Add a link argument that is missing from the pkgconfig .pc file

[oscarbenjamin]

This follows #602 and #604.

The remaining outstanding issue for flintlib/python-flint#129 is that using meson-python and pkg config is incompatible with Flint < 3.1.0. The build appears to succeed but at runtime import fails with:

ImportError: /home/oscar/.pyenv/versions/python-flint-3.12/lib/python3.12/site-packages/flint/flint_base/flint_context.cpython-312-x86_64-linux-gnu.so: undefined symbol: flint_cleanup

Here flint_cleanup is just the first symbol from libflint that is looked up when python-flint's flint module is imported. Actually no symbols are found and so even if I comment out the use of flint_cleanup I just get an error with the next symbol.

It turns out that this is because of a bug in Flint's pkgconfig configuration that was fixed in Flint 3.1.0 by adding -lflint to flint.pc: flintlib/flint#1647. I have confirmed that if I manually edit flint.pc to add -lflint then the problem is solved for Flint 3.0.1 and everything seems to work fine.

This leaves python-flint with a choice:

• Drop support for Flint < 3.1.0.
• Work around the buggy flint.pc configuration.

I'm exploring the how to work around the buggy flint.pc config by adding something in the meson build files to add -lflint manually but I have not found a solution that works. I tried adding

add_global_arguments('-lflint', language: 'c')

but that did not seem to have any effect. I also tried adding

link_args: '-lflint',

to every extension_module and this seemed to resolve some unrecognised symbols but not all of them and so it instead fails with:

ImportError: /home/oscar/.pyenv/versions/python-flint-3.12/lib/python3.12/site-packages/flint/types/fmpz.cpython-312-x86_64-linux-gnu.so: undefined symbol: partitions_fmpz_fmpz

I don't see exactly what is special about the function partitions_fmpz_fmpz in this situation:
https://github.com/flintlib/python-flint/blob/1ce152dffc356af69b1d4c2ea0eb08854f3d733b/src/flint/flintlib/partitions.pxd#L10
https://github.com/flintlib/python-flint/blob/1ce152dffc356af69b1d4c2ea0eb08854f3d733b/src/flint/types/fmpz.pyx#L709

Is there a simple way to edit the meson.build files (or otherwise) that is more or less equivalent to adding the -lflint argument to flint.pc?

[rgommers]

Is there a simple way to edit the meson.build files (or otherwise) that is more or less equivalent to adding the -lflint argument to flint.pc?

Something like this using declare_dependency should work (untested, but I have code like this somewhere):

flint_dep = dependency('flint')
if flint_dep.version().version_compare('<3.1')
    flint_dep = declare_dependency(
        dependencies: flint_dep,
        link_args: ['-lflint']),
    )
endif

[eli-schwartz]

I would have suggested much the same except with cc.find_library('flint') instead of the string -lflint.

[oscarbenjamin]

Thanks both. Setting -lflint I get a link error when using the local build of flint:

cc  -o src/flint/pyflint.cpython-312-darwin.so src/flint/pyflint.cpython-312-darwin.so.p/meson-generated_src_flint_pyflint.pyx.c.o -Wl,-dead_strip_dylibs -Wl,-headerpad_max_install_names -Wl,-undefined,dynamic_lookup -bundle -Wl,-undefined,dynamic_lookup -Wl,-rpath,/Users/enojb/work/dev/python-flint/.local/lib /Users/enojb/work/dev/python-flint/.local/lib/libgmp.dylib /Users/enojb/work/dev/python-flint/.local/lib/libmpfr.dylib -lflint
ld: library 'flint' not found
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Setting LIBRARY_PATH gets me to a working build on OSX:

LIBRARY_PATH=$(pwd)/.local/lib PKG_CONFIG_PATH=$(pwd)/.local/lib/pkgconfig python -m build

That's probably acceptable because I think it will work for someone who has a system-wide install that is already in the appropriate paths. I'll check cc.find_library but I guess that wold need C_INCLUDE_DIR etc to be set as well.

[oscarbenjamin]

I'll check cc.find_library but I guess that wold need C_INCLUDE_DIR etc to be set as well.

No, it doesn't seem to make any difference whether I use -lflint or cc.find_library. I guess find_library is more robust or something so I'll go with that.

[oscarbenjamin]

Thanks both.

I have tested this and everything seems to be working in CI now for flintlib/python-flint#129. The CI failures now are just a sporadic segfault on OSX (that I think is unrelated...) and mesonbuild/meson#12401 which fails the 3.13-dev build.

That is enough for python-flint to have a working meson-python setup!

[eli-schwartz]

I guess find_library is more robust or something so I'll go with that.

It is guaranteed to be resolved at setup time and isn't prone to changing depending on whether you return to a previously existing build directory + forget to export the same environment variables.