microsoft / microsoft/TypeScript
Recursive tuple cannot be computed through generic, but valid in a declarative form
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描述
### 🔎 Search Terms
ts2589 "Type instantiation is excessively deep and possibly infinite"
### 🕗 Version & Regression Information
- This is the behavior in every version I tried, and I reviewed the FAQ for entries about ts2589
- I was unable to test this on prior versions before v4.7.0 because `infer T extends R` syntax not introduced
### ⏯ Playground Link
https://www.typescriptlang.org/play/?ts=5.9.3#code/C4TwDgpgBAYg9nKBeKBvAUFKAbCBDAEwEsA7AcwC4oByPagGkygCcIBnYKgbXjgF1GAXwDc6dKEhQAogA8weEgQA8AFQB8yKCqgQZwCIrZomWXIVKUopAGYRmUADKisWVhyo27UAEo69BgiMFEC4+dEEoAH4oLgd6KAA6JNl5RQBZYKVvNT4oKhIIADc7UXFwaBSFAgySEFU-fUMoYNCNJBMtBoCjLk97GCJmDnikhL6fdmBc6K5KxSUBoeA1EeS5Kpq670mcvJi+UoloFUmAQU055V41UQB6W5dHx4A9AD8tcqsSDgVgIjw-nASFYjLoAMbsNhEYrYEBQAgQCBgZqKKBgOBsKEAI1hX2spCI+gSAAoAEwAVgAHABOACUYiOWkmACFNFxaAwmRxmQd0EA
### 💻 Code
```ts
type Foo = {
leading: 'a',
rest: [Foo],
};
type Expand = T extends {
leading: infer L;
rest: infer R extends any[]
} ? [L, ...ExpandMany] : never;
type ExpandMany =
T extends [infer First, ...infer Rest] ? [Expand, ...ExpandMany] : [];
type TestA = Expand;
// ^~ Type instantiation is excessively deep and possibly infinite.(2589)
type TestB = ['a', TestB];
```
### 🙁 Actual behavior
`TestA` meant to be:
```
TestA
-> Expand
-> ['a', ...ExpandMany<[Foo]>]
-> ['a', ...[Expand]]
-> ['a', Expand]
-> ['a', TestA]
```
which is identical to `TestB` but TS complains the instantiation cannot stop.
### 🙂 Expected behavior
Stop expansion at first reference at appeared structure `Expand`, that is:
```
type TestA = Expand;
// ^?~ type TestA = ['a', Expand]
// or more intelligent `type TestA = ['a', TestA]`
```
### Additional information about the issue
This code is useful when `Foo` is `as const` inferred from a runtime constant, and we want a tuple-like typing calculated from `Foo`. Since TypeScript support self-referential tuple by declarative just like `TestB`, it would be better for support that in a computed way like `Expand`.
贡献指南
从这里开始
- 先读完整个 Issue,再读项目的贡献指南。
- 在 Issue 下留言说明你要接手 —— 这能避免两个人做同样的事。
- Fork 仓库,在一个分支上完成修改。
- 提交 Pull Request,并在描述里引用这个 Issue 编号。
调研方向
从链接的 TypeScript Playground 示例开始,确认 TestA 出现 TS2589 错误,而 TestB 会被接受。跟踪递归条件类型和元组类型的实例化过程,然后将完成定义为:允许计算形式在自引用元组上稳定下来,同时不使递归诊断发生回归。
由索引模型根据 Issue 内容生成。
评估
- 技术栈
- typescript
- 领域
- compilers
- Issue 类型
- 缺陷
- 难度
- 5/5
- 预计耗时
- 一周以上
- 活跃度
- 停滞
- 描述清晰度
- 基本清楚
- 新手友好度
- 35/100