perf: avoid allocating static strings via custom builder methods by overlookmotel · Pull Request #10421 · rolldown/rolldown

overlookmotel · 2026-07-23T22:54:47Z

Follow-on after #10018, continuation of #10420.

Custom AST builder methods (previously methods of AstFactory) take &strs. They allocate the string into arena, to obtain a &'ast str (allocator lifetime). Where the string is a &'static str, it's unnecessary to allocate into arena to extend the lifetime.

In these cases, use standard AST builder methods provided by Oxc, and skip the allocation.

Before:

BindingIdentifier::new_id(SPAN, "__rolldown_default__", &self.ast_builder)

After:

BindingIdentifier::new(SPAN, "__rolldown_default__", &self.ast_builder)

overlookmotel · 2026-07-23T22:55:00Z

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Copilot

Pull request overview

This PR continues the AST-construction perf work by avoiding arena allocations when constructing AST nodes with &'static str names. It replaces rolldown’s custom *_id_* builder extension helpers (which copy &str into the arena) with Oxc’s per-type constructors that can accept string literals directly.

Changes:

Replaced Expression::new_id_ref_expr(..) with Expression::new_identifier(..) for string-literal identifiers to avoid allocating into the arena.
Replaced BindingIdentifier::new_id(..) / IdentifierName::new_id_name(..) with BindingIdentifier::new(..) / IdentifierName::new(..) for string-literal names.
Cleaned up now-unneeded extension-trait imports in affected modules.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
crates/rolldown/src/hmr/impl_traverse_for_hmr_ast_finalizer.rs	Avoids arena allocation when constructing the runtime `registerFactory` callee expression from a string literal.
crates/rolldown/src/hmr/hmr_ast_finalizer.rs	Avoids arena allocations for several runtime helper references and `"__rolldown_default__"` identifier construction.
crates/rolldown_plugin_vite_web_worker_post/src/ast_visitor.rs	Switches member/identifier constructions to Oxc constructors using string literals; removes unused imports.
crates/rolldown_plugin_vite_build_import_analysis/src/ast_utils.rs	Switches identifier/name construction to Oxc constructors using string literals; removes unused imports.

codspeed-hq · 2026-07-23T23:33:43Z

Merging this PR will not alter performance

✅ 7 untouched benchmarks
⏩ 10 skipped benchmarks¹

_{Comparing om/07-23-perf_avoid_allocating_static_strings_via_custom_builder_methods (45449fc) with om/07-23-perf_pass_string_literals_to_ast_builder_methods (ea4ede0)²}

10 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/07-23-perf_pass_string_literals_to_ast_builder_methods (66a13fa) during the generation of this report, so ad8882d was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

hyfdev

— Review by @hyfdev, assisted by GPT-5

graphite-app · 2026-07-24T03:38:46Z

Merge activity

Jul 24, 3:38 AM UTC: hyfdev added this pull request to the Graphite merge queue.
Jul 24, 3:56 AM UTC: Merged by the Graphite merge queue.

) Follow-on after #10018, continuation of #10420. Custom AST builder methods (previously methods of `AstFactory`) take `&str`s. They allocate the string into arena, to obtain a `&'ast str` (allocator lifetime). Where the string is a `&'static str`, it's unnecessary to allocate into arena to extend the lifetime. In these cases, use standard AST builder methods provided by Oxc, and skip the allocation. Before: ```rust BindingIdentifier::new_id(SPAN, "__rolldown_default__", &self.ast_builder) ``` After: ```rust BindingIdentifier::new(SPAN, "__rolldown_default__", &self.ast_builder) ```

Follow-on after #10018, continuation of #10420 and #10421. When converting `&'static str`s to `Str`s, use `Str::from` instead of `Str::from_str_in`. The difference is that `from_str_in` performs an allocation (in arena), whereas `from` is a zero-cost no-op conversion at runtime. When the `&str` already has a `'static` lifetime, it's unnecessary to extend it by allocating it into arena. Before: ```rs TemplateElementValue { raw: Str::from_str_in("/@vite/lazy?id=", &self.ast_builder), cooked: None, } ``` After: ```rs TemplateElementValue { raw: Str::from("/@vite/lazy?id="), cooked: None } ```

Follow-on after #10018, continuation of #10420 and #10421. Where we already have a `Str<'ast>` or `Ident<'ast>`, avoid converting it into a `&str` and then allocating it back into arena again to convert back to `Str` or `Ident`. Just re-use the existing `Str` / `Ident`. This avoids unnecessary arena allocations, and in the case of `Ident`, it avoids re-hashing the string too.

This was referenced Jul 23, 2026

refactor: shorten AST builder code #10418

Merged

refactor: pass arrays to AST builder methods #10419

Merged

overlookmotel marked this pull request as ready for review July 23, 2026 23:25

overlookmotel requested review from IWANABETHATGUY, hyfdev, sapphi-red and shulaoda as code owners July 23, 2026 23:25

Copilot AI review requested due to automatic review settings July 23, 2026 23:25

Copilot started reviewing on behalf of overlookmotel July 23, 2026 23:26 View session

Copilot AI reviewed Jul 23, 2026

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overlookmotel force-pushed the om/07-23-perf_avoid_allocating_static_strings_via_custom_builder_methods branch from b0f8850 to 45449fc Compare July 24, 2026 00:02

overlookmotel force-pushed the om/07-23-perf_pass_string_literals_to_ast_builder_methods branch from ea4ede0 to 66a13fa Compare July 24, 2026 00:02

IWANABETHATGUY approved these changes Jul 24, 2026

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hyfdev approved these changes Jul 24, 2026

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graphite-app Bot added the graphite: merge-when-ready label Jul 24, 2026

graphite-app Bot force-pushed the om/07-23-perf_pass_string_literals_to_ast_builder_methods branch from 66a13fa to f38313a Compare July 24, 2026 03:44

graphite-app Bot requested a review from h-a-n-a as a code owner July 24, 2026 03:44

graphite-app Bot force-pushed the om/07-23-perf_avoid_allocating_static_strings_via_custom_builder_methods branch from 45449fc to c6cf426 Compare July 24, 2026 03:45

graphite-app Bot removed the graphite: merge-when-ready label Jul 24, 2026

Base automatically changed from om/07-23-perf_pass_string_literals_to_ast_builder_methods to main July 24, 2026 03:55

graphite-app Bot merged commit c6cf426 into main Jul 24, 2026
32 checks passed

graphite-app Bot deleted the om/07-23-perf_avoid_allocating_static_strings_via_custom_builder_methods branch July 24, 2026 03:56

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perf: avoid allocating static strings via custom builder methods#10421

perf: avoid allocating static strings via custom builder methods#10421
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