perf(parser): defer calculation of Modifier spans

[overlookmotel]

Small perf optimization.

The Span of a modifier is only required when an error is raised (cold path).

Don't eagerly calculate and store the full span in Modifier, only store the span's start. Calculate the span's end lazily only when it's needed (which it only is if source contains syntax errors).

[overlookmotel]

• perf(parser): defer calculation of Modifier spans #20823 : 2 dependent PRs (#20824 , #20826 ) 👈 (View in Graphite)
• perf(parser): remove branch from parse_modifiers #20821
• perf(parser): reduce Kind to ModifierKind conversions in eat_modifiers_before_declaration #20820
• refactor(parser): shorten code handling illegal modifiers #20781
• perf(parser): fast path for no syntax errors when checking modifiers #20748
• perf(parser): remove a lookahead from eat_modifiers_before_declaration #20755
• refactor(parser): nest modifiers types in modules #20754
• refactor(parser): re-order modifiers code #20753
• perf(parser): store Modifiers on stack #20742
• perf(parser): add Modifiers::get method #20741
• refactor(parser): rename ModifierKinds::empty to none #20740
• refactor(parser): rename ModifierFlags to ModifierKinds #20739
• refactor(parser): simplify ModifierFlags #20738
• refactor(parser): import from std at top level #20737
• refactor(parser): remove Modifier::is_static() #20736
• refactor(parser): remove dead code from modifier parsing #20735
• main

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[codspeed-hq]

Merging this PR will not alter performance

✅ 48 untouched benchmarks
⏩ 8 skipped benchmarks¹

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_{Comparing om/03-28-perf_parser_defer_calculation_of_modifier_spans (055a7ac) with main (eb02c88)²}

Footnotes

1. 8 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. ↩

2. No successful run was found on main (055a7ac) during the generation of this report, so eb02c88 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[Copilot]

Pull request overview

This PR optimizes modifier handling in oxc_parser by deferring full Span reconstruction for modifiers until it’s actually needed (primarily diagnostics), reducing work on the hot parsing path.

Changes:

• Replace stored Modifier.span: Span with Modifier.span_start: u32 and reconstruct spans lazily via Modifier::span().
• Update modifier parsing/collection to record only start offsets.
• Update diagnostics and call sites to use modifier.span() instead of the removed modifier.span field.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
crates/oxc_parser/src/modifiers.rs	Changes Modifier to store only span_start, adds lazy span() reconstruction, and updates modifier parsing/collection paths accordingly.
crates/oxc_parser/src/js/module.rs	Adjusts duplicate export-modifier diagnostic construction to match the new Modifier::new(span_start, kind) API.
crates/oxc_parser/src/js/class.rs	Updates diagnostics call sites to use modifier.span() accessor.
crates/oxc_parser/src/diagnostics.rs	Updates modifier-related diagnostics to label using modifier.span() instead of a stored span field.

[camc314]

Merge activity

• Mar 29, 3:31 PM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Mar 29, 3:40 PM UTC: The Graphite merge queue removed this pull request due to removal of a downstack PR #20820.
• Mar 29, 3:40 PM UTC: camc314 added this pull request to the Graphite merge queue.
• Mar 29, 3:41 PM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Mar 29, 3:41 PM UTC: The merge label '0-merge' was removed. This PR will no longer be merged by the Graphite merge queue
• Mar 29, 3:42 PM UTC: camc314 added this pull request to the Graphite merge queue.
• Mar 29, 4:19 PM UTC: The Graphite merge queue removed this pull request due to downstack failures on PR #20820.
• Mar 29, 4:43 PM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Mar 29, 4:43 PM UTC: camc314 added this pull request to the Graphite merge queue.
• Mar 29, 4:43 PM UTC: Merged by the Graphite merge queue.