Allow a no-op default_package key for a plugin platform (#45364)

packages/flutter_tools/lib/src/plugins.dart

@@ -81,7 +81,7 @@ class Plugin {
 
     final Map<String, PluginPlatform> platforms = <String, PluginPlatform>{};
 
-    if (platformsYaml[AndroidPlugin.kConfigKey] != null) {
+    if (_providesImplementationForPlatform(platformsYaml, AndroidPlugin.kConfigKey)) {
       platforms[AndroidPlugin.kConfigKey] = AndroidPlugin.fromYaml(
         name,
         platformsYaml[AndroidPlugin.kConfigKey] as YamlMap,
@@ -89,27 +89,27 @@ class Plugin {
       );
     }
 
-    if (platformsYaml[IOSPlugin.kConfigKey] != null) {
+    if (_providesImplementationForPlatform(platformsYaml, IOSPlugin.kConfigKey)) {
       platforms[IOSPlugin.kConfigKey] =
           IOSPlugin.fromYaml(name, platformsYaml[IOSPlugin.kConfigKey] as YamlMap);
     }
 
-    if (platformsYaml[LinuxPlugin.kConfigKey] != null) {
+    if (_providesImplementationForPlatform(platformsYaml, LinuxPlugin.kConfigKey)) {
       platforms[LinuxPlugin.kConfigKey] =
           LinuxPlugin.fromYaml(name, platformsYaml[LinuxPlugin.kConfigKey] as YamlMap);
     }
 
-    if (platformsYaml[MacOSPlugin.kConfigKey] != null) {
+    if (_providesImplementationForPlatform(platformsYaml, MacOSPlugin.kConfigKey)) {
       platforms[MacOSPlugin.kConfigKey] =
           MacOSPlugin.fromYaml(name, platformsYaml[MacOSPlugin.kConfigKey] as YamlMap);
     }
 
-    if (platformsYaml[WebPlugin.kConfigKey] != null) {
+    if (_providesImplementationForPlatform(platformsYaml, WebPlugin.kConfigKey)) {
       platforms[WebPlugin.kConfigKey] =
           WebPlugin.fromYaml(name, platformsYaml[WebPlugin.kConfigKey] as YamlMap);
     }
 
-    if (platformsYaml[WindowsPlugin.kConfigKey] != null) {
+    if (_providesImplementationForPlatform(platformsYaml, WindowsPlugin.kConfigKey)) {
       platforms[WindowsPlugin.kConfigKey] =
           WindowsPlugin.fromYaml(name, platformsYaml[WindowsPlugin.kConfigKey] as YamlMap);
     }
@@ -178,7 +178,13 @@ class Plugin {
   static List<String> _validateMultiPlatformYaml(YamlMap yaml) {
     bool isInvalid(String key, bool Function(YamlMap) validate) {
       final dynamic value = yaml[key];
-      return value is YamlMap && !validate(value);
+      if (!(value is YamlMap)) {
+        return false;
+      }
+      if (value.containsKey('default_package')) {
+        return false;
+      }
+      return !validate(value);
     }
     final List<String> errors = <String>[];
     if (isInvalid(AndroidPlugin.kConfigKey, AndroidPlugin.validate)) {
@@ -213,6 +219,16 @@ class Plugin {
     return errors;
   }
 
+  static bool _providesImplementationForPlatform(YamlMap platformsYaml, String platformKey) {
+    if (!platformsYaml.containsKey(platformKey)) {
+      return false;
+    }
+    if (platformsYaml[platformKey].containsKey('default_package')) {
+      return false;
+    }
+    return true;
+  }
+
   final String name;
   final String path;
 

packages/flutter_tools/test/general.shard/plugin_parsing_test.dart

@@ -125,5 +125,28 @@ void main() {
       expect(webPlugin.fileName, 'web_plugin.dart');
       expect(windowsPlugin.pluginClass, 'WinSamplePlugin');
     });
+
+    test('A default_package field is allowed', () {
+      const String pluginYamlRaw =
+          'platforms:\n'
+          ' android:\n'
+          '  default_package: sample_package_android\n'
+          ' ios:\n'
+          '  default_package: sample_package_ios\n'
+          ' linux:\n'
+          '  default_package: sample_package_linux\n'
+          ' macos:\n'
+          '  default_package: sample_package_macos\n'
+          ' web:\n'
+          '  default_package: sample_package_web\n'
+          ' windows:\n'
+          '  default_package: sample_package_windows\n';
+
+      final dynamic pluginYaml = loadYaml(pluginYamlRaw);
+      final Plugin plugin =
+      Plugin.fromYaml(_kTestPluginName, _kTestPluginPath, pluginYaml);
+
+      expect(plugin.platforms, <String, PluginPlatform> {});
+    });
   });
 }