Add docs on 'Create app flavors for Windows and Linux'

sites/docs/src/content/deployment/flavors-ios.md

@@ -555,10 +555,16 @@ To learn about them, consult
 To learn about creating and using flavors, consult
 the following resources:
 
+* [Set up Flutter flavors for Android][]
+* [Set up Flutter flavors for Linux][]
+* [Set up Flutter flavors for Windows][]
 * [How to set up Flutter & Firebase with Multiple Flavors
   using the FlutterFire CLI][flutterfire-cli]
 * [Build flavors in Flutter (Android and iOS) with different
   Firebase projects per flavor Flutter Ready to Go][flavors-firebase]
 
+[Set up Flutter flavors for Android]: /deployment/flavors
+[Set up Flutter flavors for Linux]:   /deployment/flavors-linux
+[Set up Flutter flavors for Windows]: /deployment/flavors-windows
 [flutterfire-cli]: https://codewithandrea.com/articles/flutter-firebase-multiple-flavors-flutterfire-cli/
 [flavors-firebase]: https://medium.com/@animeshjain/build-flavors-in-flutter-android-and-ios-with-different-firebase-projects-per-flavor-27c5c5dac10b

sites/docs/src/content/deployment/flavors-linux.md

@@ -0,0 +1,324 @@
+---
+title: Set up Flutter flavors for Linux
+shortTitle: Flavors (Linux)
+description: >-
+  How to create Flutter flavors for Linux desktop apps.
+---
+
+This guide shows you how to create Flutter flavors for
+Linux desktop apps.
+
+:::note
+To create app flavors for other platforms,
+visit the pages on setting up flavors for:
+
+* [Android][]
+* [iOS and macOS][]
+* [Windows][]
+:::
+
+## Overview {: #overview }
+
+A Flutter flavor represents a collection of settings that define
+how a specific version of your app builds and runs.
+For example, a flavor can determine which window title,
+application ID, API endpoint, asset set, and logging configuration
+applies to a build.
+
+On Linux, Flutter uses [CMake][] to configure and build
+the native desktop runner.
+When you run `flutter run` or `flutter build` with the `--flavor` flag,
+Flutter writes the flavor name into
+`linux/flutter/ephemeral/generated_config.cmake` as the
+`FLUTTER_APP_FLAVOR` variable, and isolates the build outputs
+in a flavor-specific directory.
+
+:::important
+The `generated_config.cmake` file is included from
+`linux/flutter/CMakeLists.txt`, so `FLUTTER_APP_FLAVOR`
+only becomes visible in your top-level `CMakeLists.txt` **after**
+the `add_subdirectory(${FLUTTER_MANAGED_DIR})` line.
+Any `if(DEFINED FLUTTER_APP_FLAVOR)` block placed before that line
+is silently skipped.
+:::
+
+The following table illustrates the build directories that Flutter creates
+when a project defines two flavors (`staging`, `production`)
+and two build modes (`debug`, `release`):
+
+| Flavor     | Build mode | Output directory                                     |
+|------------|------------|------------------------------------------------------|
+| staging    | debug      | `build/linux/<arch>/staging/debug/bundle/`           |
+| production | debug      | `build/linux/<arch>/production/debug/bundle/`        |
+| staging    | release    | `build/linux/<arch>/staging/release/bundle/`         |
+| production | release    | `build/linux/<arch>/production/release/bundle/`       |
+{:.table .table-striped}
+
+[CMake]: https://cmake.org/
+[Android]: /deployment/flavors
+[iOS and macOS]: /deployment/flavors-ios
+[Windows]: /deployment/flavors-windows
+
+## Configure CMake for flavors (optional) {: #configure-cmake }
+
+Passing `--flavor` works on Linux without any project configuration.
+Existing Flutter projects support flavors with no template updates
+or configuration changes required.
+When you pass `--flavor`, Flutter isolates the build directory,
+populates `appFlavor`, and filters flavor-specific assets automatically.
+
+Complete the following optional steps only if you want to
+differentiate the native runner per flavor—for example,
+its GTK application ID or window title.
+This example configures two flavors called `staging` and `production`.
+
+1.  Create a new Flutter project called `flavors_example`:
