Flutter extension

The Flutter family of extensions help fill in common settings for software built with the Flutter framework.

The Flutter extensions require Snapcraft 7 and lower and are currently only supported with the core18 base. Snaps using cores higher than core18 should instead use the Flutter plugin with the GNOME extension.

There are four extensions in the family. Each tracks a different Flutter build release channel:

  • flutter-stable for the stable channel

  • flutter-beta for the beta channel

  • flutter-master for the main channel

  • flutter-dev for the dev channel

When using these extensions, the Flutter plugin is optional. The plugin drives the build process while the extension handles its dependencies.

Included parts

The Flutter extensions add the following parts to the project file. The gnome-3-28-extension part is noteworthy, as it provides many of the dependent components that Flutter-based apps need.

Included parts
snapcraft.yaml
gnome-3-28-extension:
  build-packages:
    - gcc
    - libgtk-3-dev
  make-parameters:
    - PLATFORM_PLUG=gnome-3-28-1804
  plugin: make
  source: $SNAPCRAFT_EXTENSIONS_DIR/desktop
  source-subdir: gnome
flutter-extension:
  build-snaps:
    - flutter/latest/stable
  override-pull: |
    flutter channel stable
    flutter config --enable-linux-desktop
    flutter upgrade
    flutter doctor
  plugin: nil

Included interface connections

The Flutter extensions connect the following snap-wide plugs.

Included snap-wide plugs
snapcraft.yaml
plugs:
  gnome-3-28-1804:
    default-provider: gnome-3-28-1804
    interface: content
    target: $SNAP/gnome-platform
  gtk-3-themes:
    default-provider: gtk-common-themes
    interface: content
    target: $SNAP/data-dir/themes
  icon-themes:
    default-provider: gtk-common-themes
    interface: content
    target: $SNAP/data-dir/icons
  sound-themes:
    default-provider: gtk-common-themes
    interface: content
    target: $SNAP/data-dir/sounds

They also connect the following plugs in apps that use the extensions.

Included app plugs
snapcraft.yaml
plugs:
  - desktop
  - desktop-legacy
  - gsettings
  - opengl
  - wayland
  - x11

Included environment variables

The extensions add one runtime environment variable:

Included runtime environment variables
snapcraft.yaml
environment:
  SNAP_DESKTOP_RUNTIME: $SNAP/gnome-platform

Included layouts

The Flutter extensions add the following layouts:

Included layouts
snapcraft.yaml
layout:
  /usr/share/libdrm:
    bind: $SNAP/gnome-platform/usr/share/libdrm
  /usr/share/xml/iso-codes:
    bind: $SNAP/gnome-platform/usr/share/xml/iso-codes

Example expanded project files

Here’s an example of the result of a project file that uses a Flutter extension. It demonstrates the added plugs, packages, variables, and layouts that the extension adds to the project file immediately prior to build.

This example contains the difference between the original file and the output of the snapcraft expand-extensions command. Some of the text has been altered for ease of reading.

The file is based on the my-flutter-app project.

Expanded project file for my-flutter-app
 name: my-flutter-app
 version: '1.0'
 summary: An example Flutter snap
 description: |
   An example showing how Flutter programs can be packaged as snaps.

 base: core18
 confinement: strict
 grade: stable

 apps:
   my-flutter-app:
     command: my_flutter_app
-    extensions:
-      - flutter-stable
+    command-chain:
+      - snap/command-chain/desktop-launch
+    plugs:
+      - desktop
+      - desktop-legacy
+      - gsettings
+      - opengl
+      - wayland
+      - x11

 parts:
   my-flutter-app:
     source: .
     plugin: flutter
     flutter-target: lib/main.dart
+  gnome-3-28-extension:
+    build-packages:
+      - gcc
+      - libgtk-3-dev
+    make-parameters:
+      - PLATFORM_PLUG=gnome-3-28-1804
+    plugin: make
+    source: $SNAPCRAFT_EXTENSIONS_DIR/desktop
+    source-subdir: gnome
+  flutter-extension:
+    build-snaps:
+      - flutter/latest/stable
+    override-pull: |
+      flutter channel stable
+      flutter config --enable-linux-desktop
+      flutter upgrade
+      flutter doctor
+    plugin: nil
+
+assumes:
+  - snapd2.43
+
+plugs:
+  gnome-3-28-1804:
+    default-provider: gnome-3-28-1804
+    interface: content
+    target: $SNAP/gnome-platform
+  gtk-3-themes:
+    default-provider: gtk-common-themes
+    interface: content
+    target: $SNAP/data-dir/themes
+  icon-themes:
+    default-provider: gtk-common-themes
+    interface: content
+    target: $SNAP/data-dir/icons
+  sound-themes:
+    default-provider: gtk-common-themes
+    interface: content
+    target: $SNAP/data-dir/sounds
+
+environment:
+  SNAP_DESKTOP_RUNTIME: $SNAP/gnome-platform
+
+layout:
+  /usr/share/libdrm:
+    bind: $SNAP/gnome-platform/usr/share/libdrm
+  /usr/share/xml/iso-codes:
+    bind: $SNAP/gnome-platform/usr/share/xml/iso-codes