Add JDK discovery for user-writable paths on Windows and macOS (#269)

- Windows: `%LocalAppData%\Android\*jdk*` - matches `jdk-21`, `jdk-21.0.8.1-hotspot`, `microsoft-21.jdk`, etc.
- macOS: `~/Library/Android/*jdk*/` - supports both bundle (`Contents/Home`) and flat JDK structures
- Both integrated into `MicrosoftOpenJdkLocations.GetMicrosoftOpenJdks()` discovery chain
- Rely on `TryGetJdkInfo()` for validation
- Add parameterized tests for multiple folder naming patterns

Co-authored-by: Jonathan Peppers <jonathan.peppers@microsoft.com>

Author: Copilot

src/Xamarin.Android.Tools.AndroidSdk/Jdks/JdkLocations.MacOS.cs

@@ -31,6 +31,42 @@ static IEnumerable<string> GetUnixConfiguredJdkPaths (Action<TraceLevel, string>
 
 		const   string  MacOSJavaVirtualMachinesRoot    = "/Library/Java/JavaVirtualMachines";
 
+		protected static IEnumerable<JdkInfo> GetMacOSUserFileSystemJdks (Action<TraceLevel, string> logger)
+		{
+			if (!OS.IsMac) {
+				return Array.Empty<JdkInfo> ();
+			}
+
+			// Search ~/Library/Android/*jdk*/ (matches microsoft-21.jdk, jdk-21, etc.)
+			var libraryAndroidRoot = Path.Combine (Environment.GetFolderPath (Environment.SpecialFolder.UserProfile), "Library", "Android");
+			if (!Directory.Exists (libraryAndroidRoot)) {
+				return Array.Empty<JdkInfo> ();
+			}
+
+			IEnumerable<string> dirs;
+			try {
+				dirs = Directory.EnumerateDirectories (libraryAndroidRoot, "*jdk*");
+			}
+			catch (IOException) {
+				return Array.Empty<JdkInfo> ();
+			}
+
+			var toHome = Path.Combine ("Contents", "Home");
+			var paths = new List<string> ();
+			foreach (var dir in dirs) {
+				// Check for macOS .jdk bundle structure (Contents/Home)
+				var bundleHome = Path.Combine (dir, toHome);
+				if (Directory.Exists (bundleHome)) {
+					paths.Add (bundleHome);
+				} else {
+					// Flat JDK structure - let TryGetJdkInfo validate
+					paths.Add (dir);
+				}
+			}
+
+			return FromPaths (paths, logger, "~/Library/Android/*jdk*/");
+		}
+
 		protected static IEnumerable<JdkInfo> GetMacOSSystemJdks (string pattern, Action<TraceLevel, string> logger, string? locator = null)
 		{
 			if (!OS.IsMac) {

src/Xamarin.Android.Tools.AndroidSdk/Jdks/JdkLocations.Windows.cs

@@ -54,6 +54,34 @@ protected static IEnumerable<JdkInfo> GetWindowsFileSystemJdks (string pattern,
 			}
 		}
 
+		protected static IEnumerable<JdkInfo> GetWindowsUserFileSystemJdks (Action<TraceLevel, string> logger)
+		{
+			if (!OS.IsWindows) {
+				yield break;
+			}
+
+			var root = Path.Combine (Environment.GetFolderPath (Environment.SpecialFolder.LocalApplicationData), "Android");
+			if (!Directory.Exists (root)) {
+				yield break;
+			}
+
+			IEnumerable<string> homes;
+			try {
+				// Match any folder containing "jdk" (jdk-21, microsoft-21.jdk, jdk-21.0.8.1-hotspot, etc.)
+				homes = Directory.EnumerateDirectories (root, "*jdk*");
+			}
+			catch (IOException) {
+				yield break;
+			}
+
+			foreach (var home in homes) {
+				var jdk = JdkInfo.TryGetJdkInfo (home, logger, @"%LocalAppData%\Android\*jdk*");
+				if (jdk == null)
+					continue;
+				yield return jdk;
+			}
+		}
+
 		protected static IEnumerable<JdkInfo> GetWindowsRegistryJdks (
 				Action<TraceLevel, string> logger,
 				string  parentKey,

src/Xamarin.Android.Tools.AndroidSdk/Jdks/MicrosoftOpenJdkLocations.cs

@@ -12,9 +12,11 @@ class MicrosoftOpenJdkLocations : JdkLocations {
 		internal static IEnumerable<JdkInfo> GetMicrosoftOpenJdks (Action<TraceLevel, string> logger)
 		{
 			return GetMacOSSystemJdks ("microsoft-*.jdk", logger)
+				.Concat (GetMacOSUserFileSystemJdks (logger))
 				.Concat (GetWindowsFileSystemJdks (Path.Combine ("Android", "openjdk", "jdk-*"), logger))
 				.Concat (GetWindowsFileSystemJdks (Path.Combine ("Microsoft", "jdk-*"), logger))
 				.Concat (GetWindowsRegistryJdks (logger, @"SOFTWARE\Microsoft\JDK", "*", @"hotspot\MSI", "Path"))
+				.Concat (GetWindowsUserFileSystemJdks (logger))
 				.OrderByDescending (jdk => jdk, JdkInfoVersionComparer.Default);
 		}
 	}

