fix(doctor): add an alternative path for the Dart plugin (#163215)

It seems like with some recent plugin/IDE version, the path for the Dart
plugin has changed from `<base path>/Dart` to `<base path>/dart`,
causing `flutter doctor` to incorrectly assume that the plugin is not
installed.

Add `dart` as an alternative to the existing `Dart` package name.

Fixes #163214.

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we expect every widget to implement].
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- [x] I listed at least one issue that this PR fixes in the description
above.
- [ ] I updated/added relevant documentation (doc comments with `///`).
- [ ] I added new tests to check the change I am making, or this PR is
[test-exempt].
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Fixes] where supported.
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Author: kszczek

packages/flutter_tools/lib/src/android/android_studio_validator.dart

@@ -76,7 +76,7 @@ class AndroidStudioValidator extends DoctorValidator {
       );
       plugins.validatePackage(
         messages,
-        <String>['Dart'],
+        <String>['Dart', 'dart'],
         'Dart',
         IntelliJPlugins.kIntellijDartPluginUrl,
       );

packages/flutter_tools/lib/src/intellij/intellij_validator.dart

@@ -109,7 +109,7 @@ abstract class IntelliJValidator extends DoctorValidator {
       );
       plugins.validatePackage(
         messages,
-        <String>['Dart'],
+        <String>['Dart', 'dart'],
         'Dart',
         IntelliJPlugins.kIntellijDartPluginUrl,
       );

packages/flutter_tools/test/general.shard/intellij/intellij_test.dart

@@ -52,7 +52,7 @@ void main() {
     );
 
     final List<ValidationMessage> messages = <ValidationMessage>[];
-    plugins.validatePackage(messages, <String>['Dart'], 'Dart', 'download-Dart');
+    plugins.validatePackage(messages, <String>['Dart', 'dart'], 'Dart', 'download-Dart');
     plugins.validatePackage(
       messages,
       <String>['flutter-intellij', 'flutter-intellij.jar'],
@@ -156,7 +156,7 @@ Manifest-Version: 1.0
     final IntelliJPlugins plugins = IntelliJPlugins(_kPluginsPath, fileSystem: fileSystem);
 
     final List<ValidationMessage> messages = <ValidationMessage>[];
-    plugins.validatePackage(messages, <String>['Dart'], 'Dart', 'download-Dart');
+    plugins.validatePackage(messages, <String>['Dart', 'dart'], 'Dart', 'download-Dart');
     plugins.validatePackage(
       messages,
       <String>['flutter-intellij', 'flutter-intellij.jar'],
@@ -188,11 +188,38 @@ Manifest-Version: 1.0
     );
 
     expect(
-      () =>
-          plugins.validatePackage(<ValidationMessage>[], <String>['Dart'], 'Dart', 'download-Dart'),
+      () => plugins.validatePackage(
+        <ValidationMessage>[],
+        <String>['Dart', 'dart'],
+        'Dart',
+        'download-Dart',
+      ),
       returnsNormally,
     );
   });
+
+  // Regression test for https://github.com/flutter/flutter/issues/163214
+  testWithoutContext(
+    'IntelliJPlugins can find the Dart plugin with a lowercase package name',
+    () async {
+      final IntelliJPlugins plugins = IntelliJPlugins(_kPluginsPath, fileSystem: fileSystem);
+      final Archive dartJarArchive = buildSingleFileArchive('META-INF/plugin.xml', r'''
+<idea-plugin>
+  <name>Dart</name>
+  <version>242.24931</version>
+</idea-plugin>''');
+      writeFileCreatingDirectories(
+        fileSystem.path.join(_kPluginsPath, 'dart', 'lib', 'dart.jar'),
+        ZipEncoder().encode(dartJarArchive)!,
+      );
+
+      final List<ValidationMessage> messages = <ValidationMessage>[];
+      plugins.validatePackage(messages, <String>['Dart', 'dart'], 'Dart', 'download-Dart');
+
+      expect(messages.length, equals(1));
+      expect(messages.single.message, equals('Dart plugin version 242.24931'));
+    },
+  );
 }
 
 const String _kPluginsPath = '/data/intellij/plugins';