fix(cli): do not crash on no rules configured

[silvenon]

In the case when a flat config has no rules defined, the resolved config for a file is undefined.

// eslint.config.js
export default [{}]

This causes the CLI utility to fail to destructure rules out of it:

❯ npx eslint-config-prettier src/utils/toast.tsx
Cannot destructure property 'rules' of 'undefined' as it is undefined.

and it's also necessary to initialize rules as well, because Object.entries(undefined) is an error.

This will achieve the same behavior as a legacy configuration:

// .eslintrc.cjs
module.exports = {}

❯ npx eslint-config-prettier src/utils/toast.tsx
No rules that are unnecessary or conflict with Prettier were found.

Fixes #288.

---

Important

Fixes CLI crash in bin/cli.js by setting default rules = {} for flat configs with no rules, ensuring consistent behavior with legacy configurations.

• Behavior:
  • Fixes CLI utility crash in bin/cli.js when flat config has no rules defined by setting default rules = {} during destructuring.
  • Ensures consistent behavior with legacy configuration by outputting "No rules that are unnecessary or conflict with Prettier were found." when no rules are present.
• Misc:
  • Fixes [CLI] Handle undefined computed config #288.

^{This description was created by for 0b82629. You can customize this summary. It will automatically update as commits are pushed.}

Summary by CodeRabbit

Summary by CodeRabbit

• Bug Fixes
  • Improved stability by preventing potential errors when configuration objects or their properties are missing.
  • Ensured the CLI runs smoothly even with empty or missing configuration files.

[changeset-bot]

🦋 Changeset detected

Latest commit: cd29dcb

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
eslint-config-prettier	Patch

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Click here if you're a maintainer who wants to add another changeset to this PR

[coderabbitai]

Walkthrough

The change updates the destructuring of the rules property from configuration objects within the CLI script. It now safely handles cases where the configuration object or its rules property might be undefined by providing default empty objects, preventing runtime errors when accessing rules on undefined configurations. A new test verifies the CLI runs without error when given an empty config.

Changes

File(s)	Change Summary
bin/cli.js	Modified destructuring of rules from config objects to provide default empty objects for safety.
test/cli.test.js	Added a test case "empty config" that runs the CLI against an empty config fixture to ensure no runtime error.
test/fixtures/empty-config/eslint.config.mjs	Added a new empty ESLint config exporting a default array with a single empty object.
.changeset/lazy-dingos-cheat.md	Added a changeset documenting a patch update fixing CLI crash when no rules are configured.

Assessment against linked issues

Objective	Addressed	Explanation
Handle undefined computed config in CLI, ensuring no runtime failure (#288)	✅

Poem

A hop and a skip, with configs in tow,
No more undefined, the errors won't show.
With empty objects, we safely proceed,
The CLI now handles each config's need.
🐇✨ Bugs are out, and all is right—
Hopping along with code so bright!

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[ellipsis-dev]

Important

Looks good to me! 👍

Reviewed everything up to 0b82629 in 30 seconds. Click for details.

• Reviewed 13 lines of code in 1 files
• Skipped 0 files when reviewing.
• Skipped posting 2 draft comments. View those below.
• Modify your settings and rules to customize what types of comments Ellipsis leaves. And don't forget to react with 👍 or 👎 to teach Ellipsis.

1. bin/cli.js:63

• Draft comment:
  Good use of destructuring with a default. This change ensures that if a config is undefined, 'rules' defaults to an empty object, avoiding errors when calling Object.entries().
• Reason this comment was not posted:
  Confidence changes required: 0% <= threshold 50% None

2. bin/cli.js:63

• Draft comment:
  Good fix: defaulting 'rules' to {} prevents the destructuring error. Consider adding an inline comment referencing issue #288 to document why we use this fallback.
• Reason this comment was not posted:
  Confidence changes required: 0% <= threshold 50% None

Workflow ID: wflow_p2ecqH4CC3QoYznk

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[silvenon]

I didn't find an (easy) way to incorporate this into tests, I would probably have to mock config files, not sure if it's worth it. Let me know if I missed something.

[JounQin]

I didn't find an (easy) way to incorporate this into tests, I would probably have to mock config files, not sure if it's worth it. Let me know if I missed something.

An e2e test case could be added? And some comments could be added at least.

[silvenon]

Since running the CLI doesn't allow me to specify the config, what kind of an E2E test did you have in mind? What I can do is pass a non-JS file like foo. Legacy configs will still give those the their default config when running npx eslint --print-config foo, while flat configs will be much more strict and apply only to JS extensions.

It would pick up your project's eslint.config.js, but it would still output undefined, which is what's needed. Would that be good enough?

[JounQin]

exec in custom fixture cwd?

[silvenon]

Great idea, done ✅

[coderabbitai]

Actionable comments posted: 0

🧹 Nitpick comments (1)

test/cli.test.js (1)

81-87: Good addition of a test case for empty config scenario.

This test effectively verifies that the CLI doesn't crash when encountering an empty configuration, which directly addresses issue #288 mentioned in the PR objectives. The test runs the CLI script as a child process against a fixture with an empty config and implicitly checks that no error occurs.

A few suggestions to strengthen this test:

1. Consider asserting the expected CLI output (should be "No rules that are unnecessary or conflict with Prettier were found.")
2. Add a comment explaining what the test is checking and its relationship to issue #288

test("empty config", (done) => {
+  // Verifies that the CLI doesn't crash with empty configs (issue #288)
+  // The fixture contains an eslint.config.mjs that exports [{}]
  childProcess.exec(
    `node ${path.join(process.cwd(), "bin/cli.js")} index.js`,
    { cwd: path.join(__dirname, "fixtures/empty-config") },
-    done
+    (error, stdout) => {
+      expect(error).toBeNull();
+      expect(stdout.trim()).toBe("No rules that are unnecessary or conflict with Prettier were found.");
+      done();
+    }
  );
});

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• GitHub Check: Test on windows-latest with Node.js 22
• GitHub Check: Test on windows-latest with Node.js 20
• GitHub Check: Test on windows-latest with Node.js 18
• GitHub Check: Test on windows-latest with Node.js 16

[Copilot]

Copilot encountered an error and was unable to review this pull request. You can try again by re-requesting a review.

[Copilot]

Pull Request Overview

This PR fixes a bug in the CLI where an empty flat configuration (i.e., one with no rules specified) mistakenly caused a crash.

• Fixes CLI crash by defaulting missing rules to an empty object
• Adds a test to verify CLI behavior with an empty configuration
• Updates changeset metadata for the patch release

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

File	Description
test/fixtures/empty-config/eslint.config.mjs	Provides an empty configuration for testing
test/cli.test.js	Adds a test verifying the CLI does not crash with empty config
.changeset/lazy-dingos-cheat.md	Documents the patch release for this bug fix

Comments suppressed due to low confidence (1)

test/cli.test.js:82

• Consider asserting the output message or exit code in the empty config test to ensure that the CLI behavior matches the expected "No rules that are unnecessary or conflict with Prettier were found." message.

test("empty config", (done) => {