fix(formatter): preserve newline between self-closing JSX element and single-char text by jsmecham · Pull Request #21149 · oxc-project/oxc

jsmecham · 2026-04-08T00:38:55Z

Summary

When a self-closing JSX element is followed by a newline and text whose first word is a single alphabetic character (e.g. I have another footnote.), the formatter incorrectly treated the newline as a soft break — collapsing it and merging the element and text onto the same line. This is a semantic change: JSX renders newlines between siblings as spaces in the DOM, so removing the newline alters the rendered output.

Input

const App = () => (
  <div>
    I have a footnote.
    <FootnoteRef i18nKey="footnote1" />
    I have another footnote.
    <FootnoteRef i18nKey="footnote2" />
  </div>
);

Before (incorrect)

const App = () => (
  <div>
    I have a footnote.
    <FootnoteRef i18nKey="footnote1" />I have another footnote.
    <FootnoteRef i18nKey="footnote2" />
  </div>
);

After (matches Prettier)

const App = () => (
  <div>
    I have a footnote.
    <FootnoteRef i18nKey="footnote1" />
    I have another footnote.
    <FootnoteRef i18nKey="footnote2" />
  </div>
);

Root cause

In the Newline arm of the JSX child list formatter (child_list.rs), there is a heuristic that treats a newline as a soft break when the next word is a single character. This was designed for the punctuation-connector pattern — e.g. <div>First</div>\n,<div>Second</div> — where a single-char punctuation like , or - connects two JSX elements.

However, the heuristic also fired when the single-character word was the start of a text run followed by more words (e.g. "I" in "I have another footnote."), because it didn't check what followed the single-char word.

Fix

The fix distinguishes between punctuation connectors and alphabetic text starters:

Punctuation (,, ., etc.) → always a soft break, regardless of what follows
Single alphabetic character (I, a, etc.) followed by more words → hard break (text content, semantically significant newline)

Added is_single_alphabetic_character() to JsxWord and updated the soft-break condition to (!is_single_char_alphabetic || !is_next_next_word).

Prettier conformance: no regressions (746/753 JS, 591/601 TS — unchanged).

AI Disclosure

This PR was co-authored with Claude Code (AI assistant), as noted in the commit. The fix was reviewed, tested against the full Prettier conformance suite, and verified to produce no regressions.

codspeed-hq · 2026-04-08T00:44:33Z

Merging this PR will not alter performance

✅ 44 untouched benchmarks
⏩ 7 skipped benchmarks¹

_{Comparing jsmecham:fix/jsx-self-closing-newline-before-single-char-text (3623d2b) with main (c60eea7)}

7 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. ↩

leaysgur

This change seems to introduce new diffs in the following cases.

// single-char punctuation followed by more text after newline
const PunctuationThenText = () => (
  <div>
    <Comp />
    , more text here
  </div>
);

Could you please take a look?

jsmecham · 2026-04-08T14:15:10Z

Good catch, thanks! The original !is_next_next_word guard was too broad — it correctly prevented collapsing I have another footnote. but also incorrectly prevented collapsing , more text here (where , is a punctuation connector, not the start of a text run).

The fix distinguishes the two cases by checking whether the single character is alphabetic:

Punctuation (,, ., etc.) → always a soft break, regardless of what follows
Alphabetic (I, a, etc.) followed by more words → hard break (text content, preserve the newline)

Added is_single_alphabetic_character() to JsxWord and updated the condition accordingly. Also added a test fixture (issue-21149.jsx) covering both cases.

jsmecham · 2026-04-08T15:06:00Z

One additional note on the is_single_alphabetic_character() check: Prettier's separatorNoWhitespace doesn't actually distinguish between alphabetic and punctuation — it uses child.length === 1 uniformly. Our check is our own heuristic on top of that.

char::is_alphabetic() in Rust covers all Unicode letters (including CJK, Arabic, Cyrillic, etc.), so international text starters like 中, ا, А are handled correctly. The gap is non-alphabetic text starters like digits (1 item) or emoji (😀 text), which would still be treated as soft breaks. These seem unlikely enough in real JSX that it's probably fine for now, but worth noting as a known limitation.

