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docs: bun bake - #45751
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Updated 9:05 AM PT - Oct 17th, 2026
❌ @alii, your commit 6d1dce4 has some failures in 🧪 To try this PR locally: bunx bun-pr 45751That installs a local version of the PR into your bun-45751 --bun |
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Updated 9:05 AM PT - Oct 17th, 2026
❌ @alii, your commit 1e973fb has some failures in 🧪 To try this PR locally: bunx bun-pr 45751That installs a local version of the PR into your bun-45751 --bun |
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Updated 8:07 AM PT - Oct 18th, 2026
✅ @alii, your commit 64753e1ee68df9d1d826c445c59334516bb493eb passed in 🧪 To try this PR locally: bunx bun-pr 45751That installs a local version of the PR into your bun-45751 --bun |
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This PR adds build plugins to `bun bake`, from a `bake.config.ts` file. It is the second step of the new Bake design (https://github.com/alii/bake-rfc), after #45682. ```ts // bake.config.ts import { defineConfig } from "bun:bake"; import tailwind from "bun-plugin-tailwind"; export default defineConfig({ plugins: [tailwind], }); ``` - The plugins are Bun plugins (`{ name, setup(build) }`). The dev server runs them on the pages and the files that the pages import, the same as the plugins in `[serve.static] plugins` of `bunfig.toml`. - The default export can also be a function. It gets `{ mode: "development" }`. - `bun:bake` is a new built-in module. It has one function, `defineConfig`, which returns its argument. It resolves only where `bun bake` is (the Bake feature flag). - The plugins of `bunfig.toml` still apply, before the plugins of `bake.config.ts`. How it works - `internal/bake.ts` loads `bake.config.ts` before it starts the server, and checks it. Then it gives the plugin objects and their names to the VM (`$newRustFunction("bake/config/plugins.rs", "setConfigPlugins")`). The VM keeps them in `bake_config_plugins` (a JS array) and `bake_config_plugin_names`. - The server already keeps the names of the `bunfig.toml` plugins on the VM, and loads them when a route needs plugins. Now it also starts that load when only `bake.config.ts` has plugins, and `loadAndResolvePluginsForServe` takes plugin objects as well as module names. - The dev server's Tailwind check (which bundles the Tailwind CSS again after a change) also looks at the names of the `bake.config.ts` plugins. What `bun bake` rejects, with an error - A default export that is not an object or a function. - An option other than `plugins`. - A plugin that is not an object or a function, has no `name`, or has no `setup()`. As in `Bun.build()`, a function with `name` and `setup` is a plugin. `bun bake` now always reloads `app/server.ts` in place on a change, as `bun --hot` does, so it has no `--watch` and `--hot`: - The CLI sets `HotReload::Hot` for `bun bake`. `bun bake --watch` is an unknown argument, and `bun --watch bake` is an error, also with `--check`. The CLI records `--watch` in `ctx.debug.watch_flag`, because `HotReload::Watch` alone does not tell it from `--hot` with `--check`. `bun bake --check` still runs as `--watch` (it starts again after a change, to type check again), as `bun --check` does with `--hot`. - An error that a change to `app/server.ts` or `bake.config.ts` can fix no longer exits: the process shows it and reloads after the fix, as under `bun --hot`. An error in the arguments, in the names of the pages, or "nothing to serve" still exits with code 1, because no change to a loaded file can fix it. - A bad `--port` or `--host` must not leave the process waiting for a change: the shared flag parser (`internal/serve_cli.ts`) takes a port only as a whole number from 0 to 65535, and a `Bun.serve()` failure at the start exits 1 when `--port` or `--host` is set. `bun ./index.html` gets the same port check: `--port=abc` is an error there too. - A mistake that `bun bake` finds in the arguments or the app's files (a `BakeError`) prints as one line, `error: <message>`, with no stack trace into `internal/bake.ts`. Then the process exits 1, or waits for a change when one can fix it. "Nothing to serve" now says what to add. An error that the app's own code throws keeps its stack trace. - `Bun__loadBuiltinEntryPoint` marks the promise of the built-in entry point as handled. The VM reports its rejection; before, the rejection tracker reported it a second time. `bun ./index.html` gets this too. - The plugins load once. When `bake.config.ts` changes, `bun bake` prints `"bake.config.ts" changed. Restart "bun bake" to use the new plugins.