Support 'browser-only' Theia

[sdirix]

Adds tooling, adapts the current code base and provides an example application for the new 'browser-only' Theia application target. This target generates a Theia frontend application which can run without a backend, transforming the Theia application to a static site.

Implements #12852

What it does

Adapts tooling to:

• support new 'browser-only' application target
• support new 'frontendOnly' and 'frontendOnlyPreload' module declaration
• use http-server when starting 'browser-only' applications

Replaces backend services with browser-only variants

• implementation of BrowserFS-based filesystem
• implementation of 'ServiceConnectionProvider' which timeouts for all requests, enabling loading all Theia packages

Adds a browser-only example application and api-samples showcasing the customization of the new BrowserFS-based filesystem.

How to test

Build and run the 'browser-only' Theia example.

You can also find a hosted variant here.

Note that you can build the 'browser-only' Theia even without building the Node native parts via:

yarn install --ignore-scripts
yarn browser-only prepare:no-native
yarn browser-only build

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]

This works really well. Good job 👍

I have a few remarks and questions on some of the changes here though.

[sdirix]

We're currently working on updating the branch on the latest state of master as well as incorporating the feedback of @msujew. I'll ping you once it's ready to be reviewed again.

[sdirix]

Hi @msujew,
Thanks again for your review! I updated the PR to the latest state of Theia and integrated all your review comments.

The license check complains about browserfs although it's MIT licensed. Do you know why this is the case and how we can resolve the issue?

[msujew]

@sdirix I had to trigger the license harvesting manually on clearlydefined.io. It's now correctly recognized 👍

I'll take another look at this PR once I'm back from vacation (second week of January).

[JonasHelming]

@msujew could we maybe get this in for January?

[paulalexwilson]

The landscape of theia plugin types and deployment modes is feeling somewhat complex from a relative outsider looking in:

• Theia Extensions
• Theia Plugins (deprecated?)
• VS Code Extensions
• Headless (Daemon?) Plugins
• FrontendOnly Mode

It would be great if this PR also added some statement around how this interacts with existing plugin/extension types and what limitations exist.

[msujew]

Great, looks good to me.

[msujew]

@paulalexwilson I don't think that the documentation change makes sense in the scope of this PR. Feel free to create a separate issue though, and someone might pick it up. Note that in general, the browser-only Theia version is supposed to eventually support all features of Theia that are possible without a dedicated backend (which is basically everything except for running a terminal). See #12852 for open tasks and further discussion.

[sdirix]

I rebased on latest master to get rid of the conflict in the Changelog. No further changes were done.

[erlmachinedev]

@sdirix Thanks for the valuable contribution 👍 I just tested the feature from 56cf3db but I see no syntax highlighting for Lua, json, etc..

Probably the default language setup should work well (even without extensions). The file icon type is fetched properly and indicated at the explorer tab but the Monaco editor seems doesn't highlight syntax yet.

The same issue is present on the demo app https://minimal--browseronly-theia.netlify.app/#

P.S. If there is a need to attach dedicated issue (supported by reproduction steps), please let me know. I guess the issue is that syntax highlighting for the most common languages should work "from a box" (see the next screenshot).

[msujew]

@erlmachinedev Given that all syntax highlighting is currently exclusively contributed by vscode extensions, this is expected behavior. This will work as usual once extension support will be added. I think we won't support dedicated syntax highlighting for the browser-only mode, as it's just as much work as adding real support for vscode extensions.

[sdirix]

Hi @erlmachinedev,
Thanks for your interest in "browser-only" Theia. This feature is currently in a MVP state: It can already be used to build applications, however there are many missing features compared to regular Theia. I updated the original issue (#12852) with the current state and a list of missing features.