document/set up support tooling for editor integrations

[RonnyPfannschmidt]

follow-up to jgirardet/sublack#31
deferred from pre-commit/pre-commit#838

as i conversed with sublack author, it became apparent that its pretty hard/tricky to integrate pre-commit/black for example with editor integrations (in order to fix exact project set-ups)

i wonder if the issue can be elevated/helped in some way

[jgirardet]

hi @asottile .
Indeed using tempfile is not a big performance issue. I tested.
The main problem. is the pre-commit running time.

@RonnyPfannschmidt asked me for using same version of black (in editor and command line) via pre-commit.
I see 2 ways of doing it keeping run time as slow as possible:

• pre-commit could have a "skip-pre-commit" ;-) option to directly run the hook, skipping all the precommit stuf. if it accepts arguments we are ultimate.
• expose the hook path via a "hook info" option or something like this so we could run directly the right executable from pre-commit repo.

[RonnyPfannschmidt]

@jgirardet would it be sufficient to limit the pre-commit hook run to only/exactly the black hook, if the env is cached already that might be really quick

[asottile]

pre-commit could have a "skip-pre-commit" ;-) option to directly run the hook, skipping all the precommit stuf. if it accepts arguments we are ultimate.

I'm not sure what you mean here, that's essentially what pre-commit run <hookid> --files ... is

[jgirardet]

the idea was to run black via precommit but without the whole bunch of things that pre commit do, to save some time.

[asottile]

there isn't really anything that pre-commit does beyond collect the args and subprocess, last time I profiled it it essentially boiled down to:

1. 5%: python interpreter startup
2. 80%: import of pkg_resources module
3. 1%: subprocess to determine git rev-parse --show-toplevel
4. 1%: parsing yaml configurations
5. 1%: subprocess git ls-files to cross reference --files
6. 1% subprocess git diff to know when files change

And factoring out pkg_resources isn't easy.

[asottile]

some rough numbers:

$ time ~/opt/venv/bin/python -c ''

real	0m0.028s
user	0m0.020s
sys	0m0.008s

$ time ~/opt/venv/bin/python -c 'import pre_commit.main'

real	0m0.185s
user	0m0.169s
sys	0m0.017s

$ time pre-commit run echo --verbose --files setup.py
[echo] echo..............................................................Passed
hookid: echo

setup.py


real	0m0.204s
user	0m0.181s
sys	0m0.025s

[jgirardet]

thank you for your answers @asottile

[asottile]

Note that pkg_resources will be factored out in the next release: pre-commit/pre-commit#840

[RonnyPfannschmidt]

@asottile great job, thanks 👍

[asottile]

feel free to send PRs for editor integrations -- going to close this since there isn't really anything actionable at the moment