Data loss: Custom editors do not properly deal with extension host restarts

[bpasero]

Steps to Reproduce:

1. install an extension that leverages custom editors (non-text based, like Luna paint or Hex editor)
2. open a folder
3. open a file in hex editor or luna paint
4. make the editor dirty
5. add a folder to the workspace
6. the extension host restarts
7. click on another editor
8. click back into the custom editor

=> the custom editor is gone and so is the data

[bpasero]

Unfortunately this can result in data loss as you can see from the video below:

[lramos15]

I can't reproduce this using luna paint.

[bpasero]

Here is how it reproduces for me with Luna paint running out of sources (auto save disabled):

[lramos15]

Hmm. Seems like a race condition, I follow those exact steps and still can't repro. I would be willing to investigate with you.

[bpasero]

The more I think about it, the more I feel we really should stop restarting extension hosts: #69335

[sbatten]

We must restart the extension host in the event the workspace is no longer trusted, so perhaps custom editors need to participate in that transition to avoid data loss

[bpasero]

Fyi, yesterday I pushed support for IFileWorkingCopyManager#destroy which returns a Promise and is used for notebooks, e.g. when an extension is uninstalled or gets disabled. The gist is, this method will:

• unregister any working copy it owns
• trigger a save for dirty working copies
• and if that fails, will resolve any existing backup for the working copy and save that to disk instead

However, I think this issue is more tricky for (non-text) custom editors, because we do not really know how the extension has implemented the save method to persist the changes to disk.

If we cannot restore the dirty editor properly after the extension host has restarted, we should at least make sure to reopen the editor with the dirty contents (= backup) after the extension host has started again.

[lramos15]

From my discussion with Matt it appears the solution to this issue revolves around persisting the model managers upon extension host restart and syncing the models and webviews to the new ext host.

[Ark-kun]

Would the issue be solved if the custom editor was just resolved again (call resolveCustomTextEditor) for all documents opened in custom editors?

[bpasero]

One idea from @alexdima was to introduce a participation model for extension host restarts: any component can veto the restart and thus custom editors could show a modal dialog to users in case this is needed and veto the restart.

[bpasero]

#182558 addressed this 👍

[Tyriar]

Verified, but I think #183778 is a core problem.