From aee69073cdb8086d393f12474c6177e75467ceaa Mon Sep 17 00:00:00 2001 From: Patrick Palka Date: Wed, 3 Jun 2020 16:40:28 -0400 Subject: [PATCH] c++: constrained nested partial specialization [PR92103] 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. --- gcc/cp/pt.c | 19 ++++++++-------- .../g++.dg/cpp2a/concepts-partial-spec7.C | 22 +++++++++++++++++++ 2 files changed, 32 insertions(+), 9 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-partial-spec7.C diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c index 38a771b8e6f..f5d1442a400 100644 --- a/gcc/cp/pt.c +++ b/gcc/cp/pt.c @@ -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); } } diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-partial-spec7.C b/gcc/testsuite/g++.dg/cpp2a/concepts-partial-spec7.C new file mode 100644 index 00000000000..5b3afce3bc7 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-partial-spec7.C @@ -0,0 +1,22 @@ +// PR c++/92103 +// { dg-do compile { target c++20 } } + +template +struct traits +{ + template + struct equal_to + { static constexpr bool value = false; }; + + template requires (M == N) + struct equal_to + { static constexpr bool value = true; }; + + template requires (M < 0) || (N < 0) + struct equal_to + { }; +}; + +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" } -- 2.30.2