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

[vs-code-engineering]

Error Message

Cannot read properties of undefined (reading 'toString')

Stack Trace

    at (anonymous) (./src/vs/editor/contrib/inlineCompletions/browser/view/inlineEdits/inlineEditsViews/inlineEditsLineReplacementView.ts:251:103)
    at fn (./src/vs/base/common/observableInternal/observables/baseObservable.ts:89:15)
    at nb._recompute (./src/vs/base/common/observableInternal/observables/derivedImpl.ts:201:23)
    at nb.get (./src/vs/base/common/observableInternal/observables/derivedImpl.ts:159:10)
    at nb.readObservable (./src/vs/base/common/observableInternal/observables/derivedImpl.ts:344:27)
    at nb.read (./src/vs/base/common/observableInternal/observables/baseObservable.ts:54:17)
    at nb._computeFn (./src/vs/base/browser/dom.ts:2553:69)
    at nb._recompute (./src/vs/base/common/observableInternal/observables/derivedImpl.ts:201:23)
    at nb.get (./src/vs/base/common/observableInternal/observables/derivedImpl.ts:159:10)
    at nb.readObservable (./src/vs/base/common/observableInternal/observables/derivedImpl.ts:344:27)
    at nb.read (./src/vs/base/common/observableInternal/observables/baseObservable.ts:54:17)
    at rZt.readEffect (./src/vs/base/browser/dom.ts:2616:5)
    at l (./src/vs/base/browser/dom.ts:2593:15)
    at getChildren (./src/vs/base/browser/dom.ts:2589:34)
    at l (./src/vs/base/browser/dom.ts:2589:21)
    at getChildren (./src/vs/base/browser/dom.ts:2605:37)
    at nb._recompute (./src/vs/base/common/observableInternal/observables/derivedImpl.ts:201:23)
    at nb.get (./src/vs/base/common/observableInternal/observables/derivedImpl.ts:159:10)
    at nb.readObservable (./src/vs/base/common/observableInternal/observables/derivedImpl.ts:344:27)
    at nb.read (./src/vs/base/common/observableInternal/observables/baseObservable.ts:54:17)

Raw Stack Trace (minified)

