fix(formatter): preserve trailing comma in TSX arrow functions with default type params by jsmecham · Pull Request #21151 · oxc-project/oxc

jsmecham · 2026-04-08T01:13:56Z

Summary

When a single-parameter generic arrow function in a .tsx file has a default type (e.g. <Options = any>), the formatter was incorrectly removing the trailing comma. Prettier preserves it as <Options = any,>.

The existing should_force_trailing_comma_for_arrow_function logic handles the simple case (<T,>) correctly, but it also skipped forcing the comma when the parameter had a default type. Prettier's equivalent only skips the forced comma when a constraint (extends clause) is present — not for default types. This PR aligns with that behavior.

Input

const AppWrapper = <Options = any,>({
  appName,
}: {
  appName: string;
}) => null;

const getProps = <T = Record<string, unknown>,>(
  option: T | undefined,
): Partial<T> => ({});

Before (incorrect)

const AppWrapper = <Options = any>({ appName }: { appName: string }) => null;

const getProps = <T = Record<string, unknown>>(
  option: T | undefined,
): Partial<T> => ({});

After (matches Prettier)

const AppWrapper = <Options = any,>({ appName }: { appName: string }) => null;

const getProps = <T = Record<string, unknown>,>(
  option: T | undefined,
): Partial<T> => ({});

Root cause

In should_force_trailing_comma_for_arrow_function (type_parameters.rs), the early-return condition checked for both a constraint and a default type:

// Before
if params.first().is_some_and(|t| t.constraint().is_some() || t.default().is_some()) {
    return false;
}

Prettier's equivalent only skips forcing the comma when a constraint is present. See Prettier source.

Fix

Removed || t.default().is_some() from the condition:

// After
if params.first().is_some_and(|t| t.constraint().is_some()) {
    return false;
}

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.

…efault type params Trailing commas are required in single-param generic arrow functions in .tsx files to disambiguate from JSX. A default type alone does not disambiguate, so the comma must still be forced — only a constraint (extends clause) provides sufficient disambiguation. Closes oxc-project#21150 Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

codspeed-hq · 2026-04-08T05:01:55Z

Merging this PR will not alter performance

✅ 44 untouched benchmarks
⏩ 7 skipped benchmarks¹

_{Comparing jsmecham:fix/tsx-trailing-comma-with-default-type-param (ea5bfe1) with main (eab13b3)²}

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. ↩
No successful run was found on main (addcd02) during the generation of this report, so eab13b3 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

leaysgur

Thank you~!

graphite-app · 2026-04-08T05:35:31Z

Merge activity

Apr 8, 5:35 AM UTC: @jsmecham we removed the merge queue label because we could not find a Graphite account associated with your GitHub profile.

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# 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 01:13

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

jsmecham force-pushed the fix/tsx-trailing-comma-with-default-type-param branch from 5208845 to ea5bfe1 Compare April 8, 2026 01:16

leaysgur approved these changes Apr 8, 2026

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leaysgur added the 0-merge Merge with Graphite Merge Queue label Apr 8, 2026

graphite-app Bot removed the 0-merge Merge with Graphite Merge Queue label Apr 8, 2026

leaysgur merged commit 4da53e5 into oxc-project:main Apr 8, 2026
34 checks passed

Boshen mentioned this pull request Apr 13, 2026

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

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fix(formatter): preserve trailing comma in TSX arrow functions with default type params#21151

fix(formatter): preserve trailing comma in TSX arrow functions with default type params#21151
leaysgur merged 1 commit intooxc-project:mainfrom
jsmecham:fix/tsx-trailing-comma-with-default-type-param

jsmecham commented Apr 8, 2026 •

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

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Summary

Input

Before (incorrect)

After (matches Prettier)

Root cause

Fix

AI Disclosure

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codspeed-hq Bot commented Apr 8, 2026

Merging this PR will not alter performance

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graphite-app Bot commented Apr 8, 2026

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jsmecham commented Apr 8, 2026 •

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