https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120503
--- Comment #2 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Nathaniel Shead <nsh...@gcc.gnu.org>: https://gcc.gnu.org/g:7921bb4afcb7a3be8e10e63b10acfc2bfa477cae commit r16-3233-g7921bb4afcb7a3be8e10e63b10acfc2bfa477cae Author: Nathaniel Shead <nathanielosh...@gmail.com> Date: Fri Aug 8 23:23:18 2025 +1000 c++: Implement P2115R0 linkage changes for unnamed unscoped enums [PR120503] We currently list P2115R0 as implemented, but only the modules changes had been done. This patch implements the linkage changes so that unnamed unscoped enums will use the name of the first enumerator for linkage purposes. This is (strictly speaking) a breaking change, as code that previously relied on unnamed enumerations being internal linkage may have overloads using those types become exposed and clash with other functions in a different TU that have been similarly exposed. As such this feature is only implemented for C++20. No ABI flag warning is provided, partly because C++20 is still an experimental standard, but also because any affected functions could not have been part of an ABI until this change anyway. A number of testcases that are testing for behaviour of no-linkage types are adjusted to use an enumeration with no values, so that the pre-C++20 and post-C++20 behaviour is equivalently tested. In terms of implementation, I had originally considered adjusting the DECL_NAME of the enum, as with 'name_unnamed_type', but this ended up being more complicated as it had unwanted interactions with the existing modules streaming and with name lookup and diagnostic messages. This patch instead uses a new function to derive this case. The standard says that ([dcl.enum] p11) such an enum "...is denoted, for linkage purposes, by its underlying type and its first enumerator", so we need to add a new mangling production as well to handle this. PR c++/120503 PR c++/120824 gcc/cp/ChangeLog: * cp-tree.h (TYPE_UNNAMED_P): Adjust for enums with enumerators for linkage purposes. (enum_with_enumerator_for_linkage_p): Declare. * decl.cc (name_unnamed_type): Adjust assertions to handle enums with enumerators for linkage purposes. (grokdeclarator): Use a typedef name for enums with enumerators for linkage purposes. (enum_with_enumerator_for_linkage_p): New function. (finish_enum_value_list): Reset type linkage for enums with enumerators for linkage purposes. * mangle.cc (write_unnamed_enum_name): New function. (write_unqualified_name): Handle enums with enumerators for linkage purposes. * tree.cc (decl_linkage): Fixup unnamed enums. gcc/testsuite/ChangeLog: * g++.dg/abi/mangle32.C: Remove enumerator list. * g++.dg/cpp0x/linkage2.C: Likewise. * g++.dg/ext/vector26.C: Likewise. * g++.dg/other/anon3.C: Likewise. * g++.dg/abi/mangle83.C: New test. * g++.dg/modules/enum-15_a.C: New test. * g++.dg/modules/enum-15_b.C: New test. include/ChangeLog: * demangle.h (enum demangle_component_type): Add enumeration DEMANGLE_COMPONENT_UNNAMED_ENUM. libiberty/ChangeLog: * cp-demangle.c (d_unnamed_enum): New function. (d_unqualified_name): Call it. (cplus_demangle_type): Handle unscoped unnamed types (Ue, Ul, etc.) (d_count_templates_scopes): Handle unnamed enums. (d_find_pack): Likewise. (d_print_comp_inner): Print unnamed enums. * testsuite/demangle-expected: Add tests. Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com> Reviewed-by: Jason Merrill <ja...@redhat.com>
