fix(js): Fix comment placement in empty function params by sorafujitani · Pull Request #18482 · prettier/prettier

sorafujitani · 2025-12-14T11:45:19Z

Description

Fixes an issue where comments in empty function parameters were incorrectly moved after the fat arrow operator (=>) or into the function body.

The problem was caused by handleCommentInEmptyParens not being included in handleOwnLineComment. When a comment is on its own line inside empty parameters, it was processed by handleOwnLineComment, but since handleCommentInEmptyParens was only in handleRemainingComment, the comment was incorrectly attached to the function body as a leading comment.

Additionally, handleLastFunctionArgComments was being evaluated before the empty params case, causing it to match and move the comment to the function body.

Example:

Input:

(
  // foo
) => {}

Before fix:

() =>
  // foo
  {};

After fix:

(
  // foo
) => {};

Solution:

Added handleCommentInEmptyParens to handleOwnLineComment before handleLastFunctionArgComments
Added formatting logic to preserve line breaks for line comments while keeping block comments inline

Changes

src/language-js/comments/handle-comments.js: Added handleCommentInEmptyParens to handleOwnLineComment, added condition to exclude comments in return value parentheses
src/language-js/print/function-parameters.js: Added formatting for dangling line comments with proper indentation and line breaks

Checklist

I've added tests to confirm my change works.
(If changing the API or CLI) I've documented the changes I've made (in the docs/ directory).
(If the change is user-facing) I've added my changes to changelog_unreleased/javascript/18482.md file following changelog_unreleased/TEMPLATE.md.
I've read the contributing guidelines.

Fixes #18208

pkg-pr-new · 2025-12-14T11:46:52Z

Open in StackBlitz

yarn add https://pkg.pr.new/@prettier/plugin-hermes@18482.tgz

yarn add https://pkg.pr.new/@prettier/plugin-oxc@18482.tgz

yarn add https://pkg.pr.new/prettier@18482.tgz

commit: f1a7472

netlify · 2025-12-14T11:46:57Z

✅ Deploy Preview for prettier ready!

Built without sensitive environment variables

Name	Link
🔨 Latest commit	`73e0a08`
🔍 Latest deploy log	https://app.netlify.com/projects/prettier/deploys/693ea352de6e2f00086f3d55
😎 Deploy Preview	https://deploy-preview-18482--prettier.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

To edit notification comments on pull requests, go to your Netlify project configuration.

netlify · 2025-12-14T11:48:17Z

✅ Deploy Preview for prettier ready!

Built without sensitive environment variables

Name	Link
🔨 Latest commit	`276491e`
🔍 Latest deploy log	https://app.netlify.com/projects/prettier/deploys/693ea36f6f00fb0008f07281
😎 Deploy Preview	https://deploy-preview-18482--prettier.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

To edit notification comments on pull requests, go to your Netlify project configuration.

netlify · 2025-12-14T11:50:35Z

✅ Deploy Preview for prettier ready!

Built without sensitive environment variables

Name	Link
🔨 Latest commit	`f1a7472`
🔍 Latest deploy log	https://app.netlify.com/projects/prettier/deploys/6953c121440e5c000814bfd7
😎 Deploy Preview	https://deploy-preview-18482--prettier.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

To edit notification comments on pull requests, go to your Netlify project configuration.

fisker · 2025-12-29T12:08:39Z

src/language-js/print/function-parameters.js

-          ) === ")",
-      }),
+      danglingComments,
+      hasDanglingLineComment && danglingComments ? softline : "",


I don't think this change is need.

@fisker
tested removing these changes, but the tests fail
without them. The indent and softline additions are necessary to:

Properly indent line comments in empty params: (// foo\n) => {} → (\n // foo\n) => {}

Add line break after comments

#18540 should already fixed it.

@fisker

#18540 corrected the detection logic, but printer-side changes still appear to be necessary.

