Ensure that new editors get unique ids

[fordhurley]

This restores the behavior from when TextEditor was written in Coffeescript and extended the Model class.

Description of the Change

With this change, editors opened after restoring the window state will get assigned IDs starting from max(editor IDs) + 1.

Alternate Designs

An alternative could be to select the lowest available unique ID. This would require a more complicated ID generator, but is certainly possible if a more dense ID space is desirable.

Why Should This Be In Core?

Assuming that editor IDs are supposed to be unique, this is a bug in core.

Benefits

Packages that look up editor instances by ID will be able to resolve to the correct editor.

Possible Drawbacks

I'm not aware of any drawbacks.

Applicable Issues

Fixes #16454.

[maxbrunsfeld]

Thanks for fixing this. Could you add a test?

[fordhurley]

I'm not very familiar with writing jasmine tests, but I gave it a shot. If someone more experienced could provide guidance, I'd be happy to expand this a bit. I would personally prefer a test that actually checks for uniqueness of all IDs after initializing the workspace with a mixture of deserialized and "fresh" editors. The test I wrote is more a test of the exact bug this PR fixes, than protection against future regressions. I confirmed that it fails before this fix and passes after, at least...

[maxbrunsfeld]

The test looks fine to me. I'll merge this if CI passes.

[maxbrunsfeld]

@fordhurley It looks like your new test if failing on our CI.

[fordhurley]

Yup, it passed only when run in isolation (atom --test spec/text-editor-spec.js). I just took another stab at it.

[maxbrunsfeld]

Thanks @fordhurley!