support previewing staging patches

packages/shorebird_cli/lib/src/commands/preview_command.dart

@@ -397,6 +397,18 @@ This is only applicable when previewing Android releases.''',
       }
     }
 
+    final progress = logger.progress('Using ${track.name} track');
+    try {
+      await setChannelOnLinuxApp(
+        channel: track.name,
+        bundleDirectory: appDirectory,
+      );
+      progress.complete();
+    } on Exception catch (error) {
+      progress.fail('$error');
+      return ExitCode.software.code;
+    }
+
     final executableFile = appDirectory.listSync().whereType<File>().first;
 
     await process.run('chmod', ['+x', executableFile.path]);
@@ -847,10 +859,10 @@ This is only applicable when previewing Android releases.''',
         throw Exception('Unable to find shorebird.yaml');
       }
 
-      final yaml = YamlEditor(shorebirdYaml.readAsStringSync())
-        ..update(['channel'], channel);
-
-      shorebirdYaml.writeAsStringSync(yaml.toString(), flush: true);
+      await _setChannelInShorebirdYaml(
+        channel: channel,
+        shorebirdYamlFile: shorebirdYaml,
+      );
     });
   }
 
@@ -882,26 +894,10 @@ This is only applicable when previewing Android releases.''',
         ),
       );
 
-      if (!shorebirdYamlFile.existsSync()) {
-        throw Exception('Unable to find shorebird.yaml');
-      }
-
-      final yamlText = shorebirdYamlFile.readAsStringSync();
-      final yaml = loadYaml(yamlText) as YamlMap;
-      final yamlChannel = yaml['channel'];
-
-      if (yamlChannel == null && channel == DeploymentTrack.stable.channel) {
-        // We would be updating the channel to the default value.
-        return;
-      }
-
-      if (yamlChannel == channel) {
-        // Updating this channel would be a no-op.
-        return;
-      }
-
-      final yamlEditor = YamlEditor(yamlText)..update(['channel'], channel);
-      shorebirdYamlFile.writeAsStringSync(yamlEditor.toString(), flush: true);
+      await _setChannelInShorebirdYaml(
+        channel: channel,
+        shorebirdYamlFile: shorebirdYamlFile,
+      );
 
       // This is equivalent to `zip --no-dir-entries`
       // Which does NOT create entries in the zip archive for directories.
@@ -924,6 +920,52 @@ This is only applicable when previewing Android releases.''',
       tempDir.deleteSync(recursive: true);
     });
   }
+
+  /// Sets the channel property in the shorebird.yaml file if none is set.
+  Future<void> setChannelOnLinuxApp({
+    required String channel,
+    required Directory bundleDirectory,
+  }) async {
+    final shorebirdYamlFile = File(
+      p.join(
+        bundleDirectory.path,
+        'data',
+        'flutter_assets',
+        'shorebird.yaml',
+      ),
+    );
+
+    await _setChannelInShorebirdYaml(
+      channel: channel,
+      shorebirdYamlFile: shorebirdYamlFile,
+    );
+  }
+
+  Future<void> _setChannelInShorebirdYaml({
+    required String channel,
+    required File shorebirdYamlFile,
+  }) async {
+    if (!shorebirdYamlFile.existsSync()) {
+      throw Exception('Unable to find shorebird.yaml');
+    }
+
+    final yamlText = shorebirdYamlFile.readAsStringSync();
+    final yaml = loadYaml(yamlText) as YamlMap;
+    final yamlChannel = yaml['channel'];
+
+    if (yamlChannel == null && channel == DeploymentTrack.stable.channel) {
+      // We would be updating the channel to the default value.
+      return;
+    }
+
+    if (yamlChannel == channel) {
+      // Updating this channel would be a no-op.
+      return;
+    }
+
+    final yamlEditor = YamlEditor(yamlText)..update(['channel'], channel);
+    shorebirdYamlFile.writeAsStringSync(yamlEditor.toString(), flush: true);
+  }
 }
 
 /// Extension on [Release] that exposes the active platforms (e.g. platforms