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

[vs-code-engineering]

Error Message

Cannot read properties of undefined (reading 'isLoading')

Stack Trace

    at sht._getButtonConfiguration (./src/vs/sessions/contrib/changes/browser/changesView.ts:173:0)
    at buttonConfigProvider (./src/vs/sessions/contrib/changes/browser/changesView.ts:155:0)
    at configProvider (./src/vs/platform/actions/browser/buttonbar.ts:120:0)
    at yye.p [as value] (./src/vs/platform/actions/browser/buttonbar.ts:238:0)
    at xye._deliver (./src/vs/base/common/event.ts:1354:12)
    at xye.fire (./src/vs/base/common/event.ts:1385:8)
    at xye.resume (./src/vs/base/common/event.ts:1534:11)
    at (anonymous) (./src/vs/base/common/event.ts:1573:9)

Raw Stack Trace (minified)

TypeError: Cannot read properties of undefined (reading 'isLoading')     at sht._getButtonConfiguration (out/vs/sessions/sessions.desktop.main.js:4147:15090)     at buttonConfigProvider (out/vs/sessions/sessions.desktop.main.js:4147:14771)     at wW.update (out/vs/sessions/sessions.desktop.main.js:2029:26721)     at yye.p [as value] (out/vs/sessions/sessions.desktop.main.js:2029:28511)     at xye._deliver (out/vs/sessions/sessions.desktop.main.js:405:3066)     at xye.fire (out/vs/sessions/sessions.desktop.main.js:405:3385)     at xye.resume (out/vs/sessions/sessions.desktop.main.js:405:4674)     at out/vs/sessions/sessions.desktop.main.js:405:5031

Details

Property	Value
Bucket ID	ba4f0320-ec05-8260-d7ec-f1edc3a6cf5d
Version	1.116.0-insider
Commit	47add6df
Last Seen	Fri Apr 10 2026 23:57:04 GMT+0000 (Coordinated Universal Time)
Platforms	Mac, Windows
Product	Agents

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This issue was automatically created from the VS Code Errors Dashboard

[vs-code-engineering]

Regression Details

• Product: Agents
• Regression type: new
• Last release without this error: 1.116.0-insider (0271b4d2)
• First release with this error: 1.116.0-insider (1ec46de1)
• Commit range: 0271b4d2...1ec46de1

Related Error Buckets

These additional error buckets are tracked by this issue (v1.116.0-insider):

Bucket ID	Error Message	Users
ba4f0320	Cannot read properties of undefined (reading 'isLoading')	6
078489cc	Cannot read properties of undefined (reading 'isLoading')	6

Analysis

The error occurs in changesView.ts (Agents sessions-specific code) when _getButtonConfiguration tries to read isLoading from an undefined value. The deminified stack shows:

at (anonymous) (changesView.ts:173:0)
at (anonymous) (changesView.ts:155:0)
at configProvider (buttonbar.ts:120:0)
at (anonymous) (buttonbar.ts:238:0)
at (anonymous) (lazyObservableValue.ts:58:67)
at (anonymous) (autorunImpl.ts:103:11)

This is an Agents-specific regression in the changes view button configuration, likely caused by an observable dependency becoming undefined during a reactive update cycle.

Generated by errors-agents-regression-scan · ◷

[vs-code-engineering]

🔍 Error Investigation

Summary

The error Cannot read properties of undefined (reading 'isLoading') occurs in ChangesButtonBarWidget._getButtonConfiguration() when the reviewState parameter is undefined. The reviewState value is captured from a derivedOpts observable (reviewStateObs) inside an autorun closure. Although the observable's computation function always returns an object, the VS Code observable system's Derived._recompute() silently catches computation errors via onBugIndicatingError — if the computation throws (e.g., a nested service call fails), the internal _value remains undefined (its initial state), and this undefined propagates through the closure to the button config callback. A subsequent menu change event (delivered via DebounceEmitter.resume()) triggers the callback, causing the crash.

Culprit Commit

Field	Value
Commit	a9d50bd7
Author	@lszomoru
PR	#308781
Message	Sessions - fix title menu context when switching between views
Why	This is the only commit in the regression range (0271b4d2...1ec46de1) that modifies changesView.ts. It moves the "Title actions" autorun from the ChangesViewPane constructor to onVisible(), changing the lifecycle of renderDisposables. This alters when ChangesButtonBarWidget is created/destroyed and when updateActions() fires, exposing a latent timing issue where reviewStateObs computation can fail during view initialization.

Code Flow

sequenceDiagram
    participant V as ChangesViewPane.onVisible()
    participant W as ChangesButtonBarWidget
    participant D as reviewStateObs (derivedOpts)
    participant M as MenuWorkbenchButtonBar
    participant E as DebounceEmitter

    V->>V: renderDisposables.clear()
    V->>V: Title actions autorun → updateActions()
    V->>W: createInstance(ChangesButtonBarWidget)
    W->>D: reviewStateObs.read(reader)
    Note over D: ⚠️ If computation throws<br/>(e.g. service not ready),<br/>error caught by onBugIndicatingError,<br/>_value stays undefined
    D-->>W: returns undefined (or valid object)
    W->>M: new MenuWorkbenchButtonBar(..., buttonConfigProvider closure)
    M->>M: menu.onDidChange(update) + update()
    Note over E: Menu change queued<br/>(debounced)
    E->>M: resume() → fire() → update()
    M->>W: buttonConfigProvider(action)
    W->>W: _getButtonConfiguration(action, outgoingChanges, undefined)
    Note over W: 💥 reviewState.isLoading<br/>TypeError: Cannot read properties<br/>of undefined

Loading

Affected Files

File	Role
src/vs/sessions/contrib/changes/browser/changesView.ts	Crash site (_getButtonConfiguration L173) and root cause (reviewStateObs derivation L104-139, autorun closure L141-159)
src/vs/platform/actions/browser/buttonbar.ts	MenuWorkbenchButtonBar — calls buttonConfigProvider during update() (L120, L238)
src/vs/base/common/observableInternal/observables/derivedImpl.ts	Derived._recompute() silently catches computation errors, leaving _value as undefined (L195-228)

Repro Steps

1. Open VS Code Insiders (Agents product) with a session active
2. Switch between views or trigger the Changes view to re-render (causing onVisible() → renderDisposables.clear() cycle)
3. The error is non-deterministic — it occurs when the reviewStateObs derived observable's computation fails during initialization (depends on service readiness)
4. The RUN_SESSION_CODE_REVIEW_ACTION_ID action must be present in the ChatEditingSessionChangesToolbar menu for the code path to reach line 173

Fix Proposal

Fix location: src/vs/sessions/contrib/changes/browser/changesView.ts → _getButtonConfiguration() (line 172)

Approach: Add a defensive null guard on reviewState before accessing .isLoading. This handles the case where reviewStateObs returns undefined due to a silently failed computation:

if (action.id === RUN_SESSION_CODE_REVIEW_ACTION_ID) {
    if (!reviewState) {
        return { showIcon: true, showLabel: false, isSecondary: true };
    }
    // existing logic...
}

Additionally, the autorun at line 141 should provide a fallback value when reading reviewStateObs:

const reviewState = reviewStateObs.read(reader) ?? { isLoading: false, commentCount: undefined };

Recommended Owner

@lszomoru — culprit commit author and primary contributor to the Sessions changes view code in this regression range

Generated by errors-investigate · ● 17.3M · ◷