[Unhandled Error] Cannot read properties of undefined (reading 'clearTodoListWidget')

[vs-code-engineering]

Error Message

Cannot read properties of undefined (reading 'clearTodoListWidget')

Stack Trace

    at cC.setModel (./src/vs/workbench/contrib/chat/browser/widget/chatWidget.ts:1984:0)
    at Bx.showModel (./src/vs/workbench/contrib/chat/browser/widgetHosts/viewPane/chatViewPane.ts:749:0)
    at async Bx.clear (./src/vs/workbench/contrib/chat/browser/widgetHosts/viewPane/chatViewPane.ts:801:0)

Raw Stack Trace (minified)

TypeError: Cannot read properties of undefined (reading 'clearTodoListWidget')     at cC.setModel (out/vs/sessions/sessions.desktop.main.js:2372:65120)     at Bx.showModel (out/vs/sessions/sessions.desktop.main.js:3093:75430)     at async Bx.clear (out/vs/sessions/sessions.desktop.main.js:3093:76120)

Details

Property	Value
Bucket ID	5cf9162c-66b9-8a2a-c2a5-1895e8cedbe0
Version	1.115.0-insider
Commit	41dd792b
Last Seen	Wed Apr 08 2026 23:17:30 GMT+0000 (Coordinated Universal Time)
Platforms	Mac, Windows, Linux
Product	Agents

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This issue was automatically created from the VS Code Errors Dashboard

[vs-code-engineering]

�� Error Investigation

Summary

The error Cannot read properties of undefined (reading 'clearTodoListWidget') occurs when ChatWidget.setModel() is called after the widget has been disposed. During an async showModel() call (triggered by ChatViewPane.clear()), the widget can be torn down at an await point (updateWidgetLockState), leaving inputPartDisposable.value as undefined. When the await resumes, setModel() tries to access this.inputPart.clearTodoListWidget(...), but inputPart (backed by the disposed MutableDisposable) returns undefined, causing the crash.

Culprit Commit

Field	Value
Commit	d7b18589
Author	@justschen
PR	#307689
Message	batched confirmations above the input v1
Why	This commit added this.inputPart.clearTodoListWidget(model.sessionResource, false) to setModel() (line 1985). Before this commit, the async race condition in showModel() existed but was harmless because no code in that region accessed this.inputPart on a potentially disposed widget. The new clearTodoListWidget call introduced the crash surface.

Code Flow

sequenceDiagram
    participant User as User Action
    participant VP as ChatViewPane
    participant W as ChatWidget
    participant MD as MutableDisposable

    User->>VP: clear() / close panel
    VP->>VP: showModel(CancellationToken.None)
    VP->>VP: await updateWidgetLockState()
    Note over VP: Async gap - await in progress
    User->>VP: Panel disposed (e.g. layout change)
    VP->>W: dispose()
    W->>MD: inputPartDisposable.dispose()
    Note over MD: value = undefined
    Note over VP: Await resumes
    VP->>W: setModel(model)
    W->>W: this.inputPart (getter)
    Note over W: inputPartDisposable.value! returns undefined
    W->>W: undefined.clearTodoListWidget()
    Note over W: TypeError: Cannot read properties of undefined

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Affected Files

File	Role
src/vs/workbench/contrib/chat/browser/widget/chatWidget.ts	Crash site — setModel() at line 1985 accesses this.inputPart without disposal guard
src/vs/workbench/contrib/chat/browser/widgetHosts/viewPane/chatViewPane.ts	Trigger — clear() calls showModel(CancellationToken.None) which cannot be cancelled on disposal
src/vs/workbench/contrib/chat/browser/widget/input/chatInputPart.ts	Data flow — defines clearTodoListWidget() on ChatInputPart, accessed via the disposed inputPartDisposable

Repro Steps

1. Open VS Code Insiders (1.115.0+) with Copilot/Agents enabled
2. Open the Chat view pane and start a session (especially an Agent/Copilot session to trigger updateWidgetLockState)
3. Click "New Chat" (triggers clear()) and immediately close/collapse the Chat panel or switch layouts
4. The race is timing-dependent: the disposal must occur during the await updateWidgetLockState() call inside showModel(), before setModel() is called
5. The error is non-deterministic but more likely on slower machines or when canResolveChatSession() takes longer to resolve

Fix Proposal

Fix location: src/vs/workbench/contrib/chat/browser/widget/chatWidget.ts → setModel()

2. Secondary fix (belt-and-suspenders): In chatViewPane.ts showModel(), add a disposal check (if (this._store.isDisposed) return;) after the await updateWidgetLockState() call (line 728) and before this._widget.setModel(model) (line 739). This prevents calling into the widget at all when the view pane is disposed.
3. Optional improvement: Consider using a cancellable token in clear() instead of CancellationToken.None, tied to the view pane's lifecycle, so the async operation can be properly cancelled on disposal.

Recommended Owner

@justschen — culprit commit author (PR #307689 "batched confirmations above the input v1"), Microsoft VS Code team member

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