1.6.0rc1: detection for llvm-flang not working

[h-vetinari]

Describe the bug
I've built meson 1.6.0rc1 for conda-forge, in order to test it against the scipy build: conda-forge/scipy-feedstock#287

We had a working build on windows based on v1.5.2 (including a backport of #13323), however, meson 1.6.0rc1 runs into:

[1289/1383] Linking target scipy/linalg/_interpolative.cp313-win_amd64.pyd
FAILED: scipy/linalg/_interpolative.cp313-win_amd64.pyd 
"flang"  -Wl,/MACHINE:X64 -Wl,/OUT:scipy/linalg/_interpolative.cp313-win_amd64.pyd scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/meson-generated__interpolativemodule.c.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/meson-generated__interpolative-f2pywrappers.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_dfft.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_id_rand.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_id_rtrans.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idd_frm.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idd_house.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idd_id.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idd_id2svd.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idd_qrpiv.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idd_sfft.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idd_snorm.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idd_svd.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_iddp_aid.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_iddp_asvd.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_iddp_rid.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_iddp_rsvd.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_iddr_aid.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_iddr_asvd.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_iddr_rid.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_iddr_rsvd.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idz_frm.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idz_house.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idz_id.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idz_id2svd.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idz_qrpiv.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idz_sfft.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idz_snorm.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idz_svd.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idzp_aid.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idzp_asvd.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idzp_rid.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idzp_rsvd.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idzr_aid.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idzr_asvd.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idzr_rid.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_idzr_rsvd.f.obj scipy/linalg/_interpolative.cp313-win_amd64.pyd.p/src_id_dist_src_prini.f.obj "-LC:/bld/scipy-split_1728536448862/_build_env/Library/lib/clang/5.0.0" "-Wl,/release" "-Wl,/nologo" "-Wl,/OPT:REF" "-Wl,/DLL" "-Wl,/IMPLIB:scipy\linalg\_interpolative.cp313-win_amd64.lib" "scipy/libg77_abi_wrappers.a" "scipy/lib_fortranobject.a" "-Wl,--version-script=C:/bld/scipy-split_1728536448862/work/scipy/_build_utils/link-version-pyinit.map" "C:/bld/scipy-split_1728536448862/_h_env/Library/lib/lapack.lib" "C:/bld/scipy-split_1728536448862/_h_env/Library/lib/blas.lib" "%PREFIX%\libs\python313.lib" "C:/bld/scipy-split_1728536448862/_h_env/Library/lib/cblas.lib" "-lflang" "-lpgmath"
LINK : warning LNK4044: unrecognized option '/-version-script=C:/bld/scipy-split_1728536448862/work/scipy/_build_utils/link-version-pyinit.map'; ignored
LINK : fatal error LNK1181: cannot open input file 'pgmath.lib'
flang.exe: error: linker command failed with exit code 1181 (use -v to see invocation)

[1290/1383] Linking target scipy/linalg/_solve_toeplitz.cp313-win_amd64.pyd
lld-link: warning: ignoring unknown argument '-Wl,--version-script=C:/bld/scipy-split_1728536448862/work/scipy/_build_utils/link-version-pyinit.map'

[1291/1383] Compiling C++ object scipy/optimize/_highs/_highs_wrapper.cp313-win_amd64.pyd.p/meson-generated__highs_wrapper.cpp.obj
ninja: build stopped: subcommand failed.

ERROR Backend subprocess exited when trying to invoke build_wheel

The fact that the build tries to link to pgmath is a dead give-away that we've fallen into the wrong flang compiler class:

meson/mesonbuild/compilers/fortran.py

Line 461 in 7396839

return search_dirs + ['-lflang', '-lpgmath']

Not idea yet what broke this.

To Reproduce
Run the build for conda-forge/scipy-feedstock#287

Expected behavior
A passing build (as was the case with #13323 applied on top of 1.5.2)

system parameters

• Is this a cross build or just a plain native build (for the same computer)?
  • native
• what operating system (e.g. MacOS Catalina, Windows 10, CentOS 8.0, Ubuntu 18.04, etc.)
  • windows-2022 image in azure pipelines
• what Python version are you using e.g. 3.8.0
  • python 3.10-3.13
• what meson --version
  • 1.6.0rc1
• what ninja --version if it's a Ninja build
  • 1.12.1

CC @rgommers

[eli-schwartz]

Not a whole lot has changed there, but one thing that did was 5399d3d. Can you check it out? It looks potentially suspicious.

[h-vetinari]

To be clear, you're asking to test whether a revert of 5399d3d on top of 1.6.0rc1 works?

[h-vetinari]

Apologies, I've just now seen that this was due to an infrastructure change that accidentally caused a very old version of flang to get pulled in. Once a current-generation LLVM flang is used, things work again as expected. Sorry for the noise, and thanks for the quick help! 🙏