[Xamarin.Android.Tools.AndroidSdk] Probe for Zulu JDK (#114)

Context: https://www.azul.com/downloads/zulu-community/

Commit 237642c removed support for the ancient
`microsoft_dist_openjdk_*` versions, replacing it with the newer
[Microsoft OpenJDK][0].

One problem with this change is one of *compatibility*:
`microsoft_dist_openjdk_` was a build of JDK 1.8, while
Microsoft OpenJDK only provides builds for JDK 11 and later.
This is a problem, as the [Visual Studio Android Designer][1]
currently requires JDK 1.8, and is not yet compatible with JDK 11.

Add support to probe for for [Azul Zulu OpenJDK][2] installation
directories, as Zulu provides updated JDK 1.8 installers.

Additionally, refactor and centralize the JDK Location logic.
Previously, `JdkInfo.GetKnownSystemJdkInfos()` would return all of
the Windows installation locations before the macOS/Linux/etc.
locations, which made it possible for Windows and non-Windows
platforms to return paths in an inconsistent order.  Introduce a new
`JdkLocations` helper, and add new subclasses for each specific JDK
location, so that `JdkInfo.GetKnownSystemJdkInfos()` can be *unified*
across macOS/Linux & Windows, increasing consistency.

Add a new `tools/ls-jdks` tool, to make it easier to print all probed
JDK locations.

[0]: https://www.microsoft.com/openjdk
[1]: https://docs.microsoft.com/en-us/xamarin/android/user-interface/android-designer/designer-walkthrough?tabs=windows
[2]: https://www.azul.com/downloads/zulu-community/?package=jdk

Author: jonpryor

Xamarin.Android.Tools.sln

@@ -1,4 +1,4 @@
-Microsoft Visual Studio Solution File, Format Version 12.00
+Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio Version 16
 VisualStudioVersion = 16.0.30709.64
 MinimumVisualStudioVersion = 10.0.40219.1
@@ -10,6 +10,10 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Android.Build.Bas
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Microsoft.Android.Build.BaseTasks-Tests", "tests\Microsoft.Android.Build.BaseTasks-Tests\Microsoft.Android.Build.BaseTasks-Tests.csproj", "{4F5FD01C-B5A6-4F9F-91CE-3E78B3F942AC}"
 EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "tools", "tools", "{19FE1B44-DB71-4F97-A07E-085888690DAE}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "ls-jdks", "tools\ls-jdks\ls-jdks.csproj", "{3D2ADF77-62C7-4E0E-AB29-BDD266B7D56D}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -32,11 +36,18 @@ Global
 		{4F5FD01C-B5A6-4F9F-91CE-3E78B3F942AC}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{4F5FD01C-B5A6-4F9F-91CE-3E78B3F942AC}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{4F5FD01C-B5A6-4F9F-91CE-3E78B3F942AC}.Release|Any CPU.Build.0 = Release|Any CPU
+		{3D2ADF77-62C7-4E0E-AB29-BDD266B7D56D}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{3D2ADF77-62C7-4E0E-AB29-BDD266B7D56D}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{3D2ADF77-62C7-4E0E-AB29-BDD266B7D56D}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{3D2ADF77-62C7-4E0E-AB29-BDD266B7D56D}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {BA1CD771-F00B-4DE8-93EE-7690D81F6A5A}
 	EndGlobalSection
+	GlobalSection(NestedProjects) = preSolution
+		{3D2ADF77-62C7-4E0E-AB29-BDD266B7D56D} = {19FE1B44-DB71-4F97-A07E-085888690DAE}
+	EndGlobalSection
 EndGlobal

src/Xamarin.Android.Tools.AndroidSdk/AndroidSdkInfo.cs

@@ -185,7 +185,7 @@ public static void DetectAndSetPreferredJavaSdkPathToLatest (Action<TraceLevel,
 
 			logger          = logger ?? DefaultConsoleLogger;
 
-			var latestJdk   = JdkInfo.GetMicrosoftOpenJdks (logger).FirstOrDefault ();
+			var latestJdk   = MicrosoftOpenJdkLocations.GetMicrosoftOpenJdks (logger).FirstOrDefault ();
 			if (latestJdk == null)
 				throw new NotSupportedException ("No Microsoft OpenJDK could be found.  Please re-run the Visual Studio installer or manually specify the JDK path in settings.");
 

src/Xamarin.Android.Tools.AndroidSdk/JdkInfo.cs

@@ -285,78 +285,20 @@ public static IEnumerable<JdkInfo> GetKnownSystemJdkInfos (Action<TraceLevel, st
 			logger  = logger ?? AndroidSdkInfo.DefaultConsoleLogger;
 
