Initial scaffold: Sinatra map app with Tauri desktop shell

Sinatra backend serving a basic Leaflet map, wrapped in a Tauri
desktop shell that starts the same server in a native window.

src-tauri/Cargo.toml

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+[package]
+name = "maptool"
+version = "0.1.0"
+description = "Desktop shell for the MapTool mapping application"
+edition = "2021"
+rust-version = "1.77"
+
+[lib]
+name = "maptool_lib"
+crate-type = ["staticlib", "cdylib", "rlib"]
+
+[build-dependencies]
+tauri-build = { version = "2", features = [] }
+
+[dependencies]
+tauri = { version = "2", features = [] }
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+
+[[bin]]
+name = "maptool"
+path = "src/main.rs"

src-tauri/build.rs

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+fn main() {
+    tauri_build::build()
+}

src-tauri/src/lib.rs

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+#[cfg(not(debug_assertions))]
+use std::process::{Child, Command};
+#[cfg(not(debug_assertions))]
+use std::sync::Mutex;
+
+#[cfg(not(debug_assertions))]
+use tauri::Manager;
+
+#[cfg(not(debug_assertions))]
+struct ServerProcess(Mutex<Option<Child>>);
+
+pub fn run() {
+    let builder = tauri::Builder::default();
+
+    #[cfg(not(debug_assertions))]
+    let builder = builder.setup(|app| {
+        let child = spawn_server(&app.handle())
+            .expect("failed to start the Sinatra server (is Ruby/Bundler installed?)");
+        app.manage(ServerProcess(Mutex::new(Some(child))));
+        Ok(())
+    });
+
+    let app = builder
+        .build(tauri::generate_context!())
+        .expect("error while building the tauri application");
+
+    app.run(|_app_handle, event| {
+        #[cfg(not(debug_assertions))]
+        if let tauri::RunEvent::ExitRequested { .. } = event {
+            if let Some(state) = _app_handle.try_state::<ServerProcess>() {
+                if let Some(mut child) = state.0.lock().unwrap().take() {
+                    let _ = child.kill();
+                }
+            }
+        }
+    });
+}
+
+// In development, `beforeDevCommand` (see tauri.conf.json) already starts the
+// Sinatra server, so the window just points at it. In a packaged build there
+// is no such hook, so the shell starts the server itself, next to the bundled
+// resources, and stops it again when the window closes.
+//
+// NOTE: this assumes a Ruby + Bundler installation on the target machine.
+// Producing a fully self-contained bundle (no external Ruby dependency)
+// requires embedding a Ruby runtime as a sidecar (e.g. via tebako) — see
+// docs/architecture.adoc for the open follow-up.
+#[cfg(not(debug_assertions))]
+fn spawn_server(app: &tauri::AppHandle) -> std::io::Result<Child> {
+    let resource_dir = app
+        .path()
+        .resource_dir()
+        .expect("failed to resolve the resource directory");
+
+    Command::new("bundle")
+        .args(["exec", "puma", "-C", "config/puma.rb"])
+        .current_dir(resource_dir)
+        .spawn()
+}

src-tauri/src/main.rs

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+// Prevents an additional console window on Windows in release builds.
+#![cfg_attr(not(debug_assertions), windows_subsystem = "windows")]
+
+fn main() {
+    maptool_lib::run();
+}

src-tauri/tauri.conf.json

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+{
+  "$schema": "https://schema.tauri.app/config/2",
+  "productName": "MapTool",
+  "version": "0.1.0",
+  "identifier": "net.priesol.maptool",
+  "build": {
+    "beforeDevCommand": "bundle exec puma -C ../config/puma.rb",
+    "devUrl": "http://127.0.0.1:4567",
+    "frontendDist": "http://127.0.0.1:4567"
+  },
+  "app": {
+    "windows": [
+      {
+        "title": "MapTool",
+        "width": 1200,
+        "height": 800,
+        "minWidth": 800,
+        "minHeight": 600
+      }
+    ],
+    "security": {
+      "csp": null
+    }
+  },
+  "bundle": {
+    "active": true,
+    "targets": "all",
+    "icon": [
+      "icons/32x32.png",
+      "icons/128x128.png",
+      "icons/128x128@2x.png",
+      "icons/icon.icns",
+      "icons/icon.ico"
+    ],
+    "resources": {
+      "../Gemfile": "Gemfile",
+      "../Gemfile.lock": "Gemfile.lock",
+      "../app.rb": "app.rb",
+      "../config.ru": "config.ru",
+      "../config/*": "config/",
+      "../public/*": "public/",
+      "../views/*": "views/"
+    }
+  }
+}