This fixes a bunch of long standing issues in our tracker where a build wouldn't finish because of importing user code. It's common for backend apps to spawn some open ended tasks like subscribing to Deno KV or other things. This addresses another problem of having to set up ENV vars just for the build, even though they are technically not required to build islands.

This also gives a roughly ~30% performance boost on cold starts (at least on deno.com). Unfortunately, this does require some breaking changes. But I believe the performance improvements + removing the footgun of loading user code during build is well worth it. This work is also a precursor in case we want to exploring moving to vite at some point in the future.

Breaking changes

1. Build options have moved to the builder.

  // main.ts
- const app = new App({ build: { outDir: "dist/" } })
+ const app = new App()

  // dev.ts
- const builder = new Builder();
+ const builder = new Builder({ outDir: "dist/" });

2. Another breaking change is how file based routes are loaded. Since they're prepared and loaded by the builder the API changed.

  // main.ts
  const app = new App()
    .use(staticFiles())
  
- await fsRoutes(app, {
-   loadIsland: (path) => import(`./islands/${path}`),
-   loadRoute: (path) => import(`./routes/${path}`),
- }); 
+ app.fsRoutes()

You can optionally change the islandDir or routeDir by passing that to the Builder:

// dev.ts
const builder = new Builder({
  islandDir: "/path/to/islands", 
  routeDir: "/path/to/routes"
});

3. Import app lazily in dev.ts. Passing app to builder.build() is not necessary anymore.

- import { app } from "./main.ts";

  const builder = new Builder({ target: "safari12" });
  
  if (Deno.args.includes("build")) {
-    await builder.build(app);
+    await builder.build();
  } else {
-   await builder.listen(app);
+   await builder.listen(() => import("./main.ts"));
  }

4. The production run command has changed. It's now using deno serve

  // deno.json
  {
    "tasks": {
      "dev": "deno run -A --watch=static/,routes/ dev.ts",
      "dev": "deno run -A dev.ts build",
-     "start": "deno run -A main.ts",
+     "start": "deno serve -A _fresh/server.js",
    }
  }

Remove this bit in main.ts:

  // main.ts
  
- if (import.meta.main) {
-   await app.listen()
- }

Fixes #2240
Fixes #2640
Fixes #2592
Fixes #1843