perf(transformer): use `ReplaceWith` instead of `TakeIn` by overlookmotel · Pull Request #24015 · oxc-project/oxc

overlookmotel · 2026-07-01T15:36:41Z

Replace take_in with replace_with in as many places as possible in transformer. See #24012 for explanation of the advantage of replace_with.

This has only a minimal perf effect according to Codspeed benchmarks (1% improvement). But it does cut the number of arena allocations on TS files by 50%, so reduces memory usage.

overlookmotel · 2026-07-01T15:37:02Z

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codspeed-hq · 2026-07-01T15:46:07Z

Merging this PR will improve performance by 3.45%

⚠️

Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 1 improved benchmark
✅ 51 untouched benchmarks
⏩ 19 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	`BASE`	`HEAD`	Efficiency
⚡	Simulation	`codegen[RadixUIAdoptionSection.jsx]`	124.8 µs	120.6 µs	+3.45%

Tip

Curious why this is faster? Comment @codspeedbot explain why this is faster on this PR, or directly use the CodSpeed MCP with your agent.

_{Comparing om/07-01-perf_transformer_use_replacewith_instead_of_takein_ (0f9d621) with om/07-01-feat_ast_implement_replacewith_on_all_ast_types (4c8d572)²}

19 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 om/07-01-feat_ast_implement_replacewith_on_all_ast_types (8b03eea) during the generation of this report, so a0151ad was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

Copilot

Pull request overview

Refactors the Rust transformer to prefer ReplaceWith over TakeIn in mutation patterns where the original node is immediately overwritten, reducing arena allocations (notably for TS-heavy inputs) while keeping transformation semantics the same.

Changes:

Converted many AST rewrite sites to use replace_with(...) closures instead of take_in(...) + re-assignment.
Simplified a few transformation helpers to avoid requiring an allocator solely for take_in.
Updated allocation tracking snapshot to reflect reduced arena allocations.

Reviewed changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tasks/track_memory_allocations/allocs_transformer.snap	Updates allocation snapshot numbers after reducing arena allocations.
crates/oxc_transformer/src/typescript/namespace.rs	Uses `ReplaceWith` for initializer rewrites in namespace handling.
crates/oxc_transformer/src/typescript/class.rs	Rewrites computed key sequencing using `replace_with`.
crates/oxc_transformer/src/typescript/annotations.rs	Unwraps TS-syntax expressions / consequent rewriting via `replace_with`.
crates/oxc_transformer/src/plugins/tagged_template_transform.rs	Rewrites tagged template transform to use `replace_with`.
crates/oxc_transformer/src/plugins/styled_components.rs	Refactors `withConfig` call rewrite to use `replace_with`.
crates/oxc_transformer/src/lib.rs	Refactors “wrap last expression statement in return” logic to use `replace_with`.
crates/oxc_transformer/src/jsx/refresh.rs	Uses `replace_with` for call/assignment wrapping to avoid dummy nodes.
crates/oxc_transformer/src/jsx/jsx_impl.rs	Switches JSX expression replacement to `replace_with`.
crates/oxc_transformer/src/es2026/explicit_resource_management.rs	Replaces several statement/body rewrites with `replace_with`, including program-body restructuring.
crates/oxc_transformer/src/es2022/class_properties/super_converter.rs	Refactors super assignment/update expression rewrites to `replace_with`.
crates/oxc_transformer/src/es2022/class_properties/private_field.rs	Uses `replace_with` in multiple private-field transforms to reduce arena churn.
crates/oxc_transformer/src/es2022/class_properties/constructor.rs	Refactors super call replacement to `replace_with`.
crates/oxc_transformer/src/es2020/optional_chaining.rs	Uses `replace_with` for object/callee sequencing and `eval?.()` rewrite.
crates/oxc_transformer/src/es2020/nullish_coalescing_operator.rs	Refactors `??` logical-expression transform to use `replace_with`.
crates/oxc_transformer/src/es2018/object_rest_spread.rs	Refactors sequence/block wrapping to use `replace_with`.
crates/oxc_transformer/src/es2017/async_to_generator.rs	Uses `replace_with` for arrow-body “expression → return” conversion.
crates/oxc_transformer/src/es2016/exponentiation_operator.rs	Refactors pow conversions and sequencing to use `replace_with`.
crates/oxc_transformer/src/decorator/legacy/mod.rs	Uses `replace_with` for computed key capture assignment.
crates/oxc_transformer/src/common/arrow_function_converter.rs	Refactors arrow-function conversion and super-call sequencing to use `replace_with`.
crates/oxc_transformer_plugins/src/replace_global_defines.rs	Uses `replace_with` to unwrap `ChainExpression` without allocator-dependent `take_in`.
crates/oxc_transformer_plugins/src/module_runner_transform.rs	Refactors dynamic import transform to use `replace_with`.

