From 3ea64aad06a2b32739028bae03b9b9a5691d2d30 Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Fri, 10 Mar 2023 14:55:27 -0500
Subject: [PATCH] c++: passing one ttp to another [PR108179]
I kept trying to improve our choice of how many levels of outer_args to add,
when really the problem was that outer_args are for PARM and for this
reverse deduction we should be adding the outer arguments for ARG.
I spent quite a while trying to get DECL_CONTEXT set consistently on
template template parameters that have gone through
reduce_template_parm_level before I realized I could just use
current_scope().
PR c++/108179
PR c++/104107
PR c++/95036
gcc/cp/ChangeLog:
* pt.cc (coerce_template_template_parms): Use args from
DECL_CONTEXT (arg_tmpl) instead of outer_args.
gcc/testsuite/ChangeLog:
* g++.dg/template/ttp35.C: New test.
---
gcc/cp/pt.cc | 34 ++++++++++++++-------------
gcc/testsuite/g++.dg/template/ttp35.C | 7 ++++++
2 files changed, 25 insertions(+), 16 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/template/ttp35.C
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index d75c4395c8a8..ddbd73371b99 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -8110,22 +8110,24 @@ coerce_template_template_parms (tree parm_tmpl,
tree pargs = template_parms_level_to_args (parm_parms);
- /* 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);
- }
+ /* PARM and ARG might be at different template depths, and we want to
+ pass the right additional levels of args when coercing PARGS to
+ ARG_PARMS in case we need to do any substitution into non-type
+ template parameter types.
+
+ OUTER_ARGS are not the right outer levels in this case, as they are
+ the args we're building up for PARM, and for the coercion we want the
+ args for ARG. If DECL_CONTEXT isn't set for a template template
+ parameter, we can assume that it's in the current scope. In that case
+ we might end up adding more levels than needed, but that shouldn't be
+ a problem; any args we need to refer to are at the right level. */
+ tree ctx = DECL_CONTEXT (arg_tmpl);
+ if (!ctx && DECL_TEMPLATE_TEMPLATE_PARM_P (arg_tmpl))
+ ctx = current_scope ();
+ tree scope_args = NULL_TREE;
+ if (tree tinfo = get_template_info (ctx))
+ scope_args = TI_ARGS (tinfo);
+ pargs = add_to_template_args (scope_args, pargs);
pargs = coerce_template_parms (arg_parms, pargs, NULL_TREE, tf_none);
if (pargs != error_mark_node)
diff --git a/gcc/testsuite/g++.dg/template/ttp35.C b/gcc/testsuite/g++.dg/template/ttp35.C
new file mode 100644
index 000000000000..4847ea46ae18
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/ttp35.C
@@ -0,0 +1,7 @@
+// PR c++/108179
+
+template <class T, T X, template <T> class F>
+struct Foo {};
+
+template <class T0, class T1, T1 X, template <T1> class F>
+void f(Foo<T1, X, F>) {}
--
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