+
+    ```console title="console"
+    $ flutter create flavors_example
+    $ cd flavors_example
+    ```
+
+1.  Configure flavor-specific application IDs in `linux/CMakeLists.txt`:
+
+    Open `linux/CMakeLists.txt` and find the
+    `add_subdirectory(${FLUTTER_MANAGED_DIR})` line.
+    Set the `APPLICATION_ID` per flavor immediately after that line:
+
+    ```cmake title="linux/CMakeLists.txt"
+    # Flutter library and tool build rules.
+    set(FLUTTER_MANAGED_DIR "${CMAKE_CURRENT_SOURCE_DIR}/flutter")
+    add_subdirectory(${FLUTTER_MANAGED_DIR})
+
+    if(DEFINED FLUTTER_APP_FLAVOR)
+      if(FLUTTER_APP_FLAVOR STREQUAL "staging")
+        set(APPLICATION_ID "com.example.staging")
+      elseif(FLUTTER_APP_FLAVOR STREQUAL "production")
+        set(APPLICATION_ID "com.example.production")
+      endif()
+    endif()
+    ```
+
+    `APPLICATION_ID` must be configured after
+    `add_subdirectory(${FLUTTER_MANAGED_DIR})` because
+    `FLUTTER_APP_FLAVOR` only becomes available at this point,
+    and before `add_subdirectory("runner")` where `APPLICATION_ID` is consumed.
+
+    :::important
+    Leave `set(BINARY_NAME ...)` unchanged.
+    The Flutter CLI resolves the executable path by parsing that line literally,
+    so renaming the binary per flavor prevents `flutter run`
+    from launching the app.
+    :::
+
+1.  Verify that your flavors run correctly:
+
+    Run the `staging` flavor:
+
+    ```console title="console"
+    $ flutter run -d linux --flavor staging
+    ```
+
+    Run the `production` flavor:
+
+    ```console title="console"
+    $ flutter run -d linux --flavor production
+    ```
+
+## Launch a flavor {: #launch-a-flavor }
+
+After you configure flavors for your app,
+run, build, or test a specific flavor using the `--flavor` flag
+with the Flutter CLI.
+
+### Run a flavor in debug mode {: #run-a-flavor }
+
+To run a specific flavor during development,
+pass the `--flavor` option to `flutter run`:
+
+```console title="console"
+$ flutter run -d linux --flavor <flavor_name>
+```
+
+Replace `<flavor_name>` with the name of your flavor
+(for example, `staging` or `production`).
+
+### Build a release binary {: #build-a-flavor }
+
+To build a release executable for a specific flavor,
+pass the `--flavor` option to `flutter build`:
+
+```console title="console"
+$ flutter build linux --flavor <flavor_name>
+```
+
+Flutter outputs the compiled bundle to
+`build/linux/<arch>/<flavor_name>/release/bundle/`.
+
+### Run tests with a flavor {: #test-a-flavor }
+
+The `--flavor` option also works with `flutter test` and `flutter drive`,
+allowing you to run unit, widget, or integration tests
+against a specific flavor configuration:
+
+```console title="console"
+$ flutter test --flavor <flavor_name>
+```
+
+## Use flavors in Flutter code {: #use-flavors-in-code }
+
+After adding flavors,
+you can adjust app behavior—such as selecting API endpoints,
+toggling features, or setting analytics keys—based on the active flavor.
+
+The Flutter framework provides the `appFlavor` constant in the `services`
+library, which retrieves the flavor name passed to the `--flavor` flag
+during `flutter run` or `flutter build`.
+
+1.  **Import the services library:**
+
+    Add the following import to your Dart file:
+
+    ```dart
+    import 'package:flutter/services.dart';
+    ```
+
+1.  **Read the flavor value:**
+
+    Use the `appFlavor` constant in your application logic
+    (often in `main()`) to handle flavor-specific configuration:
+
+    ```dart
+    void main() {
+      if (appFlavor == 'production') {
+        Config.apiUrl = 'https://api.example.com';
+      } else if (appFlavor == 'staging') {
+        Config.apiUrl = 'https://staging.api.example.com';
+      }
+
+      runApp(const MyApp());
+    }
+    ```
+
+    :::note
+    The value of `appFlavor` matches the string passed to the `--flavor` flag.
+    If you run or build without specifying a flavor,
+    `appFlavor` returns `null` and the build uses the
