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

[bryanchen-d]

Error Message

Cannot read properties of undefined (reading 'dimensions')

Stack Trace

    at get dimensions (node_modules/@<REDACTED: user-file-path>:1:243732) [not deminified]
    at get dimensions (node_modules/@<REDACTED: user-file-path>:1:46482) [not deminified]
    at get dimensions (node_modules/@<REDACTED: user-file-path>:1:256726) [not deminified]
    at Gf._updatePtyDimensions (./src/vs/workbench/contrib/terminal/browser/terminalInstance.ts:2015:0)
    at Est._resizeXCallback (./src/vs/workbench/contrib/terminal/browser/terminalInstance.ts:815:0)
    at Est._debounceResizeX (./src/vs/workbench/contrib/terminal/browser/terminalResizeDebouncer.ts:82:7)
    at (anonymous) (./src/vs/base/common/decorators.ts:84:7)

Raw Stack Trace (minified)

TypeError: Cannot read properties of undefined (reading 'dimensions')     at get dimensions (node_modules/@<REDACTED: user-file-path>:1:243732)     at get dimensions (node_modules/@<REDACTED: user-file-path>:1:46482)     at get dimensions (node_modules/@<REDACTED: user-file-path>:1:256726)     at Gf._updatePtyDimensions (out/vs/workbench/workbench.desktop.main.js:3812:3213)     at Est._resizeXCallback (out/vs/workbench/workbench.desktop.main.js:3808:36605)     at Est._debounceResizeX (out/vs/workbench/workbench.desktop.main.js:3808:18469)     at out/vs/workbench/workbench.desktop.main.js:483:14481

Details

Property	Value
Bucket ID	898464de-34d7-b9de-5210-c3a013ba2800
Version	1.111.0
Commit	ce099c1e
Last Seen	2026-03-12
Platforms	Windows, Mac, Linux
Product	VSCode

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This issue was automatically created from the VS Code Errors Dashboard

[vs-code-engineering]

Related Error Buckets

These additional error buckets are tracked by this issue (v1.118.0-insider, Agents product):

Bucket ID	Error Message	Version
64fe3779	Cannot read properties of undefined (reading 'dimensions')	1.118.0-insider

10 users, 14 hits on commit f2b51f3f. Same xterm terminal dimensions error (terminalInstance.ts → terminalResizeDebouncer.ts), now appearing in the Agents product stream.

Generated by errors-triage · ● 7M · ◷

[vs-code-engineering]

🔍 Error Investigation

Summary

The terminal throws TypeError: Cannot read properties of undefined (reading 'dimensions') when a debounced horizontal resize callback fires after the xterm terminal instance has been disposed. The @debounce(100) decorator on TerminalResizeDebouncer._debounceResizeX uses a raw setTimeout that is not cancelled on disposal, causing it to access xterm's dimensions getter on a terminal whose internal renderer has already been torn down. This is a latent bug in TerminalResizeDebouncer that was surfaced by the xterm.js upgrade from beta.167 → beta.168 in the 1.111 cycle (PR #299073), which likely changed the dimensions getter to throw on a disposed renderer instead of returning undefined. With ~900K affected users in 1.111.0, the impact is high.

Culprit Commit

The underlying bug is pre-existing — the @debounce timer was never properly cancelled on disposal since TerminalResizeDebouncer was first introduced. The xterm.js upgrade that surfaced it as a visible error:

Field	Value
Commit	ff87f0d (via merge)
Author	@anthonykim1
PR	#299073
Message	Bump xterm for imageAdded api
Why	Upgraded xterm.js from beta.167 to beta.168. The new xterm version's dimensions getter now throws when the internal renderer is disposed, instead of returning undefined. This surfaced the pre-existing bug where the debounce timer fires on a disposed terminal.

Note: The xterm bump is the trigger, not the root cause. The true defect is in TerminalResizeDebouncer — the @debounce(100) decorator stores its timer as this['$debounce$_debounceResizeX'] which is never cleaned up by Disposable.dispose(). The _resizeXJob and _resizeYJob idle callbacks are properly registered as disposables, but the debounce timer is not.

Code Flow

sequenceDiagram
    participant Layout as Terminal Layout
    participant Resize as _resize()
    participant Debouncer as TerminalResizeDebouncer
    participant Decorator as debounce(100ms)
    participant Callback as _resizeXCallback
    participant Update as _updatePtyDimensions
    participant Xterm as xterm.raw.dimensions

    Layout->>Resize: layout triggers resize
    Resize->>Debouncer: resize(cols, rows, false)
    Debouncer->>Decorator: _debounceResizeX(cols)
    Note over Decorator: setTimeout(100ms) set
    Note over Debouncer: Terminal disposed<br/>before timeout fires
    Decorator->>Callback: timeout fires → _resizeXCallback(cols)
    Callback->>Update: _updatePtyDimensions(xterm.raw)
    Update->>Xterm: rawXterm.dimensions
    Note over Xterm: Internal renderer is undefined<br/>TypeError: Cannot read properties<br/>of undefined (reading 'dimensions')

Loading

Affected Files

File	Role
src/vs/workbench/contrib/terminal/browser/terminalResizeDebouncer.ts	Root cause — debounce(100) timer not cancelled on disposal
src/vs/workbench/contrib/terminal/browser/terminalInstance.ts	Crash site — _updatePtyDimensions at line 2015 accesses rawXterm.dimensions
src/vs/base/common/decorators.ts	Infrastructure — debounce decorator uses raw setTimeout with no disposal hook

Repro Steps

1. Open VS Code with an integrated terminal visible
2. Trigger a terminal resize (e.g., resize the editor panel, split terminals)
3. Immediately close/destroy the terminal within 100ms of the resize
4. The debounced _debounceResizeX callback fires after the terminal is disposed
5. Error is thrown inside xterm's dimensions getter

This is a race condition — the 100ms debounce window is the critical period. Rapidly opening/closing/resizing terminals increases the likelihood of hitting it.

Fix Proposal

Bypass identified: The debounce decorator stores a setTimeout handle on this['$debounce$_debounceResizeX'] which is invisible to the Disposable disposal mechanism. The timer fires on a disposed instance.

Why it fails: After TerminalResizeDebouncer is disposed, the 100ms debounce timer can still fire, calling _resizeXCallback which calls _updatePtyDimensions(xterm.raw). Xterm's dimensions getter accesses its internal _renderService.dimensions, but the render service has been torn down during disposal.

Fix location: src/vs/workbench/contrib/terminal/browser/terminalResizeDebouncer.ts → _debounceResizeX() and/or dispose()

Approach: Replace the debounce decorator with a disposable-aware debounce — use a MutableDisposable wrapping a timeout (similar to _resizeXJob/_resizeYJob) instead of the decorator. This makes the debounce timer lifecycle-managed like the other timers in the class. Alternatively, override dispose() to clear the debounce timer by reading this['$debounce$_debounceResizeX'] and calling clearTimeout(), or add a disposed guard in _debounceResizeX to check this._store.isDisposed before calling _resizeXCallback.

Recommended Owner

@Tyriar — Terminal area owner (owns integrated terminal quality/UX, xterm.js, and terminal-rendering). The bug is in terminal resize lifecycle management.

Generated by errors-investigate · ● 11.9M · ◷