Store the Turbopack module cache in a Map (#98947)
Maps are faster than Objects for map-like usecases such as the module
cache
The one complexity is `require.cache` which exposes the module cache as
an object, this however is an extremely rare usecase, so we support it
via a runtime module that re-exposes the module cache as an Object using
a `Proxy`.
### Performance
Measured with `bench/module-cost`
Module **execution** time — the phase that actually hits the cache:
| measurement | obj | map | delta | 95% CI | rel |
| --- | --- | --- | --- | --- | --- |
| client commonjs | 13.60 ms | 13.00 ms | **−0.60 ms** | [−0.65, −0.30]
| −4.4% |
| pages api commonjs | 21.59 ms | 20.64 ms | **−0.95 ms** | [−1.39,
−0.74] | −4.4% |
| pages api esm | 33.24 ms | 32.55 ms | **−0.69 ms** | [−1.06, −0.47] |
−2.1% |
| client esm | 20.55 ms | 20.60 ms | +0.05 ms | [−0.25, +0.30] | noise |
Caveat: this benchmark is a deep require chain that deliberately slams
this codepath, so this really just confirms the claim that Maps are
faster and this is relevant to the bundled codepaths.
---------
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
