@letmaik Is it possible to provide a sample that can reproduce this issue? It will be helpful to diagnose the issue correctly rather than doing some guess works.

Extracting a minimal example will take some effort (I can do it but currently I'm quite busy), I was hoping you guys have some debugger kung fu which would expose the root of the exception easily. In the mean time I was trying to debug the exception under a source-built VS Code (and then simply loading my extension into it via a .vsix file), but I got stuck at the boundary of some extension host proxy for the tree view. Let me know if you'd still like a minimal example, then I'll try to create one within the next weeks.

@letmaik This error can happen due to various reasons. I also have couple of variety of examples which cannot reproduce this. Hence, asking for the sample.

I also get that error. I have a tree provider that is refreshed whenever the active editor changes and shows only for certain file types. This is the relevant code:

    getChildren(element?: Import): Thenable<Import[]> {
        if (!element) {
            let editor = window.activeTextEditor;
            if (editor && editor.document.languageId === "antlr") {
                let dependencies = this.backend.getDependencies(editor.document.fileName);
                let imports: Import[] = [];
                for (let dep of dependencies) {
                    imports.push(new Import(dep, TreeItemCollapsibleState.None));
                }
                return new Promise(resolve => {
                    resolve(imports);
                });
            }
        }

        return Promise.resolve([]);
    }

It all works nicely until the line return Promise.resolve([]); is executed the first time (usually for a file with a language id I don't want). From this moment on, switching to a supported type that returns a filled array (not an empty one), gives that said error.

@mike-lischke Thanks for the snippet. I will use it to reproduce and fix it.

Hey guys,

I believe I have the same error on typescript files.
Here is the screenshot of what callstack I found:

Not much, but the issue desapeared when I turned off 'TypeScript Hero' extension. HTH.

@letmaik @mike-lischke Unfortunately, I could not reproduce this bug with any of the tree samples I have, even after using the partial sample from @mike-lischke

I pushed an hypothetical fix which will be available in tomorrows insiders. Can you please verify your issue using that?

Thanks

@sandy081 I just pulled from master and ran vs code from there, it's fixed :) If you want to figure out why it's fixed you could install my extension https://github.com/letmaik/vscode-git-tree-compare and see what the behaviour is in the last vs code release vs master (look at the console where an exception will be if you open a git managed folder)

Thanks @letmaik

I think this bug is not fully solved and your fix only hides the problem. I see the same behaviour as back then. Like in the past this issue appears randomly and not always, but it's quite reproducible.

@letmaik Can you please provide steps to reproduce?

Yes, it's not minimal but it's very suitable for debugging:

• Clone the debug-issue40357 branch of https://github.com/letmaik/vscode-git-tree-compare
• Run npm install and then run the extension with F5 in vs code
• You will see log output in the debugging console for each call to getChildren and getTreeItem including the returned values. You will see that in all cases getChildren returns a non-empty array and you will see there is a corresponding number of getTreeItem calls following that, again with the correct content.
• If things work correctly, you see at least one tree item, otherwise none.

@letmaik Thanks for the steps. Since this issue was closed, opened a new issue with the steps described by you.