 			return GetEnvironmentVariableJdks ("JI_JAVA_HOME", logger)
-				.Concat (GetWindowsJdks (logger))
-				.Concat (GetConfiguredJdks (logger))
-				.Concat (GetMacOSMicrosoftOpenJdks (logger))
+				.Concat (JdkLocations.GetPreferredJdks (logger))
+				.Concat (XAPrepareJdkLocations.GetXAPrepareJdks (logger))
+				.Concat (MicrosoftOpenJdkLocations.GetMicrosoftOpenJdks (logger))
+				.Concat (AzulJdkLocations.GetAzulJdks (logger))
+				.Concat (OracleJdkLocations.GetOracleJdks (logger))
+				.Concat (VSAndroidJdkLocations.GetVSAndroidJdks (logger))
 				.Concat (GetEnvironmentVariableJdks ("JAVA_HOME", logger))
 				.Concat (GetPathEnvironmentJdks (logger))
 				.Concat (GetLibexecJdks (logger))
 				.Concat (GetJavaAlternativesJdks (logger))
 				;
 		}
 
-		static IEnumerable<JdkInfo> GetConfiguredJdks (Action<TraceLevel, string> logger)
-		{
-			return GetConfiguredJdkPaths (logger)
-				.Select (p => TryGetJdkInfo (p, logger, "monodroid-config.xml"))
-				.Where (jdk => jdk != null)
-				.Select (jdk => jdk!)
-				.OrderByDescending (jdk => jdk, JdkInfoVersionComparer.Default);
-		}
-
-		static IEnumerable<string> GetConfiguredJdkPaths (Action<TraceLevel, string> logger)
-		{
-			var config = AndroidSdkUnix.GetUnixConfigFile (logger);
-			foreach (var java_sdk in config.Root.Elements ("java-sdk")) {
-				var path    = (string) java_sdk.Attribute ("path");
-				yield return path;
-			}
-		}
-
-		internal static IEnumerable<JdkInfo> GetMicrosoftOpenJdks (Action<TraceLevel, string> logger)
-		{
-			foreach (var dir in GetMacOSMicrosoftOpenJdks (logger))
-				yield return dir;
-			if (Path.DirectorySeparatorChar != '\\')
-				yield break;
-			foreach (var dir in AndroidSdkWindows.GetJdkInfos (logger)) {
-				yield return dir;
-			}
-		}
-
-		static IEnumerable<JdkInfo> GetMacOSMicrosoftOpenJdks (Action<TraceLevel, string> logger)
-		{
-			return GetMacOSMicrosoftOpenJdkPaths ()
-				.Select (p => TryGetJdkInfo (p, logger, "/Library/Java/JavaVirtualMachines/microsoft-*.jdk"))
-				.Where (jdk => jdk != null)
-				.Select (jdk => jdk!)
-				.OrderByDescending (jdk => jdk, JdkInfoVersionComparer.Default);
-		}
-
-		static IEnumerable<string> GetMacOSMicrosoftOpenJdkPaths ()
-		{
-			var root    = "/Library/Java/JavaVirtualMachines";
-			var pattern = "microsoft-*.jdk";
-			var toHome  = Path.Combine ("Contents", "Home");
-			var jdks    = AppDomain.CurrentDomain.GetData ($"GetMacOSMicrosoftJdkPaths jdks override! {typeof (JdkInfo).AssemblyQualifiedName}")
-				?.ToString ();
-			if (jdks != null) {
-				root    = jdks;
-				toHome  = "";
-				pattern = "*";
-			}
-			if (!Directory.Exists (root)) {
-				yield break;
-			}
-			foreach (var dir in Directory.EnumerateDirectories (root, pattern)) {
-				var home = Path.Combine (dir, toHome);
-				if (!Directory.Exists (home))
-					continue;
-				yield return home;
-			}
-		}
-
-		static JdkInfo? TryGetJdkInfo (string path, Action<TraceLevel, string> logger, string locator)
+		internal static JdkInfo? TryGetJdkInfo (string path, Action<TraceLevel, string> logger, string locator)
 		{
 			JdkInfo? jdk = null;
 			try {
@@ -369,13 +311,6 @@ static IEnumerable<string> GetMacOSMicrosoftOpenJdkPaths ()
 			return jdk;
 		}
 
-		static IEnumerable<JdkInfo> GetWindowsJdks (Action<TraceLevel, string> logger)
-		{
-			if (!OS.IsWindows)
-				return Enumerable.Empty<JdkInfo> ();
-			return AndroidSdkWindows.GetJdkInfos (logger);
-		}
-
 		static IEnumerable<JdkInfo> GetEnvironmentVariableJdks (string envVar, Action<TraceLevel, string> logger)
 		{
 			var java_home = Environment.GetEnvironmentVariable (envVar);

