- >8 --

Since the arguments 'pargs' passed to the coerce_template_parms from
coerce_template_template_parms are always a full set, we need to make sure
we always pass the parameters of the most general template because if the
template is partially instantiated then the levels won't match up.  In the
testcase below during said call to coerce_template_parms the parameters
are {X, Y} both level 1, but the arguments are {{int}, {N, M}}, which
leads to a crash during auto deduction of X and Y.

	PR c++/110566

gcc/cp/ChangeLog:

	* pt.cc (coerce_template_template_parms): Simplify by using
	DECL_INNERMOST_TEMPLATE_PARMS and removing redundant asserts.
	Always pass the parameters of the most general template to
	coerce_template_parms.

gcc/testsuite/ChangeLog:

	* g++.dg/template/ttp38.C: New test.
---
 gcc/cp/pt.cc                          | 12 +++++-------
 gcc/testsuite/g++.dg/template/ttp38.C | 12 ++++++++++++
 2 files changed, 17 insertions(+), 7 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/template/ttp38.C

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index d882e9dd117..8723868823e 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -8073,12 +8073,10 @@ coerce_template_template_parms (tree parm_tmpl,
   tree parm, arg;
   int variadic_p = 0;
 
-  tree parm_parms = INNERMOST_TEMPLATE_PARMS (DECL_TEMPLATE_PARMS (parm_tmpl));
-  tree arg_parms_full = DECL_TEMPLATE_PARMS (arg_tmpl);
-  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);
+  tree parm_parms = DECL_INNERMOST_TEMPLATE_PARMS (parm_tmpl);
+  tree arg_parms = DECL_INNERMOST_TEMPLATE_PARMS (arg_tmpl);
+  tree gen_arg_tmpl = most_general_template (arg_tmpl);
+  tree gen_arg_parms = DECL_INNERMOST_TEMPLATE_PARMS (gen_arg_tmpl);
 
   nparms = TREE_VEC_LENGTH (parm_parms);
   nargs = TREE_VEC_LENGTH (arg_parms);
@@ -8134,7 +8132,7 @@ coerce_template_template_parms (tree parm_tmpl,
 	scope_args = TI_ARGS (tinfo);
       pargs = add_to_template_args (scope_args, pargs);
 
-      pargs = coerce_template_parms (arg_parms, pargs, NULL_TREE, tf_none);
+      pargs = coerce_template_parms (gen_arg_parms, pargs, NULL_TREE, tf_none);
       if (pargs != error_mark_node)
 	{
 	  tree targs = make_tree_vec (nargs);
diff --git a/gcc/testsuite/g++.dg/template/ttp38.C b/gcc/testsuite/g++.dg/template/ttp38.C
new file mode 100644
index 00000000000..7d25d291e81
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/ttp38.C
@@ -0,0 +1,12 @@
+// PR c++/110566
+// { dg-do compile { target c++20 } }
+
+template<template<int N, int M> class>
+struct A;
+
+template<class T>
+struct B {
+  template<int X, int Y> struct C;
+};
+
+using type = A<B<int>::C>;
-- 
2.41.0.376.gcba07a324d