fix(formatter): switch case comments by ematipico · Pull Request #9303 · biomejs/biome

ematipico · 2026-03-02T21:20:54Z

Summary

Closes #2786

Found the fix with AI

Test Plan

Added a test

Docs

changeset-bot · 2026-03-02T21:20:58Z

🦋 Changeset detected

Latest commit: c43e45d

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

This PR includes changesets to release 13 packages

Name	Type
@biomejs/biome	Patch
@biomejs/cli-win32-x64	Patch
@biomejs/cli-win32-arm64	Patch
@biomejs/cli-darwin-x64	Patch
@biomejs/cli-darwin-arm64	Patch
@biomejs/cli-linux-x64	Patch
@biomejs/cli-linux-arm64	Patch
@biomejs/cli-linux-x64-musl	Patch
@biomejs/cli-linux-arm64-musl	Patch
@biomejs/wasm-web	Patch
@biomejs/wasm-bundler	Patch
@biomejs/wasm-nodejs	Patch
@biomejs/backend-jsonrpc	Patch

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coderabbitai · 2026-03-02T21:25:31Z

Walkthrough

This pull request addresses an idempotence issue in the JavaScript formatter where trailing line comments after case clauses were causing unstable output across multiple formatting passes. The fix introduces a conditional guard in the case clause formatter to prevent block statement hugging when a trailing comment follows the case colon. Changes include updates to the case clause formatter logic, new test coverage for switch statements with inline trailing comments, and documentation via a changeset file.

Suggested labels

A-Formatter, L-JavaScript

Suggested reviewers

dyc3

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'fix(formatter): switch case comments' directly addresses the main change—fixing formatter idempotence for switch case comments.
Description check	✅ Passed	The description references the linked issue `#2786`, discloses AI assistance, and mentions a test was added, all relevant to the changeset.
Linked Issues check	✅ Passed	The PR implementation aligns with issue `#2786` objectives: adds a guard to prevent comment dissociation, ensures idempotent formatting of switch case comments, and includes a test case.
Out of Scope Changes check	✅ Passed	All changes (formatter logic, test cases, and changeset documentation) are directly scoped to fixing switch case comment idempotence per issue `#2786`.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

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📝 Generate docstrings (commit on current branch)

🧪 Generate unit tests (beta)

Create PR with unit tests
Post copyable unit tests in a comment
Commit unit tests in branch fix/idempotence-switch-ase

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coderabbitai

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In @.changeset/fix-switch-case-comment-idempotence.md:
- Line 5: Update the changeset body in
.changeset/fix-switch-case-comment-idempotence.md to include a before/after
formatter diff code block showing the concrete visible change (use a unified
diff-style snippet); insert a fenced code block (```diff) containing the
original lines (prefixed with -) and the formatted lines (prefixed with +) —
e.g., show the "-case 1337: {", "-  // ELITE", "-  console.log(\"x is cool\");",
"-}" and the corresponding "+case 1337: // ELITE", "+{", "+  console.log(\"x is
cool\");", "+}" lines — so users can see the exact formatting change.

ℹ️ Review info

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 1003229 and f583ef5.

⛔ Files ignored due to path filters (1)

crates/biome_js_formatter/tests/specs/js/module/statement/switch_comment.js.snap is excluded by !**/*.snap and included by **

📒 Files selected for processing (4)

.changeset/fix-switch-case-comment-idempotence.md
crates/biome_js_formatter/src/js/auxiliary/case_clause.rs
crates/biome_js_formatter/tests/quick_test.rs
crates/biome_js_formatter/tests/specs/js/module/statement/switch_comment.js

coderabbitai · 2026-03-02T21:25:34Z

.changeset/fix-switch-case-comment-idempotence.md

+"@biomejs/biome": patch
+---
+
+Fixed [#2786](https://github.com/biomejs/biome/issues/2786): The formatter no longer produces different output on subsequent runs when a `case` clause has a trailing line comment followed by a single block statement.