leaysgur · 2026-04-09T04:23:09Z

/oxfmt-ecosys

github-actions · 2026-04-09T04:23:18Z

Oxfmt Ecosystem CI

suite	oxfmt@latest	refs/pull/21149/head branch
cnpm/cnpmcore	✅	✅
monkeytypegame/monkeytype	❌	✅
eggjs/egg	✅	✅
actualbudget/actual	❌	✅
fastify/fastify-vite	✅	✅
Comfy-Org/ComfyUI_frontend	✅	✅
vuejs/core	✅	✅
AmanVarshney01/create-better-t-stack	✅	✅
huggingface/huggingface.js	✅	✅
fuma-nama/fumadocs	✅	✅
openclaw/openclaw	❌	✅
mastodon/mastodon	✅	✅
formatjs/formatjs	❌	✅
rolldown/rolldown	✅	✅
aidenybai/react-grab	✅	✅
cloudflare/agents	✅	✅
vuejs/pinia	❌	✅
vercel/turborepo	✅	✅
dyad-sh/dyad	✅	✅
npmx-dev/npmx.dev	✅	✅
tale/headplane	❌	✅
lichess-org/lila	✅	✅
getsentry/sentry-javascript	❌	✅

leaysgur

LGTM w/ minor suggestions:

Please add a brief code comment noting that this alphabetic/punctuation heuristic and how Prettier handles
The two fixture files (issue-21148.jsx and issue-21149.jsx) could be merged into one?

… single-char text

jsmecham · 2026-04-09T13:53:58Z

LGTM w/ minor suggestions:

Please add a brief code comment noting that this alphabetic/punctuation heuristic and how Prettier handles

The two fixture files (issue-21148.jsx and issue-21149.jsx) could be merged into one?

Sounds good. I think I've addressed these now. Let me know if you're happy with the comments or if you'd like me to revise.

