[Xamarin.Android.Build.Tasks] Warnings and errors for compileSdkVersion, targetSdkVersion, and minSdkVersion

Context #1768

Google has the following guidance for these three values:

> minSdkVersion (lowest possible) <= targetSdkVersion == compileSdkVersion (latest SDK)

This commit adds a new Task `CheckGoogleSdkRequirements` which is responsible for checking
these values. It will be enabled by default but the task can be disabled via the
`AndroidEnableGooglePlayStoreChecks` property.

Author: dellis1972

Documentation/guides/BuildProcess.md

@@ -709,6 +709,14 @@ when packaing Release applications.
 
     Added in Xamarin.Android 8.3.
 
+- **AndroidEnableGooglePlayStoreChecks** – A bool property
+    which allows developers to disable the following Google Play
+    Store checks, XA1004, XA1005 and XA1006. This is useful for 
+    developers who are not targeting the Google Play Store and do
+    not wish to run those checks.
+
+    Added in Xamarin.Android 8.4.
+
 ### Binding Project Build Properties
 
 The following MSBuild properties are used with

Documentation/guides/messages/README.md

@@ -46,6 +46,9 @@
 + [XA1000](xa1000.md): There was an problem parsing {file}. This is likely due to incomplete or invalid xml.
 + [XA1001](xa1001.md): AndroidResgen: Warning while updating Resource XML '{filename}': {Message}
 + [XA1002](xa1002.md): We found a matching key '{Key}' for '{Item}'. But the casing was incorrect. Please correct the casing
++ [XA1003](xa1003.md): Your application is running on a version of Android ({compileSdk}) that is more recent than your targetSdkVersion specifies ({targetSdk}). Set your targetSdkVersion to the highest version of Android available to match your TargetFrameworkVersion ({compileSdk}).
++ [XA1004](xa1004.md): The TargetFrameworkVersion ({compileSdk}) should not be lower than targetSdkVersion ({targetSdk})
++ [XA1005](xa1005.md): The minSdkVersion ({minSdk}) is greater than targetSdkVersion. Please change the value such that minSdkVersion is less than or equal to targetSdkVersion ({targetSdk}).
 
 ### XA2xxx Linker
 

Documentation/guides/messages/xa1003.md

@@ -0,0 +1,7 @@
+# Compiler Warning XA1003
+
+Your application is running on a version of Android (compileSdk) that
+is more recent than your targetSdkVersion specifies (targetSdk).
+
+Set your targetSdkVersion to the highest version of Android available
+to match your TargetFrameworkVersion (compileSdk).

Documentation/guides/messages/xa1004.md

@@ -0,0 +1,4 @@
+# Compiler Error XA1004
+
+The TargetFrameworkVersion (compileSdk) should not be lower
+than targetSdkVersion (targetSdk).

Documentation/guides/messages/xa1005.md

@@ -0,0 +1,6 @@
+# Compiler Error XA1005
+
+The minSdkVersion (minSdk) is greater than targetSdkVersion.
+
+Please change the value such that minSdkVersion is less than
+or equal to targetSdkVersion (targetSdk).

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

@@ -0,0 +1,51 @@
+using System;
+using System.Collections.Generic;
+using Microsoft.Build.Utilities;
+using Microsoft.Build.Framework;
+using System.IO;
+using System.Linq;
+
+using Java.Interop.Tools.Cecil;
+using Xamarin.Android.Tools;
+
+namespace Xamarin.Android.Tasks
+{
+	public class CheckGoogleSdkRequirements : Task 
+	{
+		[Required]
+		public string TargetFrameworkVersion { get; set; }
+
+		[Required]
+		public string ManifestFile { get; set; }
+
+		public override bool Execute ()
+		{
+			ManifestDocument manifest = new ManifestDocument (ManifestFile, this.Log);
+
+			var compileSdk = MonoAndroidHelper.SupportedVersions.GetApiLevelFromFrameworkVersion (TargetFrameworkVersion);
+
+			if (!int.TryParse (manifest.GetMinimumSdk (), out int minSdk)) {
+				minSdk = 1;
+			}
+			if (!int.TryParse (manifest.GetTargetSdk (), out int targetSdk)) {
+				targetSdk = compileSdk.Value;
+			}
+
+			//We should throw a warning if the targetSdkVersion is lower than compileSdkVersion(TargetFrameworkVersion).
+			if (targetSdk < compileSdk) {
+				Log.LogCodedWarning ("XA1003", $"Your application is running on a version of Android ({compileSdk}) that is more recent than your targetSdkVersion specifies ({targetSdk}). Set your targetSdkVersion to the highest version of Android available to match your TargetFrameworkVersion ({compileSdk}).");
+			}
+			//We should throw an error if the compileSdkVersion(TargetFrameworkVersion) is lower than targetSdkVersion.
+			if (compileSdk < targetSdk) {
+				Log.LogCodedError ("XA1004", $"The TargetFrameworkVersion ({compileSdk}) should not be lower than targetSdkVersion ({targetSdk})");
+			}
+
+			//We should throw an error if the minSdkVersion is greater than targetSdkVersion.
+			if (minSdk > targetSdk) {
+				Log.LogCodedError ("XA1005", $"The minSdkVersion ({minSdk}) is greater than targetSdkVersion. Please change the value such that minSdkVersion is less than or equal to targetSdkVersion ({targetSdk}).");
+			}
+
+			return !Log.HasLoggedErrors;
+		}
+	}
+}

