Fix zspmv_openmp.cpp missing in srcdist

[cgohlke]

QuTiP 4.5.3 fails to build from source distribution on PyPI, e.g. on Windows:

c1xx: fatal error C1083: Cannot open source file: 'qutip/cy/openmp/src/zspmv_openmp.cpp': No such file or directory

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Changelog
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Fixed error checking for null matrix in essolve.
Added option for specifying resolution in Bloch.save function.

[coveralls]

Coverage remained the same at 63.189% when pulling 8645164 on cgohlke:patch-1 into 469b18c on qutip:master.

[jakelishman]

Can you fully show your build process, and did this work with a previous version of QuTiP? It builds fine for me from pip sdist on all major platforms with a simple

pip install qutip

and the sdist of 4.5.2 seems to be missing the same file.

Officially we don't support building with OpenMP from pip sdist (only git), but to be fair, it should have worked. In the interests of better semantics, can you change the new line in MANIFEST.in to

graft qutip/**/src

Technically there's only the one file that doesn't get tagged in (I hope), but logically the principle is that anything in a src directory should be distributed in the sdist.

[cgohlke]

You are right, I forgot to mention that my build is not using pip and explicitly enables --with-openmp. Same for version 4.5.2 but I didn't report until now.

[jakelishman]

Ah ok, that makes it easier to understand what happened - the MANIFEST.in file got added at some point before the 4.5.2 release, but its mere presence overrides the content of setuptools' package_data option, in which we do add the requisite files.

If it's not desperately urgent, are you able to build from the git branch at 4.5.3 instead temporarily? I can merge this PR, but we're hoping to put out 4.6.0 in about two weeks' time (which I'll make sure has this patch), and our release process is still very manual - I'd rather not have to repeat it another time if I can avoid it!

Sorry this file got lost when MANIFEST.in turned up.

[cgohlke]

Sure. It's not urgent at all.