graphite-app · 2026-07-05T14:43:37Z

Merge activity

Jul 5, 2:43 PM UTC: Dunqing added this pull request to the Graphite merge queue.
Jul 5, 2:50 PM UTC: Merged by the Graphite merge queue.

Replace `take_in` with `replace_with` in as many places as possible in transformer. See #24012 for explanation of the advantage of `replace_with`. This has only a minimal perf effect according to Codspeed benchmarks (1% improvement). But it does cut the number of arena allocations on TS files by 50%, so reduces memory usage.

### 🚀 Features - 260425f semantic/examples: Include unresolved references (#24214) (camc314) - 2d9b0b3 minifier: Fold boolean-literal ternary branches in value contexts (#24110) (Dunqing) - 61fbf10 ast: Implement `ReplaceWith` on all AST types (#24013) (overlookmotel) - 7db7a29 allocator: Add `ReplaceWith` trait (#24012) (overlookmotel) - 4eb074e mangler: Add `reserved` option for names that must not be mangled (#24041) (Dunqing) - 2e62012 data_structures: Add `StringExt` trait (#24006) (overlookmotel) - 60e7160 minifier: Drop side-effect-free IIFEs whose result is unused (#23967) (Dunqing) - 26dd9e2 ast: Add method to widen inherited enum ref to parent ref (#23961) (overlookmotel) ### 🐛 Bug Fixes - e8b50ee transformer: Clean up semantics for stripped TypeScript syntax (#24180) (camc314) - d966d0b react_compiler: Remove clippy allows (#24168) (Boshen) - 854ef8d react_compiler: Compile generic functions instead of over-bailing on type-param hoisting (#24158) (Boshen) - 093586c react_compiler: Align memoization cache-slot allocation with Babel (#24157) (Boshen) - 09c8f59 react_compiler: Normalize snapshot fixture paths (#24142) (camc314) - f13df97 react_compiler: Drop stray empty statement from catch bindings (#24133) (Boshen) - cb2a505 react_compiler: Codegen destructuring reassignment targets (#24131) (Boshen) - b82c394 react_compiler: Propagate codegen invariants instead of emitting empty bodies (#24128) (Boshen) - 5771982 react_compiler: Render unchanged programs as source in fixture snapshots (#24129) (Boshen) - 4b16e1a transformer/async-to-generator: Preserve direct eval scope flags (#24136) (camc314) - 4e9194f react_compiler: Lower `delete obj.prop` to Property/ComputedDelete (#24123) (Boshen) - 0b25582 ast: Type binding node `typeAnnotation` as `TSTypeAnnotation | null` (#23113) (Boshen) - 018c0e5 transformer: Hoist lowered async declarations (#22770) (camc314) - 652fbaf mangler: Keep names of destructured exported bindings (#24036) (Dunqing) - e274415 minifier: Don't drop global calls that throw despite pure arguments (#23917) (Dunqing) - 59abb30 minifier: Only merge string literals in `try_fold_add` when the inner operator is `+` (#23622) (Jerry Zhao) ### ⚡ Performance - c5ca77b transformer: Avoid cloning refresh options (#24191) (camc314) - bf1a151 react_compiler: Compile out debug printers (#24184) (Boshen) - abb44a0 transformer: Build fixed object-rest arguments (#24190) (camc314) - a4db731 isolated_declarations: Use `ReplaceWith` instead of `TakeIn` (#24016) (overlookmotel) - ff10855 transformer: Use `ReplaceWith` instead of `TakeIn` (#24015) (overlookmotel) - bd49aff ecmascript: Avoid heap-allocating Math.min/max/imul operands (#23941) (Lawrence Lin) - e4b708b react_compiler: Skip compiled files before prefilters (#24171) (Boshen) - c59f2fe rust: Return impl ExactSizeIterator from slice-backed accessors (#24144) (Boshen) - 5d6d04a codegen: SWAR-skip boring byte runs in sourcemap line/column scan (#24023) (Boshen) - a55e0be traverse: Reduce string operations in `get_var_name_from_node` (#24007) (overlookmotel) - e6d48e1 transformer/nullish_coalescing: Move cold path into separate function (#23989) (overlookmotel) - c4e35b5 transformer/object_rest_spread: Pre-allocate capacity in `Vec` (#23988) (overlookmotel) - 527b8e5 transformer/decorators: Narrow type earlier (#23987) (overlookmotel) ### 📚 Documentation - 30d17f5 allocator: Clarify docs for `TakeIn::take_in_box` (#24093) (overlookmotel) - 675e6a8 ast: Correct doc comment for `PrivateFieldExpression` (#24008) (overlookmotel) - e4c30e6 minifier: Explain what `dce` mode means (#23994) (Dunqing) - 37cbf88 ast_macros: Document fields of `StructDetails` (#23959) (overlookmotel) - 4de3e54 ast: Correct doc comment (#23948) (overlookmotel) Co-authored-by: Boshen <[email protected]>

