fix: guard against empty viewport range in diff editor gutter clip (fixes #316032)

[vs-code-engineering]

🔧 Error Fix

Summary

Property	Value
Error	Invalid clipping range: [37, 37)
Bucket	5c896f3a-1b03-ede7-83e9-9035cdc4464d
Hits / Users (1.119.0)	2800 / 780
Platforms	Mac, Windows, Linux

The diff editor gutter layout code calls OffsetRange.clip() on preferredViewPortRange without first verifying that the range is non-empty. OffsetRange.tryCreate() returns undefined only when start > endExclusive, but returns an empty range (start === endExclusive) as a valid object. The existing guard checked nullability and that preferredParentRange was non-empty, but missed checking preferredViewPortRange for emptiness. When preferredViewPortRange is empty (e.g., [37, 37)), clip() throws BugIndicatingError.

Fixes #316032
Recommended reviewer: @hediet

Culprit Commit

This is a long-standing bug, not a recent regression. The incomplete guard has been present since the gutter feature was originally authored by @hediet. The error appears across multiple versions (1.112.0 through 1.119.0).

Code Flow

graph TD
    A["ResizeObserver callback"] --> B["editorGutter.ts: render()"]
    B --> C["editorGutter.ts: transaction()"]
    C --> D["gutterFeature.ts: layout() :313"]
    D --> E{"preferredViewPortRange non-null?"}
    E -->|yes| F{"preferredParentRange non-empty?"}
    F -->|yes| G["preferredViewPortRange.clip() :313"]
    G --> H["offsetRange.ts: clip() :170"]
    H --> I{"this.isEmpty?"}
    I -->|yes - BUG| J["throw BugIndicatingError"]

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Affected Files

• src/vs/editor/browser/widget/diffEditor/features/gutterFeature.ts — missing emptiness check for preferredViewPortRange
• src/vs/editor/common/core/ranges/offsetRange.ts — clip() correctly throws on empty range (not a bug here)

Repro Steps

1. Open a diff editor in VS Code
2. Resize the editor such that the viewport range becomes very small (margin values cause endExclusive - margin - itemHeight to equal margin)
3. The gutter layout triggers via ResizeObserver and preferredViewPortRange is created as an empty range [N, N)
4. clip() is called on the empty range, throwing the error

How the Fix Works

Chosen approach (src/vs/editor/browser/widget/diffEditor/features/gutterFeature.ts): Added !preferredViewPortRange.isEmpty to the guard condition at line 312, alongside the existing preferredParentRange non-empty check. Also replaced the manual start < endExclusive comparison with the idiomatic .isEmpty property for both ranges. This fixes at the data producer (the guard that decides whether to call clip()), not the crash site (clip() itself), following the principle of fixing where invalid data flows into the throwing function.

Recommended Owner

@hediet — author and maintainer of the diff editor gutter feature code.

errors-fix-driver — cycle 11

Trigger: cron_review_comments · Head: c61f61b81c49f0337860f6a968a0f484c167b130 (c61f61b)

Item	Action
CI (all checks)	✅ All passing
Review threads	None (0 unresolved)
Merge state	blocked (awaiting human approval)

Push: no (nothing to fix) · Copilot rerequested: no (no push)

Ready gate: PR already marked ready; awaiting human approval from @hediet.

errors-fix-driver — cycle 12

Trigger: cron_review_comments · Head: c61f61b81c49f0337860f6a968a0f484c167b130 (c61f61b)

Item	Action
CI (all checks)	✅ All passing
Review threads	None (0 unresolved)
Merge state	blocked (awaiting human approval)

Push: no (nothing to fix) · Copilot rerequested: no (no push)

Ready gate: PR already marked ready; awaiting human approval from @hediet.

errors-fix-driver — cycle 13

Trigger: cron_review_comments · Head: c61f61b81c49f0337860f6a968a0f484c167b130 (c61f61b)

Item	Action
CI (all checks)	✅ All passing
Review threads	None (0 unresolved)
Merge state	blocked (awaiting human approval)

Push: no (nothing to fix) · Copilot rerequested: no (no push)

Ready gate: PR already marked ready; awaiting human approval from @hediet.

Generated by errors-fix-driver · ● 6.3M · ◷

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