pyreon

Bundling Mistakes

Generated from .agents/rules/anti-patterns.md (the same source as MCP get_anti_patterns). Each entry is a real mistake + its fix; where a detector code is listed, the linter / pyreon doctor / MCP validate catches it automatically.

A dev-only check that reads a REST parameter keeps the parameter in production.

signal()'s read closure was (...args) => { if (dev && args.length) warn(); … } — the bundler folds the warning away but not the signature, so production shipped (...e)=> and every signal READ could materialize an array it never looked at. Put the dev and prod shapes in two declarations chosen by the dev gate (const read = process.env.NODE_ENV !== 'production' ? (...args) => … : () => …). Reference: packages/core/reactivity/src/signal.ts.

A client guard that ships a name list the ELEMENT already answers.

Refusing on* handler attributes on the client used EVENT_HANDLER_ATTRS (~160 names, ~0.8 KB gz — the largest item in a minimal app bundle), yet a content attribute is only ever compiled into a handler when the element's interface defines that IDL handler, so key in el is the engine's exact answer. The client asks the element (isElementEventHandlerAttr); SSR, with no element, keeps the list. Two traps: happy-dom defines far fewer handlers than Chromium (no onload on <div>/<meta>, none on MathML), so the refusal must be proven in real Chromium, not happy-dom; and a shared guard must take the predicate as a PARAMETER (@pyreon/head's isHeadAttrSafe), because importing the list anywhere in a client module ships it. Measure these by bundling a real app with every @pyreon/* package INCLUDED — per-package budgets externalize @pyreon/core, where the list lived, and showed the win as −14 B. Reference: packages/core/core/src/url-guard.ts:isElementEventHandlerAttr, runtime-dom/src/tests/event-handler-attr.browser.test.tsx.

A barrel is a reachability edge; sideEffects, not /* @__PURE__ */, fixes it

An index.ts that export *s every layer makes one import reach every module-level call (api.endpoint(…), s.object(…), mock(routes)). Annotating each call @__PURE__ barely helps because the arguments are calls too; sideEffects is decided per module.

  • The declaration must be true: use the array form naming files with real module-scope effects.

  • Emit a package.json (with "type": "module") beside generated output so the result does not depend on the consuming app's config.

  • Unused data (fixture tables, route arrays) survives minification wherever reachable. Keep dev surfaces out of the production entry (./dev, like @pyreon/server/client).

  • Code: packages/tools/lathe/src/emit/{entries,package-marker}.ts. Test: lathe/src/tests/entry-points.test.ts (run with and without the marker; the no-marker half catches barrel regressions).

A prop-gated optional feature cannot tree-shake

A branch on a runtime prop is reachable code. In @pyreon/charts, geometry and marks tree-shake as imports, but navigator, dataZoom and brush are props.x === true branches inside packages/fundamentals/charts/src/engine/Chart.tsx, so every chart import pays for them. An optional feature tree-shakes only when it is an import: register it at module load into a core slot (like setThemeEngine, setStyleExtraction). Detect by bundling the minimal import and grepping for a symbol only the optional half defines; a size budget only says something grew.

A bundle assertion keyed on a generated identifier is vacuous

Minification renames seedFaker, so not.toContain('seedFaker') always passes. Assert on external import specifiers (@faker-js/faker) and string data. Pair every "must be absent" suite with a control that bundles everything (export *) and requires each marker present. Reference: lathe/src/tests/entry-points.test.ts:DEV_MARKERS.

A bundle assertion keyed on a generated identifier is vacuous

Minification renames it, so expect(bundle).not.toContain('seedFaker') passes with the module bundled. Assert on what minification cannot touch: external import specifiers (@faker-js/faker) and string data (a fixture uuid). Pair every "must be absent" suite with a control that bundles the module (via export *, so every surface is reached) and requires each marker present; otherwise the suite also passes when the emitter produces nothing. Reference: lathe/src/tests/entry-points.test.ts:DEV_MARKERS.

Bundling Mistakes