perf: use numeric suffixes for faster concatenation

[LingyuCoder]

Summary

This is an experimental follow-up to #14852 for measuring a smaller naming optimization against the indexed-name approach in #15222.

• Keep the existing NameAllocator and find_new_name collision handling.
• Skip readable-identifier lookup and splitting only when faster module concatenation is enabled, so conflicts use numeric suffixes such as foo_0.
• Preserve the legacy module-concatenation naming path unchanged when the experiment is disabled.

Related links

• perf: avoid parsing concatenated module codegen #14852
• perf: use indexed names for faster concatenation #15222

Validation

• cargo check -p rspack_core
• pnpm --filter @rspack/tests test FasterModuleConcatenation.test.js (84 passed)
• Two Callgrind runs produced the same 77,932,283 instruction count

Checklist

• Tests updated.
• Documentation not required for this experiment.

[github-actions]

📦 Binary Size-limit

Comparing 5e6ff53 to chore: fix lint and formatting by harpsealjs

⏳ The base commit triggered a linux binding build, but its binary size data has not been generated yet, so the size comparison is skipped.

Please re-run this workflow once the ecosystem-benchmark data for that commit is published.

Warning

Reference only — not the real baseline. The base commit's data isn't ready yet, so this compares against the nearest earlier commit that has data (3857d21) for a rough estimate:

❌ Size increased by 244.00KB from 68.20MB to 68.44MB (⬆️0.35%)

[github-actions]

Rsdoctor Bundle Diff Analysis

Found 5 projects in monorepo, 5 projects with changes.

📊 Quick Summary

Project	Total Size	Gzip Size	Change	Gzip Change
popular-libs	1.7 MB	556.7 KB	-	-
react-1k	823.1 KB	218.4 KB	-	-
react-10k	5.6 MB	1.3 MB	-	-
react-5k	2.7 MB	669.3 KB	-	-
ui-components	4.9 MB	1.4 MB	-	-

📋 Detailed Reports (Click to expand)

📁 popular-libs

Path: ../build-tools-performance/cases/popular-libs/dist/rsdoctor-data.json

⚠️ No baseline data found - Unable to perform comparison analysis

Metric	Current	Baseline	Change
📊 Total Size	1.7 MB	-	-
🗜️ Gzip Size	556.7 KB	-	-
📄 JavaScript	1.7 MB	-	-
🎨 CSS	0 B	-	-
🌐 HTML	289.0 B	-	-
📁 Other Assets	0 B	-	-

📁 react-1k

Path: ../build-tools-performance/cases/react-1k/dist/rsdoctor-data.json

⚠️ No baseline data found - Unable to perform comparison analysis

Metric	Current	Baseline	Change
📊 Total Size	823.1 KB	-	-
🗜️ Gzip Size	218.4 KB	-	-
📄 JavaScript	822.7 KB	-	-
🎨 CSS	0 B	-	-
🌐 HTML	328.0 B	-	-
📁 Other Assets	0 B	-	-

📁 react-10k

Path: ../build-tools-performance/cases/react-10k/dist/rsdoctor-data.json

⚠️ No baseline data found - Unable to perform comparison analysis

Metric	Current	Baseline	Change
📊 Total Size	5.6 MB	-	-
🗜️ Gzip Size	1.3 MB	-	-
📄 JavaScript	5.6 MB	-	-
🎨 CSS	21.0 B	-	-
🌐 HTML	328.0 B	-	-
📁 Other Assets	0 B	-	-

📁 react-5k

Path: ../build-tools-performance/cases/react-5k/dist/rsdoctor-data.json

⚠️ No baseline data found - Unable to perform comparison analysis

Metric	Current	Baseline	Change
📊 Total Size	2.7 MB	-	-
🗜️ Gzip Size	669.3 KB	-	-
📄 JavaScript	2.7 MB	-	-
🎨 CSS	21.0 B	-	-
🌐 HTML	328.0 B	-	-
📁 Other Assets	0 B	-	-

📁 ui-components

Path: ../build-tools-performance/cases/ui-components/dist/rsdoctor-data.json

⚠️ No baseline data found - Unable to perform comparison analysis

Metric	Current	Baseline	Change
📊 Total Size	4.9 MB	-	-
🗜️ Gzip Size	1.4 MB	-	-
📄 JavaScript	4.8 MB	-	-
🎨 CSS	112.5 KB	-	-
🌐 HTML	328.0 B	-	-
📁 Other Assets	0 B	-	-

Generated by Rsdoctor GitHub Action

[codspeed]

Merging this PR will improve performance by 25.06%

⚠️ 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
✅ 48 untouched benchmarks
⏩ 47 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	rust@concatenate_module_code_generation	33.7 ms	26.9 ms	+25.06%

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 seal/concat-numeric-suffix (5e6ff53) with seal/concat-local-ident (d84ab09)}

Footnotes

1. 47 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. ↩