fix(treeshake): preserve side-effect-free spread arguments in manual-pure chains

[IWANABETHATGUY]

Follow-up to #10427.

#10427 restored the eagerly-evaluated child effects of manual-pure chains, but its eager-child walk maps every spread argument to an unknown side effect. So a manual-pure chain wrapping a statically-safe spread — make(...[]).value, make(...'').value, make(...[])() — is now retained wholesale, even though spreading an array, string, or template literal only runs built-in iterators. Rollup drops these.

Fix

Surface spread arguments distinctly from plain eager children (new EagerChild enum) and analyze them with analyze_spread_argument, mirroring oxc's Argument::may_have_side_effects:

• array / string / template-literal operands are analyzed through the (oxc-gated) expression analyzer, so a side-effectful element (make(...[effect()])) or a nested spread (make(...[...x])) still retains the statement;
• any other operand stays conservatively unknown, since evaluating or iterating it may run a user-defined Symbol.iterator.

Tests

New unit test test_manual_pure_chains_drop_side_effect_free_spreads covers both directions: safe literal spreads become removable, while effectful or opaque spreads stay retained — including the nested-spread (...[...x]) and bare-identifier (...x) cases that must not under-retain.

[netlify]

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[codspeed-hq]

Merging this PR will not alter performance

✅ 7 untouched benchmarks
⏩ 10 skipped benchmarks¹

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_{Comparing fix/manual-pure-safe-spreads (1578552) with main (cd742e7)}

Footnotes

1. 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. ↩

[hyfdev]

Merge activity

• Jul 24, 6:07 AM UTC: The merge label 'graphite: merge-when-ready' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Jul 24, 6:07 AM UTC: hyfdev added this pull request to the Graphite merge queue.
• Jul 24, 6:13 AM UTC: Merged by the Graphite merge queue.