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

@@ -0,0 +1,99 @@
+using Microsoft.Build.Framework;
+using NUnit.Framework;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.IO;
+using Xamarin.Android.Tasks;
+using Xamarin.Android.Tools;
+using Xamarin.ProjectTools;
+
+namespace Xamarin.Android.Build.Tests {
+	[TestFixture]
+	public class CheckGoogleSdkRequirmentsTests : BaseTest {
+		List<BuildErrorEventArgs> errors;
+		List<BuildWarningEventArgs> warnings;
+		MockBuildEngine engine;
+
+		[SetUp]
+		public void Setup ()
+		{
+			var path = Path.Combine ("temp", TestName);
+			engine = new MockBuildEngine (TestContext.Out, errors = new List<BuildErrorEventArgs> (), warnings = new List<BuildWarningEventArgs> ());
+			var referencePath = CreateFauxReferencesDirectory (Path.Combine (path, "references"), new [] {
+				new ApiInfo { Id = "27", Level = 27, Name = "Oreo", FrameworkVersion = "v8.1",  Stable = true },
+				new ApiInfo { Id = "28", Level = 28, Name = "Pie", FrameworkVersion = "v9.0",  Stable = true },
+			});
+			MonoAndroidHelper.RefreshSupportedVersions (new [] {
+				Path.Combine (referencePath, "MonoAndroid"),
+			});
+		}
+
+		[TearDown]
+		public void TearDown ()
+		{
+			var path = Path.Combine ("temp", TestName);
+			Directory.Delete (Path.Combine (Root, path), recursive: true);
+		}
+
+		string CreateManiestFile (int minSDk, int targetSdk) {
+			var manifest = Path.Combine (Root, "temp", TestName, "AndroidManifest.xml");
+			File.WriteAllText (manifest, string.Format (@"<manifest xmlns:android='http://schemas.android.com/apk/res/android' android:versionCode='1' android:versionName='1.0' package='Foo.Foo'>
+	<uses-sdk android:minSdkVersion = '{0}' android:targetSdkVersion = '{1}' />
+</manifest>
+", minSDk, targetSdk));
+			return manifest;
+		}
+
+		[Test]
+		public void CheckManifestIsOK ()
+		{
+			var task = new CheckGoogleSdkRequirments () {
+				BuildEngine = engine,
+				TargetFrameworkVersion = "v9.0",
+				ManifestFile = CreateManiestFile (10, 28),
+			};
+			Assert.True (task.Execute (), "Task should have succeeded.");
+			Assert.AreEqual (0, errors.Count, "There should be 0 errors reported.");
+			Assert.AreEqual (0, warnings.Count, "There should be 0 warnings reported.");
+		}
+
+		[Test]
+		public void CheckManifestTargetSdkLowerThanCompileSdk ()
+		{
+			var task = new CheckGoogleSdkRequirments () {
+				BuildEngine = engine,
+				TargetFrameworkVersion = "v9.0",
+				ManifestFile = CreateManiestFile (10, 27),
+			};
+			Assert.True (task.Execute (), "Task should have succeeded.");
+			Assert.AreEqual (0, errors.Count, "There should be 0 errors reported.");
+			Assert.AreEqual (1, warnings.Count, "There should be 1 warning reported.");
+		}
+
+		[Test]
+		public void CheckManifestCompileSdkLowerThanTargetSdk ()
+		{
+			var task = new CheckGoogleSdkRequirments () {
+				BuildEngine = engine,
+				TargetFrameworkVersion = "v8.1",
+				ManifestFile = CreateManiestFile (10, 28),
+			};
+			Assert.False (task.Execute (), "Task should have failed.");
+			Assert.AreEqual (1, errors.Count, "There should be 1 error reported.");
+			Assert.AreEqual (0, warnings.Count, "There should be 0 warnings reported.");
+		}
+
+		[Test]
+		public void CheckManifestMinSdkLowerThanTargetSdk ()
+		{
+			var task = new CheckGoogleSdkRequirments () {
+				BuildEngine = engine,
+				TargetFrameworkVersion = "v8.1",
+				ManifestFile = CreateManiestFile (28, 27),
+			};
+			Assert.False (task.Execute (), "Task should have failed.");
+			Assert.AreEqual (1, errors.Count, "There should be 1 error reported.");
+			Assert.AreEqual (0, warnings.Count, "There should be 0 warnings reported.");
+		}
+	}
+}

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Xamarin.Android.Build.Tests.csproj

@@ -85,6 +85,7 @@
     <Compile Include="Tasks\ValidateJavaVersionTests.cs" />
     <Compile Include="ZipArchiveExTests.cs" />
     <Compile Include="ConvertResourcesCasesTests.cs" />
+    <Compile Include="Tasks\CheckGoogleSdkRequirmentsTests.cs" />
   </ItemGroup>
   <ItemGroup>
     <Content Include="Expected\GenerateDesignerFileExpected.cs">

src/Xamarin.Android.Build.Tasks/Utilities/ManifestDocument.cs

@@ -111,6 +111,14 @@ public string GetMinimumSdk () {
 			return minAttr.Value;
 		}
 
+		public string GetTargetSdk () {
+			var targetAttr = doc.Root.Element ("uses-sdk")?.Attribute (androidNs + "targetSdkVersion");
+			if (targetAttr == null) {
+				return SdkVersionName;
+			}
+			return targetAttr.Value;
+		}
+
 		TaskLoggingHelper log;
 
 		public ManifestDocument (string templateFilename, TaskLoggingHelper log) : base ()

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Build.Tasks.csproj

@@ -568,6 +568,7 @@
     <Compile Include="Tasks\LayoutLocationInfo.cs" />
     <Compile Include="Tasks\LayoutTypeFixup.cs" />
     <Compile Include="Tasks\LayoutWidget.cs" />
+    <Compile Include="Tasks\CheckGoogleSdkRequirements.cs" />
     <None Include="Resources\desugar_deploy.jar">
       <Link>desugar_deploy.jar</Link>
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>