Move mirror_state.json under meta repository

[ikhoon]

mirror_state.json is automatically created for Git mirror repositories and updated when new commits are found in the upstream repository while running mirroring tasks.

There is no problem when mirroring the entire repository, but if a specific path of a repository is mirrored, mirror_state.json can be updated by the changes not included in the path. As there is no change in the corresponding path, the new commit history would be unnecessary from users' point of view.

I propose to move mirror_state.json under the internal meta repository to keep users' repository clean when there are no changes in the actual content.

[ikhoon]

@ghkim3221 suggested an idea that filters out mirror_state.json from Watcher to mitigate the problem:

The issue might be hard to apply because many users already have their mirror_state.json in each repository. It may be a huge break.
As a simple workaround, how about not notifying Watchers if mirror_state.json is changed? More generally, we can introduce a filter to Watcher excluding files that trigger the notification.

[minwoox]

FYI:
One of the reasons that we store mirror_state.json in the repository is to guarantee atomicity in a simple way.

[0x1306e6d]

Thank you!!!
May I try to send a PR?

[ikhoon]

May I try to send a PR?

There is a dependency on this feature. If mirror_state.json is migrated to meta, the file name of mirror_state.json should be changed to <mirror_id>_mirror_state.json to avoid conflicts with other mirrors. As mirror_id is an optional value, we need to fill mirror_id for all mirror configurations first.

I was implementing #838 (review) but haven't finished yet.

@ghkim3221 suggested an idea that filters out mirror_state.json from Watcher to mitigate the problem:

What do you think of sending a PR for this first? Otherwise, would you wait until #838 is merged?

[0x1306e6d]

Oh, I was being ambiguous.

What do you think of sending a PR for this first?

This is what I also intended. Let me prepare!