ABI break in fmt 11.1.0 - 11.1.3 blocking conda-forge builds

[bdice]

conda-forge builds of fmt 11.1.0 through 11.1.3 have all failed due to an ABI break on Windows that was uncovered during downstream tests of libmamba. @saraedum identified this as the breaking symbol:

-??$vformat_to@D@detail@v11@fmt@@YAXAEAV?$buffer@D@012@V?$basic_string_view@D@12@V?$basic_format_args@Vcontext@v11@fmt@@@12@Vlocale_ref@012@@Z
+??$vformat_to@D@detail@v11@fmt@@YAXAEAV?$buffer@D@012@V?$basic_string_view@D@12@V?$basic_format_args@Vcontext@v11@fmt@@@12@Ulocale_ref@012@@Z

A few users have requested a newer fmt release, which probably requires a fix for this (if this is indeed the root cause -- I have not verified if there are any other ABI breaks). The failure logs can be seen here: conda-forge/fmt-feedstock#55

The error looks like:

import: 'libmambapy'
Traceback (most recent call last):
  File "D:\bld\fmt_1737954208540\test_tmp\run_test.py", line 2, in <module>
    import libmambapy
  File "D:\bld\fmt_1737954208540\_test_env\Lib\site-packages\libmambapy\__init__.py", line 7, in <module>
    raise e
  File "D:\bld\fmt_1737954208540\_test_env\Lib\site-packages\libmambapy\__init__.py", line 4, in <module>
    from libmambapy.bindings import *  # noqa: F401,F403
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ImportError: DLL load failed while importing bindings: The specified procedure could not be found.

I attempted to demangle the symbols above, and got:

- void __cdecl fmt::v11::detail::vformat_to<char>(class fmt::v11::detail::buffer<char> &, class fmt::v11::basic_string_view<char>, class fmt::v11::basic_format_args<class fmt::v11::context>, class fmt::v11::detail::locale_ref)
+ void __cdecl fmt::v11::detail::vformat_to<char>(class fmt::v11::detail::buffer<char> &, class fmt::v11::basic_string_view<char>, class fmt::v11::basic_format_args<class fmt::v11::context>, struct fmt::v11::detail::locale_ref)

That points to this commit as the source of the change: f213d83

[vitaut]

Thanks for reporting. Does changing struct to class in

fmt/include/fmt/base.h

Line 2274 in 7f76955

struct locale_ref {

resolve the issue?

[vitaut]

Should be fixed in 3401ce2. Will make a patch release shortly.

[bdice]

Thank you! Apologies I wasn’t able to test that change sooner.

[vitaut]

BTW it was released as https://github.com/fmtlib/fmt/releases/tag/11.1.4.