[vscode] TreeItem fails to render if it has a command tied to it

[tetchel]

#4975 seems to have regressed since #5556, on TreeItems which have their command field set.

root ERROR [hosted-plugin: 73] [ERRO: 03:36:57.738 extension.js.on():43]: Unhandled promise rejection: TypeError: Converting circular structure to JSON
    at JSON.stringify (<anonymous>)
    at Function.MessageFactory.replyOK (/home/theia/node_modules/@theia/plugin-ext/lib/api/rpc-protocol.js:280:103)
    at /home/theia/node_modules/@theia/plugin-ext/lib/api/rpc-protocol.js:158:51
    at process._tickCallback (internal/process/next_tick.js:68:7)

You can see that I had to not set command on my TreeItems to work around this bug. eclipse-archived/codewind-vscode@92b5683

It also appears to be intermittent with some treeitems, but happens every time with others - I could not figure out what caused the difference.

@akosyakov since you fixed this originally

[akosyakov]

Please have a look at it after #5665 gets merged, plugin trees were refactored to allow state restoration.

[tolusha]

@tetchel Is this issue still reproducible since #5665 has been merged?

[tetchel]

Sorry, I verified this like a month ago! It's fixed.