Prevent serialization of phosphor widgets when command calls from plugin

[vzhukovs]

What it does

This changes proposal adds a check for return value after command been executed from third-party plugin.

The initial problem steps to reproduce:

1. Call from third-party plugin internal command, which returns a widget, e.g. workbench.files.action.focusFilesExplorer
   packages/plugin-ext/src/main/browser/command-registry-main.ts#L80
2. Executes command which returns a widget:
   packages/navigator/src/browser/navigator-contribution.ts#L241
3. Phosphor widget tries to be serialized into JSON, to be provided into plugin, but JSON serializer catch exception with message: TypeError: Converting circular structure to JSON

We need to check return type of the value that is executed and if there is a phosphor widget, return undefined. Anyway, there is no need to pass the whole widget into plugin as callback value.

Fixes issue: #7853

Signed-off-by: Vladyslav Zhukovskyi vzhukovs@redhat.com

How to test

This can be reached by using test plugin, located here.

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]

Could you check this PR instead: #7957?

[vzhukovs]

Could you check this PR instead: #7957?

Sure, one moment

[vzhukovs]

@akosyakov I've checked #7957, seems, that your PR also fixes this problem too.

[vzhukovs]

Going to close this PR as redundant. @akosyakov thanks for the fix!