Support for using .git/SQUASH_MSG in Git commit message box

[philipstarkey]

Currently the VS Code Git commit message box automatically synchronises with the contents of .git/MERGE_MSG (provided you have not entered your own commit message yet into VS Code).

I would like to request support for VS Code to do the same with .git/SQUASH_MSG (produced when running git merge <branch> --squash). This would provide better integration between VS code git related VS Code extensions which often have the ability to perform a squash merge via the extension GUI but do not typically replicate any of the existing VS Code git interface (commit message box and changed file list).

[daniel-j-davis]

@joaomoreno I wouldn't mind taking this on, and I've looked through the code so I have a pretty good idea of what's required to implement this. Just one question, though — is there any situation where .git/MERGE_MSG and .git/SQUASH_MSG are both present? If so: which one do we think should take precedence as the 'default' commit message?

[philipstarkey]

@daniel-j-davis my suggestion would be to follow what git-gui does since it's bundled with git. Looks like it preferences MERGE_MSG over SQUASH_MSG (see here)

[daniel-j-davis]

That makes sense, and that's what I was thinking too. I'll put a PR in shortly!

[isidorn]

I got this to partially work by:

1. Having a SQUASH_MSG file with some content like "HELLO"
2. Creaing a local branch git co -b isidorn/deleteme
3. git merge master --squash
4. The SQUASH_MSG file sometimes gets filled with content, like the following
5. SO it seems like the content of the SQUASH_MSG file is not constant for me, and changes once I do a squash

Reopening this for discussion. I also might be doing something wrong.
Bonus bug: when chaning the content of the SQUASH_MSG the scm input does not reg resized and ends up looking broken (picture attached).
So I would recommend that we revert this PR and polish it a bit more.

Squashed commit of the following:

commit 639a21b145ba38007a2b5ee9d4233ac6a6067e89
Author: Daniel Imms <tyriar@tyriar.com>
Date:   Tue Jun 30 06:39:30 2020 -0700

    Add ending period to terminal launch notification messages
    
    Fixes #101344

commit 01d0314308fdf83801c3d7abf43b7a2702ea9263
Author: Daniel Imms <tyriar@tyriar.com>
Date:   Tue Jun 30 05:22:31 2020 -0700

    Change troubleshoot button to 'Open Help'
    
    Fixes #101345

[daniel-j-davis]

It worked fine (and always displayed the intended (?) squash msg), but maybe it's because I was only squashing another branch that only had one commit? I concur that it seems like the contents of SQUASH_MSG aren't always consistent though, now that I've tried with a branch with more than one commit.

EDIT: It seems like it displays all of the squashed commits in one message, prefaced by

Squashed commit of the following:
<some commits>

As for the bonus bug, is that issue exclusive to SQUASH_MSG or does it also happen if you change the contents of MERGE_MSG? @isidorn

[joaomoreno]

@isidorn You're not supposed to manually create or edit the SQUASH_MSG file. This is a file created by git during the git merge <branch> --squash command. When you run this command you will have a commit pending... and the input box should be prepopulated with a template commit message. Can you try this again?

Thanks for the input box issue though, will try to repro.

[philipstarkey]

EDIT: It seems like it displays all of the squashed commits in one message, prefaced by

Squashed commit of the following:
<some commits>
...

This was the intended behaviour behind this feature request. I'm not expecting VS Code to do anything magical here with SQUASH_MSG. It should just be taking the entire contents of the file as other graphical git tools do (and as a command line call to git commit does if SQUASH_MSG exists).

I do not think the PR needs reverting.

[joaomoreno]

Added another commit, since the MERGE_MSG can exist but just have no content. In that case we should take SQUASH_MSG.

@isidorn Please verify once again, now the feature is clearer.

[isidorn]

Sorry for the confusion, just was not very clear to me.
I will verify this later today.

[isidorn]

Adding verified label since the git commit gets nicely preopulated with the squash message.