⚠️ Potential issue | 🟡 Minor

Add a tiny before/after formatter diff in the changeset body.

Nice summary, but this formatter fix should include a concrete formatting diff so users can see the visible behaviour change at a glance.

Suggested changeset snippet

Fixed [`#2786`](https://github.com/biomejs/biome/issues/2786): The formatter no longer produces different output on subsequent runs when a `case` clause has a trailing line comment followed by a single block statement. +```diff +-case 1337: { +- // ELITE ++case 1337: // ELITE ++{ + console.log("x is cool"); + } +```

As per coding guidelines: for formatter changes in changesets, show formatting changes using diff code blocks.

📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change

Fixed [#2786](https://github.com/biomejs/biome/issues/2786): The formatter no longer produces different output on subsequent runs when a `case` clause has a trailing line comment followed by a single block statement.

---

package: `@biomejs/biome`

type: patch

---

Fixed [`#2786`](https://github.com/biomejs/biome/issues/2786): The formatter no longer produces different output on subsequent runs when a `case` clause has a trailing line comment followed by a single block statement.

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed. In @.changeset/fix-switch-case-comment-idempotence.md at line 5, Update the changeset body in .changeset/fix-switch-case-comment-idempotence.md to include a before/after formatter diff code block showing the concrete visible change (use a unified diff-style snippet); insert a fenced code block (```diff) containing the original lines (prefixed with -) and the formatted lines (prefixed with +) — e.g., show the "-case 1337: {", "- // ELITE", "- console.log(\"x is cool\");", "-}" and the corresponding "+case 1337: // ELITE", "+{", "+ console.log(\"x is cool\");", "+}" lines — so users can see the exact formatting change.

codspeed-hq · 2026-03-02T21:34:59Z

Merging this PR will not alter performance

✅ 58 untouched benchmarks
⏩ 156 skipped benchmarks¹

_{Comparing fix/idempotence-switch-ase (c43e45d) with main (3bc07ab)}

156 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

dyc3

👍

dyc3 · 2026-03-02T21:36:52Z

crates/biome_js_formatter/tests/quick_test.rs

revert quick test

ematipico requested review from a team March 2, 2026 21:21

github-actions bot added A-Formatter Area: formatter L-JavaScript Language: JavaScript and super languages labels Mar 2, 2026

coderabbitai bot reviewed Mar 2, 2026

View reviewed changes

dyc3 approved these changes Mar 2, 2026

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crates/biome_js_formatter/tests/quick_test.rs

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revert quick test

fix(formatter): switch case comments

c43e45d

ematipico force-pushed the fix/idempotence-switch-ase branch from f583ef5 to c43e45d Compare March 2, 2026 22:00

ematipico merged commit 464910c into main Mar 2, 2026
15 of 16 checks passed

ematipico deleted the fix/idempotence-switch-ase branch March 2, 2026 22:01

github-actions bot mentioned this pull request Mar 2, 2026

ci: release #9301

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fix(formatter): switch case comments#9303

fix(formatter): switch case comments#9303
ematipico merged 1 commit intomainfrom
fix/idempotence-switch-ase

ematipico commented Mar 2, 2026

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-Fixed [#2786](https://github.com/biomejs/biome/issues/2786): The formatter no longer produces different output on subsequent runs when a `case` clause has a trailing line comment followed by a single block statement.
+---
+package: `@biomejs/biome`
+type: patch
+---
+Fixed [`#2786`](https://github.com/biomejs/biome/issues/2786): The formatter no longer produces different output on subsequent runs when a `case` clause has a trailing line comment followed by a single block statement.

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ematipico commented Mar 2, 2026

Summary

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🦋 Changeset detected

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coderabbitai bot commented Mar 2, 2026

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codspeed-hq bot commented Mar 2, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Merging this PR will not alter performance

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changeset-bot bot commented Mar 2, 2026 •

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