Can bypass pre-commit checks using `git gui`

[denizgenc]

Can't commit via regular git:

But you can commit via git gui:

(note the "secret access key ID" is simply a random 40 character string. Any resemblance to existing or future key IDs is purely coincidental)

[0atman]

So why does this happen? Atom and VSCode and Emacs and vim are OK...

[denizgenc]

tl;dr: I believe the cause of the issue might be that git-gui doesn't look in the right place for the pre-commit hooks that we install, since we change the git core.hooksPath variable to something else.

To try and figure out why this happens, I spent this morning looking at the git-gui source, found here: https://github.com/prati0100/git-gui

The following are a collection of notes I took, roughly following the order of function invocations when a commit is made. Function names link to the lines in which they are found in the source files, for convenience.

git-gui.sh

• Seems to be primary controller for the GUI. All the buttons and menus are defined here.
• The function do_commit is what is called to create commits in the first place. It only does one thing, which is that it calls a function named commit_tree, which can be found in lib/commit.tcl.

Going into lib/commit.tcl:

• commit_tree has a bunch of code that we're not interested in. Near the end, starting on line 236, we have the pre-commit hook related code.

  The first actual line of code sets a variable (fd_ph) to the output of a function, called githook_read, called with the string argument pre-commit. This function is found in git-gui.sh, again.

Back to git-gui.sh, looking at the function githook_read:

• The function takes an argument called hook_name and then a variable number of arguments following it using the args keyword.
• The first line sets the variable pchook to the output of gitdir hooks $hook_name. gitdir is yet another function in the git-gui.sh file.
  • Long story short^*, gitdir will return $_gitdir/hooks/pre-commit.
• This might be the beginning of the issue.

What is $_gitdir?

• $_gitdir is assigned to $env(GIT_DIR) during "repository setup". The env variable is built in and represents the environment variables on the machine, and the GIT_DIR environment variable represents the .git found in a repo.

  This might be the cause of the issue. It's probably the case that when githook_read executes the githooks, it's looking in the wrong place for the hooks.

  As part of the installation script, gds-pre-commit changes the core.hooksPath variable for git, which changes where git searches for hooks. It doesn't seem that git-gui uses this variable, from what I can tell.

---

Long story long - gitdir:

• This function takes a variable number of arguments, since its only argument is args.

• What this function does is check if args is equal to an empty string. If so, it simply returns the existing _gitdir global variable.

  If there are arguments passed to it, it uses eval to essentially create a filesystem path, starting from _gitdir, with each successive argument in $args representing the next folder.

  (An explanation of this can be found in the eval documentation - see specifically the paragraph and example following on from "Note that in the most common case...")

• In our case, gitdir is called in githook_read with the arguments hooks $hook_name, where $hook_name was set by commit_tree to be pre-commit. ↩

[ciaranevans-xydus]

Apologies for reviving an extremely dead thread @denizgenc - it is nice to see that it's back to the CS for me when I have an issue though 🤣

Did a fix for git gui and git hooks get implemented? I can see this issue was closed and your notes are very thorough, but I don't yet see how I can install a git hook and have it run via a git gui commit...? Unless I've mis-read something..

From what I understand, the only way would be to install the hook in the traditional .git/hooks folder, rather than use:

git config core.hooksPath <our-hooks-dir>

[0atman]

We no longer support this, please see the readme, which states:

We used to vendor our own bundle of pre-commit and detect-secrets. This was too brittle for us to support, we now recommend installing the off-the-shelf tools

I'd recommend asking this question on the pre-commit framework forums. Good luck!

[ciaranevans-xydus]

No worries @0atman - Worth the punt to see if the fix was easy to remember!