[Unhandled Error] potential listener LEAK detected, popular

[vs-code-engineering]

Error Message

potential listener LEAK detected, popular

Stack Trace

    at a.create (./src/vs/base/common/event.ts:1062:14)
    at K8t._event (./src/vs/base/common/event.ts:1262:33)
    at KU.xtermReady (./src/vs/workbench/contrib/terminalContrib/links/browser/terminal.links.contribution.ts:80:0)
    at (anonymous) (./src/vs/workbench/contrib/terminal/browser/detachedTerminal.ts:79:10)
    at task (./src/vs/base/common/async.ts:412:12)

Raw Stack Trace (minified)

Error     at a.create (out/vs/workbench/workbench.desktop.main.js:403:18382)     at K8t._event (out/vs/workbench/workbench.desktop.main.js:405:1807)     at KU.xtermReady (out/vs/workbench/workbench.desktop.main.js:4102:59681)     at out/vs/workbench/workbench.desktop.main.js:2773:7950     at out/vs/workbench/workbench.desktop.main.js:406:74764

Details

Property	Value
Bucket ID	12e29ad9-9a0d-b1be-fb9f-2a8d310dd550
Version	1.115.0-insider
Commit	3d70aab9
Last Seen	Sun Apr 05 2026 23:50:48 GMT+0000 (Coordinated Universal Time)
Platforms	Windows, Mac, Linux
Product	VSCode

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This issue was automatically created from the VS Code Errors Dashboard

[vs-code-engineering]

Regression Details

• Regression type: new
• Last release without this error: 1.115.0-insider (8c85df12)
• First release with this error: 1.115.0-insider (3d70aab9)
• Commit range: 8c85df12...3d70aab9

This listener LEAK originates in terminal.links.contribution.ts → detachedTerminal.ts during xterm link provider setup. The leak was introduced in the Apr 3 insider build. Currently affecting 108 users across Windows, Mac, and Linux.

Generated by errors-regression-scan · ◷

[vs-code-engineering]

🔍 Error Investigation

Summary

The TerminalLinkContribution.xtermReady() method subscribes to onDidRemoveLinkProvider (line 80) outside the isDetachedTerminalInstance guard, causing every DetachedTerminal to add a listener to the singleton TerminalLinkProviderService emitter — even though detached terminals never use external link providers. As AI chat features (e.g. terminal tool invocations via DetachedTerminalCommandMirror/DetachedTerminalSnapshotMirror) create many detached terminals during a session, the listener count on the singleton emitter exceeds the global leak warning threshold of 175, triggering a ListenerLeakError with kind popular.

Culprit Commit

No single commit in the regression window (8c85df12...3d70aab9) modified terminal or event files. The 9 commits in the range touch Sessions, Chat hooks, testing, and build infrastructure — none modify terminal.links.contribution.ts, detachedTerminal.ts, terminalLinkProviderService.ts, or event.ts. This is a latent bug that crossed the detection threshold due to increasing detached terminal usage from AI/chat features. The regression is a threshold-crossing event, not a code change.

Code Flow

sequenceDiagram
    participant Chat as Chat Terminal Tool
    participant TS as TerminalService
    participant DT as DetachedTerminal
    participant TLC as TerminalLinkContribution
    participant TLPS as TerminalLinkProviderService (singleton)
    participant Emitter as Emitter._onDidRemoveLinkProvider

    Chat->>TS: createDetachedTerminal()
    TS->>DT: new DetachedTerminal(xterm, options)
    Note over DT: Constructor iterates<br/>contributions, calls xtermReady()
    DT->>TLC: xtermReady(xterm)
    Note over TLC: ⚠️ Root cause: line 80 is<br/>outside isDetachedTerminalInstance<br/>guard (lines 72-79)
    TLC->>TLPS: onDidRemoveLinkProvider(callback)
    TLPS->>Emitter: subscribe(callback)
    Note over Emitter: 💥 LeakageMonitor.check()<br/>listener count > 175 threshold<br/>→ ListenerLeakError("popular")

Loading

Affected Files

File	Role
src/vs/workbench/contrib/terminalContrib/links/browser/terminal.links.contribution.ts	Root cause — line 80 subscribes to onDidRemoveLinkProvider outside the detached-terminal guard
src/vs/workbench/contrib/terminalContrib/links/browser/terminalLinkProviderService.ts	Singleton service whose _onDidRemoveLinkProvider emitter accumulates leaked listeners
src/vs/workbench/contrib/terminal/browser/detachedTerminal.ts	Creates contributions and calls xtermReady() on each one (line 79)
src/vs/workbench/contrib/terminal/browser/chatTerminalCommandMirror.ts	Primary creator of DetachedTerminal instances via chat tool invocations
src/vs/base/common/event.ts	Leak detection infrastructure — LeakageMonitor.check() fires ListenerLeakError

Repro Steps

1. Open VS Code Insiders (1.115.0+)
2. Use Copilot/AI chat with terminal tool invocations (e.g., ask the agent to run multiple terminal commands)
3. As each command creates a DetachedTerminalCommandMirror or DetachedTerminalSnapshotMirror, a new DetachedTerminal is created
4. Each DetachedTerminal adds a listener to the singleton onDidRemoveLinkProvider emitter
5. After ~175 detached terminals are created (without being disposed), the ListenerLeakError fires
6. The error is non-deterministic — it depends on how many detached terminals accumulate before disposal. Long AI coding sessions with many terminal commands are more likely to trigger it.

Fix Proposal

Fix location: src/vs/workbench/contrib/terminalContrib/links/browser/terminal.links.contribution.ts → xtermReady()

Approach: Move line 80 (linkManager.add(this._terminalLinkProviderService.onDidRemoveLinkProvider(...))) inside the existing if (!isDetachedTerminalInstance(this._ctx.instance)) block (lines 72-79). Detached terminals never set externalProvideLinksCb (that only happens inside the if block on lines 73-78), so the onDidRemoveLinkProvider handler is a no-op for them. Moving it inside the guard eliminates the unnecessary listener accumulation on the singleton emitter.

Current code (lines 72-80):

if (!isDetachedTerminalInstance(this._ctx.instance)) {
    for (const linkProvider of this._terminalLinkProviderService.linkProviders) {
        linkManager.externalProvideLinksCb = linkProvider.provideLinks.bind(linkProvider, this._ctx.instance);
    }
    linkManager.add(this._terminalLinkProviderService.onDidAddLinkProvider(e => {
        linkManager.externalProvideLinksCb = e.provideLinks.bind(e, this._ctx.instance as ITerminalInstance);
    }));
}
linkManager.add(this._terminalLinkProviderService.onDidRemoveLinkProvider(() => linkManager.externalProvideLinksCb = undefined));

Fixed: move line 80 inside the if block, before the closing }.

Recommended Owner

@Tyriar — area owner for integrated terminal quality/features/UX, and co-owner of chat-terminal. This issue spans terminal link infrastructure and chat-driven detached terminal creation, both in Daniel's domain. (Already assigned to @bryanchen-d who can coordinate.)

Generated by errors-investigate · ◷