fix(formatter): keep spread with callback on same line

[Dunqing]

Summary

When a function call has exactly 2 arguments where the first is a spread element and the second is a callback function, oxfmt was incorrectly breaking the arguments onto multiple lines, while Prettier keeps them on the same line.

Before (wrong):

target(
  ...argument,
  () => {
    // code
  },
);

After (correct, matches Prettier):

target(...argument, () => {
  // code
});

Root Cause

In arguments_grouped_layout, first.as_expression() returns None for SpreadElement (since it's not an Expression variant), causing the function to return early without checking if the last argument could be grouped.

Fix

The fix passes the optional expression directly to should_group_last_argument_impl, which already handles None correctly for the same-type checking. This simplifies the code while fixing the issue.

Fixes #18930
Fixes #18971

Test plan

• Added test fixture with various spread + callback patterns
• All 154 formatter tests pass
• Prettier conformance unchanged (99.07% JS, 98.17% TS)

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR fixes a formatter inconsistency with Prettier when formatting function calls with exactly 2 arguments where the first is a spread element and the second is a callback function. Previously, oxfmt incorrectly broke these onto multiple lines, while Prettier keeps them on the same line.

Changes:

• Modified arguments_grouped_layout to properly handle SpreadElement as the first argument by passing it as None to should_group_last_argument_impl instead of early returning
• Added comprehensive test fixtures covering spread + callback patterns including arrow functions, traditional functions, and multi-argument cases

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
crates/oxc_formatter/src/print/call_like_expression/arguments.rs	Fixed logic to allow grouping last argument (callback) when first argument is a spread element by avoiding early return on first.as_expression()
crates/oxc_formatter/tests/fixtures/js/call-expression/spread-with-callback.js	Added test input covering various spread + callback scenarios including the reported issues
crates/oxc_formatter/tests/fixtures/js/call-expression/spread-with-callback.js.snap	Expected test output confirming spread and callback stay on same line as per Prettier

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[codspeed-hq]

Merging this PR will not alter performance

✅ 46 untouched benchmarks
⏩ 3 skipped benchmarks¹

---

_{Comparing fix-spread-callback-formatting (646aef2) with main (dd0f754)}

Footnotes

1. 3 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. ↩

[Dunqing]

• fix(formatter): preserve comment between callee and optional chaining operator #19020
• fix(formatter): remove unnecessary parentheses for single-member union types #19018
• refactor(formatter): handle TSParenthesizedType with unreachable statement #19017
• fix(formatter): preserve parentheses around await with private field access #19014
• fix(formatter): preserve parentheses around nested sequence expressions #19013
• fix(formatter): add space before type annotation with leading comment #19012
• fix(formatter): keep spread with callback on same line #18999 👈 (View in Graphite)
• main

---

How to use the Graphite Merge Queue

Add either label to this PR to merge it via the merge queue:

• 0-merge - adds this PR to the back of the merge queue
• hotfix - for urgent hot fixes, skip the queue and merge this PR next

You must have a Graphite account in order to use the merge queue. Sign up using this link.

An organization admin has enabled the Graphite Merge Queue in this repository.

Please do not merge from GitHub as this will restart CI on PRs being processed by the merge queue.

This stack of pull requests is managed by Graphite. Learn more about stacking.

[graphite-app]

Merge activity

• Feb 6, 5:03 AM UTC: leaysgur added this pull request to the Graphite merge queue.
• Feb 6, 5:20 AM UTC: Merged by the Graphite merge queue.