Everyone's raving about Copilot's code suggestions, but has anyone actually audited the quality? Specifically, the TypeScript types it generates.
We built a script to diff Copilot's inferred types against our internal, hand-rolled library definitions. The results were... illuminating. For a supposedly "context-aware" tool, it hallucinates or oversimplifies complex generics with alarming frequency.
Example from our event-bus library:
```typescript
// Our definition
publish(topic: K, payload: EventMap[K], options?: PublishOptions): Promise;
// Copilot's common suggestion
publish(topic: string, payload: any): Promise;
```
The cost? Not just technical debt. This introduces:
* Uncaught runtime errors that static analysis would've caught.
* Increased review cycles as seniors catch these type erosions.
* Bloat from manual overrides and `@ts-ignore` comments.
The math: Our team spends ~5 hours/week cleaning up vague types from Copilot-accepted suggestions. That's ~$15k/year in dev time at our rates, just to downgrade type safety. "Productivity boost" indeed.
show the math