feat: Add default download handler

.changes/default-download.md

@@ -0,0 +1,5 @@
+---
+tauri: "patch:enhance"
+---
+
+Tauri will now allow downloads (`<a href="..." download="...">`) on local URLs (devPath/frontendDist) by default, essentially matching the behavior of browsers. This behavior can be overwritting by providing a custom [download handler](https://docs.rs/tauri/latest/tauri/webview/struct.WebviewWindowBuilder.html#method.on_download) in Rust.

crates/tauri/src/webview/mod.rs

@@ -572,6 +572,18 @@ tauri::Builder::default()
           false
         }
       }));
+    } else {
+      // If no download handler was provided we provide a default handler
+      // that behaves similar to a browser by saving the file into the Downloads dir if the current url is local.
+      let label = pending.label.clone();
+      let manager = manager.manager_owned();
+      pending.download_handler.replace(Arc::new(move |_| {
+        if let Some(w) = manager.get_webview(&label) {
+          w.url().map(|url| w.is_local_url(&url)).unwrap_or(false)
+        } else {
+          false
+        }
+      }));
     }
 
     let label_ = pending.label.clone();