Cannot read properties of null (reading 'label') in TreeViewExtImpl.getTreeItemLabel

[Lythenas]

Bug Description:

The "SonarLint Issues Location" view thing (not sure what to call it, it is in the file explorer at the bottom, expandable) is not working. When trying to expand it, it throws the following error:

2023-10-16T10:44:49.509Z root ERROR Failed to fetch children for 'SonarLint.IssueLocations' TypeError: Cannot read properties of null (reading 'label')
    at TreeViewExtImpl.getTreeItemLabel (/home/theia/node_modules/@theia/plugin-ext/lib/plugin/tree/tree-views.js:261:40)
    at TreeViewExtImpl.getItemLabel (/home/theia/node_modules/@theia/plugin-ext/lib/plugin/tree/tree-views.js:269:28)
    at /home/theia/node_modules/@theia/plugin-ext/lib/plugin/tree/tree-views.js:315:36
    at processTicksAndRejections (node:internal/process/task_queues:96:5)
    at async Promise.all (index 0)

Steps to Reproduce:

1. Install the SonarLint plugin: https://open-vsx.org/extension/SonarSource/sonarlint-vscode (last tested on version 3.13)
2. Expand the "SonarLint Issues Location" view in the file explorer
3. Nothing shows up in the expanded view
4. See above error in the browser console and log

Additional Information

• Operating System: Ubuntu 22.04 but running in docker Ubuntu 18.04 image
• Theia Version: 1.34.4

[msujew]

@Lythenas Can you test whether this affects the latest version of Theia (preferably using the current master branch)? The version you're using is fairly old.

[Lythenas]

I just tried it on gitpod (first time using that). And I see the same error:

2023-10-22T12:43:23.887Z root ERROR Failed to fetch children for 'SonarLint.IssueLocations' TypeError: Cannot read properties of null (reading 'label')
    at TreeViewExtImpl.getTreeItemLabel (/workspace/theia/examples/browser/lib/backend/plugin-host.js:19131:40)
    at TreeViewExtImpl.getItemLabel (/workspace/theia/examples/browser/lib/backend/plugin-host.js:19139:28)
    at /workspace/theia/examples/browser/lib/backend/plugin-host.js:19198:36
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
    at async Promise.all (index 0)

[msujew]

I see. Seems like vscode is a bit lax in what it accepts as return values from data tree providers. Extensions aren't actually allowed to return null or undefined, but seems like the SonarLint extension does anyway, see here. I've submitted a fix for this in https://github.com/eclipse-theia/theia/pull/13018.

[Lythenas]

Thanks for the quick response, that fixes the issue.

I think the sonarlint plugin might have more issues. On gitpod the webviews were not working, but they worked before on my local setup. But I will open new issues if I run into anything.

[msujew]

On gitpod the webviews were not working

That's because webviews are served on subdomains which aren't routed correctly to Gitpod - that behavior is expected. Theia webviews need special reverse proxying.