` Also in this PR: `bun bake` reads the `host` option of the `app/server.ts` export when it has no `hostname`, as `Bun.serve()` does (a review comment on #45682). Not in this PR - Vite-style plugins (`transform`, `load` and other hooks). `bun bake` takes Bun plugins. - A restart of the process when `bake.config.ts` changes, so the new plugins apply on their own. Today `bun bake` asks for a restart. A follow-up PR. - The types of `bun:bake` and the docs are in the docs PR (#45751), to merge when Bake is on in a release. Until then, `bun --check` on a project with `bake.config.ts` reports that `bun:bake` has no types. Tests - `test/cli/bake/bake.test.ts`: a `bake.config.ts` plugin (in a `defineConfig` function, with `mode`) and a `bunfig.toml` plugin both change the CSS of a page; a plugin function sees the project as `build.config.root` when there is no bunfig.toml; each error above; the restart note; a reload of `app/server.ts` on the same server, with no flag; `--watch` is refused. - `test/bake/serve-plugins-dev-server.test.ts`, `test/bake/dev/css.test.ts`, `test/bake/hmr-socket-protocol.test.ts` and the `Bun.serve` HTML tests pass, for the `bunfig.toml` plugins.
This was referenced Oct 18, 2026
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This PR adds `.tsx` and `.jsx` pages to `bun bake`, and frameworks in `bake.config.ts`. It is the next step of the new Bake design (https://github.com/alii/bake-rfc), after #45902. ```tsx // app/pages/blog/[slug].tsx export default function Post({ params }) { return <h1>{params.slug}</h1>; } ``` - A framework decides how files become routes and how a route becomes HTML. `bun bake` has a default framework: the `.tsx` and `.jsx` pages of `app/pages/`, in Next.js pages style (`index.tsx`, `[slug].tsx`, `_layout.tsx` for layouts; files and folders that start with `_` are not pages). - The default framework uses the project's own `react` and `react-dom`, not a copy in Bun. It streams the HTML from the server, then hydrates it in the browser. Fast Refresh keeps the state of a page when you edit it. - Before it starts, `bun bake` checks the project's React for the default framework. It exits with a one-line error when React is not installed, when the version is not 18 or 19, or when `react` and `react-dom` are different versions. Each error gives the `bun add` command that fixes it. - A plugin in `bake.config.ts` can bring its own framework instead. Its `framework` is the same object as the `framework` of the `app` option of `Bun.serve()`, read by the same parser: its routers (`fileSystemRouterTypes`: folder, style, entry points, extensions, layouts), `serverComponents`, `reactFastRefresh`, `builtInModules` and `plugins`. ```ts export default { plugins: [{ name: "my-framework", framework: { fileSystemRouterTypes: [{ root: "src/routes", style: "nextjs-pages", serverEntryPoint: "./framework/server.ts", clientEntryPoint: "./framework/client.ts", clientPages: true, }], }, }], }; ``` A plugin with a `framework` needs no `setup()`. Two plugins with a framework are an error. `.html` pages in `app/pages/` and `app/server.ts` work with every framework. - A router type has a new option, `clientPages`. With it, the pages and layouts also go into the browser build, and the client entry point loads those of the current route from `route` of `bun:bake/client`, to hydrate the server's HTML. It cannot be used with `serverComponents`, where the browser gets the client components instead. The default framework sets it. How it works - `internal/bake.ts` checks the `framework` of a plugin when it loads `bake.config.ts`: it runs the parser of `Bun.serve()` on it (`checkFramework`), and resolves its entry points from the project root. A mistake is then a one-line error of `bake.config.ts`, and `bun bake` waits for a fix. - `internal/bake.ts` gives the framework to