Support pure ESM with TypeScript

[chasingmaxwell]

I'm migrating a TypeScript project to output pure ESM. As part of that effort, I need to update every import which was previously extensionless, to specify a ".js" extension (even though the file in the source directory has a ".ts" extension). Like this:

// old way
import aThing from '../a/module';

// new way
import aThing from '../a/module.js';

It seems like unimported is unable to determine that ../a/module.js should be resolved to ../a/module.ts and so it reports almost all files as being unimported.

I've been referencing this guide for the migration to pure ESM.

[smeijer]

I think resolve always tries to resolve the import using the path + one of the allowed extensions. To support this case, we might need to check for the direct import first, before we pass the path to resolve.

Maybe we can add something right before the fallback:

unimported/src/traverse.ts

Lines 141 to 145 in b849105

	// if nothing else works out :(
	return {
	type: 'unresolved',
	path: path,
	};

// scratch / pseudo
try {
  const extension = config.extension.find(extension => path.endsWith(extension));
  if (extension) {
    return {
      type: 'source_file',
      path: resolve.sync(path.slice(0, -extension.length), {
        basedir: cwd,
        extensions: [extension],
        moduleDirectory: config.moduleDirectory,
      }).replace(/\\/g, '/'),
    }
  }
} catch (e) {}

[chasingmaxwell]

Looks like we'll have to add that in a few places though if we want it to work with aliases and module-relative paths as well.

[chasingmaxwell]

I could see it being applied to all relative paths across the board, but enabled with config. Either in a very targeted way with "esm": true or maybe more open-ended with regex path transformations or something "pathTransforms": { "/\.js/", ".ts" }.

[smeijer]

I'm curious if it would "just work" if we were to add an empty extension to the array. Like ['.js', '.tsx', '']

[chasingmaxwell]

When I tried that I received a "Failed parsing util" error message with exit code 1.

[chasingmaxwell]

I have it working for my project with an added pathTransforms config property. If that sounds good to you, I can create a pull request.

[smeijer]

A pull would be sweet! Thanks.

[chasingmaxwell]

I created the PR. A couple notes about tests:

1. I could not get all the tests to pass locally (even on the main branch with no changes). It seems there might be a compatibility issue with my environment.
2. I did not create any new tests. It was unclear to me where the test should be added. Maybe just a new scenario to the cli integration tests? If you can provide some guidance there I'll add a test for handling the new configuration property.

[chasingmaxwell]

Here's a PR to fix the build/test failures I was seeing on the main branch: #69

[chasingmaxwell]

I've also added a test for the pathTransforms config in my PR #67

[chasingmaxwell]

@smeijer thank you for merging #69 (and sorry I never got back around to addressing your feedback). Now the checks for #67 are passing. If that's good to merge it'll close out this issue.

[smeijer]

🎉 This issue has been resolved in version 1.23.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[maclockard]

Ran into an issue using this solution with .tsx, filed here: #163