@chchwy Great news! Thank you for working on this. A recovery feature is certainly needed and one thing we discussed on discord a while ago among the many permutations of possible recovery methods was the following:

In addition to your proposals outlined here which covers the cases related to files actually existing untouched by the OS or Pencil2D automatic removal, we discussed the necessity to add a direct file copy / backup functionality which would occur prior to opening the actual file making a carbon copy of the file in the state previous to starting the work session.

Ideally this would make a copy, number it and allow Pencil2D users to have up to X number of copies handy to recover from unforeseen bugs and to cover the cases where all the files are wiped without trace or the PCLX files are "zeroed" out becoming a garbage file.

These issues have been found to occur by a combination of the OS privacy & security handling, Pencil2D's unseen memory leaks and an interruption of the saving procedure.

This was my proposal:
https://discordapp.com/channels/342369662710972417/342670204351938562/662025930683842579

This was @scribblemaniac 's proposal at the time (along some thoughts related to the actual implementation):
https://discordapp.com/channels/342369662710972417/342670204351938562/662048769373896716

In summary, and after some afterthought, while we've discussed auto save ideas for months we managed to settle that having backup files on the same folder was agreeable.

If the user dislikes the idea of having extra packed or unpacked (PCL) backup files on the project folder (a la Blender), at most we could move it to APPDATA and keep the list of backups there so we can load them without issues.

The reason I mention using the APPDATA folder as opposed to the TEMP which has the unpacked version of the working file during a work session is because this folder tends to be erased either by the OS or by the users and due to the privacy keepers in each Os getting more annoying, using that folder for recovery seems an inconvenient risk.

Besides even though we now have a direct access to the TEMP folder, since there was also a conversation about moving settings to APPDATA in preparation for MyPaint brush configuration settings, there could also be a direct access to APPDATA via a similar button in case people want to explore the potential backups manually along other settings.

Thanks @Jose-Moreno. I didn't know there is a proposal. It would be great to be written down somewhere (forum etc.) rather than buried in the discord chat history.

I read both your proposal. They are great and I agree with most of the opinions. Many of your ideas have been in my mind for a long time. However, this PR is focusing on the recovery part. I will send more PRs sooner or later for the file-save things.

This is a great step forward, I look forward seeing this merged.
I've made two observations so far:

1. When creating a new project, the main file is never created and images are of course not exported either so the recovery popup never shows. This is expected since we don't have any data yet but maybe we should consider saving changes gradually to the temp folder instead of only on project load, as there is otherwise no gain for those people working on something but never saves.
2. When loading a project, making changes and killing the application, the dialog shows as expected. The layers however has been renamed and the camera layer (in my case) moved to the top.

Mmm...the layers should be renamed only when the main.xml is damaged. I will check again.

@candyface I fixed the layer renaming issue

Just found that Windows will clear the temp folder even if force closing the app by the task manager. So you will need an actual crash to test this feature on Windows.

I'd have preferred if this was reviewed before merging.

@scribblemaniac you can still review any code anytime if you like, I would appreciate it. I am trying to utilize my limited time and making progress.

I agree with @scribblemaniac, let's try to keep the PR process and make sure things are reviewed and accepted by at least one before merging. You can still utilize your limited time but making progress should be a team effort. That's just my two cent.

Right. I will follow next time.