tests/Xamarin.Android.Tools.AndroidSdk-Tests/JdkInfoTests.cs

@@ -271,5 +271,91 @@ public void Version_ThrowsNotSupportedException ()
 				Directory.Delete (dir, recursive: true);
 			}
 		}
+
+		[Test]
+		[TestCase ("jdk-21.0.99")]
+		[TestCase ("jdk-21.0.8.1-hotspot")]
+		[TestCase ("microsoft-21.jdk")]
+		public void GetKnownSystemJdkInfos_DiscoversWindowsUserJdk (string folderName)
+		{
+			if (!OS.IsWindows) {
+				Assert.Ignore ("This test is only valid on Windows.");
+				return;
+			}
+
+			var userJdkRoot = Path.Combine (Environment.GetFolderPath (Environment.SpecialFolder.LocalApplicationData), "Android");
+			var testJdkDir = Path.Combine (userJdkRoot, folderName);
+
+			try {
+				CreateFauxJdk (testJdkDir, releaseVersion: "21.0.99", releaseBuildNumber: "1", javaVersion: "21.0.99-1");
+
+				Action<TraceLevel, string> logger = (level, message) => {
+					Console.WriteLine ($"[{level}] {message}");
+				};
+
+				var jdks = JdkInfo.GetKnownSystemJdkInfos (logger).ToList ();
+				var foundJdk = jdks.FirstOrDefault (j => j.HomePath == testJdkDir);
+
+				Assert.IsNotNull (foundJdk, $"Expected to find JDK at {testJdkDir} with folder name '{folderName}'");
+				Assert.AreEqual (@"%LocalAppData%\Android\*jdk*", foundJdk.Locator, $"Locator should indicate user JDK path for folder '{folderName}'");
+				Assert.AreEqual (new Version (21, 0, 99, 1), foundJdk.Version);
+			}
+			finally {
+				if (Directory.Exists (testJdkDir))
+					Directory.Delete (testJdkDir, recursive: true);
+				// Clean up the parent directories if they're empty
+				if (Directory.Exists (userJdkRoot) && !Directory.EnumerateFileSystemEntries (userJdkRoot).Any ())
+					Directory.Delete (userJdkRoot);
+			}
+		}
+
+		[Test]
+		[TestCase ("microsoft-21.jdk", false)]
+		[TestCase ("jdk-21", true)]
+		[TestCase ("jdk-21.0.8.1-hotspot", true)]
+		[TestCase ("temurin-21.jdk", false)]
+		public void GetKnownSystemJdkInfos_DiscoversMacOSUserJdk (string folderName, bool isFlat)
+		{
+			if (!OS.IsMac) {
+				Assert.Ignore ("This test is only valid on macOS.");
+				return;
+			}
+
+			var userJdkRoot = Path.Combine (Environment.GetFolderPath (Environment.SpecialFolder.UserProfile), "Library", "Android");
+			string testJdkDir;
+			string testJdkBundle;
+
+			if (isFlat) {
+				// Flat structure: release file directly in folder
+				testJdkDir = Path.Combine (userJdkRoot, folderName);
+				testJdkBundle = testJdkDir;
+			} else {
+				// Bundle structure: Contents/Home inside folder
+				testJdkBundle = Path.Combine (userJdkRoot, folderName);
+				testJdkDir = Path.Combine (testJdkBundle, "Contents", "Home");
+			}
+
+			try {
+				CreateFauxJdk (testJdkDir, releaseVersion: "21.0.99", releaseBuildNumber: "1", javaVersion: "21.0.99-1");
+
+				Action<TraceLevel, string> logger = (level, message) => {
+					Console.WriteLine ($"[{level}] {message}");
+				};
+
+				var jdks = JdkInfo.GetKnownSystemJdkInfos (logger).ToList ();
+				var foundJdk = jdks.FirstOrDefault (j => j.HomePath == testJdkDir);
+
+				Assert.IsNotNull (foundJdk, $"Expected to find JDK at {testJdkDir} with folder name '{folderName}' (isFlat={isFlat})");
+				Assert.AreEqual ("~/Library/Android/*jdk*/", foundJdk.Locator, $"Locator should indicate user JDK path for folder '{folderName}'");
+				Assert.AreEqual (new Version (21, 0, 99, 1), foundJdk.Version);
+			}
+			finally {
+				if (Directory.Exists (testJdkBundle))
+					Directory.Delete (testJdkBundle, recursive: true);
+				// Clean up the parent directories if they're empty
+				if (Directory.Exists (userJdkRoot) && !Directory.EnumerateFileSystemEntries (userJdkRoot).Any ())
+					Directory.Delete (userJdkRoot);
+			}
+		}
 	}
 }