Support VS Code Default Language Icons

[martin-fleck-at]

What it does

Add support for default language icons similar to VS Code:

• Extend language service with necessary methods
• Create CSS rules for contributed language icons
• Use language icons if theme sets 'showLanguageModeIcons'
• Ensure custom theme can override language icons

Fixes #13013

How to test

• Provide a plugin with a language contribution that adds a custom default language icon, ideally a "known" language like python
• Install Material Icon Theme which already provides custom icons for the same language.
• Switch file icon themes to see that everything is working as expected:
  • None: no icons shown
  • File Icons (Theia): uses our default language icon
  • Material Icon Theme: uses icon from the theme

Follow-ups

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 behave in accordance with the review guidelines

[msujew]

Provide a plugin with a language contribution that adds a custom default language icon, ideally a "known" language like python

Can you provide such a plugin? As far as I can tell, the builtin plugins don't contribute such an icon to any language.

[martin-fleck-at]

@msujew Thank you for having a look! I pushed an example to https://github.com/eclipse-theia/theia/tree/issues/13013_sample or you can download the zipped vsix:

• Add custom light and dark icon for Python files

[tsmaeder]

@msujew are you reviewing this one?

[martin-fleck-at]

I rebased the branch onto main as there was a conflict in scanner-theia.ts.

[msujew]

Thanks for the example plugin. This change works well for me 👍

I've encountered a very minor issue during testing. After installing the extension (but before changing the color/icon theme), any open editor keeps the old icon (while it correctly updates in the navigator). After changing to another theme, everything is updated as expected. This shouldn't stop this change from getting merged though.

[martin-fleck-at]

@msujew Very good catch! I added a commit that should fix that problem. It was just adding an event so I thought it would be faster than to create a follow up issue ;-)

[msujew]

Awesome, thanks for the update @martin-fleck-at 👍

The new changes look good as well. Now without any further critique :)

[bvenreply]

Hello @martin-fleck-at, what is the intent behind the addition of these single quotes? I don't think this is valid syntax, these properties are just being discarded from the css stylesheet at the moment.

I'm taking a look in the context of #13096 btw.

[martin-fleck-at]

Hi @bvenreply, you are definitely right that they are not producing valid CSS syntax. My best guess is that I did it by mistake and for some reason just didn't notice. I don't see any reason why it would be like that as it is also not like that for any other pixel value. Thank you for discovering this! If you are already working on an issue I'd be grateful if you could take care of this but I can also create a separate change if necessary.

[bvenreply]

Thank you @martin-fleck-at, I believe I'll be able to take care of this myself in the course of #13096. If not I'll let you know.