github-actions Bot added the A-transformer Area - Transformer / Transpiler label Jul 1, 2026

overlookmotel mentioned this pull request Jul 1, 2026

feat(ast): implement ReplaceWith on all AST types #24013

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This was referenced Jul 1, 2026

perf(isolated_declarations): use ReplaceWith instead of TakeIn #24016

Merged

perf(minifier): use ReplaceWith instead of TakeIn #24017

Merged

perf(parser): use ReplaceWith instead of TakeIn #24018

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overlookmotel assigned Dunqing Jul 1, 2026

overlookmotel marked this pull request as ready for review July 1, 2026 16:36

overlookmotel requested a review from Dunqing as a code owner July 1, 2026 16:36

Copilot AI review requested due to automatic review settings July 1, 2026 16:36

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overlookmotel force-pushed the om/07-01-feat_ast_implement_replacewith_on_all_ast_types branch from 24991e8 to c6bc59b Compare July 1, 2026 18:01

overlookmotel force-pushed the om/07-01-perf_transformer_use_replacewith_instead_of_takein_ branch from d61e3e8 to 547d76d Compare July 1, 2026 18:01

graphite-app Bot force-pushed the om/07-01-feat_ast_implement_replacewith_on_all_ast_types branch from c6bc59b to 4c8d572 Compare July 2, 2026 01:39

graphite-app Bot force-pushed the om/07-01-perf_transformer_use_replacewith_instead_of_takein_ branch from 547d76d to 9d36ab6 Compare July 2, 2026 01:40

overlookmotel force-pushed the om/07-01-feat_ast_implement_replacewith_on_all_ast_types branch from 4c8d572 to 8b03eea Compare July 2, 2026 21:50

overlookmotel force-pushed the om/07-01-perf_transformer_use_replacewith_instead_of_takein_ branch from 9d36ab6 to 0f9d621 Compare July 2, 2026 21:50

Dunqing approved these changes Jul 5, 2026

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graphite-app Bot force-pushed the om/07-01-feat_ast_implement_replacewith_on_all_ast_types branch from 8b03eea to 61fbf10 Compare July 5, 2026 14:44

graphite-app Bot requested a review from camc314 as a code owner July 5, 2026 14:44

graphite-app Bot force-pushed the om/07-01-perf_transformer_use_replacewith_instead_of_takein_ branch from 0f9d621 to ff10855 Compare July 5, 2026 14:45

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Base automatically changed from om/07-01-feat_ast_implement_replacewith_on_all_ast_types to main July 5, 2026 14:49

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graphite-app Bot deleted the om/07-01-perf_transformer_use_replacewith_instead_of_takein_ branch July 5, 2026 14:50

oxc-guard Bot mentioned this pull request Jul 6, 2026

release(crates): oxc v0.139.0 #24218

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perf(transformer): use `ReplaceWith` instead of `TakeIn`#24015

perf(transformer): use `ReplaceWith` instead of `TakeIn`#24015
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Merging this PR will improve performance by 3.45%

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