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[03:17:13] <toad_polo> As I tweak several modules with compiled backends, I am realizing that PEP 517's build isolation seems to prevent caching between builds, for better or for worse :(

[03:24:22] <njs> there's two kinds of isolation... pip tries to isolate the build from the usual python environment, and also, it likes to build in a temporary directory because the pip devs have a deep distrust of build backends leaving clutter behind

[03:24:33] <njs> the former is I think what "build isolation" has mostly meant

[03:25:01] <njs> the latter is something pip has been doing for a very long time... but I guess now that we're pushing people to go through pip instead of running setup.py directly, people might be hitting it more?

[03:25:53] <njs> there's an old issue somewhere about 'why does pip insist on copying hundreds of megabytes on every build', and it was also a major point of discussion during the PEP 517 stuff

[03:26:39] <njs> (one of the major reasons that PEP 517 has an sdist generation hook, was to give pip a way to semi-efficiently copy a source tree into a temporary directory)

[03:27:03] <toad_polo> Well, `tox` also needs to be able to build an `sdist`.

[03:27:47] <njs> yeah, there are other reasons why sdist generation is useful

[03:28:13] <njs> but that's how the pip behavior ended up getting pulled into the PEP 517 threads

[03:30:01] <njs> oh here it is: https://github.com/pypa/pip/issues/2195

[03:31:37] <njs> IMO if you give pip an already-unpacked directory it should use it without copying, but so far the pip devs have not come around to my point of view on that :-)

[03:33:35] <njs> see e.g. https://www.mail-archive.com/distutils-sig@python.org/msg26035.html and replies

[04:17:13] <bn_work> tdsmith: thanks for the reply, can you provide more detail on how I would do that?