Check the new venv detection/handling

[ev-br]

Supposedly it is going to land in meson 0.62. cf mesonbuild/meson#9788

[eli-schwartz]

It is now merged to meson git master and will indeed be present in 0.62.0.

[ev-br]

OK, spot-checked $ meson setup build -Dpython.install_env="auto" with a pre-release 0.62.0rc. Worked great, did detect the virtualenv. Great!
To fully switch over from the --prefix + PYTHONPATH workflow, a quick question @eli-schwartz : what would be the canonical way to uninstall the result of $ meson install -C build? E.g., with pip it's pip uninstall <packagename>, with explicit prefix it's easy to keep the artifacts in-tree, so git clean -xdf works. Manually removing files in site-packages is asking for trouble however.

[eli-schwartz]

Meson creates a rule for ninja uninstall similar to the autotools convention for make uninstall.

[ev-br]

(finally) tried ninja uninstall. First, need to $ cd build (obvious in retrospect). Then $ ninja uninstall does not completely remove the contents of .../site-packages/mc_lib: it chokes on e.g. lattices/__pycache__ directories and reports that lattices/ is not empty. The net result is that site_packages/mc_lib folder still exists. Compare to pip uninstall which removes it all.