ENH: build cache that plays nicely with git worktree/asv

[jbrockmendel]

cython is pretty good about avoiding unnecessary compilations, but that doesn't play nicely with git worktree or asv

Two ways this could work:

1. An explicit cache that sits next to the "real" .git repo

2. If in a worktree directory, scan other directories in the worktree to see if we can re-use already-cythonized results from there.

I'm not sure how to make version 2 work with asv.

[scoder]

I'm not sure I understand your problem description. Could you update it with some details? Are you suggesting that there is a problem with checking out different branches or something like that? What does asv refer to here? A link would help.

[jbrockmendel]

I'm not sure I understand your problem description. Could you update it with some details? Are you suggesting that there is a problem with checking out different branches or something like that?

Refresher on git worktree:

~/Desktop/pd/ is where I keep all my pandas branches
pd/pandas/ has master checked out
pd/pandas/.git is the actual repo

git worktree add ../foo foo creates a foo branch and checks it out in pd/foo/, and the pd/foo/.git file is a single-line file telling git where to find the actual repo directory.

If I were to just check out a new branch directly inside the pd/pandas/ directory, the cythonized .c files would still be there, so would not need to be re-cythonized. But when a new branch is instantiated in a worktree directory, the .pyx files need to be cythonized from scratch, which is what I'd like to avoid.

What does asv refer to here? A link would help.

https://github.com/airspeed-velocity/asv

A benchmarking tool. The relevant behavior is that it will also check out existing branches in fresh directories and build from scratch, which can be a real pain point.