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:

1. Added handleCommentInEmptyParens to handleOwnLineComment before handleLastFunctionArgComments
2. 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