leaysgur

Thank you~ 👍🏻

# Oxlint ### 💥 BREAKING CHANGES - 382958a span: [**BREAKING**] Remove re-exports of string types from `oxc_span` crate (#21246) (overlookmotel) - c4aedfa str: [**BREAKING**] Add `static_ident!` macro (#21245) (overlookmotel) - 7354f3c linter: [**BREAKING**] Error on no matched files (#21144) (camc314) ### 🚀 Features - 91f2c79 linter/eslint-jest-plugin: Implemented `prefer-importing-jest-globals` rule (#21303) (Said Atrahouch) - a02f32c linter: Add release version for existing rules (#21363) (camchenry) - b9e93da linter: Allow tagging rules with release version (#21362) (camchenry) - f99ecda oxlint: Gate `vite.config.ts` recognition behind `VP_VERSION` env var (#21298) (leaysgur) - cf459d3 linter: Implement suggestion for `no-empty-function` rule (#21347) (Mikhail Baev) - 7213d61 linter: Adding pending suggestions fix to `valid_expect` rules. (#21249) (Said Atrahouch) - ae45312 linter: Introduce `--type-check-only` flag (#21184) (camc314) - 1ce8b90 linter: Implemented `valid-expect-in-promise` vitest and jest rule (#21170) (Said Atrahouch) - 39f7fda linter: Add auto-fix to `unicorn/prefer-default-parameters` (#21166) (yefan) - 15574bc linter/unicorn: Implement consistent-template-literal-escape (#21126) (AliceLanniste) - c5c8c03 linter/prefer-readonly-parameter-types: Move rule from nursery to pedantic (#21114) (camc314) - 1893be1 linter/no-useless-default-assignment: Move rule from nursery to correctness (#21113) (camc314) - 5462ff9 linter/strict-void-return: Move rule from nursery to pedantic (#21115) (camc314) - c2989bd linter/no-unnecessary-type-parameters: Move rule from nursery to suspicious (#21112) (camc314) - 79d339a linter/no-unnecessary-qualifier: Move rule from nursery to style (#21111) (camc314) ### 🐛 Bug Fixes - b577efc linter/unicorn: Handle optional chaining in `prefer-array-flat` and `no-invalid-remove-event-listener` (#21299) (Mikhail Baev) - 5e55735 oxlint/lsp: Skip .git directories in LSP walkers (#21316) (camc314) - ec7f6ed oxlint, oxfmt: Apply `check_for_writer_error` to `.flush()` (#21343) (Craig Morrison) - a17a08a linter/no-useless-assignment: Handle continue edges in loop analysis (#21358) (camc314) - a0eac12 linter/array-type: Move match to first stmt (#21357) (camc314) - 1b3abc3 linter: Exclude boundary tokens from JSXText whitespace check in isSpaceBetweenTokens (#21313) (bab) - ecbcf5e linter: More info to summary output for GitHub formatter (#21330) (Théo LUDWIG) - a0a8c62 linter/no-fallthrough: Check from start of switch case for empty lines (#21324) (Josh Cartmell) - 36f0bc4 linter/no-cycle: Report all cyclic dependencies inside a file (#21259) (camc314) - 3f80536 linter: Ignore regex flags other than `g`/`u`/`v` in `prefer-string-replace-all` (#21203) (bab) - f21d3aa linter/unicorn: Report on optional in `require-number-to-fixed-digits-argument` rule (#21207) (Mikhail Baev) - af8e122 linter: Render each config error as a separate diagnostic (#21120) (bab) - a950f55 linter/unicorn: Do not report on optionals in `no-single-promise-in-promise-methods` (#21157) (Mikhail Baev) - 472f8ee linter: Mark complete comment for unused disable directives + lsp fix (#21092) (copilot-swe-agent) - edd0865 linter/no-array-index-key: False positive when index is inside an expression within a template literal (#21123) (bab) - 7e8d520 linter/unicorn: Report on optional `foo?.postMessage` in `require-post-message-target-origin` rule (#21104) (Mikhail Baev) ### ⚡ Performance - addcd02 napi/parser, linter/plugins: Raw transfer deserializer for `Vec`s use shift instead of multiply where possible (#21142) (overlookmotel) - 3068ded napi/parser, linter/plugins: Shift before add when calculating positions in raw transfer deserializer (#21141) (overlookmotel) - eb400b8 napi/parser, linter/plugins: Remove `uint32` buffer view (#21140) (overlookmotel) - 7a86613 linter/plugins: Use `Int32Array`s for tokens and comments buffers (#21136) (overlookmotel) - 8c51121 napi/parser, linter/plugins: Raw transfer deserialize `Span` fields as `i32`s (#21135) (overlookmotel) - bc1bcdd napi/parser, linter/plugins: Inline trivial raw transfer field deserializers into node object definitions (#21134) (overlookmotel) - c0278ab napi/parser, linter/plugins: Use `Int32Array` in raw transfer deserializer (#21132) (overlookmotel) - 43482c7 linter/plugins: Use `>>` not `>>>` in binary search loops (#21129) (overlookmotel) ### 📚 Documentation - 7888280 linter: Move config docs for `no-restricted-exports` (#21360) (camchenry) - 162d26c linter: Improve docs for `typescript/array-type` (#21356) (camchenry) - a2dbaec linter: Add missing docs for options for `typescript/class-literal-property-style` (#21355) (camchenry) - 79593eb linter: Improve docs for `typescript/consistent-type-assertions` (#21353) (camchenry) - f9d20d2 linter: Move config option docs for `typescript/no-empty-object-type` (#21352) (camchenry) - a8f650d linter: Add missing config option docs for `prefer-string-start-ends-with` (#21332) (camchenry) - cfd8a4f linter: Don't rely on old eslint doc for available globals (#21334) (Nicolas Le Cam) - 03865fa linter: Jest/prefer-snapshot-hint: add doc comment for snapshot hint mode (#21290) (camchenry) - a6fe09b linter: Add missing docs for config options in `react` plugin (#21289) (camchenry) - 60eaf47 linter: Add missing docs for config options in unicorn plugin (#21288) (camchenry) - c3c2055 linter: `jsx-a11y/label-has-associated-control`: document the `assert` options (#21287) (camchenry) - a928ed9 linter: Add missing config docs for vitest plugin rules (#21285) (camchenry) - 7e07c7c linter: `id-length`: move enum docs to doc comments (#21281) (camchenry) - 9746bdf linter: Add missing docs for `class-methods-use-this` config (#21278) (camchenry) - 6ffe7a5 linter: Move docs for `Target` variant onto enum (#21277) (camchenry) - 305350d linter/plugins: Correct comments (#21130) (overlookmotel) # Oxfmt ### 💥 BREAKING CHANGES - 382958a span: [**BREAKING**] Remove re-exports of string types from `oxc_span` crate (#21246) (overlookmotel) ### 🚀 Features - e3081e1 oxfmt: Gate `vite.config.ts` recognition behind `VP_VERSION` env var (#21295) (leaysgur) - 5b0b573 oxfmt: Update prettier to 3.8.2 (#21294) (leaysgur) - 0d67834 oxfmt: Show hint for all files are ignored case (#21154) (leaysgur) ### 🐛 Bug Fixes - 2871fc2 oxfmt: Non idempotent formatting on comments in TS (#20449) (Cat Chen) - ec7f6ed oxlint, oxfmt: Apply `check_for_writer_error` to `.flush()` (#21343) (Craig Morrison) - 1a8c225 formatter: Preserve newline between self-closing JSX element and single-char text (#21149) (Justin Mecham) - 407b725 oxfmt: Indent dangling comments in empty enum with block indent (#21163) (Leonabcd123) - d13fd37 formatter: Remove extra outer parentheses on return with JSDoc type cast (#21109) (bab) - 22babde oxfmt: Fix unicode char escaping (#21162) (leaysgur) - 4da53e5 formatter: Preserve trailing comma in TSX arrow functions with default type params (#21151) (Justin Mecham) - 94fe774 oxfmt: Handle paths with consecutive leading slashes (#21155) (leaysgur) - 50c389b oxfmt: Support `.editorconfig` `quote_type` (#20989) (leaysgur) ### ⚡ Performance - 0ce619f formatter: Use `Allocator::alloc_concat_strs_array` instead of `StringBuilder::from_strs_array_in` (#21339) (overlookmotel)

