[V6] `module` defaults is not `esnext`

@DanielRosenwasser がすでに取り組んでいます。

2026年4月1日 から。

### 🔎 Search Terms

"module", "default", "esnext", "v6"

### 🕗 Version & Regression Information

This changed between versions V5 and V6

### ⏯ Playground Link

This isn't an issue in Playground, because you're required to enter a value for the `module`.

~~https://www.typescriptlang.org/play/?#code/FASwtgDg9gTgLgAgGZSsmUwIEQDoD0KUuAVgM5QB22CA7iHABYIDeCcAnhAKYBcO5KjQC+AbmDAAxlQoAbbrllQA5gAoiASlFA~~

### 💻 Code

- `package.json`

```json
{
"name": "testcase",
"version": "1.0.0",
"type": "module",
"dependencies": {
"typescript": "6.0.2"
}
}
```

- `index.ts`

```ts
import foo from "./foo.json" with { type: "json" };

console.log(foo);
```

1. `npm install`
2. `npc tsc index.ts`

### 🙁 Actual behavior

```
index.ts:1:30 - error TS2823: Import attributes are only supported when the '--module' option is set to 'esnext', 'node18', 'node20', 'nodenext', or 'preserve'.

1 import foo from "./foo.json" with { type: "json" };
~~~~~~~~~~~~~~~~~~~~~
```

### 🙂 Expected behavior

No error because `module` defaults to `esnext`.

### Additional information about the issue

In [_Announcing TypeScript 6.0_](https://devblogs.microsoft.com/typescript/announcing-typescript-6-0/#simple-default-changes), it says _**`module` defaults to `esnext`**: Similarly, the new default `module` is `esnext`, acknowledging that ESM is now the dominant module format._

But in [_TSConfig Reference_](https://www.typescriptlang.org/tsconfig/#module), it's _`CommonJS` if `target` is `ES5`; `ES6`/`ES2015` otherwise._

In the code, I don't think the default value is `esnext`. Otherwise, we wouldn't be getting the TS2823 error.