Bug(typescript-estree): always parse mts/mjs as ESM for non-type-aware parsing

[fisker]

Before You File a Bug Report Please Confirm You Have Done The Following...

• I have tried restarting my IDE and the issue persists.
• I have updated to the latest version of the packages.
• I have searched for related issues and found none that matched my issue.
• I have read the FAQ and my problem is not listed.

Relevant Package

typescript-estree

Playground Link

No response

Repro Code

import { parse } from "@typescript-eslint/typescript-estree"

const ast = parse('await(1)', {
  project: false,
  filePath: 'foo.mts'
})

console.log(ast.body[0].expression)

ESLint Config

N/A

tsconfig

None

Expected Result

The expression should be AwaitExpression instead of CallExpression.

Actual Result

As described above.

Additional Info

No response

Versions

package	version
@typescript-eslint/typescript-estree	7.8.0
TypeScript	5.4.5
node	20

[JoshuaKGoldberg]

Editing the title because it took me a moment to figure this out. 😄

[goldentrash]

I tried to fix this issue! See #9121.
Below is a screenshot of the result.

• If the file is ESM
  

• If the file is not ESM
  

[github-actions]

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[goldentrash]

In /tyscript-estree/src/convert.ts/Converter/convertNode, modifying sourceType when it is case SyntaxKind.SourceFile does not make sense, below is the detail.

I tried modifying the sourceFile in convertNode with extension === ts.Extension.Mjs || extension === ts.Extension.Mts, but only the AST root (SourceFile) is changed, not the multiple child Nodes.

It appears that before convertNode is called, the ts AST is fully constructed via ts.createSourceFile and then changed to the estree AST via convertNode.

[goldentrash]

In /tyscript-estree/src/create-program/createSourceFile.ts/createSourceFile, adjusting setExternalModuleIndicator, parameter of the ts.createSourceFile, doesn't make sense, below is the detail.

First, I checked how typescript's default setExternalModuleIndicator works.

1. Traverses all expressions in the source code.
2. Find ESM expressions like export.
3. Returns that Node.
4. If no nodes were found, it returns the metadata node of the SourceFile.

The default setExternalModuleIndicator is inappropriate because the intent is to parse ESM files as ESM, even if they don't have an ESM expression like export.

However, I think it would be difficult to create a proper metadata node and insert it into the SourceFile, and it would rely too strongly on an external module (typescript).

[goldentrash]

In /tyscript-estree/src/create-program/createSourceFile.ts/createSourceFile, adjusting impliedNodeFormat, parameter of the ts.createSourceFile, doesn't work, below is the detail.

The Interface annotation says "Controls the format the file is detected as", so I was expecting that, but modifying the impliedNodeFormat didn't achieve the desired result. It seems to be a parameter related to js Emit, not AST construction.