microsoft / microsoft/TypeScript
Type alias circularly references itself
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Description
### 🔎 Search Terms
circular reference, generic, error TS2456, recursive
### 🕗 Version & Regression Information
- This is the behavior in every version I tried, and I reviewed the FAQ for entries about circular reference
### ⏯ Playground Link
https://www.typescriptlang.org/play/?ts=5.8.2#code/C4TwDgpgBAYg9nAKuaBeKBvAsAKClAMwQH4AuKAIwQBsIBDAOwG5cBfFnXUSKAIToDOEAKK0AthAbAAPIgB8UdPCQooAMky58AYwAWAS2oATAE6TyAYQCuA4HDGiIEqQG0Auh3zcI5RB3a4XKrWtvaOzsCKfIIi4pIyAOS6AIwJchxAA
### 💻 Code
```ts
type FooType = {
foo?: boolean;
};
type BaseElement = FooType & {
children: CustomElement[];
type: T;
};
type CustomElement = BaseElement<'h1'>;
```
### 🙁 Actual behavior
When defining a recursive type structure using a generic type, TypeScript incorrectly reports a `Type alias 'CustomElement' circularly references itself.(2456)` error, even though the type should be resolvable.
It gets weird when you move `type: T;` line above the `children: CustomElement[];` and the error disappears. Also removing `FooType` will resolve the issue.
### 🙂 Expected behavior
In the first place the code should not throw any errors, in the second place the behavior should not change by reordering records of a type.
### Additional information about the issue
_No response_
Contributor guide
Research direction
Start with the linked TypeScript Playground reproduction and compare the two member orderings in the generic intersection type. Trace the circular-reference diagnostic for recursive type aliases and determine why adding FooType changes it; done means the valid recursive structure no longer reports TS2456 and member order does not change the result.
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
- Clearly specified
- Newbie friendliness
- 35/100