Cache downloaded patches

[cweagans]

Right now, all patches are downloaded unconditionally every time they're applied. We should download them once and store them in the Composer cache. If we store the SHA-1 of the patch in composer.lock, and then save the patch as $sha1OfPatch.patch in the cache dir, offline installs with patches are possible.

Obviously, this wouldn't need to happen for local patches - only ones where we'd normally download them.

[mustanggb]

This would be welcome.

[sminnee]

Would it be possible/desirable to inline the entirety of the patch into the composer.lock file itself? Then you would be able to run "composer update" on your local environment, and distribute your composer.lock file to other environments with more confidence of the patches integrity when composer install is run.

It would bloat out the length of composer.lock, but does that actually have any practical downside?

[cweagans]

main now caches patch downloads. It uses the global composer cache, so if you're already caching this in your builds to speed up composer install, it should Just Work ™️

[mustanggb]

Haven't tested it yet, but great news.