jsmecham requested review from Dunqing and leaysgur as code owners April 8, 2026 00:38

github-actions Bot added A-formatter Area - Formatter C-bug Category - Bug labels Apr 8, 2026

jsmecham force-pushed the fix/jsx-self-closing-newline-before-single-char-text branch from fb482c6 to a0df864 Compare April 8, 2026 00:46

leaysgur requested changes Apr 8, 2026

View reviewed changes

jsmecham force-pushed the fix/jsx-self-closing-newline-before-single-char-text branch from a0df864 to 92e2492 Compare April 8, 2026 14:13

leaysgur reviewed Apr 9, 2026

View reviewed changes

fix(formatter): preserve newline between self-closing JSX element and…

3623d2b

… single-char text

jsmecham force-pushed the fix/jsx-self-closing-newline-before-single-char-text branch from 92e2492 to 3623d2b Compare April 9, 2026 13:45

leaysgur approved these changes Apr 10, 2026

View reviewed changes

leaysgur merged commit 1a8c225 into oxc-project:main Apr 10, 2026
33 checks passed

Boshen mentioned this pull request Apr 13, 2026

release(apps): oxlint v1.60.0 && oxfmt v0.45.0 #21375

Merged

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

fix(formatter): preserve newline between self-closing JSX element and single-char text#21149

fix(formatter): preserve newline between self-closing JSX element and single-char text#21149
leaysgur merged 1 commit intooxc-project:mainfrom
jsmecham:fix/jsx-self-closing-newline-before-single-char-text

jsmecham commented Apr 8, 2026 •

edited

Loading

Uh oh!

codspeed-hq Bot commented Apr 8, 2026 •

edited

Loading

Uh oh!

leaysgur left a comment

Uh oh!

jsmecham commented Apr 8, 2026

Uh oh!

jsmecham commented Apr 8, 2026

Uh oh!

leaysgur commented Apr 9, 2026

Uh oh!

github-actions Bot commented Apr 9, 2026 •

edited by Boshen

Loading

Uh oh!

leaysgur left a comment

Uh oh!

jsmecham commented Apr 9, 2026

Uh oh!

leaysgur left a comment

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

Uh oh!

Conversation

jsmecham commented Apr 8, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Summary

Input

Before (incorrect)

After (matches Prettier)

Root cause

Fix

AI Disclosure

Uh oh!

codspeed-hq Bot commented Apr 8, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Merging this PR will not alter performance

Footnotes

Uh oh!

leaysgur left a comment

Choose a reason for hiding this comment

Uh oh!

jsmecham commented Apr 8, 2026

Uh oh!

jsmecham commented Apr 8, 2026

Uh oh!

leaysgur commented Apr 9, 2026

Uh oh!

github-actions Bot commented Apr 9, 2026 • edited by Boshen Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Oxfmt Ecosystem CI

Uh oh!

leaysgur left a comment

Choose a reason for hiding this comment

Uh oh!

jsmecham commented Apr 9, 2026

Uh oh!

leaysgur left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

jsmecham commented Apr 8, 2026 •

edited

Loading

codspeed-hq Bot commented Apr 8, 2026 •

edited

Loading

github-actions Bot commented Apr 9, 2026 •

edited by Boshen

Loading