Array.from(it: Iterable<X> | Iterable<Y>) fails; […it] works but returns Array<X | Y>; both should return Array<X> | Array<Y>

还没有人认领这个 Issue。

### 🔎 Search Terms

Array.from is currently declared as

```ts
from(iterable: Iterable | ArrayLike): T[];
```

This means that unions of distinct iterable types cannot be turned into arrays of the same type.

```ts
let foo: Iterable | Iterable = /* ... */;
let q: Array | Array = Array.from(foo); // Fails type checking, cannot find overload (2769)
```

The array splat operator has a different problem: it tries to create an array that is a union of both types.

```ts
let foo: Iterable | Iterable = /* ... */;
let q: Array | Array = [...foo]; // Fails type checking, not assignable to type (2322)
```

My instinct is that there should be some way to use variadic types here, but tbh I don't really know how.

Does this need new syntax? Or does it work within the existing type system?

### 🕗 Version & Regression Information

Since at least 4.0; prior to 4.0 it still fails but Array.from did not support taking an Iterable.

Still around in 6.0.0-dev.20251009

### ⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.9.3&ssl=19&ssc=1&pln=11&pc=1#code/PTAEHUFMBsGMHsC2lQBd5oBYoCoE8AHSAZVgCcBLA1UABWgEM8BzM+AVwDsATAGiwoBnUENANQAd0gAjQRVSQAUCEmYKsTKGYUAbpGF4OY0BoadYKdJMoL+gzAzIoz3UNEiPOofEVKVqAHSKymAAmkYI7NCuqGqcANag8ABmIjQUXrFOKBJMggBcISGgoAC0oACCbvCwDKgU8JkY7p7ehCTkVDQS2E6gnPCxGcwmZqDSTgzxxWWVoASMFmgYkAAeRJTInN3ymj4d-jSCeNsMq-wuoPaOltigAKoASgAywhK7SbGQZIIz5VWCFzSeCrZagNYbChbHaxUDcCjJZLfSDbExIAgUdxkUBIursJzCFJtXydajBVDtUAAMXgGAAvKAAJIKMgMaTuAA8glQlE4zAAfKAAD5MllszmcdiIaTffkAbmCyS4sHqjTQZDwFTIrLwVLYiAAFMlaflqbSAJSgADeihKJXcNAAjqatTquTzhoKRa6mBzJdLZaAGT68AFkvqjRaFQBfRXK1WZDXEBZ1SPwU00+CWm12tyQJ0u7W+7m8gXCypFvB+qUysiChkAbQCzeN8AAujHgiocM0PGQvIh4H02RwaF83GZmOwGMxIPxYNB1IkR3oRF4AEQAUVWDEQC3066S2PX4AcqAA5MIAHKQCTroIqADyXzI70Ec60+auqEcClc0jwUAnEHHRhiwfQUAQRBoWES5xwkIdohEAwOGxFMWDYLhuCCEogA

### 💻 Code

```ts
type Foo = Iterable | Iterable;

function tryArrayFrom(foo: Foo) {
let q: Array | Array = Array.from(foo);
}

function trySplat(foo: Foo) {
let q: Array | Array = [...foo];
}
```

### 🙁 Actual behavior

_for tryArrayFrom_
No overload matches this call.
Overload 1 of 4, '(iterable: Iterable | ArrayLike): string[]', gave the following error.
Argument of type 'Foo' is not assignable to parameter of type 'Iterable | ArrayLike'.
Type 'Iterable' is not assignable to type 'Iterable | ArrayLike'.
Type 'Iterable' is not assignable to type 'Iterable'.
The types returned by '[Symbol.iterator]().next(...)' are incompatible between these types.
Type 'IteratorResult' is not assignable to type 'IteratorResult'.
Type 'IteratorYieldResult' is not assignable to type 'IteratorResult'.
Type 'IteratorYieldResult' is not assignable to type 'IteratorYieldResult'.
Type 'number' is not assignable to type 'string'.
Overload 2 of 4, '(arrayLike: ArrayLike): (string | number)[]', gave the following error.
Argument of type 'Foo' is not assignable to parameter of type 'ArrayLike'.
Property 'length' is missing in type 'Iterable' but required in type 'ArrayLike'.

_for trySplat_
Type '(string | number)[]' is not assignable to type 'string[] | number[]'.
Type '(string | number)[]' is not assignable to type 'string[]'.
Type 'string | number' is not assignable to type 'string'.
Type 'number' is not assignable to type 'string'.

### 🙂 Expected behavior

Array.from a union of Iterables should return a union of Arrays.

### Additional information about the issue

_No response_

首先在链接的 TypeScript Playground 中重现两个示例，并比较已声明的 Array.from 重载与展开行为。调查 Iterable 和 Iterable 的联合类型是如何推断的，然后确定现有的类型系统机制是否能够在不引入新语法的情况下生成 Array | Array。当两个示例都能以预期的联合类型通过类型检查，并且涵盖相关回归时，即视为完成。

由索引模型根据 Issue 内容生成。