[bug] Tauri v2 asset_resolver is empty for dev

[mildred]

Describe the bug

For Tauri v2, in rust code, and only when running in dev, the app.asset_resolver object have no assets (iter over them yields nothing). However in production, the application assets are correctly listed.

In particular, the localhost plugin does not work in dev

Reproduction

$ npm create tauri-app@latest -- --beta

> npx
> create-tauri-app --beta

✔ Project name · tauri_app_test
✔ Choose which language to use for your frontend · TypeScript / JavaScript - (pnpm, yarn, npm, bun)
✔ Choose your package manager · npm
✔ Choose your UI template · Vanilla
✔ Choose your UI flavor · TypeScript
✔ Would you like to setup the project for mobile as well? · no

Template created! To get started run:
  cd tauri_app_test
  npm install
  npm run tauri dev

$ cd tauri_app_test
$ npm install
$ sed -i s/com.tauri.dev/test-app.example.org/ src-tauri/tauri.conf.json

create assets:

$ mkdir -p public
$ touch public/public-asset.js src/src-asset.js

update index.html to include both assets:

    <script src="/src/src-asset.js" defer></script>
    <script src="/public-asset.js" defer></script>

in src/main.rs:

// Prevents additional console window on Windows in release, DO NOT REMOVE!!
#![cfg_attr(not(debug_assertions), windows_subsystem = "windows")]

// Learn more about Tauri commands at https://tauri.app/v1/guides/features/command
#[tauri::command]
fn greet(name: &str) -> String {
    format!("Hello, {}! You've been greeted from Rust!", name)
}

fn main() {
    tauri::Builder::default()
        .plugin(tauri_plugin_shell::init())
        .invoke_handler(tauri::generate_handler![greet])
        .setup(|app| {
            let asset_resolver = app.asset_resolver();
            println!("asset list start");
            for asset in asset_resolver.iter() {
                println!("asset: {}", asset.0);
            }
            println!("asset list stop");
            Ok(())
        })
        .run(tauri::generate_context!())
        .expect("error while running tauri application");
}

Running npm run tauri dev:

asset list start
asset list stop

In the DOM inspector, network tab, both assets are loaded fine though

Running npm run tauri build followed by running the built executable ./src-tauri/target/release/tauri_app_test:

asset list start
asset: /assets/index-0M1iEA7z.js
asset: /index.html
asset: /public-asset.js
asset: /assets/index-XlHJ6GfY.css
asset list stop

src-asset.js is not there, but if we configure rollup to load this asset it will appear, in vite.config.js, set:

import { defineConfig } from "vite";

// https://vitejs.dev/config/
export default defineConfig(async () => ({

  // Vite options tailored for Tauri development and only applied in `tauri dev` or `tauri build`
  //
  // 1. prevent vite from obscuring rust errors
  clearScreen: false,
  // 2. tauri expects a fixed port, fail if that port is not available
  server: {
    port: 1420,
    strictPort: true,
    watch: {
      // 3. tell vite to ignore watching `src-tauri`
      ignored: ["**/src-tauri/**"],
    },
  },

  build: {
    rollupOptions: {
      input: {
        index: './index.html',
        src_asset: 'src/src-asset.js',
      }
    }
  }
}));

Now, running the built app, it shows the asset:

asset list start
asset: /public-asset.js
asset: /assets/index-XlHJ6GfY.css
asset: /index.html
asset: /assets/src_asset-BSKcq9xs.js
asset: /assets/index-0M1iEA7z.js
asset list stop

Expected behavior

same assets shown for dev and for build

Full tauri info output

[✔] Environment
    - OS: Fedora 40 X64
    ✔ webkit2gtk-4.1: 2.44.2
    ✔ rsvg2: 2.57.1
    ✔ rustc: 1.79.0 (129f3b996 2024-06-10)
    ✔ cargo: 1.79.0 (ffa9cf99a 2024-06-03)
    ✔ rustup: 1.27.1 (54dd3d00f 2024-04-24)
    ✔ Rust toolchain: stable-x86_64-unknown-linux-gnu (default)
    - node: 22.4.1
    - yarn: 1.22.22
    - npm: 10.8.1

[-] Packages
    - tauri [RUST]: 2.0.0-beta.24
    - tauri-build [RUST]: 2.0.0-beta.19
    - wry [RUST]: 0.41.0
    - tao [RUST]: 0.28.1
    - @tauri-apps/api [NPM]: 2.0.0-beta.15
    - @tauri-apps/cli [NPM]: 2.0.0-beta.22

[-] App
    - build-type: bundle
    - CSP: unset
    - frontendDist: ../dist
    - devUrl: http://localhost:1420/
    - framework: React
    - bundler: Rollup

Stack trace

No response

Additional context

I am running a HTTP webserver in rust, triggered from the javascript side, and aimed at serving files for the system browser in order to print them. I need those assets to be served to this web server like the localhost plugin. This is to workaround the lack of print options in Tauri (and WebkitGtk). The app I am working on is : https://github.com/mildred/web_docs

[FabianLars]

Thanks for the extensive report! I'd say this counts as a duplicate of #8411 though, but PRs for that are already open.