OpenE2K/gcc
2
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

c++: constrained nested partial specialization [PR92103]

Browse Source 
When determining the most specialized partial specialization of a
primary template that is nested inside a class template, we first
tsubst the outer template arguments into the TEMPLATE_DECL of each
partial specialization, and then check for satisfaction of each of the
new TEMPLATE_DECL's constraints.

But tsubst_template_decl does not currently guarantee that constraints
from the original DECL_TEMPLATE_RESULT get reattached to the new
DECL_TEMPLATE_RESULT.  In the testcase below, this leads to the
constraints_satisfied_p check in most_specialized_partial_spec to
trivially return true for each of the partial specializations.

I'm not sure if such a guarantee would be desirable, but in this case we
can just check constraints_satisfied_p on the original TEMPLATE_DECL
instead of on the tsubsted TEMPLATE_DECL here, which is what this patch
does (alongside some reorganizing).

gcc/cp/ChangeLog:

	PR c++/92103
	* pt.c (most_specialized_partial_spec): Reorganize the loop over
	DECL_TEMPLATE_SPECIALIZATIONS.  Check constraints_satisfied_p on
	the original template declaration, not on the tsubsted one.

gcc/testsuite/ChangeLog:

	PR c++/92103
	* g++.dg/cpp2a/concepts-partial-spec7.C: New test.
This commit is contained in:
Patrick Palka 2020-06-03 16:40:28 -04:00
parent 3fb68f2e66
commit aee69073cd
2 changed files with 32 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
gcc/cp/pt.c
View File

@ -24488,21 +24488,22 @@ most_specialized_partial_spec (tree target, tsubst_flags_t complain)
for (t = DECL_TEMPLATE_SPECIALIZATIONS (main_tmpl); t; t = TREE_CHAIN (t))
{
tree spec_args;
tree spec_tmpl = TREE_VALUE (t);
const tree ospec_tmpl = TREE_VALUE (t);
tree spec_tmpl;
if (outer_args)
{
/* Substitute in the template args from the enclosing class. */
++processing_template_decl;
spec_tmpl = tsubst (spec_tmpl, outer_args, tf_none, NULL_TREE);
spec_tmpl = tsubst (ospec_tmpl, outer_args, tf_none, NULL_TREE);
--processing_template_decl;
if (spec_tmpl == error_mark_node)
return error_mark_node;
}
else
spec_tmpl = ospec_tmpl;
if (spec_tmpl == error_mark_node)
return error_mark_node;
spec_args = get_partial_spec_bindings (tmpl, spec_tmpl, args);
tree spec_args = get_partial_spec_bindings (tmpl, spec_tmpl, args);
if (spec_args)
{
if (outer_args)
@ -24511,9 +24512,9 @@ most_specialized_partial_spec (tree target, tsubst_flags_t complain)
/* Keep the candidate only if the constraints are satisfied,
or if we're not compiling with concepts. */
if (!flag_concepts
|| constraints_satisfied_p (spec_tmpl, spec_args))
|| constraints_satisfied_p (ospec_tmpl, spec_args))
{
list = tree_cons (spec_args, TREE_VALUE (t), list);
list = tree_cons (spec_args, ospec_tmpl, list);
TREE_TYPE (list) = TREE_TYPE (t);
}
}

22
gcc/testsuite/g++.dg/cpp2a/concepts-partial-spec7.C Normal file
View File

@ -0,0 +1,22 @@
// PR c++/92103
// { dg-do compile { target c++20 } }
template<int M>
struct traits
{
template<int N>
struct equal_to
{ static constexpr bool value = false; };
template<int N> requires (M == N)
struct equal_to<N>
{ static constexpr bool value = true; };
template<int N> requires (M < 0) || (N < 0)
struct equal_to<N>
{ };
};
static_assert(traits<0>::equal_to<0>::value);
static_assert(!traits<0>::equal_to<1>::value);
static_assert(traits<-1>::equal_to<0>::value); // { dg-error "not a member" }