its own `Bun.serve()` through a private function (`setPages`), not a new public option. `ServerConfig` parses the plugin's object with `Framework::from_js`, or makes the default with `Framework::bake_pages`. - With `clientPages`, the dev server adds the page and its layouts to the client graph, traces them into the route's browser bundle, and writes their IDs into `config.route` of the bundle. The browser runtime gives them to `bun:bake/client` as `route.page()` and `route.layouts()`. - A change to a page changes both its server copy and its browser copy. The browser runtime used to see only "server code changed" and dropped the JavaScript part of the update. When `config.route` is set, it now applies that part too, so Fast Refresh updates the page in place. - In the dev server, `bun:bake/client` and `bun:bake/server` now resolve for every framework. Before, they resolved only with server components. The HMR runtime always provides them. Fixes in the same code - Two pages with the same URL pattern (`[a].tsx` and `[b].tsx`) panicked with "TODO: propagate aliased route error". The router now reports its usual "Multiple pages matching the same route pattern is ambiguous" error, with both files, and keeps serving. - A route of the server (`app/server.ts` routes, `.html` pages) with the same path as a framework page hid the page with no message. The dev server now prints `error: The server has a route "/about", which hides the page app/pages/about.ts`, and keeps serving. It checks when the server sets its routes (at the start and on a reload of `app/server.ts`) and when the router adds a page; the test covers the start. - A request for the browser bundle of a route whose router has no client entry point panicked (`assertion failed: self.current_chunk_len > 0`). It now gets a 404, and `meta.modules` is empty for such a route. Not in this PR - `bun bake build` (a production build). - A custom routing style: `style` is one of the three Next.js styles. The function form in the types was never implemented. - The docs of frameworks in `bake.config.ts` and of `route`. They go in the docs PR (#45751). Tests - `test/cli/bake/bake.test.ts`: the default framework with a layout and a param, next to an `.html` page and `app/server.ts` routes; the three React errors; a framework plugin with its own folder (`src/routes`) and extension, no React and no client entry point; `clientPages` puts only the current route's page in its browser bundle; two pages with the same pattern; a page that an `app/server.ts` route hides; two frameworks; a framework that the parser rejects; a framework entry point that cannot be found; `clientPages` with `serverComponents`. - `test/bake/dev/react-spa.test.ts`: in the test browser, a page of the default framework hydrates (a click changes the state), then an edit to the page keeps the state (`clicks 2`, not a reload). - All of the new tests fail on the released Bun. React 18 (the test suite's) and React 19 both pass the hydration test locally. - In `test/bake/`, 31 tests fail locally: the `production`, `server-sourcemap`, `react-response`, `ssg-pages-router` and `request-cookies` tests install the experimental React of the server components framework first, and that install fails on my machine's package mirror. The rest pass. CI runs them all.
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This PR adds the docs for
bun bake(#45682). Merge it when Bake is on in a release build.docs/bundler/bake.mdx(new), in the "Development Server" group: pages inapp/pages/,app/server.ts, the flags, and whatBun.main,import.meta.mainandprocess.argvare underbun bake.docs/runtime/utils.mdx:Bun.mainis an empty string when no file is the entry point, as underbun bake.packages/bun-types/bun.d.ts: the same note in the JSDoc ofBun.main.docs/bundler/bake.mdx:bake.config.tsand its plugins, and the options ofBun.serve()that theapp/server.tsexport can have (from the PR after add bun bake: serve app/pages and app/server.ts #45682).packages/bun-types/bake.d.ts(new): the types ofbun:bake(defineConfig,Config,ConfigEnv), with a fixture intest/integration/bun-types/fixture/bake.ts.Before merging, update the warning at the top of
bake.mdx. It says that release builds needBUN_FEATURE_FLAG_EXPERIMENTAL_BAKE=1.