Optimize strict module factory chunks (#98421)
### What?
Reduce Turbopack ECMAScript chunk size by emitting strict module
factories in a shared strict-mode scope instead of repeating `"use
strict"` in every factory.
The chunk format now chooses among the existing flat representation, a
mixed representation with flat non-strict factories plus a nested strict
array, and an all-strict representation that wraps the complete chunk in
a strict IIFE. Each factory is generated through the existing single
code path; the production minimizer removes its redundant directive when
the factory is created inside a strict wrapper. Browser and Node.js
emitters share the mode selection and serialization implementation,
while the runtime remains compatible with the existing flat format.
### Why?
ECMAScript modules are always strict, so large chunks currently repeat
the same directive across many factories. Moving strictness to the scope
where those factories are created removes redundant bytes without
copying arrays or changing strict/sloppy execution semantics.
For `bench/basic-app`, this reduces total raw JavaScript by 16,831 bytes
(0.161%). Partitioning factories changes compression behavior, resulting
in a 1,286-byte (0.051%) gzip increase across all JavaScript; format
selection therefore remains based on emitted raw bytes.
### How?
- Determine each chunk item's strictness from the already-collected
chunk metadata.
- Generate every factory once with its normal directive, then rely on
the minimizer to remove redundant directives inside strict wrappers.
- Compare the expected minified directive bytes removed with the exact
wrapper bytes added and keep small chunks in the existing flat format.
- Keep non-strict factories flat in mixed chunks and append strict
factories as an array produced by a strict IIFE.
- Wrap the complete registration/export in a strict IIFE when every
factory is strict, keeping those factories flat and avoiding a nested
array entirely.
- Use the shorter arrow IIFE when the target supports it, with a
function IIFE fallback for older targets.
- Preserve source-map sections, scope-hoisted module IDs, factory
naming, and ordering within each partition.
- Add focused strict, sloppy, mixed, all-strict, old-target, and
below-threshold coverage and update affected Turbopack snapshots.
### Verification
- `cargo nextest run -p turbopack-tests -E 'test(snapshot)'`
- `cargo clippy -p turbopack-ecmascript -p turbopack-browser -p
turbopack-nodejs`
- `pnpm build-all`
- `pnpm --dir turbopack/crates/turbopack-ecmascript-runtime/js
check:nodejs`
- `bench/basic-app` production Turbopack build, repeated to confirm
deterministic size totals
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Co-authored-by: vercel-fleet-prod[bot] <318278635+vercel-fleet-prod[bot]@users.noreply.github.com>
Co-authored-by: Tobias Koppers <1365881+sokra@users.noreply.github.com>