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

@@ -0,0 +1,20 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.IO;
+using System.Linq;
+using System.Text;
+
+namespace Xamarin.Android.Tools {
+
+	class AzulJdkLocations : JdkLocations {
+
+		internal static IEnumerable<JdkInfo> GetAzulJdks (Action<TraceLevel, string> logger)
+		{
+			return GetMacOSSystemJdks ("zulu-*.jdk", logger)
+				.Concat (GetWindowsFileSystemJdks (Path.Combine ("Zulu", "zulu-*"), logger))
+				.Concat (GetWindowsRegistryJdks (logger, @"SOFTWARE\Azul Systems\Zulu", "zulu-*", null, "InstallationPath"))
+				.OrderByDescending (jdk => jdk, JdkInfoVersionComparer.Default);
+		}
+	}
+}

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

@@ -0,0 +1,62 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.IO;
+using System.Linq;
+
+namespace Xamarin.Android.Tools {
+
+	partial class JdkLocations {
+
+		static IEnumerable<JdkInfo> GetUnixPreferredJdks (Action<TraceLevel, string> logger)
+		{
+			return GetUnixConfiguredJdkPaths (logger)
+				.Select (p => JdkInfo.TryGetJdkInfo (p, logger, "monodroid-config.xml"))
+				.Where (jdk => jdk != null)
+				.Select (jdk => jdk!)
+				.OrderByDescending (jdk => jdk, JdkInfoVersionComparer.Default);
+		}
+
+		static IEnumerable<string> GetUnixConfiguredJdkPaths (Action<TraceLevel, string> logger)
+		{
+			var config = AndroidSdkUnix.GetUnixConfigFile (logger);
+			foreach (var java_sdk in config.Root.Elements ("java-sdk")) {
+				var path    = (string) java_sdk.Attribute ("path");
+				yield return path;
+			}
+		}
+
+		const   string  MacOSJavaVirtualMachinesRoot    = "/Library/Java/JavaVirtualMachines";
+
+		protected static IEnumerable<JdkInfo> GetMacOSSystemJdks (string pattern, Action<TraceLevel, string> logger, string? locator = null)
+		{
+			if (!OS.IsMac) {
+				return Array.Empty<JdkInfo>();
+			}
+			locator = locator ?? Path.Combine (MacOSJavaVirtualMachinesRoot, pattern);
+			return FromPaths (GetMacOSSystemJvmPaths (pattern), logger, locator);
+		}
+
+		static IEnumerable<string> GetMacOSSystemJvmPaths (string pattern)
+		{
+			var root    = MacOSJavaVirtualMachinesRoot;
+			var toHome  = Path.Combine ("Contents", "Home");
+			var jdks    = AppDomain.CurrentDomain.GetData ($"GetMacOSMicrosoftJdkPaths jdks override! {typeof (JdkInfo).AssemblyQualifiedName}")
+				?.ToString ();
+			if (jdks != null) {
+				root    = jdks;
+				toHome  = "";
+				pattern = "*";
+			}
+			if (!Directory.Exists (root)) {
+				yield break;
+			}
+			foreach (var dir in Directory.EnumerateDirectories (root, pattern)) {
+				var home = Path.Combine (dir, toHome);
+				if (!Directory.Exists (home))
+					continue;
+				yield return home;
+			}
+		}
+	}
+}

