microsoft / microsoft/TypeScript

Ghost error appearing after signature help in inferred signatures with rest parameter

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Bug Domain: check: Error Instability Help Wanted Needs Human Review
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Description

### 🔎 Search Terms

signature help inference signature rest spread nested

### 🕗 Version & Regression Information

- This is the behavior in every version I tried

### ⏯ Playground Link

https://www.typescriptlang.org/play/?ts=6.0.0-dev.20250803#code/KYDwDg9gTgLgBASwHY2FAZgQwMbDgBQTGEwCMAbPAbwCg44wjgAeAQQBo4AhOAXjiTAAbmgB8AChgALBAGcAXHA5wyi8QH1FrAJR9R3bYq4BuGgF8aNGAE9icAMIQhmKAkwo2+-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-GNpgsLZu2uW5+weeByAgC9-W2AA6bCIWAS0Y2ARRSl2RpWCTTBrGYdxrFEN89CeF5+SECBJ04GUoDYsUoDg0BIFgJDB3gbBMFQTpoDtWQAGlgCafgACIAAFgEYjIAHo0B-VThNE8S8Lk0JeOgeBLgQvsB0eH0EGkewROAMSoGsRRmBsnTXDwrcK2VMioAo5h8GTYhYGsaSaNPehsMw7S7N0hQHFs+yJLooI4DYKBOmVbNK283zqNETVgBgTh7A8ndlSoUU-XECKXHSrQ0tkQNiPgMwwocYYkv0YqADJ8W9YBKuq+q6vSxqCrgHqQLgEkooSvCQrpfEppcxAkDi1yJJJJBUihNAaQW5k8DMGCzgM8AjLgGw7FYchyBCq1NhFAoSpzcrpvimL5sUZBXigOAAEU4Aseh5zgABrGSIHQf7tl8LjTEM-jLrwApyx8jJrvIDYipEjLtxzfyIECmwQq8Nbcc8lQkGsbYQZRlIcEydlXpmj6ZIW17JJWsmFuowHAdo+hYf8U6+OMntEPMoSROwKQXOihynO2Iptkltb5Yk56svIyiMbujZRDy7ZWAAJmvApTe2UpjZPcQsOwmrYpJHU4AiuXZtka96HQNQNMUOm0ZgDGsbV93Nu20hdtEd8+QyNhTaeeOrYFuAaQ6lLlHKW36GUikYD9lTWWxDk05jiY4AAHyUePzYrp4QGuVJLmD-2GaD9k3ZisOdqgGkDc1Wuk9CBDLSDCAIG-aBNeVT9Rx-ANxDk60x4nqA5M4KgzG0TDGGILO4Es6z3oche6ghTBkDk7Q6I3yxh+VLgXBXqeoNjL8xygee5IfqAV7Xo0t53sAPeB9ZZH2sAvcE7RgAQj-nJU+58kCX2vucO+3BMAAC8n6ZWnjGEcK9P4P0we-P+G8AFMGAVZUBrlwFyUgagGBV9dA33gr2O4yE4CkAwWobYIBfDhzQCXAuzB2JFmXu-Wu38n6V0ISvTi-geJnX4qrMAyZOg+QhCKTh6DxAAEYyG720jLDux84EQDPhfTgGh3yoU6BoTCEFOjaCcaESwri3FAA

### 💻 Code

```ts
///

// @strict: true
// @target: esnext
// @lib: esnext

//// export interface Pipeable {
//// pipe(this: A, ab: (_: A) => B): B;
//// }
////
//// type Covariant = (_: never) => A;
////
//// interface VarianceStruct {
//// readonly _V: string;
//// readonly _A: Covariant
;
//// readonly _E: Covariant;
//// readonly _R: Covariant;
//// }
////
//// declare const EffectTypeId: unique symbol;
////
//// interface Variance {
//// readonly [EffectTypeId]: VarianceStruct;
//// }
////
//// interface Effect
//// extends Variance,
//// Pipeable {}
////
//// interface Class extends Pipeable {
//// new (): Fields;
//// }
////
//// interface TaggedErrorClass extends Class {
//// readonly _tag: Tag;
//// }
////
//// declare const TaggedError: (identifier?: string) => <
//// Tag extends string,
//// Fields
//// >(
//// tag: Tag,
//// fieldsOr: Fields
//// ) => TaggedErrorClass<
//// Tag,
//// {
//// readonly _tag: Tag;
//// }
//// >;
////
//// declare const log: (
//// ...message: ReadonlyArray
//// ) => Effect;
////
//// export const categoriesKey = "@effect/error/categories";
////
//// export declare const withCategory: >(
//// ...categories: Categories
//// ) => , Ret, C extends { new (...args: Args): Ret }>(
//// C: C
//// ) => C & {
//// new (...args: Args): Ret & {
//// [categoriesKey]: { [Cat in Categories[number]]: true };
//// };
//// };
////
//// export type AllKeys = E extends { [categoriesKey]: infer Q }
//// ? keyof Q
//// : never;
//// export type ExtractAll = Cats extends any
//// ? Extract
//// : never;
////
//// export declare const catchCategory: <
//// E,
//// const Categories extends Array>,
//// A2,
//// E2,
//// R2
//// >(
//// ...args: [
//// ...Categories,
//// f: (err: ExtractAll) => Effect
//// ]
//// ) => (
//// effect: Effect
//// ) => Effect
>, R | R2>;
////
//// class FooError extends TaggedError()("FooError", {}).pipe(
//// withCategory("domain")
//// ) {}
////
//// class BarError extends TaggedError()("BarError", {}).pipe(
//// withCategory("system", "domain")
//// ) {}
////
//// class BazError extends TaggedError()("BazError", {}).pipe(
//// withCategory("system")
//// ) {}
////
//// declare const baz: (
//// x: number
//// ) => Effect;
////
//// export const program = baz(1).pipe(catchCategory("domain",/*1*/ (_) => log(_._tag)));

verify.getSemanticDiagnostics([]);
goTo.marker("1");
edit.insert(",");
verify.signatureHelpPresentForTriggerReason({
kind: "characterTyped",
triggerCharacter: ",",
});
edit.backspace(1);
verify.signatureHelpPresentForTriggerReason({
kind: "retrigger",
});
verify.getSemanticDiagnostics([]);
```

### 🙁 Actual behavior

It's sometimes a little bit tricky to reproduce it in the playground but steps are pretty easy:
1. position ur cursor after `"domain",` in the last statement
2. insert `,`
3. this should trigger the signature help
4. now remove the inserted comma character
5. the signature help should still be visible at this point
6. error is reported

### 🙂 Expected behavior

Given the code is exactly the same at the step 6 as it is before any steps are taken, I don't expect this code to report any errors. Any edit outside of the `catchCategory`'s argument list makes the error go away (a further indication the error should not be there) but edits inside that argument list don't make it go away.

### Additional information about the issue

_No response_

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the inline fourslash.ts test and reproduce the edit, signature-help, backspace, and diagnostic sequence in the Playground example. Trace the signature-help retrigger path for the inferred rest-parameter call. Done means the unchanged code produces no semantic diagnostic after the comma is removed while signature help remains visible.

Written by the indexing model from the issue text.

Assessment

Tech stack
typescript
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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