Declare side-effecting modules so bundlers have better hints for what can be tree-shaken#21365
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Declare side-effecting modules so bundlers have better hints for what can be tree-shaken#21365NullVoxPopuli wants to merge 6 commits intomainfrom
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📊 Size reportTarball size — dist/dev -1.32%↓
dist/prod -1.45%↓
smoke-tests/v2-app-hello-world-template/dist -31%↓
🤖 This report was automatically generated by wyvox/pkg-size |
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This was referenced May 3, 2026
NullVoxPopuli
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May 4, 2026
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a manual lint, of sorts
Two purely-additive bundler hints that let consumer bundlers (vite/rolldown, webpack, esbuild) tree-shake aggressively through ember-source's internal barrel re-exports without requiring any source-file restructuring. 1. **`"sideEffects": false` on `ember-source/package.json`** - declares that no module in this package has top-level side effects that need to be preserved if the module's exports are unused. The bundler can then DCE re-exports through `index.ts` barrels that currently anchor the rest of the graph in place. This is safe in practice because rollup's chunking groups symbols with their side effects: any chunk containing the classic `Component` class also contains the `setInternalComponentManager(CURLY_COMPONENT_MANAGER, Component)` call, the `setHelperManager` registrations live in the chunk that holds `helper.ts`, etc. Importing a symbol from a chunk pulls the chunk's side effects along; apps that don't reach those symbols don't need their side effects either. 2. **`treeshake.moduleSideEffects` callback in `rollup.config.mjs`** - the package-level `sideEffects: false` declarations on `@glimmer/debug`, `@glimmer/debug-util`, and `@glimmer/local-debug-flags` get lost when rolldown emits shared chunks (debug code from these packages can leak into chunks that the renderer-only path then pulls in). The callback re-asserts module purity at the chunk level so leaked debug code drops out of the renderer-only path. Measured against `smoke-tests/v2-app-hello-world-template`: | | raw | gzip | | - | - | - | | before | 251.05 KB | 79.75 KB | | after | 172.99 KB | 55.31 KB | Classic `v2-app-template` and v1 `app-template` smoke tests still build and pass. `pnpm test:node` 20/20. `pnpm vite build --mode development` (full dev test suite app) builds clean. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
`sideEffects: false` declares a contract that's invisible to reviewers: any module-level mutation (`set*Manager(...)`, `Foo.reopenClass(...)`, `_backburner = new Backburner(...)`) silently rots the contract. Bundlers will drop these side effects when the symbol they ride along with isn't imported. Adds a `pnpm test:tree-shake` script that bundles each pure-today entry point with rollup as if a consumer imported it for side effects only, and asserts nothing survives. Regression in any known-pure entry fails CI with an actionable message. Today the list is 23 entries — `@glimmer/util`, `@glimmer/destroyable`, `@ember/owner`, `@ember/version`, etc. The 43 currently-impure entries (@ember/-internals/glimmer, @ember/runloop, @glimmer/runtime, …) are omitted because they have known top-level side effects that sideEffects: false promises bundlers can drop in practice anyway. Patch: agadoo's bundled acorn pins ecmaVersion 11 (ES2020), which chokes on private class fields and other ES2022+ syntax that appears in dist. The patch bumps it to `'latest'`. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Of the three entries previously in PURE_INTERNAL_PACKAGES, only `@glimmer/debug` actually contributes to the hello-world bundle size: | array contents | hello-world raw | gzip | | - | - | - | | `[]` (no callback) | 181.12 KB | 57.82 KB | | `['@glimmer/debug-util']` | 181.12 KB | 57.82 KB | | `['@glimmer/local-debug-flags']` | 181.12 KB | 57.82 KB | | `['@glimmer/debug']` | 172.99 KB | 55.35 KB | | all three | 172.99 KB | 55.31 KB | `@glimmer/debug-util` and `@glimmer/local-debug-flags` are already inferred pure by rolldown's static analysis (their content either has no top-level statements that look like side effects, or gets fully stripped by the LOCAL_DEBUG macro in prod builds). Re-asserting them adds nothing. Inlined the array since the callback now checks a single path prefix. Added a note explaining the measurement so the next person adding to the list does so with data, not pattern-matching. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Demo:
bundler hints that let consumer bundlers (vite/rolldown, webpack, esbuild) tree-shake aggressively through ember-source's internal barrel re-exports without requiring any source-file restructuring.
for the ember-source dist/tarball, the result is that chunks shake out a bit differently.