experimental: remote builder (formerly build-slim)

[Aukevanoost]

Tracking issue for the experimental remote builder (formerly build-slim) and its road to feature-parity with Angular's @angular/build:application builder.

Rename: the builder is now registered as remote (was build-slim). Source moved to packages/angular/src/builders/remote/.

What is the remote builder?

A micro-frontend remote builder that runs only the Native Federation build (buildForFederation) and skips Angular's main buildApplication / serveWithVite pipeline entirely. It produces just the federation artifacts (exposes + shared + chunks). It does not serve them — dev serving is external (the host's dev server or any static file server). In watch mode it rebuilds artifacts to disk on change. The remote runs inside a host shell that owns polyfills, the index document, and bootstrapping.

Source: packages/angular/src/builders/remote/

What it already does (via the NF esbuild adapter)

buildForFederation drives the NF esbuild adapter (createAngularEsbuildContext), which already covers:

• Angular AOT compilation
• Component-level stylesheets (Sass / Less / Tailwind / PostCSS)
• Inline-font optimization for component styles
• Source maps (sourceMap)
• fileReplacements
• Browserslist target resolution
• Advanced optimization + minification (gated on dev)
• Code splitting / chunking
• Asset copying (assets), incl. watch-mode incremental copy
• stylePreprocessorOptions, inlineStyleLanguage, optimization, preserveSymlinks passthrough

Parity gaps

Everything Angular's @angular/build:application does in the execute-build / execute-post-bundle / setup-bundling layer is currently absent. Grouped by priority.

A. Output-correctness gaps that matter for a remote

• i18n / $localize (build-slim: i18n / $localize support #67) — the linker plugin never runs and inlineI18n is never called, so $localize markers survive raw in output. No localize, i18nMissingTranslation, i18nDuplicateTranslation.
• define — custom global constant replacement (adapter currently hardcodes only ngDevMode / ngJitMode).
• loader — per-extension esbuild loaders; the adapter reads builderOptions.loader but the builder never sets it.
• outputHashing — no configurable cache-busting mode.
• conditions / allowedCommonJsDependencies — custom resolution conditions and CommonJS allow-list warnings not forwarded.

B. Post-bundle steps never executed

• License extraction (3rdpartylicenses.txt) — compliance gap.
• Budgets (checkBudgets) — no bundle-size enforcement.
• Subresource Integrity (subresourceIntegrity).
• Chunk optimization (Rollup/Rolldown pass) — ships esbuild's raw chunking.
• Build-stats logging (logBuildStats + estimated transfer sizes) — no per-file size table.

C. Host-owned / by-design omissions

These are legitimately the host's responsibility for a remote — tracked so the decision is explicit, not silent.

• HTML / index.html — host-owned by design. The remote builder writes/copies no index.html (removal done: index-html.ts deleted, index schema option removed); output is strictly the federation artifacts (remoteEntry.json + referenced files) plus copied assets. Angular's index generation (script/style tag injection, preload/modulepreload/preconnect hints, CSP, baseHref / deployUrl rewriting) is also out of scope — the host owns the document and bootstraps the remote.
• Polyfills — host-owned by design. Shared runtime polyfills (zone.js, @angular/localize/init) must load once in the host as singletons; bundling them in a remote would double-load zone.js and contradicts the runtime-$localize loading model in build-slim: i18n / $localize support #67. A remote that needs a remote-specific polyfill can import it directly in an exposed entry (it runs on module load), so no polyfills builder option is planned.
• Global styles (styles[]) — host owns global styling; only inline component styles are bundled. No styles option.
• Global scripts (scripts[]) — host owns global scripts. No scripts option.
• Service worker (ngsw.json).
• SSR / prerender / appShell / outputMode / server — irrelevant to a CSR remote.
• webWorkerTsConfig — web-worker bundling.
• security.allowedHosts / autoCsp.
• Dev server / serving — removed by design. The builder produces artifacts only (in watch mode it rebuilds to disk on change); serving in dev is external — the host's dev server or any static file server pointed at the output dir. Removed the Vite server (vite-server.ts), the static middleware (static-middleware.ts), and the SSE build-notifier wiring; dropped the port and buildNotifications options. (vite stays a package dependency — still used by the full build builder's plugin path.) Consequently HMR / live-reload, ssl/proxy/host/allowedHosts dev-server options, and CORS handling are out of scope — they belong to whatever serves the remote.
  • npm-link browser reload gap (npm link + shared libraries stale federation rebuilds and no browser reload in local dev (NF v4 / Angular 21) #55): as of PR fix: Added support for npm link #93 the remote's watcher now tracks npm-link'd shared-package dirs (linkedSharedDirs fed as the 3rd arg to syncNfFileWatcher), so a save inside a linked shared lib does re-bundle fresh federation artifacts to disk in watch mode. But with no dev server / SSE notifier here, the browser is never told to reload — a linked shared-lib change served through a remote still needs a manual refresh. This is consistent with the design above (reload belongs to whatever serves the remote); it's called out so the gap is explicit rather than surprising. See the follow-up below.

Priorities

Highest-value items for remotes specifically: i18n (A), define / loader passthrough (A), and license extraction (B). Category C is host-owned and stays out of the remote builder by design.

Sub-tasks / follow-ups

• build-slim: i18n / $localize support #67 — i18n / $localize support: runtime $localize with the host providing translations, plus a self-describing i18n-manifest.json next to remoteEntry.json (option 2). Full design notes & task checklist there.

• npm link + shared libraries stale federation rebuilds and no browser reload in local dev (NF v4 / Angular 21) #55 — npm-link'd shared libraries in dev: PR fix: Added support for npm link #93 wired linkedSharedDirs into both builders' watchers so edits to a locally-linked shared package re-bundle the affected external. Landed for the remote builder:

  • Watch linked (symlinked) shared-package dirs under node_modules (3-arg syncNfFileWatcher).
  • Cache invalidation / re-bundle of the affected shared external on a linked-lib change (via rebuildForFederation with realpath'd changedFiles).

  Deferred for the remote builder (a linked-lib edit re-bundles to disk but the browser is not reloaded):

  • Browser auto-reload after a remote rebuild. The build (shell) builder broadcasts an SSE completion event; the remote has no dev server / notifier (Category C), so remote-served linked-lib edits need a manual refresh. A fix would require the remote to signal whatever serves it — e.g. a cross-process reload hook / ping to the host dev server, or a per-remote reload endpoint — rather than reintroducing an in-process SSE server.