feat(hmr): component template & style hot module replacement (#145) - #187
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lukekania merged 3 commits intoJun 9, 2026
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First slice of Hot Module Replacement: read the `hmr` flag and hot-swap
global stylesheets in place without a full page reload.
- project-resolver: parse `architect.serve.options.hmr` (base + active
serve configuration override) into `ResolvedAngularProject.hmr`;
defaults to false.
- cli: add `--hmr` / `--no-hmr` to `serve` (CLI wins over angular.json,
else inherit, else false). When HMR is on and a rebuild touches only
global stylesheet entries, emit a CSS-update instead of a reload.
- dev-server: new `DevServerEvent::CssUpdate { timestamp }` →
`event: css-update` SSE frame; the injected client swaps the
`styles.css` <link> with a cache-busted href, preserving page state.
Component template/style HMR and the `/@ng/component` update endpoint
land in follow-up slices on the milestone branch.
Runtime scaffolding for component-level HMR, ahead of the compiler
codegen that populates it.
- dev-server: new `DevServerEvent::ComponentUpdate { id, timestamp }` →
`event: angular:component-update` SSE frame; a shared `ComponentUpdates`
registry (id → update-module source) on `DevServerConfig`, served at
`GET /@ng/component?c=<id>` (text/javascript, empty 200 for unknown ids,
400 when `c` is absent) — mirrors @angular/build's component middleware.
- client: the injected script publishes a `window.__ngcHmr` bus and
dispatches `angular:component-update` to registered handlers; new
`HMR_RUNTIME_PRELUDE` binds `import.meta.hot` to that bus.
- serve: share the registry with the dev server and prepend the runtime
prelude to `main.js` on each HMR build so per-component initializers can
resolve `import.meta.hot`.
The registry stays empty and component edits still trigger a full reload
until the template-compiler emits update modules (next slice).
Lights up Angular-parity template/style HMR end to end, building on the
config plumbing, dev-server endpoint, and runtime bus from the previous
slices.
template-compiler:
- New `hmr` module: `encode_uri_component` (JS semantics), per-component
id `encodeURIComponent("relpath@Class")`, the initializer IIFE, and the
update-module codegen. The update module reuses the existing Ivy def
verbatim via the linker's var-alias technique (`var XX = i0.XX`), with
`@angular/core` arriving as the `namespaces` arg and template deps as
positional params; it reassigns only `ɵcmp` (template/style-only path).
- `CompileOptions.hmr` and `CompiledFile.hmr` carry the artifacts;
`rewrite_source` adds `import * as i0` so the appended initializer can
reach `ɵɵreplaceMetadata`.
cli:
- Thread `hmr` through `run_build_with_options`; aggregate per-component
update modules and resource→component maps into `BuildResult`; cache the
artifacts in the incremental `CachedModule`.
- serve: classify each rebuild — global stylesheet → css-update, external
component template/style → component-update(s), `.ts`/inline/unknown →
full reload — and inject the `import.meta.hot` prelude into every chunk
(eager `main.js` and lazy `chunk-*.js`).
Verified against an Angular 21 app: editing a component `.html`/`.scss`
swaps it in place via the `/@ng/component` update module and
`ɵɵreplaceMetadata`; global styles swap the `<link>`; `.ts` reloads.
lukekania
changed the base branch from
feat/hmr-component-endpoint
to
milestone/v0.11.0-builder-parity
June 9, 2026 14:09
This was referenced Jun 10, 2026
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Lights up Angular-parity template/style HMR end to end (#145), building on the config plumbing (#185) and dev-server endpoint + runtime bus (#186). Stacked on #186.
template-compiler
hmrmodule:encode_uri_component(JSencodeURIComponentsemantics), per-component idencodeURIComponent("relpath@Class"), the initializer IIFE, and the update-module codegen. The update module reuses the existing Ivy definition verbatim via the linker's var-alias technique (var ɵɵX = i0.ɵɵX), with@angular/corearriving as thenamespacesargument and template deps as positional params; it reassigns onlyɵcmp(template/style-only path).CompileOptions.hmrandCompiledFile.hmrcarry the artifacts; the source rewrite addsimport * as i0so the appended initializer can reachɵɵreplaceMetadata.cli
hmrthrough the build; aggregate per-component update modules and resource→component maps into the build result; cache the artifacts in the incremental module cache..ts/inline/unknown → full reload — and inject theimport.meta.hotprelude into every chunk (eagermain.jsand lazychunk-*.js).Verified end-to-end (Angular 21 app)
.html) → swapped in place via the/@ng/componentupdate module andɵɵreplaceMetadata; no reload, state preserved. The served module reflected the live template edit..scss) → component-update.<link>swap..ts) → full reload.The bundler correctly bound
import * as i0to the synthesized core namespace (var i0 = __ns_angular_core_...), and the initializer / update-module references resolved after bundling.Definition of done (#145)
.cssedit replaces styles in-place without reload ✅.htmltemplate re-renders the affected component without reload ✅.tsedit falls back to full reload ✅hmr: trueenables the above;hmr: false(default) keeps full-reload behavior ✅Follow-ups (deferred)
.ts) HMR detection via def diffing (currently reloads).Targets the milestone branch via the stack; retarget to it once #186 merges.