TypeError: Converting circular structure to JSON when call Focus on Files Explorer from plugin

[vzhukovs]

Bug Description:

The following code sample:

import * as theia from '@theia/plugin';

export function start(context: theia.PluginContext): void {
    theia.commands.registerCommand({
        id: 'plugin.workbench.files.action.focusFilesExplorer',
        label: 'Plugin: Focus on Files Explorer'
    }, () => theia.commands.executeCommand('workbench.files.action.focusFilesExplorer'));
}

export function stop(): void {
}

produces the exception in console:

Uncaught (in promise) TypeError: Converting circular structure to JSON
    --> starting at object with constructor 'SplitPanel'
    |     property '_layout' -> object with constructor 'ViewContainerLayout'
    --- property '_parent' closes the circle
    at JSON.stringify (<anonymous>)
    at Function.push.../../packages/plugin-ext/lib/common/rpc-protocol.js.MessageFactory.replyOK (rpc-protocol.ts:376)
    at rpc-protocol.ts:231

Steps to Reproduce:

1. Clone sample plugin: workbench-files-action-focusFilesExplorer
2. Build and copy eclipse_che_workbench_files_action_focusFilesExplorer.theia to plugin's directory
3. Run Browser Example and call command Plugin: Focus on Files Explorer

Additional Information

• Operating System: macOS 10.15.4
• Theia Version: master

[vzhukovs]

Fixed by #7957