microsoft / microsoft/TypeScript

tagged/named rest parameter participating in circular reference causes error

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#63,584 0 comments 1 reaction 0 assignees View on GitHub
Bug Domain: check: Type Circularity
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Description

### 🔎 Search Terms

named tuple element rest recursive circularly references union unions

### 🕗 Version & Regression Information

- This is the behavior in every version I tried, and I reviewed the FAQ for entries about *everything and didn't find anything relevant*

### ⏯ Playground Link

https://www.typescriptlang.org/play/?esModuleInterop=false&target=99&jsx=0&noFallthroughCasesInSwitch=false&ts=6.0.0-dev.20260416&noUnusedLocals=true&noUnusedParameters=true&noUncheckedIndexedAccess=true#code/KYDwDg9gTgLgBDAnmYcDiEIBMAiEDGActqgLwBQcVcAPnAM4xQCWAdgOaXV0DaARMz4AaOADpxGbHiIkeAXTlcqvPgBtBItllAAuOKwCuAWwBGwKCPGjJuAsW3y5AbnLlQkWAmSoAQgENbGW0ARjgKaloGJjZOCJUNMXEYP3Z2YCw9f0D7YGDHcgB6AoiSiIA9CsqKpUj+dWE4LV19YzMLRNEs6Ry8hRc3cGh4JBQ4LrsSACYwmrpGFg5ZuH4Eq3Gg4En8uOW1BKaQPUNTc0sklLSMsYDuqccXItKn5+eqqvIgA

### 💻 Code

```ts
export type GoodDocNode =
| string
| ["i", ...GoodDocNode[]]
| ["li", index: number, ...GoodDocNode[]];

export type BadDocNode1 =
| string
| ["i", ...tagged: BadDocNode1[]]
// ^^^^^^^^
| ["li", index: number, ...BadDocNode1[]];

export type BadDocNode2 =
| string
| ["i", ...BadDocNode2[]]
| ["li", index: number, ...tagged: BadDocNode2[]];
// ^^^^^^^^
```

### 🙁 Actual behavior

Error:
```
Type alias 'BadDocNode1' circularly references itself.
Type alias 'BadDocNode2' circularly references itself.
```

### 🙂 Expected behavior

No errors, because the only differences between the two is the name on the rest parameter in the tuple, nothing structurally is different.

### Additional information about the issue

_No response_

Contributor guide

Open the contributing guide

Research direction

Use the linked TypeScript Playground and the BadDocNode1/BadDocNode2 repro as the starting point; investigate circular type-alias checking for named tuple rest parameters. Done means the repro produces no circular-reference errors while the structurally equivalent GoodDocNode example remains valid.

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
Quiet
Clarity
Clearly specified
Newbie friendliness
48/100

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