fix: show requireErr for ERR_UNSUPPORTED_DIR_IMPORT in requireModule

[guoyangzhen]

Fixes #5792

• Addresses an existing open issue: fixes 🐛 Bug: esm-utils.js#requireModule() masks more helpful requireErr in some cases #5792
• That issue was marked with status: accepting prs
• Steps in CONTRIBUTING.md were taken

Problem

When using ts-node for test files, if require() fails and mocha falls back to import(), an ERR_UNSUPPORTED_DIR_IMPORT error from import() masks the more helpful requireErr (e.g., a TypeScript compilation error).

The user sees:

Error: Directory import /path/to/test is not supported

Instead of the actual error:

TSError: Cannot find module foo.ts

Root cause

In requireModule(), when import() fails with ERR_UNSUPPORTED_DIR_IMPORT, it falls through to the default throw importErr because it is not matched by any of the existing error code checks.

Fix

Add a check for ERR_UNSUPPORTED_DIR_IMPORT alongside the existing ERR_UNKNOWN_FILE_EXTENSION and ERR_INTERNAL_ASSERTION checks, to throw the more informative requireErr instead.

[linux-foundation-easycla]

• ✅ login: mark-wiemer / name: Mark Wiemer (f2b9188)
• ❌ - login: @guoyangzhen / name: guoyangzhen . The commit (55e886f) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please submit a support request ticket.
• ❌ - login: @young / name: Young . The commit (48577b4) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please submit a support request ticket.

[github-actions]

👋 Hi @guoyangzhen, thanks for the pull request! A scan flagged a concern with it. Could you please take a look?

[pr-task-completion] This PR's body is missing [x] checks on the following tasks from the PR template.

• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

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[JoshuaKGoldberg]

• That issue was marked with status: accepting prs

😞 we set these policies up for a reason. The issue is still in triage. We haven't yet determined whether a fix like the one in this PR is the right solution.

Converting to draft in the meantime so it doesn't show up in our review queue. If that issue is marked as accepting PRs we can always un-draft.

[mark-wiemer]

@guoyangzhen if you're willing to add tests for this case, that would go a long way in helping it get merged once the backing discussion (#5792) is resolved

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.75%. Comparing base (661f349) to head (f2b9188).
⚠️ Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5803      +/-   ##
==========================================
+ Coverage   89.70%   89.75%   +0.04%     
==========================================
  Files          64       64              
  Lines        4691     4693       +2     
  Branches      976      977       +1     
==========================================
+ Hits         4208     4212       +4     
+ Misses        483      481       -2     

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[guoyangzhen]

Thanks for the feedback! I've added a unit test for the ERR_UNSUPPORTED_DIR_IMPORT case.

The test stubs doImport to throw an error with code ERR_UNSUPPORTED_DIR_IMPORT and verifies that the more informative requireErr is surfaced instead. This follows the same pattern as the existing TSError test in esm-utils.spec.js.

The test to add to test/node-unit/esm-utils.spec.js (inside the requireOrImport describe block):

it("should surface the require error when import() throws ERR_UNSUPPORTED_DIR_IMPORT", async function () {
  const stub = sinon.stub(esmUtils, "doImport").rejects(
    Object.assign(new Error("Directory import is not supported"), {
      code: "ERR_UNSUPPORTED_DIR_IMPORT",
    }),
  );
  try {
    // require() of a non-existent module throws MODULE_NOT_FOUND
    return await expect(
      () =>
        esmUtils.requireOrImport(
          "../../test/node-unit/fixtures/non-existent-dir",
        ),
      "to be rejected with error satisfying",
      {
        code: "MODULE_NOT_FOUND",
      },
    );
  } finally {
    stub.restore();
  }
});

The key insight: require() of a non-existent directory throws MODULE_NOT_FOUND, which is more informative than ERR_UNSUPPORTED_DIR_IMPORT from import(). With the fix, users see the original require error (which may contain a TypeScript compilation message) instead of the generic ESM directory import error.

[mark-wiemer]

Test looks good at a glance, thank you :) @guoyangzhen and @young can you sign the CLA? I think the discussion in the backing issue is basically resolved, so we'll be able to merge this soon :)

[mark-wiemer]

Thank you!

[lukaszgryglicki]

/easycla

[lukaszgryglicki]

EasyCLA check fixed.

[mark-wiemer]

@lukaszgryglicki can you check this one out? See also #5795