Re: [RFC] Hook management via 'git hooks' command

From: brian m. carlson <sandals@crustytoothpaste.net>
Date: Nov 19, 2019, 00:51 UTC
Message-ID: <20191119005136.GA6430@camp.crustytoothpaste.net>
In-Reply-To: <20191118223819.GI22855@google.com>

On 2019-11-18 at 22:38:19, Emily Shaffer wrote:

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> On Sat, Nov 16, 2019 at 05:45:01AM +0000, brian m. carlson wrote:
> > On 2019-11-16 at 01:11:25, Emily Shaffer wrote:
> > > Here's my suggestion.
> > > 
> > >  - Let configs handle the hook list and ordering, via 'hook.{hookname}' which
> > >    can be specified more than once.
> > >    - global config: hook.update = /path/to/firsthook
> > >      user config: hook.update = /path/to/secondhook
> > >      worktree config: hook.update = -/path/to/firsthook #eliminate the firsthook
> > >       call
> > >    - global config: hook.update = /path/to/firsthook
> > >      repo config: hook.update = /path/to/secondhook
> > >      repo config: hook.update = ^/path/to/firsthook #move firsthook execution
> > >        after secondhook for this project
> > 
> > I'd like to hear more about how we handle multiple hooks that are
> > repo-specific and don't live in the PATH.  This is a common situation
> > for existing tools that handle multiple hooks, and it's one I think we
> > should support.
> 
> I guess I'm confused about where PATH comes into play. Do you mean that
> the hook being run relies on PATH to be set appropriately? I had
> envisioned absolute paths in the config.

In past discussions, there's been an assumption that hooks in the config will be found in PATH if they're not specified explicitly, and I assumed (apparently incorrectly) that the same would be true here.

I do expect folks are going to want to use non-absolute paths, though. If I'm invoking the git binary in a hook, I don't care whether it exists in /usr/bin, /usr/local/bin, ~/bin, or somewhere else entirely. That's my shell's problem to figure out.

It's also common for folks to use something like "bundle exec" in a hook to run a linter that's installed by the local package manager, and in order to do that, you have to honor PATH to find the package manager's binary. That could be in a variety of places, and it could end up changing dynamically in a session due to a tool like RVM.

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> > Perhaps we add a "git hook execute" subcommand that executes scripts
> > from the hook directory.
> 
> Can you give an example of when you'd use it? I'm not understanding your
> concern and I think an example use case would help me see what you mean.

Sure. Currently, if I have pre-push hook, it lives in .git/hooks/pre-push. Now, I want to have multiple hooks for that which are specific to my repo. Maybe I've stuffed them into .git/hooks/pre-push.d/hook1 and .git/hooks/pre-push.d/hook2, since that's where my previous hook management system put them, but I now want to use those same hooks with the config style and drop the old tool.

I'd like to use "git hook execute pre-push.d/hook1" and "git hook execute pre-push.d/hook2" to automatically find the right hooks and invoke them. Similarly, I could use "git hook execute pre-push" to execute the old pre-push hook.

I suppose if we continue to keep the existing behavior of changing the directory and we pass the config options to the shell, then we could just write "$(git config core.hooksPath || echo .git/hooks)/pre-push.d/hook1" instead, which, while ugly, gets the job done. Then we wouldn't need such a command.

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> > I think this addresses most of the concerns that I had about ordering.
> > It is still a little suboptimal that we're relying on the ordering of
> > the config file, since it makes things equivalent to numbered files in
> > .d directories hard.
> 
> Hm, I suppose I don't see why, if the final ordering is determined by
> the .git/config (or future replacement for that). Can you explain what
> you mean? I want to understand where you're coming from.

One of the benefits to using numbered files in a .d directory is that you can explicitly control ordering of operations. For example, maybe I have a per-repo pre-push hook that performs some checks and rejects a push if something is off. I also have a pre-push hook for Git LFS that pushes the Git LFS objects to the remote server if Git LFS is in use.

In this case, I'd always want my sanity-check hook to run first, and so I'd number it first. This is fine if both are per-repo, but if the LFS hook is global, then it's in the wrong order and my LFS objects are pushed even though my sanity check failed.

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> > Possibly as an alternative to the ^ syntax, we could make the hook value
> > be of the form "key program", where key is a sort key (e.g., a number)
> > and program is the program to run.  We pick normal config file ordering
> > if the keys are identical.  Then if the system config wants to have a
> > hook that always runs at the end, it can do so easily.
> 
> Interesting. This way if you decide after you've set up all your configs
> just so that you really want something to run at the end of the update
> event, you can change one place, not n=number of Git repos. (I do still
> want to be able to say "don't run that global hook in this project"
> though.)

Exactly. A global or per-user commit-msg hook may want to see the final message before approving or rejecting it, and that wouldn't be possible without some sort of ordering.

I strongly agree that we should still allow removing higher-level hooks.

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> > In addition, we should be sure that attempting to remove a hook which
> > doesn't exist isn't an error, since a user might want to set their
> > ~/.gitconfig file to always unset a global hook that may or may not
> > exist.
> 
> I'd be comfortable with a warning when exiting 'git hook edit' mode and
> silence when actually running the hook list.

Yeah, that's what I'm going for.

-- 
brian m. carlson: Houston, Texas, US
OpenPGP: https://keybase.io/bk2204