Cmake improvement with importlib metadata

[VincentRouvreau]

Fix #580

git checkout master
time cmake .
# real	0m10.676s
# user	0m13.474s
# sys	0m13.880s

git checkout cmake_improvement_with_importlib_metadata
time cmake .
# real	0m2.100s
# user	0m1.833s
# sys	0m2.096s

[mglisse]

As expected, we need a special case for pykeops, which can be installed on windows even if it cannot be imported. I don't know if we should always disable it on windows, or if we should try the import just for this package.

[VincentRouvreau]

As expected, we need a special case for pykeops, which can be installed on windows even if it cannot be imported. I don't know if we should always disable it on windows, or if we should try the import just for this package.

I did so on 848d853

[mglisse]

Is that better than if (NOT WIN32)?

[VincentRouvreau]

No, you are right. I wanted to do something smarter, like "the day fcntl will be available on windows, pykeops will work on windows", but that was not that smart...
if (NOT WIN32) on b4694d9

[mglisse]

I think it can be installed (pip install pykeops) but not imported (import pykeops). That's a detail though.

[mglisse]

Maybe the use of type hints also requires 3.8? I don't remember.

[VincentRouvreau]

In Python 3.5 for type hints

[mglisse]

Ok. Note that they added new type hinting possibilities with almost every release, so it is hard to be sure we aren't using modern things that were absent in older releases we are not testing anymore. Anyway, let's ignore this.