Compiler Pipeline Internals

Compiler pipeline internals

The spine (one screen)

Counter.ink.tsx
   ▼ P1 program    TS program + checker; resolve sibling .ink.css/.ink.scss
   ▼ P2 parse      TS AST → IRModule; bind primitives (createSignal/Memo/Effect/Ref,
                   defineComponent/Model/Emits/Slot); parse JSX; scope analysis
   ▼ P3 lower      normalize IRComponent; <Show>→IRIf, <For>, <Switch>, <Slot>→
                   IRSlotPlaceholder, <Transition>→IRTransition; events, refs, $bind
   ▼ P4 analyze    reactivity graph, cycle detection, validation → AnalyzedModule
   ▼ P5 plugin ir:post     read-only inspection; plugins push diagnostics
   ▼ P6 emit       per target: IR → Code IR (7 emitters in codegen/targets/<name>/)
   ▼ P7 print      one printer serializes any Code tree → source text + V3 source maps
   ▼ P8 plugin code:post   per-target file transformation (return replacements)

Passes are Pass<I, O> units (pipeline/types.ts), driven by pipeline/compile.ts (compile, compileIncremental). Passes are pure on their inputs; mutable state lives only on PassContext.

The IR (the architectural pivot)

• IRModule { components, contexts, imports, sourceFile } → IRComponent (props, slots, events, state, render tree, styles, runtime mode, target overrides).
• IRNode union: IRElement | IRComponentInstance | IRText | IRExprNode | IRIf | IRFor | IRSwitch | IRSlotPlaceholder | IRFragment | IRTransition (ir/render/nodes.ts; builders/visit/transform alongside).
• IRExprNode preserves the TS expression verbatim plus its IRDependencySet; codegen rewrites it per target.
• Reactivity: SymbolTable (ir/reactivity.ts); SymbolId = componentId::kind::name@offset; kinds signal | memo | effect | prop | context | ref | slot. Dependency sets record read symbols, member paths, and conditionality — this drives fine-grained per-target reactivity.
• IR is serializable (ir/serialize.ts) for on-disk caching by incremental builds; IR_VERSION is the schema version, backed by ir/migration.ts.

Contracts that hold it together (name these before changing anything)

1. IR_VERSION bumps on any breaking IR-node shape change + a migration for serialized caches. Skipping the bump silently corrupts incremental builds.
2. SymbolTable is frozen after P4. No symbol minting inside emit functions — diagnostics and codegen rely on it.
3. Per-pass purity — never stash data on IR nodes between passes; use PassContext.
4. Diagnostics never throw. User errors surface as Diagnostic via ctx.pushDiagnostic (registry: core/diagnostics/codes.ts, INK0001–INK0120). The only throws are assert-style invariant violations = compiler bugs. Plugin exceptions become INK0090; a failed component's emit becomes INK0100 and others continue.
5. A new IR node touches every target's emit — silent omissions surface as missing output. New authoring primitives need P2 binding + P3 lowering or they pass through verbatim and break consumers.
6. Emitted output has zero @inkline/core imports. The runtime-free promise is the product.

Targets and Code IR

A Target = { name, rewrites: RewriteRules, conformance?, emit(component, ctx) }, registered in codegen/registry.ts builtinRegistry. Rewrite tables describe reactive-read style (React strip-call, Vue field-access → .value, Svelte direct), setter style, ref access, attr/event casing. Emit builds a Code IR tree, not strings: JSX flavor (React/Solid/Qwik: CJsxElement), template flavor (Vue/Svelte: CTmplElement/directives/mustache), string-template flavor (Angular/Astro: CRaw + CScript). One print() serializes everything; loc: SourceLocation threads through every node so source maps survive.

Per-target slot/transition emission: <Slot> → props.children/render props (React/Solid), <slot> (Vue/Svelte), <ng-content select> (Angular). <Transition> → native (Vue), directive (Svelte), __InkTransition wrapper (React/Solid/Qwik), CSS classes (Angular/Astro). hasSlot is a real check except Qwik/Angular (always true, INK0068 — hence the :empty CSS convention). Angular target specifics: kebab-case ink-* attribute selectors, a klass input merging forwarded classes onto the root, full imports declarations, host-collapse variants — native attrs must be declared as explicit base props (fallthrough breaks on wrapper/host-collapse variants).

Testing (three layers + one hard rule)

Unit (next to source) · Codegen per target (codegen/targets/<name>/index.test.ts + __tests__/, hand-built-IR snapshots + fixture integration) · Scenario (__fixtures__/scenarios.ts — compile a fixture across all 7, mount each, assert equivalent DOM). One test file per target, never a shared multi-target test — no ALL_TARGETS loops, no importing another target's index; enforced by testing/per-target-tests.test.ts. Harnesses: @inkline/compiler/testing (IR-close) vs @inkline/test-utils (consumer-facing — prefer it outside the compiler). Bench: pnpm bench (tinybench, scripts/bench.ts, baseline comparison via runBenchSuite).

The two compile paths (divergence is by design)

• CLI path (inkline compile, used by ui/components): globs .ink.tsx, writes per-target files into targetOutDir (ui/<framework>/.inkline/), generates configured barrels (index.ts=styled, headless.ts, stories.ts namespace) and per-framework story CSF via @inkline/storybook/generator. --watch recompiles on change.
• Plugin path (@inkline/plugin, unplugin factory): matches *.ink.tsx in the bundler's transform hook, runs compileIncremental for one required target, in-memory — no barrels, no stories, no config-file loading (pair with @inkline/config-loader).

Bugs that appear on one path only are expected — test the right path, and say which paths a change affects.

Sharp edges & current gaps

• @inkline/plugin has ZERO direct tests — its coverage rides compiler fixtures and repo consumers. Highest-risk untested surface; leave coverage behind when touching it.
• Stale dist: consumers (CLI, Storybook, ui/components) use the compiler's dist/ — vp pack in core/compiler after source edits, or you're testing yesterday's compiler.
• core/core has no tests by design (inert stubs); behavior is proven in compiler scenario tests.
• Coverage on .ink.tsx is remapped via coverInkViaReact (React-target execution + composed source maps); spans are coarse — a fully-exercised component can read below 100%. Never add .ink.tsx to coverage.include (v8's uncovered-files pass would PARSE_ERROR).
• __fixtures__ are lint-exempt for vp lint but must compile lint-clean across targets in lint.test.ts; the Astro side has a known pre-existing parse-failure baseline (~74) — not regressions.
• v1 frontier (per README "v0 limitations", partially stale — trust codegen/registry.ts): component-ref forwarding (INK0070), scoped CSS/<style> blocks, async/Suspense/createResource runtime, plugin HMR, sub-expression source-map granularity. Angular/Qwik/Astro are shipped, whatever the README says.