[vscode] parse view contribution "when" clause context

[vinokurig]

What it does

There is an affects() function of the ContextKeyChangeEvent: https://github.com/theia-ide/theia/blob/b0d8292226e4ca179ed6cfa8be4e47e354ff9f61/packages/core/src/browser/context-key-service.ts#L34-L36
which evaluates if the given set of context keys has a context key that was changed.
PluginViewRegistry listens to this event and passes when clause context from the view contribution:
https://github.com/theia-ide/theia/blob/b0d8292226e4ca179ed6cfa8be4e47e354ff9f61/packages/plugin-ext/src/main/browser/view/plugin-view-registry.ts#L144
Thewhen clause context from the view contribution is a string which may be a composed expression e.g. "when": "!config.githubPullRequests.showInSCM && config.git.enabled": https://github.com/microsoft/vscode-pull-request-github/blob/d91e778705cd5af0785c5a05184ebc550334b409/package.json#L182

A map with parsed when clauses was introduced to pass separate context keys to the affects() function of the ContextKeyChangeEvent.

fixes #6015

How to test

1. Remove git from theia/examples/browser/package.json.
2. Download vscode git extension.
3. Create plugins folder in Theia's root and paste the plugin to it.
4. Clone the vscode github extension and compile it.
5. Start the github plugin as a Hosted Plugin.
6. Click the GitHub icon.

Without this fix the GitHub panel is empty,

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

[akosyakov]

@vinokurig It looks like a proper solution. 👍 I will test a bit later today.

[akosyakov]

@azatsarynnyy Could you check with vscode github extension please? I never was able to configure it properly. I will check that other extensions are still working.

[azatsarynnyy]

Sure. I'll check it.

[akosyakov]

It does now work for json outline sample extension: https://github.com/microsoft/vscode-extension-samples/tree/master/tree-view-sample

[vinokurig]

@akosyakov

It does now work for json outline sample extension: https://github.com/microsoft/vscode-extension-samples/tree/master/tree-view-sample

Looks like this controls the json outline in vscode navigator, but is there such view in theia?

[akosyakov]

@vinokurig it should be contributed by the sample extension, but it only appears when json file is opened and should disappear when it is closed

[azatsarynnyy]

I've checked it with GitHub Pull Requests extension.

config.git.enabled is true && config.githubPullRequests.showInSCM is true

config.git.enabled is true && config.githubPullRequests.showInSCM is false

config.git.enabled is false && config.githubPullRequests.showInSCM is false

[azatsarynnyy]

I'm not sure whether it's related to this PR but there's Sign in button on the view in VS Code.

I don't see it in Theia.

[akosyakov]

JSON outline works well now and the solution is better than what was before

I could not test whether it resolves the original issue though with github PR extension. @vinokurig please rely on @azatsarynnyy for it

[azatsarynnyy]

It fixes the issue with GH PR extension.
Sign in button visibility is not in the scope of this issue.