Problem description: By default, printDanglingComments doesn't perform indentation. For line comments within empty parameters, you must explicitly set indent: true:

// Without using indentation options printDanglingComments(path, options, { filter }) // Output result: (// foo) => {} ❌ Syntax error // With indentation option set to true printDanglingComments(path, options, { filter, indent: true }) // Output result: // // foo // ) => {} ✅ Correct syntax

Explanation for why these changes are needed:

indent: hasDanglingLineComment - Enables indentation only for line comments

softline - Inserts a newline after the comment to ensure the closing parenthesis ) appears on the next line

For block comments, these changes aren't necessary as they work correctly without them: (/* foo */) => {} ✅

Test case: tests/format/js/comments/function/empty-params-with-comment.js

✅ Passes when changes are applied

❌ Fails when changes are omitted (line comments remain unindented)

fisker · 2025-12-29T12:09:00Z

src/language-js/comments/handle-comments.js

+      // Make sure comment is before the function body (not in return value parentheses)
+      (!("body" in enclosingNode) ||
+        !enclosingNode.body ||
+        locStart(comment) < locStart(enclosingNode.body))) ||


Removed the redundant !("body" in enclosingNode) check
b5a97d9

@fisker
Removing !("body" in enclosingNode) causes lint errors
since some nodes (e.g., TSCallSignatureDeclaration) don't have a body property. It's
needed as a type guard.

this commit adds type guards
038a62c

We don't check body since isInArgumentOrParameterParentheses already fixed the logic.

81b7e66
fixed

fisker · 2025-12-30T04:25:49Z

Please add tests for your changes.

sorafujitani · 2025-12-30T05:06:15Z

変更内容に対するテストケースを追加してください。

added
d80ce0a

sorafujitani added 3 commits December 14, 2025 20:41

fix(js): handle own-line comments in empty function params

df0c5a3

fix(js): preserve line breaks for line comments in empty params

73e0a08

docs: add changelog for prettier#18482

276491e

Apply automated changes

f081414

fix: add type guard for body property check

6ed24cc

sorafujitani mentioned this pull request Dec 14, 2025

Comment within the arrow function's empty parameters was placed incorrectly after the fat arrow operator #18208

Closed

sorafujitani added 2 commits December 15, 2025 17:39

Merge branch 'main' into feature/cmt--empty-allow-func

57a212a

Merge branch 'main' into feature/cmt--empty-allow-func

a0c9ec1

fisker reviewed Dec 29, 2025

View reviewed changes

sorafujitani and others added 2 commits December 30, 2025 13:18

refactor: simplify handle-comments condition

b5a97d9

Apply automated changes

614c639

sorafujitani added 2 commits December 30, 2025 13:53

fix: add type guard

038a62c

spec: empty-param-with-comment

d80ce0a

sorafujitani requested a review from fisker December 30, 2025 05:21

sorafujitani added 3 commits December 30, 2025 14:21

Merge branch 'main' into feature/cmt--empty-allow-func

ca4e0a4

fix: cmt exp

81b7e66

Merge branch 'main' into feature/cmt--empty-allow-func

f1a7472

fisker mentioned this pull request Jan 13, 2026

Fix dangling comment print in function parameters #18623

Merged

4 tasks

fisker closed this in #18623 Jan 13, 2026

Uh oh!

Conversation

sorafujitani commented Dec 14, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Description

Changes

Checklist

Uh oh!

pkg-pr-new bot commented Dec 14, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

netlify bot commented Dec 14, 2025

✅ Deploy Preview for prettier ready!

Uh oh!

netlify bot commented Dec 14, 2025

✅ Deploy Preview for prettier ready!

Uh oh!

netlify bot commented Dec 14, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

✅ Deploy Preview for prettier ready!

Uh oh!

fisker Dec 29, 2025

Choose a reason for hiding this comment

Uh oh!

sorafujitani Dec 30, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

fisker Dec 30, 2025

Choose a reason for hiding this comment

Uh oh!

sorafujitani Dec 30, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

fisker Dec 29, 2025

Choose a reason for hiding this comment

Uh oh!

sorafujitani Dec 30, 2025

Choose a reason for hiding this comment

Uh oh!

sorafujitani Dec 30, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

fisker Dec 30, 2025

Choose a reason for hiding this comment

Uh oh!

sorafujitani Dec 30, 2025

Choose a reason for hiding this comment

Uh oh!

fisker commented Dec 30, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

sorafujitani commented Dec 30, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

sorafujitani commented Dec 14, 2025 •

edited

Loading

pkg-pr-new bot commented Dec 14, 2025 •

edited

Loading

netlify bot commented Dec 14, 2025 •

edited

Loading

sorafujitani Dec 30, 2025 •

edited

Loading

sorafujitani Dec 30, 2025 •

edited

Loading

sorafujitani Dec 30, 2025 •

edited

Loading

fisker commented Dec 30, 2025 •

edited

Loading

sorafujitani commented Dec 30, 2025 •

edited

Loading