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

@@ -0,0 +1,113 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.IO;
+using System.Linq;
+using System.Text;
+using System.Text.RegularExpressions;
+
+namespace Xamarin.Android.Tools {
+
+	partial class JdkLocations {
+
+		internal static string? GetWindowsPreferredJdkPath ()
+		{
+			var wow = RegistryEx.Wow64.Key32;
+			var regKey = AndroidSdkWindows.GetMDRegistryKey ();
+			if (RegistryEx.CheckRegistryKeyForExecutable (RegistryEx.CurrentUser, regKey, AndroidSdkWindows.MDREG_JAVA_SDK, wow, "bin", "java.exe"))
+				return RegistryEx.GetValueString (RegistryEx.CurrentUser, regKey, AndroidSdkWindows.MDREG_JAVA_SDK, wow);
+			return null;
+
+		}
+
+		protected static IEnumerable<JdkInfo> GetWindowsFileSystemJdks (string pattern, Action<TraceLevel, string> logger, string? locator = null)
+		{
+			if (!OS.IsWindows) {
+				yield break;
+			}
+
+			var roots = new List<string>() {
+				// "Compatibility" with existing codebases; should probably be avoided…
+				Environment.ExpandEnvironmentVariables ("%ProgramW6432%"),
+				Environment.GetFolderPath (Environment.SpecialFolder.ProgramFiles),
+				Environment.GetFolderPath (Environment.SpecialFolder.ProgramFilesX86),
+			};
+			foreach (var root in roots) {
+				if (!Directory.Exists (root))
+					continue;
+				IEnumerable<string> homes;
+				try {
+					homes = Directory.EnumerateDirectories (root, pattern);
+				}
+				catch (IOException e) {
+					continue;
+				}
+				foreach (var home in homes) {
+					if (!File.Exists (Path.Combine (home, "bin", "java.exe")))
+						continue;
+					var loc = locator ?? $"{pattern} via {root}";
+					var jdk = JdkInfo.TryGetJdkInfo (home, logger, loc);
+					if (jdk == null)
+						continue;
+					yield return jdk;
+				}
+			}
+		}
+
+		protected static IEnumerable<JdkInfo> GetWindowsRegistryJdks (
+				Action<TraceLevel, string> logger,
+				string  parentKey,
+				string  childKeyGlob,
+				string? grandChildKey,
+				string  valueName,
+				string? locator = null)
+		{
+			if (!OS.IsWindows) {
+				yield break;
+			}
+
+			var regex   = ToRegex (childKeyGlob);
+			var paths   = new List<(Version version, string path)> ();
+			var roots   = new[] { RegistryEx.CurrentUser, RegistryEx.LocalMachine };
+			var wows    = new[] { RegistryEx.Wow64.Key32, RegistryEx.Wow64.Key64 };
+			foreach (var root in roots)
+			foreach (var wow in wows) {
+				foreach (var subkeyName in RegistryEx.EnumerateSubkeys (root, parentKey, wow)) {
+					if (!regex.Match (subkeyName).Success) {
+						continue;
+					}
+					var key	    = $@"{parentKey}\{subkeyName}" +
+						(grandChildKey == null ? "" : "\\" + grandChildKey);
+					var path    = RegistryEx.GetValueString (root, key, valueName, wow);
+					if (path == null) {
+						continue;
+					}
+					var jdk     = JdkInfo.TryGetJdkInfo (path, logger, locator ?? $"Windows Registry @ {parentKey}");
+					if (jdk == null) {
+						continue;
+					}
+					yield return jdk;
+				}
+			}
+		}
+
+		static Regex ToRegex (string glob)
+		{
+			var r   = new StringBuilder ();
+			foreach (char c in glob) {
+				switch (c) {
+					case '*':
+						r.Append (".*");
+						break;
+					case '?':
+						r.Append (".");
+						break;
+					default:
+						r.Append (Regex.Escape (c.ToString ()));
+						break;
+				}
+			}
+			return new Regex (r.ToString (), RegexOptions.CultureInvariant | RegexOptions.IgnoreCase);
+		}
+	}
+}

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

@@ -0,0 +1,32 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.IO;
+using System.Linq;
+
+namespace Xamarin.Android.Tools {
+
+	partial class JdkLocations {
+
+		internal static IEnumerable<JdkInfo> GetPreferredJdks (Action<TraceLevel, string> logger)
+		{
+			if (OS.IsWindows) {
+				var path    = GetWindowsPreferredJdkPath ();
+				var jdk     = path == null ? null : JdkInfo.TryGetJdkInfo (path, logger, "Windows Registry");
+				if (jdk != null)
+					yield return jdk;
+			}
+			foreach (var jdk in GetUnixPreferredJdks (logger)) {
+				yield return jdk;
+			}
+		}
+
+		protected static IEnumerable<JdkInfo> FromPaths (IEnumerable<string> paths, Action<TraceLevel, string> logger, string locator)
+		{
+			return paths
+				.Select (p => JdkInfo.TryGetJdkInfo (p, logger, locator))
+				.Where (jdk => jdk != null)
+				.Select (jdk => jdk!);
+		}
+	}
+}

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

@@ -0,0 +1,20 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.IO;
+using System.Linq;
+using System.Text;
+
+namespace Xamarin.Android.Tools {
+
+	class MicrosoftOpenJdkLocations : JdkLocations {
+
+		internal static IEnumerable<JdkInfo> GetMicrosoftOpenJdks (Action<TraceLevel, string> logger)
+		{
+			return GetMacOSSystemJdks ("microsoft-*.jdk", logger)
+				.Concat (GetWindowsFileSystemJdks (Path.Combine ("Microsoft", "jdk-*"), logger))
+				.Concat (GetWindowsRegistryJdks (logger, @"SOFTWARE\Microsoft\JDK", "*", @"hotspot\MSI", "Path"))
+				.OrderByDescending (jdk => jdk, JdkInfoVersionComparer.Default);
+		}
+	}
+}