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🌳 fix: keep the Symbol.metadata install through tree-shaking

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`sideEffects` named metadata.js, the module holding the global install, but not the
barrel that re-exports it. A side-effect-free barrel is droppable whole, so every
bundler pruned the `export * from './metadata.js'` edge before metadata.js's own
marking was ever consulted, and the install vanished.

Measured on `import { configure } from 'cereale'`: 145 bytes through esbuild, 143
through webpack, 144 through rollup, with `Symbol.metadata` absent from all three.
It matters because tsc's decorator emit reads the well-known symbol directly —

    const _metadata = typeof Symbol === "function" && Symbol.metadata
      ? Object.create(null) : void 0;

so without it a decorated class is handed `metadata: undefined` and ends up with no
rules at all. Two places in the source promised this survived bundling; it did not.

index.js and index.ts are listed now. The cost is ~100 bytes and lands only on
imports that reach nothing else: the single-decorator, validateSync, toPlainSync,
toInstanceSync and whole-library cases are byte-identical before and after, across
all three bundlers. dist/cjs needs nothing — tsc emits `__exportStar(require(...))`,
an unconditional statement no bundler can drop.

Two new cases in treeshake.test.ts pin it, one on src and one on dist/esm, since
those are separate manifest paths and a typo in either is invisible from the other.
Both were checked by removing the entry and watching them fail.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SAcqrz3FcadkYr3xG32CjK
This commit is contained in:
Claude
2026-08-05 17:22:16 +00:00
parent c48a106a05
commit 3bd190bde6
5 changed files with 80 additions and 4 deletions
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CHANGELOG.md
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@@ -43,7 +43,7 @@ Measured, minified, across esbuild / rollup / webpack:
| What you import | esbuild | rollup | webpack |
| --- | ---: | ---: | ---: |
| `flattenErrors` | 287 | 292 | 291 |
| `flattenErrors` | 394 | 367 | 394 |
| one decorator | 1,837 | 1,823 | 1,818 |
| `validateSync` | 3,722 | 3,554 | 3,823 |
| `toPlainSync` | 7,744 | 7,769 | 7,832 |
@@ -60,6 +60,22 @@ names the rules that must not appear — and one case asserts that everything IS
everything is used, so a "shaken" result cannot come from a bundle that failed to build. Strip
the annotations and it fails with `"must be a latitude" should have been shaken out`.
The same pass shook out something that was supposed to stay. Cereale installs `Symbol.metadata`
when the runtime lacks it, and `sideEffects` named the module holding that install — but not the
barrel that re-exports it. A side-effect-free barrel is droppable as a whole, so all three
bundlers pruned the `export * from './metadata.js'` edge before metadata.js's own marking was
ever consulted: `import { configure } from 'cereale'` came out at 145 bytes through esbuild, 143
through webpack and 144 through rollup, with `Symbol.metadata` in none of them. That matters
because `tsc`'s decorator emit reads the well-known symbol directly — `typeof Symbol ===
"function" && Symbol.metadata ? Object.create(null) : void 0` — so without the install a
decorated class gets `metadata: undefined`, which is to say no rules at all.
`index.js` and `index.ts` are now listed too. It costs about 100 bytes, and only on imports that
reach nothing else; every row of the table above except the first was byte-identical before and
after, across all three bundlers. Two more cases in `treeshake.test.ts` pin it, one on the source
and one on `dist/esm`, because those are separate paths in the manifest and a typo in either is
invisible from the other side.
### Frameworks
[FRAMEWORKS.md](FRAMEWORKS.md) — a setup recipe for each, every one run before it was written,