[Xamarin.Android.Build.Tasks] Use Path.Combine() in <CalculateProjectDependencies/>

Documentation/release-notes/fix-4677.md

@@ -0,0 +1,6 @@
+#### Application and library build and deployment
+
+- [GitHub 4677](https://github.com/xamarin/xamarin-android/issues/4677):
+  On Windows, the `InstallAndroidDependencies` MSBuild target would not yet
+  install the expected Android SDK Platform or Android SDK Build-Tools
+  components in a newly configured command line build environment.

src/Xamarin.Android.Build.Tasks/Tasks/CalculateProjectDependencies.cs

@@ -53,8 +53,8 @@ public override bool RunTask ()
 				manifestApiLevel = manifest.TargetSdkVersion ?? manifest.MinSdkVersion ?? DefaultMinSDKVersion;
 			}
 			var sdkVersion = Math.Max (targetApiLevel.Value, manifestApiLevel);
-			dependencies.Add (CreateAndroidDependency ($"platforms/android-{sdkVersion}", $""));
-			dependencies.Add (CreateAndroidDependency ($"build-tools/{BuildToolsVersion}", BuildToolsVersion));
+			dependencies.Add (CreateAndroidDependency (Path.Combine ("platforms", $"android-{sdkVersion}"), $""));
+			dependencies.Add (CreateAndroidDependency (Path.Combine ("build-tools", BuildToolsVersion), BuildToolsVersion));
 			if (!string.IsNullOrEmpty (PlatformToolsVersion)) {
 				dependencies.Add (CreateAndroidDependency ("platform-tools", PlatformToolsVersion));
 			}

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/AndroidDependenciesTests.cs

@@ -1,5 +1,7 @@
 using System;
+using System.Collections.Generic;
 using System.IO;
+using System.Linq;
 using NUnit.Framework;
 using Xamarin.ProjectTools;
 
@@ -13,19 +15,42 @@ public class AndroidDependenciesTests : BaseTest
 		[Test]
 		public void InstallAndroidDependenciesTest ()
 		{
+			var path = Path.Combine (Root, "temp", TestName);
+			TestOutputDirectories [TestContext.CurrentContext.Test.ID] = path;
 			if (!CommercialBuildAvailable)
 				Assert.Ignore ("Not required on Open Source Builds");
 			var old = Environment.GetEnvironmentVariable ("ANDROID_SDK_PATH");
 			try {
-				string sdkPath = Path.Combine (Root, "temp", TestName, "android-sdk");
+				string sdkPath = Path.Combine (path, "android-sdk");
+				CreateFauxAndroidSdkDirectory (sdkPath, buildToolsVersion: "23.0.0");
+				// Provide mock version info so the `tools` component won't be downloaded.
+				File.WriteAllText (Path.Combine (sdkPath, "tools", "source.properties"), "Pkg.Revision=99.99.99");
 				Environment.SetEnvironmentVariable ("ANDROID_SDK_PATH", sdkPath);
 				var proj = new XamarinAndroidApplicationProject ();
-				using (var b = CreateApkBuilder ()) {
+				// Use `BuildHelper.CreateApkBuilder()` instead of `BaseTest.CreateApkBuilder()` so
+				// `android-sdk` can be placed beside the project directory rather than within it.
+				using (var b = BuildHelper.CreateApkBuilder (Path.Combine (path, "Project"))) {
 					string defaultTarget = b.Target;
 					b.Target = "InstallAndroidDependencies";
+					b.ThrowOnBuildFailure = false;
+					Assert.IsFalse (b.Build (proj, parameters: new string [] { "AcceptAndroidSDKLicenses=false" }), "InstallAndroidDependencies should have failed.");
+					IEnumerable<string> taskOutput = b.LastBuildOutput
+						.SkipWhile (x => !(x.StartsWith ("  Detecting Android SDK in") && x.Contains (sdkPath)))
+						.TakeWhile (x => !x.StartsWith ("Done executing task \"InstallAndroidDependencies\""))
+						.Where (x => x.StartsWith ("  Dependency to be installed:"));
+					Assert.AreEqual (2, taskOutput.Count (), "Exactly two dependencies should be identified to be installed.");
+					StringAssertEx.Contains ("Dependency to be installed: Android SDK Platform", taskOutput);
+					StringAssertEx.Contains ("Dependency to be installed: Android SDK Build-Tools", taskOutput);
+					b.ThrowOnBuildFailure = true;
 					Assert.IsTrue (b.Build (proj, parameters: new string [] { "AcceptAndroidSDKLicenses=true" }), "InstallAndroidDependencies should have succeeded.");
+					Assert.IsTrue (Directory.Exists (Path.Combine (sdkPath, "platforms")), "At least one platform should have been installed");
+					Assert.IsTrue (Directory.Exists (Path.Combine (sdkPath, "build-tools")), "At least one Build Tools version should have been installed");
 					b.Target = defaultTarget;
 					Assert.IsTrue (b.Build (proj), "build should have succeeded.");
+					taskOutput = b.LastBuildOutput
+						.SkipWhile (x => !x.StartsWith ("  ResolveSdks Outputs:"))
+						.TakeWhile (x => !x.StartsWith ("Done executing task \"ResolveSdks\""));
+					StringAssert.Contains (sdkPath, taskOutput.First (x => x.StartsWith ("    AndroidSdkPath:")));
 				}
 			} finally {
 				Environment.SetEnvironmentVariable ("ANDROID_SDK_PATH", old);