TypeError: Cannot read properties of undefined (reading 'toString')     at out/vs/workbench/workbench.desktop.main.js:905:143733     at nb._computeFn (out/vs/workbench/workbench.desktop.main.js:407:916)     at nb._recompute (out/vs/workbench/workbench.desktop.main.js:407:12496)     at nb.get (out/vs/workbench/workbench.desktop.main.js:407:11830)     at nb.readObservable (out/vs/workbench/workbench.desktop.main.js:407:14534)     at nb.read (out/vs/workbench/workbench.desktop.main.js:407:522)     at nb._computeFn (out/vs/workbench/workbench.desktop.main.js:411:24299)     at nb._recompute (out/vs/workbench/workbench.desktop.main.js:407:12496)     at nb.get (out/vs/workbench/workbench.desktop.main.js:407:11830)     at nb.readObservable (out/vs/workbench/workbench.desktop.main.js:407:14534)     at nb.read (out/vs/workbench/workbench.desktop.main.js:407:522)     at rZt.readEffect (out/vs/workbench/workbench.desktop.main.js:411:24931)     at l (out/vs/workbench/workbench.desktop.main.js:411:24752)     at out/vs/workbench/workbench.desktop.main.js:411:24723     at Array.flatMap (<anonymous>)     at l (out/vs/workbench/workbench.desktop.main.js:411:24712)     at nb._computeFn (out/vs/workbench/workbench.desktop.main.js:411:24837)     at nb._recompute (out/vs/workbench/workbench.desktop.main.js:407:12496)     at nb.get (out/vs/workbench/workbench.desktop.main.js:407:11830)     at nb.readObservable (out/vs/workbench/workbench.desktop.main.js:407:14534)     at nb.read (out/vs/workbench/workbench.desktop.main.js:407:522)     at rZt.readEffect (out/vs/workbench/workbench.desktop.main.js:411:24931)     at l (out/vs/workbench/workbench.desktop.main.js:411:24752)     at out/vs/workbench/workbench.desktop.main.js:411:24723     at Array.flatMap (<anonymous>)     at l (out/vs/workbench/workbench.desktop.main.js:411:24712)     at l (out/vs/workbench/workbench.desktop.main.js:411:24678)     at out/vs/workbench/workbench.desktop.main.js:411:24723     at Array.flatMap (<anonymous>)     at l (out/vs/workbench/workbench.desktop.main.js:411:24712)     at nb._computeFn (out/vs/workbench/workbench.desktop.main.js:411:24837)     at nb._recompute (out/vs/workbench/workbench.desktop.main.js:407:12496)     at nb.get (out/vs/workbench/workbench.desktop.main.js:407:11830)     at nb.reportChanges (out/vs/workbench/workbench.desktop.main.js:407:497)     at nb.get (out/vs/workbench/workbench.desktop.main.js:407:11737)     at nb.reportChanges (out/vs/workbench/workbench.desktop.main.js:407:497)     at Egt.endUpdate (out/vs/workbench/workbench.desktop.main.js:407:21647)     at nb.endUpdate (out/vs/workbench/workbench.desktop.main.js:407:13497)     at nb.endUpdate (out/vs/workbench/workbench.desktop.main.js:407:13497)     at nb.endUpdate (out/vs/workbench/workbench.desktop.main.js:407:13497)     at nb.endUpdate (out/vs/workbench/workbench.desktop.main.js:407:13497)     at nb.endUpdate (out/vs/workbench/workbench.desktop.main.js:407:13497)     at nb.endUpdate (out/vs/workbench/workbench.desktop.main.js:407:13497)     at nb.endUpdate (out/vs/workbench/workbench.desktop.main.js:407:13497)     at nb.endUpdate (out/vs/workbench/workbench.desktop.main.js:407:13497)     at nb.endUpdate (out/vs/workbench/workbench.desktop.main.js:407:13497)     at nb.endUpdate (out/vs/workbench/workbench.desktop.main.js:407:13497)     at nb.endUpdate (out/vs/workbench/workbench.desktop.main.js:407:13497)     at nb.endUpdate (out/vs/workbench/workbench.desktop.main.js:407:13497)     at nb.endUpdate (out/vs/workbench/workbench.desktop.main.js:407:13497)     at nb.endUpdate (out/vs/workbench/workbench.desktop.main.js:407:13497)     at nb.endUpdate (out/vs/workbench/workbench.desktop.main.js:407:13497)     at nb.endUpdate (out/vs/workbench/workbench.desktop.main.js:407:13497)     at TIe.endUpdate (out/vs/workbench/workbench.desktop.main.js:407:13497)     at lO.finish (out/vs/workbench/workbench.desktop.main.js:406:109977)     at Gi (out/vs/workbench/workbench.desktop.main.js:406:109177)     at out/vs/workbench/workbench.desktop.main.js:898:23076     at async fke.trigger (out/vs/workbench/workbench.desktop.main.js:898:51137)

Details

Property	Value
Bucket ID	4afb41a1-60de-2e83-d6c4-632bb72f171a
Version	1.115.0
Commit	41dd792b
Last Seen	Thu Apr 09 2026 23:58:38 GMT+0000 (Coordinated Universal Time)
Platforms	Linux, Windows, Mac
Product	VSCode

---

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 'toString') occurs in the inline edits line replacement view when calling .toString() on a Color value returned by getEditorBlendedColor() that is undefined. This happens because the observable framework's _recompute method catches errors thrown during color resolution (via onBugIndicatingError) and leaves the derived value as undefined, which then propagates to the .map(c => c.toString()) callback. The error affects all platforms (Linux, Windows, Mac) and has been persistent across versions 1.110.0–1.117.0 with millions of total hits (~1.6M on 1.115.0 stable alone).

Culprit Commit

No specific culprit commit was identified — the vulnerable pattern (getEditorBlendedColor(...).map(c => c.toString()) without null guard) has been present since the file was first created. The error was not introduced by a regression in a particular commit range; rather, it surfaces whenever the theme color resolution fails during observable recomputation (e.g., theme transitions, custom themes with incomplete color definitions).