+    [default flavor](#set-default-flavor).
+    :::
+
+## Customize configurations {: #customize-configurations }
+
+After adding flavors,
+you can customize native settings and assets for each configuration.
+
+### Create distinct window titles {: #create-distinct-window-titles }
+
+To help distinguish between different flavors at runtime,
+customize the native window title for each flavor.
+
+1.  In `linux/runner/CMakeLists.txt`, pass `FLUTTER_APP_FLAVOR`
+    as a preprocessor definition directly after the existing
+    `APPLICATION_ID` definition:
+
+    ```cmake title="linux/runner/CMakeLists.txt"
+    # Add preprocessor definitions for the application ID.
+    add_definitions(-DAPPLICATION_ID="${APPLICATION_ID}")
+
+    if(DEFINED FLUTTER_APP_FLAVOR AND NOT FLUTTER_APP_FLAVOR STREQUAL "")
+      add_definitions(-DFLUTTER_APP_FLAVOR="${FLUTTER_APP_FLAVOR}")
+    endif()
+    ```
+
+1.  In `linux/runner/my_application.cc`, update the window title
+    in the `my_application_activate` function:
+
+    ```c title="linux/runner/my_application.cc"
+      const gchar* window_title = "flavors_example";
+    #ifdef FLUTTER_APP_FLAVOR
+      if (g_strcmp0(FLUTTER_APP_FLAVOR, "staging") == 0) {
+        window_title = "Staging App";
+      } else if (g_strcmp0(FLUTTER_APP_FLAVOR, "production") == 0) {
+        window_title = "Production App";
+      }
+    #endif
+    ```
+
+    Then update `my_application_activate` to use `window_title`
+    instead of the hardcoded string literals:
+
+    ```c title="linux/runner/my_application.cc"
+        gtk_header_bar_set_title(header_bar, window_title);
+        ...
+        gtk_window_set_title(window, window_title);
+    ```
+
+### Configure app icons {: #configure-app-icons }
+
+On Linux, application icons are not embedded directly in the compiled
+executable binary.
+Instead, the desktop environment resolves app icons through
+`.desktop` launcher files and installed icon themes.
+
+To provide different icons or launcher entries for each flavor,
+configure your Linux package format—such as Snap, Flatpak, or Debian
+packages—to install distinct desktop entries and icon assets.
+To learn more about packaging Linux apps, refer to
+[Build and release a Linux desktop app][].
+
+### Bundle assets by flavor {: #bundle-assets }
+
+If you have assets that only apply to a specific flavor,
+configure Flutter to only bundle those assets when building that flavor.
+This prevents unused assets from increasing your application bundle size.
+
+To bundle assets conditionally,
+add the `flavors` list to an asset entry in `pubspec.yaml`:
+
+```yaml title="pubspec.yaml"
+flutter:
+  assets:
+    - assets/common/
+    - path: assets/staging/
+      flavors:
+        - staging
+    - path: assets/production/
+      flavors:
+        - production
+```
+
+To learn more, consult the [`assets` field][] in [Flutter pubspec options][].
+
+[`assets` field]: /tools/pubspec#assets
+[Flutter pubspec options]: /tools/pubspec
+
+### Set a default flavor {: #set-default-flavor }
+
+To specify a flavor to use when running or building
+without the `--flavor` flag,
+add the `default-flavor` property to `pubspec.yaml`:
+
+```yaml title="pubspec.yaml"
+flutter:
+  default-flavor: staging
+```
+
+To learn more, consult the [`default-flavor` field][] in
+[Flutter pubspec options][].
+
+[`default-flavor` field]: /tools/pubspec#default-flavor-field
+
+## More information {: #more-information }
+
+For more information on flavors and desktop deployment,
+consult the following resources:
+
+* [Set up Flutter flavors for Android][Android]
+* [Set up Flutter flavors for iOS and macOS][iOS and macOS]
+* [Set up Flutter flavors for Windows][Windows]
+* [Build and release a Linux desktop app][]
+
+[Build and release a Linux desktop app]: /deployment/linux
+[Set up Flutter flavors for Android]: /deployment/flavors
+[Set up Flutter flavors for iOS and macOS]: /deployment/flavors-ios
+[Set up Flutter flavors for Windows]: /deployment/flavors-windows