duplicate_decls was not recognizing the explicit specialization as matching the implicit specialization of g<Y> because function_requirements_equivalent_p was seeing the C constraint on the implicit one and not on the explicit.
I think that the usefulness of much of the concepts TS support is limited and waning, but I guess we can keep it around for GCC 12. Tested x86_64-pc-linux-gnu, applying to trunk and 11. PR c++/101098 gcc/cp/ChangeLog: * decl.c (function_requirements_equivalent_p): Only compare trailing requirements on a specialization. gcc/testsuite/ChangeLog: * g++.dg/concepts/explicit-spec1.C: New test. --- gcc/cp/decl.c | 4 +++- gcc/testsuite/g++.dg/concepts/explicit-spec1.C | 9 +++++++++ 2 files changed, 12 insertions(+), 1 deletion(-) create mode 100644 gcc/testsuite/g++.dg/concepts/explicit-spec1.C diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c index ebe1318d38d..0df689b01f8 100644 --- a/gcc/cp/decl.c +++ b/gcc/cp/decl.c @@ -955,7 +955,9 @@ static bool function_requirements_equivalent_p (tree newfn, tree oldfn) { /* In the concepts TS, the combined constraints are compared. */ - if (cxx_dialect < cxx20) + if (cxx_dialect < cxx20 + && (DECL_TEMPLATE_SPECIALIZATION (newfn) + <= DECL_TEMPLATE_SPECIALIZATION (oldfn))) { tree ci1 = get_constraints (oldfn); tree ci2 = get_constraints (newfn); diff --git a/gcc/testsuite/g++.dg/concepts/explicit-spec1.C b/gcc/testsuite/g++.dg/concepts/explicit-spec1.C new file mode 100644 index 00000000000..d9b6b3d1741 --- /dev/null +++ b/gcc/testsuite/g++.dg/concepts/explicit-spec1.C @@ -0,0 +1,9 @@ +// PR c++/101098 +// { dg-do compile { target concepts } } + +template<typename T> concept C = __is_class(T); +struct Y { int n; } y; +template<C T> void g(T) { } +int called; +template<> void g(Y) { called = 3; } +int main() { g(y); } base-commit: d5b1bb0d197f9141a0f0e510f8d1b598c3df9552 -- 2.27.0