Use empty blas_ldflags if no cxx is configured

[lucianopaz]

Closes #504

Major / Breaking Changes

• ...

New features

• ...

Bugfixes

• Default blas_ldflags are empty if no compiler is configured

Documentation

• ...

Maintenance

• ...

[ricardoV94]

@lucianopaz do you think it's worth it to add a test?

[lucianopaz]

In all honesty, I don’t know how to test this properly. I know that I can mock the cxx config but I’m not sure if that we’ll have us completely covered. @twiecki, could you try out this branch when there is no compiler and see if it works?

[ricardoV94]

In all honesty, I don’t know how to test this properly. I know that I can mock the cxx config but I’m not sure if that we’ll have us completely covered. @twiecki, could you try out this branch when there is no compiler and see if it works?

Why mock? Can't you use the context manager with pytensor.config.change_flags(cxx=""): ....

Edit: Or this fails more internally? If so, ignore me

[lucianopaz]

In all honesty, I don’t know how to test this properly. I know that I can mock the cxx config but I’m not sure if that we’ll have us completely covered. @twiecki, could you try out this branch when there is no compiler and see if it works?

Why mock? Can't you use the context manager with pytensor.config.change_flags(cxx=""): ....

Edit: Or this fails more internally? If so, ignore me

Yes you're right, I can use the context manager instead. I realized now that I didn't cover the potential for failures in this part of the code. If cxx -print-search-dirs fails to run for whatever reason, it can mean many things:

1. The cxx command isn't in the path and we wont be able to compile C extensions
2. The cxx command doesn't have a print-search-dirs argument (gcc and clang do have it, but I don't know if this is a standard C compiler thing)
3. Something deeper went wrong and we wont be able to compile.

I think that I'll add some guardrails for that case in this PR and write a test for it too.

[lucianopaz]

@ricardoV94, @twiecki, can I bother you to try out this PR and see if it breaks your installations that used:

• No c compiler
• Blas on Linux
• Accelerate on Mac
• MKL on Intel

[ricardoV94]

Mine doesn't seem to have changed:

Main:

python -c "import pytensor; print(pytensor.config.blas__ldflags)"
-L/home/ricardo/miniconda3/envs/pytensor/lib -llapack -lblas -lcblas -lm -Wl,-rpath,/home/ricardo/miniconda3/envs/pytensor/lib

PYTENSOR_FLAGS='cxx=""' python -c "import pytensor; print(pytensor.config.blas__ldflags)"
# IndexError: list index out of range

PR:

python -c "import pytensor; print(pytensor.config.blas__ldflags)"
-L/home/ricardo/miniconda3/envs/pytensor/lib -llapack -lblas -lcblas -lm -Wl,-rpath,/home/ricardo/miniconda3/envs/pytensor/lib

PYTENSOR_FLAGS='cxx=""' python -c "import pytensor; print(pytensor.config.blas__ldflags)"
WARNING (pytensor.tensor.blas): Using NumPy C-API based implementation for BLAS functions.

[lucianopaz]

Mine doesn't seem to have changed:

That looks fine. To add on this, I tried out using a C compiler that pytensor seems to like but I don't have installed

PYTENSOR_FLAGS='cxx="icpc"' python -c "import pytensor; print(pytensor.config.blas__ldflags)"
~/repos/pytensor/pytensor/link/c/cmodule.py:2735: UserWarning: Pytensor cxx failed to communicate its search dirs. As a consequence, it might not be possible to automatically determine the blas link flags to use.
Command that was run: icpc -print-search-dirs
Output printed to stderr: /bin/sh: 1: icpc: not found

  warnings.warn(
WARNING (pytensor.tensor.blas): Using NumPy C-API based implementation for BLAS functions.

So I think that this PR is good to be merged