Add proper file extensions when importing a typescript file from a typescript file

[rosskevin]

Problem

Given this configuration:

{
    "n/file-extension-in-import": ["error", "always"]
}

and file1.ts

import something from "./file2"

eslint will fix this with a .ts added to the import statement, which is invalid and breaks the compilation of typescript.

Solution

When a typescript file (.ts / .cts / .mts files, .cts and .mts have been supported since TypeScript 4.5) imports another typescript file, eslint will now use the proper matching file extension instead of the original referenced file extension.

This means that, for example, when a .ts file imports another .ts file, eslint will now suggest using a .js extension in the import statement.

Release

As far as I can tell, this should be good to release as a patch.

Credit

Mostly cherry-picked from https://github.com/giladgd/eslint-plugin-node/tree/dev/giladgd/fixImportExtentionFixingInTypeScript and lingering PR mysticatea#303

Thanks @giladgd

[rosskevin]

@aladdin-add I don't want to be pushy, but any chance of a quick turnaround release? I'm migrating a huge codebase and struggling without this (and my private package attempts are currently failing on my private namespace).

[aladdin-add]

can you add a few invalid tests to verify the fixer(output)?

[aladdin-add]

LGTM, I'll just cut a release - the new added tests can be landed in another PR. :)

[aladdin-add]

released in https://github.com/weiran-zsd/eslint-plugin-node/releases/tag/15.2.1 🎉

[calebeby]

@aladdin-add This behavior works in 15.2.1 but does not work in 15.2.2. In 15.2.2, the .ts extension is inserted in a TS file importing another TS file instead of inserting a .js extension. I think #24 broke this behavior.

cc @rosskevin

[rosskevin]

I'm looking at it now. I thought I added the proper valid tests but it doesn't look like it (or I just got mixed up in the process).