When checking that a constrained partial specialization is more
constrained than the primary template, we pass only the innermost level
of generic template arguments to strictly_subsumes. This leads to us
doing a nonsensical substitution from normalize_concept_check if the
full set of template arguments has multiple levels, and it causes
strictly_subsumes to sometimes erroneously return false as in the
testcase below.
Passes 'make check-c++' and also tested by building the testsuites of
cmcstl2 and range-v3. Does this look OK to commit to mainline and to
the 10 branch after a full bootstrap and regtest?
(We shouldn't need to do any substitution from strictly_subsumes here,
since processing_template_decl would always be non-zero and so
substituting in the complete set of generic template arguments should
always be a no-op I think. I can propose this as a subsequent patch for
mainline.)
gcc/cp/ChangeLog:
* pt.c (process_partial_specialization): Pass the full set of
generic template arguments to strictly_subsumes.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/concepts-partial-spec8.C: New test.
---
gcc/cp/pt.c | 2 +-
.../g++.dg/cpp2a/concepts-partial-spec8.C | 14 ++++++++++++++
2 files changed, 15 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-partial-spec8.C
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index df92f5584cf..d7f61289621 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -5062,7 +5062,7 @@ process_partial_specialization (tree decl)
if (comp_template_args (inner_args, INNERMOST_TEMPLATE_ARGS (main_args))
&& (!flag_concepts
|| !strictly_subsumes (current_template_constraints (),
- inner_args, maintmpl)))
+ main_args, maintmpl)))
{
if (!flag_concepts)
error ("partial specialization %q+D does not specialize "
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-partial-spec8.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-partial-spec8.C
new file mode 100644
index 00000000000..873cf44e407
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-partial-spec8.C
@@ -0,0 +1,14 @@
+// { dg-do compile { target c++20 } }
+
+template<int M, int N>
+concept equal = M == N;
+
+template<int M>
+struct traits
+{
+ template<int N> requires equal<M, N>
+ struct foo {};
+
+ template<int N> requires equal<M, N> && (M >= 0) // { dg-bogus "not more
constrained" }
+ struct foo<N> {};
+};
--
2.27.0.rc1.5.gae92ac8ae3
