bundler: fix quadratic naming of unminified cross-chunk bindings that share a source name

[Jarred-Sumner]

Follow-up to #40518. assign_unminified numbered each cross-chunk binding by probing name2, name3, … from 2 every time, so N bindings with the same source name (e.g. 20k modules each exporting shared, imported across two entry points) cost O(N²) hash lookups. It now remembers the last suffix handed out per base name, as NumberScope does.

test/bundler/bundler_splitting.test.ts › splitting/ManyCrossChunkExportAliasCollisions (20,000 colliding names, 15 s budget) is the guard: release x64 went 0.52 s (1.4.0) → 9.5 s (#40518) and it timed out / was marked flaky on macOS aarch64 in #40519's CI; debug build: >300 s → 11 s with this change. Output unchanged (same names, same program result).

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• src/bundler/linker_context/crossChunkNames.rs

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Walkthrough

Changes

Cross-chunk name allocation

Layer / File(s)	Summary
Reuse cached name suffixes src/bundler/linker_context/crossChunkNames.rs	assign_unminified caches the latest suffix for each base identifier and starts subsequent collision checks from that suffix. Name allocation remains collision-free.

Merge Risk: ⚪ Minimal · up to a875f

This localized change improves naming performance for colliding cross-chunk bindings without changing generated output or program behavior; no actionable merge-blocking risk remains beyond normal checks and review.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the quadratic naming performance fix for unminified cross-chunk bindings that share a source name.
Description check	✅ Passed	The description explains the performance problem, the implementation change, measured improvements, regression test, verification results, and unchanged output. It does not use the template headings, …
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Description check

Explanation

The description explains the performance problem, the implementation change, measured improvements, regression test, verification results, and unchanged output. It does not use the template headings, but it contains the required information.

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