close diff window when changes to file are discarded

[BoscoCHW]

@fcollonval
Implemented closing of diff window when the changes to file are discarded, but I copied a lot of codes from the gitFileDiff command

Fixes #911

---

Edited to link the issue

[github-actions]

👈 Launch a binder notebook on branch BoscoCHW/jupyterlab-git/close-diff-window

[fcollonval]

Thanks @BoscoCHW

We may take a slightly different approach to avoid code duplication.

When creating the diff widget at https://github.com/jupyterlab/jupyterlab-git/blob/master/src/commandsAndMenu.tsx#L854, we could add a callback on gitModel.statusChanged just after that. If the file is not changed any more (you will need to introspect gitModel.status.files), we will call widget.dispose() to close it.

[BoscoCHW]

@fcollonval
I implemented it by adding a callback when in the gitShowDiff command, though, I'm not sure if the implementation is good.
I have two questions:

1. What is the purpose for the "unmodified" status? Based on my observation, discarding changes will remove the file from gitModel.status.files
2. Do we need to disconnect the slot/callback when the widget is closed? I'm not sure how to do it.

[fcollonval]

I implemented it by adding a callback when in the gitShowDiff command.

The implementation looks good, thanks for changing it.

I have two questions:
1. What is the purpose for the "unmodified" status? Based on my observation, discarding changes will remove the file from gitModel.status.files

The unmodified status is set there. It is set only when triggering the file browser context menu because we want to display the menu to open the git history for a versioned file that is not currently modified.

But in this case, this is as you figure out. If the file is not listed in gitModel.status.files, it is unchanged. Hence you can close the diff widget.

2. Do we need to disconnect the slot/callback when the widget is closed? I'm not sure how to do it.

Theoretically, it is a good practice to do so. But the widget itself has a clean up code when disposed to remove any slot.

[fcollonval]

Thanks a lot @BoscoCHW

[welcome]

Congrats on your first merged pull request in this project! 🎉

Thank you for contributing, we are very proud of you! ❤️