Edge case on flutter/flutter/issues/135402 with test (#138814)

fixes flutter/flutter/issues/135402
Edge case that was reported by a user along with a test case specifically covering their output.

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

@@ -148,8 +148,8 @@ class Java {
     // Should look something like 'openjdk 19.0.2 2023-01-17'.
     final String longVersionText = versionLines.length >= 2 ? versionLines[1] : versionLines[0];
 
-    // The contents that matter come in the format '11.0.18' or '1.8.0_202'.
-    final RegExp jdkVersionRegex = RegExp(r'\d+\.\d+(\.\d+(?:_\d+)?)?');
+    // The contents that matter come in the format '11.0.18', '1.8.0_202 or 21'.
+    final RegExp jdkVersionRegex = RegExp(r'(?<version>\d+(\.\d+(\.\d+(?:_\d+)?)?)?)');
     final Iterable<RegExpMatch> matches =
         jdkVersionRegex.allMatches(rawVersionOutput);
     if (matches.isEmpty) {
@@ -167,7 +167,7 @@ class Java {
       _logger.printWarning(_formatJavaVersionWarning(rawVersionOutput));
       return null;
     }
-    final String? version = matches.first.group(0);
+    final String? version = matches.first.namedGroup('version');
     if (version == null || version.split('_').isEmpty) {
       _logger.printWarning(_formatJavaVersionWarning(rawVersionOutput));
       return null;

packages/flutter_tools/test/general.shard/android/java_test.dart

@@ -296,6 +296,15 @@ Java HotSpot(TM) 64-Bit Server VM (build 21+35-LTS-2513, mixed mode, sharing)
 java 21 2023-09-19 LTS
 Java(TM) SE Runtime Environment (build 21+35-LTS-2513)
 Java HotSpot(TM) 64-Bit Server VM (build 21+35-LTS-2513, mixed mode, sharing)
+''');
+        final Version? version = java.version;
+        expect(version, equals(Version(21, 0, 0)));
+      });
+      testWithoutContext('parses openjdk 21 with no patch numbers', () {
+        addJavaVersionCommand('''
+openjdk version "21" 2023-09-19
+OpenJDK Runtime Environment (build 21+35)
+OpenJDK 64-Bit Server VM (build 21+35, mixed mode, sharing)
 ''');
         final Version? version = java.version;
         expect(version, equals(Version(21, 0, 0)));