fix(android): avoid rebuilds if nothing changed

Unconditionally overwriting files where the build reruns if they changed
leads to rebuilds every time.
Only overwrite a file if its content is different to not rebuild in such
a case.

core/tauri-build/src/mobile.rs

@@ -80,20 +80,35 @@ dependencies {"
     }
   }
 
-  write(&gradle_settings_path, gradle_settings).context("failed to write tauri.settings.gradle")?;
+  // Overwrite only if changed to not trigger rebuilds
+  if std::fs::read_to_string(&gradle_settings_path)
+    .map(|o| o != gradle_settings)
+    .unwrap_or(true)
+  {
+    write(&gradle_settings_path, gradle_settings)
+      .context("failed to write tauri.settings.gradle")?;
+  }
 
-  write(&app_build_gradle_path, app_build_gradle)
-    .context("failed to write tauri.build.gradle.kts")?;
+  if std::fs::read_to_string(&app_build_gradle_path)
+    .map(|o| o != app_build_gradle)
+    .unwrap_or(true)
+  {
+    write(&app_build_gradle_path, app_build_gradle)
+      .context("failed to write tauri.build.gradle.kts")?;
+  }
 
   if !app_tauri_properties.is_empty() {
-    write(
-      &app_tauri_properties_path,
-      format!(
-        "// THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.\n{}",
-        app_tauri_properties.join("\n")
-      ),
-    )
-    .context("failed to write tauri.properties")?;
+    let app_tauri_properties_content = format!(
+      "// THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.\n{}",
+      app_tauri_properties.join("\n")
+    );
+    if std::fs::read_to_string(&app_tauri_properties_path)
+      .map(|o| o != app_tauri_properties_content)
+      .unwrap_or(true)
+    {
+      write(&app_tauri_properties_path, app_tauri_properties_content)
+        .context("failed to write tauri.properties")?;
+    }
   }
 
   println!("cargo:rerun-if-changed={}", gradle_settings_path.display());

core/tauri/build.rs

@@ -289,7 +289,13 @@ fn main() {
           .replace("{{library}}", &library);
 
         let out_path = kotlin_out_dir.join(file.file_name());
-        write(&out_path, content).expect("Failed to write kotlin file");
+        // Overwrite only if changed to not trigger rebuilds
+        if std::fs::read_to_string(&out_path)
+          .map(|o| o != content)
+          .unwrap_or(true)
+        {
+          write(&out_path, content).expect("Failed to write kotlin file");
+        }
         println!("cargo:rerun-if-changed={}", out_path.display());
       }
     }