Fixed #1278: implemented tab bar decorator & supported error marker in editor tabs

[fangnx]

What it does

Fixed #1278.

• Implemented TabBarDecorator that provides tabs with decorations, similar to what we already had for tree nodes.
• Supported diagnostic problem markers (error, warning, ...) in editor tabs in the main area. Tabs in side bars can be decorated as well in the future using the same code.
• Refactored TreeDecoration to a more generic NodeDecoration, which is currently used for decorating tree nodes and tabbar tabs.

How to test

• Open editors with errors/warnings identified. If they are in the main tab bar (horizontal), small error/warning icons should be seen overlaying on top of the file icon.
• Once problems in a file are resolved, the error/warning decorator should disappear.

Review checklist

• as an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• as a reviewer, I agree to review in accordance with the review guidelines

[vince-fugnitto]

@fangnx ping me when the PR is ready for a review 😃

[vince-fugnitto]

Few minor comments, the code is still untested on my end.

[akosyakov]

@fangnx please update the description according the project template: https://github.com/theia-ide/theia/blob/master/doc/pull-requests.md#pr-template

May I ask why did you delete in the first place? Do you use some client which does not propose it?

[vince-fugnitto]

@fangnx there still seems to be an issue regarding CI, something concerning illegal characters in the method getDecorations.

[akosyakov]

I think code-wise it looks good. I've tried changes and it behaves well in the main area. I have following concerns:

• why don't we do it in the side-bars as well? It will be consistent and we will be able to reuse to show count of changes for the scm title.
• do we a need a preference to disable decorations? It can be useful if it would cause some perf issues or a user just does not want it. Is there such preferences in VS Code? Maybe we can have a preference for problems at least, something like problem.decorations.enabled by analogy with the git.decorations.enabled.

[fangnx]

I think code-wise it looks good. I've tried changes and it behaves well in the main area. I have following concerns:

• why don't we do it in the side-bars as well? It will be consistent and we will be able to reuse to show count of changes for the scm title.
• do we a need a preference to disable decorations? It can be useful if it would cause some perf issues or a user just does not want it. Is there such preferences in VS Code? Maybe we can have a preference for problems at least, something like problem.decorations.enabled by analogy with the git.decorations.enabled.

Just did it in the side bars in the latest push, with larger problem decorators shown. I also added a preference that can turn on/off the display of problem decorators in the tab bars, as you suggested.

[akosyakov]

It works very well for me and code looks good, although pay attention to the last comment.

@vince-fugnitto Would you be fine to merge?

[vince-fugnitto]

It works very well for me and code looks good, although pay attention to the last comment.

@vince-fugnitto Would you be fine to merge?

Sure, I'll merge once your last comment has been addressed and the CI re-passes :)

[vince-fugnitto]

@fangnx can you please rebase the PR?

[fangnx]

@fangnx can you please rebase the PR?

Done ;)

[vince-fugnitto]

Please address my comments before we can successfully merge :)

[vince-fugnitto]

It works very well, really nice work :) 👍

I tested using different file types, in both the main, bottom, left and right side bars, and tested whether the preference is properly emitted and listened to.