Code Flow

sequenceDiagram
    participant Theme as ThemeService
    participant ObsColor as observeColor()
    participant Derived as derivedImpl._recompute()
    participant Blend as getEditorBlendedColor()
    participant View as LineReplacementView L251

    View->>Blend: getEditorBlendedColor(originalBorderColor, themeService)
    Blend->>ObsColor: observeColor(colorId, themeService)
    ObsColor->>Theme: getColorTheme().getColor(colorId)
    Note over Theme: Color not found (undefined)
    ObsColor-->>Derived: throw BugIndicatingError("Missing color")
    Note over Derived: catch (e) { onBugIndicatingError(e) }<br/>_value remains undefined
    Derived-->>Blend: returns undefined (not Color)
    Blend-->>View: observable value = undefined
    View->>View: .map(c => `1px solid \$\{c.toString()}`)
    Note over View: 💥 TypeError: Cannot read properties<br/>of undefined (reading 'toString')

Loading

Affected Files

File	Role
src/vs/editor/contrib/inlineCompletions/browser/view/inlineEdits/inlineEditsViews/inlineEditsLineReplacementView.ts	Crash site — line 251 calls .toString() on potentially undefined color
src/vs/editor/contrib/inlineCompletions/browser/view/inlineEdits/theme.ts	Root cause — getEditorBlendedColor() and observeColor() throw BugIndicatingError when color missing, which is swallowed by observable framework
src/vs/base/common/observableInternal/observables/derivedImpl.ts	Error absorption — _recompute() catches all errors (line 226), leaving _value as undefined
src/vs/editor/contrib/inlineCompletions/browser/view/inlineEdits/inlineEditsViews/inlineEditsSideBySideView.ts	Same pattern — lines 453, 488 have identical unguarded .toString() calls

Repro Steps

1. Open VS Code with a custom/non-default color theme (one that may not fully define inlineEdit.originalBorder or inlineEdit.tabWillAcceptOriginalBorder colors)
2. Open a file and trigger an inline edit suggestion (e.g., via Copilot inline completions)
3. The inline edit overlay renders, triggering the observable chain
4. If the theme color lookup returns undefined for one of the border colors (or during a theme transition), the error fires
5. The error is non-deterministic — it depends on theme configuration and timing of observable evaluation

Fix Proposal

Option A (call-site guards — immediate fix): Add null guards at each .map(c => c.toString()) call site.

Fix location: inlineEditsLineReplacementView.ts line 251, inlineEditsSideBySideView.ts lines 453/488, and similar patterns in jumpToView.ts and inlineEditsCustomView.ts
Approach: Change .map(c => \1px solid ${c.toString()}`)to.map(c => c ? `1px solid ${c.toString()}` : undefined)` (or use optional chaining).

Option B (root cause fix — preferred): Make getEditorBlendedColor return a fallback Color instead of propagating undefined when observeColor fails. This would prevent undefined from ever reaching callers.

Fix location: theme.ts → getEditorBlendedColor() or observeColor()
Approach: Instead of throwing BugIndicatingError when a color is missing, return a sensible default (e.g., Color.transparent or Color.black), or add a fallback in getEditorBlendedColor's .map() chain.

Note: Community PR #309156 implements Option A (null guards). It may need to be extended to cover jumpToView.ts and inlineEditsCustomView.ts which have the same unguarded pattern.

Recommended Owner

@hediet — inline completions feature area owner, authored the original code, and is already assigned as reviewer on the community fix PR #309156.

Generated by errors-investigate · ● 9.7M · ◷

[vs-code-engineering]

Related Error Buckets

These error buckets continue to appear in v1.117.0 (previously tracked since v1.115.0):

Bucket ID	Error Message	Version
4afb41a1	Cannot read properties of undefined (reading 'toString')	1.117.0

Generated by errors-triage · ◷

Generated by errors-triage · ● 5.6M · ◷