feat: implement autofix for sort-keys

[Pixel998]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request?

This PR enables autofix for the sort-keys rule so objects with unsorted keys are automatically reordered when running with --fix.

What changes did you make? (Give an overview)

• Added a fixer that reorders object keys.
• Updated tests.

Related Issues

Fixes #122

Is there anything you'd like reviewers to focus on?

[Copilot]

Pull Request Overview

This PR implements autofix functionality for the sort-keys ESLint rule, allowing objects with unsorted keys to be automatically reordered when running with the --fix option.

• Adds autofix capability to the sort-keys rule by marking it as fixable: "code"
• Implements a sorting algorithm that respects existing configuration options (asc/desc, case sensitivity, natural sorting, line-separated groups)
• Updates comprehensive test coverage with expected output for all invalid test cases

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/rules/sort-keys.js	Adds fixable metadata and implements autofix logic with key comparison and object reconstruction
tests/rules/sort-keys.test.js	Adds expected output assertions for all invalid test cases to verify autofix behavior

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[Copilot]

The comment detection logic should be documented to explain why autofix is disabled when comments are present within the object, as this might not be obvious to maintainers.

[mdjermanovic]

This aims to sort the entire object at once, not just the reported property?

[Zamiell]

@Pixel998 Are you still working on this PR?

[nzakas]

@Pixel998 are you still working on this?

[Pixel998]

Yes, I was focused on v10 work, but now that's complete I'm picking this up again.

[Pixel998]

I've implemented an autofixer for our sort-keys rule, but we need to decide how to handle comments in JSONC/JSON5 files.

Currently, when we autofix, we swap members but leave any comments in their original positions. This means that after sorting, comments can end up describing the wrong properties, which breaks documentation.

For example, consider this JSONC before sorting:

{
  // Port number for connections
  "port": 3000,
  // Database configuration
  "host": "localhost"
}

After our autofix sorts alphabetically, the members swap but the comments stay:

{
  // Port number for connections
  "host": "localhost",  // WRONG: This comment now describes the host
  // Database configuration  
  "port": 3000  // WRONG: This comment now describes the port
}

We have a few options:

1. Keep current behavior - Accept that comments become misleading after sorting
2. Don't autofix when comments are present - Safe but limits usefulness
3. Swap members with their attached comments - Preserves documentation but complex to implement

@eslint/eslint-team, what are your thoughts on this?

[DMartens]

I agree with Pixel998 that comments should also be moved together with the property (option 3).
But there are two additional design choices:

1. Which comments are included? I would say comments directly above the key (which are on their own line) and trailing comments, so:

{
	// INCLUDED
	"key": "value", // INCLUDED 
}

2. Should we fallback to using suggestions if there is an attached comment or only certain scenarios based on the comment location?

[lumirlumir]

TSC Summary: The blocker for this PR is deciding how to handle comments in JSONC/JSON5 files when auto-fixing sorting. There is currently no definitive team consensus on this change.

TSC Question: Which option should we choose from the following, and what common design convention was used when implementing auto-fix in JavaScript rules such as sort-vars or sort-imports?

1. Keep current behavior - Accept that comments become misleading after sorting
2. Don't autofix when comments are present - Safe but limits usefulness
3. Swap members with their attached comments - Preserves documentation but complex to implement

[sethamus]

@Pixel998, still working on this one? Happy to take it if not.

[mdjermanovic]

In the 2026-01-08 TSC meeting, we agreed to option 2 - don't autofix when comments are present.

https://github.com/eslint/tsc-meetings/blob/main/notes/2026/2026-01-08.md#pr-136-implement-autofix-for-sort-keys-in-eslintjson

[Pixel998]

@sethamus Thanks for checking in. I’m currently busy with other work, so please feel free to take it.