fix: guard setDimensions against disposed ptyProcessReady (fixes #315282)

[vs-code-engineering]

🔧 Error Fix

Summary

Error: Cannot read properties of undefined (reading 'then') in terminalProcessManager.ts:608

Fixes #315282
Recommended reviewer: @Tyriar

Culprit Commit

Field	Value
Commit	363a5254
PR	#314795
Author	@bryanchen-d
Message	Guard terminal resize/dispose race against xterm.js dimension getters

This PR added guards to terminalInstance.ts and terminalResizeDebouncer.ts for resize/dispose races, but missed guarding the downstream setDimensions call in terminalProcessManager.ts where ptyProcessReady can be undefined after disposal.

Code Flow

graph TD
    A["Configuration change fires during disposal"] --> B["setVisible()"]
    B --> C["_resize()"]
    C --> D["resizeDebouncer.resize()"]
    D --> E["_resizeBothCallback()"]
    E --> F["_updatePtyDimensions()"]
    F --> G["processManager.setDimensions(cols, rows, false)"]
    G --> H["this.ptyProcessReady.then() — CRASH: ptyProcessReady is undefined"]

Loading

Affected Files

• src/vs/workbench/contrib/terminal/browser/terminalProcessManager.ts
• src/vs/workbench/contrib/terminal/browser/terminalInstance.ts

Repro Steps

1. Open a terminal in VS Code
2. Trigger a command that disposes the terminal (e.g., close terminal action)
3. If a configuration change event arrives simultaneously (race condition), setDimensions is called on the already-disposed process manager
4. ptyProcessReady is undefined, calling .then() on it throws TypeError

How the Fix Works

Approach 2 (terminalInstance.ts, per @bryanchen-d's review): Dispose the _resizeDebouncer before _processManager.dispose() in terminalInstance.dispose(), so the resize callback chain is broken before ptyProcessReady gets nulled. This addresses the root cause (disposal ordering).

Recommended Owner

@Tyriar — primary terminal area owner, responsible for terminalProcessManager.ts

errors-fix-driver — cycle 13

Trigger: cron_changes_requested · Head: 7871d48508646356a4939c9b02d48220525c59cd (7871d48)

Item	Action
Review thread on terminalProcessManager.ts:608	Addressed in cycle 2 (disposal ordering fix per @bryanchen-d's suggestion). Thread unresolved — awaiting reviewer action.
CI: Compile & Hygiene (failure)	Pre-existing on main — unrelated to this PR's terminal changes.
Merge state	blocked (CHANGES_REQUESTED review from @anthonykim1 outstanding)

Push: no — no code changes needed · Copilot rerequested: skipped (no push)

Ready gate: CHANGES_REQUESTED review from @anthonykim1 still outstanding → not marking ready.

errors-fix-driver — cycle 14

Trigger: cron_changes_requested · Head: 7871d48508646356a4939c9b02d48220525c59cd (7871d48)

Item	Action
Review thread on terminalProcessManager.ts:608	Addressed in cycle 2 (disposal ordering fix per @bryanchen-d's suggestion). Thread unresolved — awaiting reviewer action.
CI: Compile & Hygiene (failure)	Pre-existing on main — unrelated to this PR's terminal changes.
Merge state	blocked (CHANGES_REQUESTED review from @anthonykim1 outstanding)

Push: no — no code changes needed · Copilot rerequested: skipped (no push)

Ready gate: CHANGES_REQUESTED review from @anthonykim1 still outstanding → not marking ready.

errors-fix-driver — cycle 15

Trigger: cron_changes_requested · Head: 7871d48508646356a4939c9b02d48220525c59cd (7871d48)

Item	Action
Review thread on terminalProcessManager.ts:608	Addressed in cycle 2 (disposal ordering fix per @bryanchen-d's suggestion). Thread unresolved — awaiting reviewer action.
CI: Compile & Hygiene (failure)	Pre-existing on main — unrelated to this PR's terminal changes.
CI: 24 other checks	All passing ✅
Merge state	blocked (CHANGES_REQUESTED review from @anthonykim1 outstanding)

Push: no — no code changes needed · Copilot rerequested: skipped (no push)

Ready gate: CHANGES_REQUESTED review from @anthonykim1 still outstanding → not marking ready. All actionable items have been addressed; awaiting human reviewer to dismiss CHANGES_REQUESTED or approve.

Generated by errors-fix-driver · ● 9.8M · ◷

[Copilot]

Pull request overview

Fixes a terminal resize/dispose race in the workbench terminal process manager by preventing setDimensions from calling .then() on a disposed/cleared ptyProcessReady promise reference.

Changes:

• Add an early-return guard in TerminalProcessManager.setDimensions when ptyProcessReady has been cleared during disposal, avoiding a Cannot read properties of undefined (reading 'then') crash.

Show a summary per file

File	Description
src/vs/workbench/contrib/terminal/browser/terminalProcessManager.ts	Add guard in setDimensions to safely no-op when ptyProcessReady is unset during disposal.

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 0

[bryanchen-d]

4 production trigger paths (Kusto, last 14d)

Pulled from RawEventsVSCode matching the Cannot read properties of undefined (reading 'then') stack at terminalProcessManager.setDimensions:

#	Trigger	Hits	Stack head
1	Editor-area terminal closed → xterm dispose → WebGL renderer dispose fires _onDidRequestRefreshDimensions synchronously → layout → _resize → _updatePtyDimensions → setDimensions	986	_disposeOfWebglRenderer → _onDidRequestRefreshDimensions.fire
2	Trash-icon close + LSP / config change cascade re-entering layout during dispose	859	closeTerminal → cascade through _languageFeaturesService
3	_onWillShutdown (reload window with terminal open)	214	shutdown handler → terminal dispose
4	Kill All / Kill from menu (_runForSelectionOrInstance)	904	command path → mass dispose

All four reach the same line: return this.ptyProcessReady.then(...) after ptyProcessReady has been nulled by the toDisposable registered in the manager's constructor. Path #1 needs no extension involvement — purely first-party code, fully natural repro (move terminal to editor area + close the tab).

Why the conditional guard is safe

The previous version of this guard was unconditional:

if (!this.ptyProcessReady) { return Promise.resolve(); }

That had the legitimate concern of hiding caller-side ordering bugs — e.g. if anything ever called setDimensions on a freshly constructed manager before createProcess completes, we'd silently swallow it.

The refined guard splits the two cases:

if (this._store.isDisposed) {
    return Promise.resolve();   // legitimate teardown race (#315282)
}
if (!this.ptyProcessReady) {
    throw new Error('TerminalProcessManager.setDimensions called before initialization');
}

DisposableStore.dispose() flips _isDisposed = true before iterating registered disposables, so by the time the toDisposable callback nulls ptyProcessReady, this._store.isDisposed is already true. That makes the disposed-vs-uninitialized distinction reliable.

Net effect:

• Post-dispose re-entrant resize during the synchronous teardown stack → silent no-op (intended; matches "resize on a dead pty" semantics).
• Pre-init call on a live manager → loud, explicit Error reaches errorTelemetry, so the underlying ordering bug stays visible.
• Combined with @bryanchen-d's reorder of _resizeDebouncer.dispose() before _processManager.dispose(), the resize-debouncer entry path (the most frequent contributor to path Open Source VS Code #1) is also eliminated at the root, leaving the guard purely as defense in depth for the other three paths.