Re: git gui replaces amend message when prepare-commit-msg hook is used

[Orgad Shaneh <orgads@gmail.com>]

On Thu, Jul 4, 2013 at 1:34 PM, John Keeping <john@keeping.me.uk> wrote:
> On Thu, Jul 04, 2013 at 12:47:28PM +0300, Orgad Shaneh wrote:
>> Hi,
>>
>> If a prepare-commit-msg hook is used, git gui executes it for "New Commit".
>>
>> If the "New Commit" is selected, and then immediately "Amend" (before
>> the hook returns), when the hook returns the message is replaced with
>> the one produced by the hook.
>
> I think this is a problem with the hook you are running.  The hook is
> given arguments specifying the message file and optionally the source of
> whatever is already in the file (see githooks(5) for details).
>
> It sounds like your hook is blindly overwriting the file, rather than
> preserving its contents in the cases where you wish to do so.

Let me try to explain.

When git gui is executed, it calls the prepare-commit-msg script with
.git/PREPARE_COMMIT_MSG as an argument.

When amend is selected, the hook is *not* called at all (what would it
prepare? The message is already committed)

Use the following hook to reproduce:
--- snip ---
#!/bin/sh

sleep 5
echo "$@" >> /tmp/hook.log
echo 'Hello hook' > "$1"
--- snip ---

Now run git gui (or press F5 if it is already running), and before 5
seconds pass, click Amend last commit. You'll see the commit's
message, but when the 5 seconds pass it is replaced with "Hello hook".
That's the bug.

- Orgad