Mangle exported names for smaller bundle sizes
This PR implements export name mangling to reduce JavaScript bundle sizes.
By shortening exported variable names (e.g., `veryLongExportName` → `a`),
we can achieve meaningful size savings, especially for modules with many
or long-named exports.
The approach leverages the existing locals/facade module split:
1. **Locals module**: Contains the actual code with mangled export names.
Export names are shortened to short identifiers (a, b, c, etc.) using
deterministic hashing to ensure stability across builds.
2. **Facade module**: Preserves original export names for CommonJS require
and namespace imports (`import * as ns`). Maps original names to the
mangled names from the locals module.
Key changes:
- Added `mangled_names: Option<BTreeMap<RcStr, RcStr>>` to `EsmExports`
to store original→mangled name mappings
- Locals module computes mangled names using `shorten_to_unique_hashes`
- Import references resolve mangled names from target module's exports
- Export code generation uses mangled names when available
- Added `shorten_to_unique_hashes` to turbo-tasks-hash for generating
short, unique JavaScript-safe identifiers
- Added `mangledName` property to `__webpack_exports_info__` for debugging
Note: Mangling is currently enabled only for modules that have star exports
(re-exports), as these are the modules that get split into locals+facade.
- Added execution tests for export name shortening and re-export chain mangling
- All 208 execution tests and 85 snapshot tests pass
- Next.js e2e tests pass
