perf(formatter): use ArenaVec and ArenaBox

[Dunqing]

This PR aims to replace the Formatter's standard Vec and Box usages with ArenaVec and ArenaBox to gain performance, which could reduce the drop overhead.

There are three key changes:

1. Change the Document's element from Vec<FormatElement<'a>>

pub struct Document<'a> {
-    elements: Vec<FormatElement<'a>>,
+    elements: &'a [FormatElement<'a>],
}

2. Change the FormatElement::interned's argument from Rc<[FormatElement<'a>]> to &'a [FormatElement<'a>]

- pub struct Interned<'a>(Rc<[FormatElement<'a>]>);
+ pub struct Interned<'a>(&'a [FormatElement<'a>]);

3. Change the FormatElement::variants's variants from Box<[Box<[FormatElement<'a>]>]> to &'a [&'a [FormatElement<'a>]]

pub struct BestFittingElement<'a> {
-    variants: Box<[Box<[FormatElement<'a>]>]>,
+    variants: &'a [&'a [FormatElement<'a>]],
}

All other changes stem from those mentioned above.

Replacing the Rc with &a reference approach was suggested and guided by @overlookmotel. Thank you!

[Dunqing]

• refactor(oxfmt): simplify wrap_format_embeded #15798
• perf(formatter): use ArenaVec and ArenaBox #15420 👈 (View in Graphite)
• feat(allocator/vec): add Vec::into_bump_slice method #15770
• main

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[codspeed-hq]

CodSpeed Performance Report

Merging #15420 will improve performances by 6.61%

_{Comparing 11-07-perf_formatter_use_arenavec_and_arenabox (28f5485) with main (e615162)¹}

Summary

⚡ 8 improvements
✅ 30 untouched
⏩ 7 skipped²

Benchmarks breakdown

	Mode	Benchmark	BASE	HEAD	Change
⚡	Simulation	formatter[App.tsx]	56.9 ms	53.4 ms	+6.46%
⚡	Simulation	formatter[RadixUIAdoptionSection.jsx]	520.6 µs	499.2 µs	+4.27%
⚡	Simulation	formatter[Search.tsx]	2.1 ms	2 ms	+4.87%
⚡	Simulation	formatter[core.js]	2.5 ms	2.4 ms	+4.86%
⚡	Simulation	formatter[errors.ts]	862.6 µs	826.5 µs	+4.38%
⚡	Simulation	formatter[handle-comments.js]	3.9 ms	3.8 ms	+4.81%
⚡	Simulation	formatter[index.tsx]	5.2 ms	4.9 ms	+6.61%
⚡	Simulation	formatter[next.ts]	3.2 ms	3 ms	+5.97%

Footnotes

1. No successful run was found on main (d98f3e5) during the generation of this report, so e615162 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

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. ↩

[leaysgur]

Merge activity

• Nov 18, 2:40 AM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Nov 18, 3:39 AM UTC: leaysgur added this pull request to the Graphite merge queue.
• Nov 18, 3:50 AM UTC: Merged by the Graphite merge queue.

[Copilot]

Pull Request Overview

This PR optimizes the formatter by replacing standard Vec and Box with arena-allocated ArenaVec and ArenaBox to reduce drop overhead and improve performance. The key changes include converting Document elements from Vec<FormatElement<'a>> to &'a [FormatElement<'a>], changing Interned from Rc<[FormatElement<'a>]> to &'a [FormatElement<'a>], and updating BestFittingElement variants to use arena-allocated slices.

• Replace reference-counted and heap-allocated collections with arena-allocated equivalents throughout the formatter
• Update hash and equality implementations to work with raw pointers instead of Rc
• Thread allocator references through method signatures where needed for arena allocation

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
crates/oxc_formatter/src/write/jsx/child_list.rs	Converts JSX child list builders to use ArenaVec and adds allocator parameters
crates/oxc_formatter/src/write/call_arguments.rs	Replaces into_boxed_slice() with into_bump_slice() and uses ArenaVec::from_array_in()
crates/oxc_formatter/src/lib.rs	Adds allocator parameter to transform method signature
crates/oxc_formatter/src/ir_transform/sort_imports/source_line.rs	Updates write method signature to accept ArenaVec
crates/oxc_formatter/src/ir_transform/sort_imports/mod.rs	Threads allocator parameter through transform and uses ArenaVec for element storage
crates/oxc_formatter/src/formatter/formatter.rs	Updates allocator() return type and intern_vec to work with ArenaVec
crates/oxc_formatter/src/formatter/format_element/mod.rs	Converts Interned from Rc to reference and updates BestFittingElement to use arena slices
crates/oxc_formatter/src/formatter/format_element/document.rs	Changes Document to store &'a [FormatElement<'a>] instead of Vec
crates/oxc_formatter/src/formatter/builders.rs	Updates BestFitting implementation to create arena-allocated variants
crates/oxc_formatter/src/formatter/buffer.rs	Converts VecBuffer to use ArenaVec and updates buffer operations with take_in()

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