https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109751
--- Comment #24 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The trunk branch has been updated by Jason Merrill <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:810bcc00156cefce7ad40fc9d8de6e43c3a04450 commit r14-3389-g810bcc00156cefce7ad40fc9d8de6e43c3a04450 Author: Jason Merrill <ja...@redhat.com> Date: Thu Aug 17 11:36:23 2023 -0400 c++: constrained hidden friends [PR109751] r13-4035 avoided a problem with overloading of constrained hidden friends by checking satisfaction, but checking satisfaction early is inconsistent with the usual late checking and can lead to hard errors, so let's not do that after all. We were wrongly treating the different instantiations of the same friend template as the same function because maybe_substitute_reqs_for was failing to actually substitute in the case of a non-template friend. But we don't actually need to do the substitution anyway, because [temp.friend] says that such a friend can't be the same as any other declaration. After fixing that, instead of a redefinition error we got an ambiguous overload error, fixed by allowing constrained hidden friends to coexist until overload resolution, at which point they probably won't be in the same ADL overload set anyway. And we avoid mangling collisions by following the proposed mangling for these friends as a member function with an extra 'F' before the name. I demangle this by just adding [friend] to the name of the function because it's not feasible to reconstruct the actual scope of the function since the mangling ABI doesn't distinguish between class and namespace scopes. PR c++/109751 gcc/cp/ChangeLog: * cp-tree.h (member_like_constrained_friend_p): Declare. * decl.cc (member_like_constrained_friend_p): New. (function_requirements_equivalent_p): Check it. (duplicate_decls): Check it. (grokfndecl): Check friend template constraints. * mangle.cc (decl_mangling_context): Check it. (write_unqualified_name): Check it. * pt.cc (uses_outer_template_parms_in_constraints): Fix for friends. (tsubst_friend_function): Don't check satisfaction. include/ChangeLog: * demangle.h (enum demangle_component_type): Add DEMANGLE_COMPONENT_FRIEND. libiberty/ChangeLog: * cp-demangle.c (d_make_comp): Handle DEMANGLE_COMPONENT_FRIEND. (d_count_templates_scopes): Likewise. (d_print_comp_inner): Likewise. (d_unqualified_name): Handle member-like friend mangling. * testsuite/demangle-expected: Add test. gcc/testsuite/ChangeLog: * g++.dg/cpp2a/concepts-friend11.C: Now works. Add template. * g++.dg/cpp2a/concepts-friend15.C: New test.
