fix: guard against disposed model in inline completions (fixes #318217)

[vs-code-engineering]

🔧 Error Fix

Summary

Error: Model is disposed! thrown from textModel._assertNotDisposed when _inlineSuggestionItems derived observable recomputes during an observable update transaction after the text model has already been disposed.

Impact: Hits across Windows, Mac, and Linux on VS Code 1.121.0 (commit f6cfa2ea). The error fires during command execution (cursor edit) when the observable derivation chain propagates changes through reportChanges → endUpdate and reaches the inline completions model’s visibility check.

Fixes #318217
Recommended reviewer: @hediet

Culprit Commit

No single culprit commit identified — this is a latent race condition where the model disposal can occur mid-transaction while derived observables are still recomputing. The inline completions model (inlineCompletionsModel.ts) has been maintained primarily by @hediet.

Code Flow

sequenceDiagram
    participant CMD as EditorCommand
    participant VM as ViewModel
    participant TX as TransactionUpdate
    participant DRV as DerivedObservable
    participant ICM as InlineCompletionsModel
    participant TM as TextModel

    CMD->>VM: executeCommands
    VM->>TX: batchChanges / endUpdate
    TX->>DRV: reportChanges
    DRV->>ICM: _inlineSuggestionItems recompute
    ICM->>TM: isVisible → getValueInRange
    TM-->>TM: _assertNotDisposed → THROWS

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Affected Files

File	Role
src/vs/editor/contrib/inlineCompletions/browser/model/inlineCompletionsModel.ts	Derived observable calls isVisible on disposed model
src/vs/editor/contrib/inlineCompletions/browser/model/inlineCompletionIsVisible.ts	Calls singleTextRemoveCommonPrefix which hits getValueInRange
src/vs/editor/contrib/inlineCompletions/browser/model/singleTextEditHelpers.ts	Calls model.getValueInRange (crash site)
src/vs/editor/common/model/textModel.ts	Throws Model is disposed! in _assertNotDisposed

Repro Steps

1. Open an editor with inline completions active (e.g., Copilot suggestions visible)
2. Execute a cursor editing command (type, delete) that triggers model disposal (e.g., close the editor tab rapidly during typing)
3. The observable update transaction propagates through endUpdate → reportChanges and reaches _inlineSuggestionItems after the model is already disposed
4. The derived tries to compute visibility, calling model.getValueInRange() on the disposed model

How the Fix Works

Chosen approach (inlineCompletionsModel.ts:524): Added if (this.textModel.isDisposed()) { return undefined; } as a guard clause at the top of the _inlineSuggestionItems derived computation, after checking for completions but before accessing the model. This prevents the derived from attempting visibility calculations on a disposed model — fixing at the point where the invalid state (disposed model) is first consumed, not at the crash site (textModel._assertNotDisposed). This follows the principle of adding a guard clause upstream of the crash site so the error path is never reached.

Alternatives considered: Wrapping the isVisible call in try/catch would hide the error from telemetry without addressing the root cause. Adding disposal checks inside singleTextRemoveCommonPrefix or inlineCompletionIsVisible would be patching at the crash site rather than the data consumer that initiates the invalid access.

Recommended Owner

@hediet — primary author and maintainer of the inline completions model and observable-based architecture in this area.

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