Enabling incremental build by avoiding task to run if there was no changes.

Author: gugavaro

build-tools/Xamarin.Android.Tools.BootstrapTasks/Xamarin.Android.Tools.BootstrapTasks/CheckApiCompatibility.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
+using System.Runtime.InteropServices;
 using Microsoft.Build.Framework;
 using Microsoft.Build.Utilities;
 
@@ -101,14 +102,19 @@ void ValidateApiCompat (string contractPath) {
 			string content;
 			using (var genApiProcess = new Process()) {
 
-				genApiProcess.StartInfo.FileName = "mono";
+				if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows)){
+  					genApiProcess.StartInfo.FileName = apiCompat;
+					genApiProcess.StartInfo.Arguments = $"{contractPath} -i {TargetImplementationPath}";
+				} else {
+					genApiProcess.StartInfo.FileName = $"mono";
+					genApiProcess.StartInfo.Arguments = $"{apiCompat} {contractPath} -i {TargetImplementationPath}";
+				}
+
 				genApiProcess.StartInfo.UseShellExecute = false;
 				genApiProcess.StartInfo.CreateNoWindow = true;
 				genApiProcess.StartInfo.RedirectStandardOutput = true;
 
 				// Get api definition for previous Api
-				var argument = $"{apiCompat} {contractPath} -i {TargetImplementationPath}";
-				genApiProcess.StartInfo.Arguments = argument;
 				genApiProcess.Start ();
 				content = genApiProcess.StandardOutput.ReadToEnd();
 				genApiProcess.WaitForExit ();

src/Mono.Android/Mono.Android.csproj

@@ -373,13 +373,20 @@
       <ReferenceOutputAssembly>False</ReferenceOutputAssembly>
     </ProjectReference>
   </ItemGroup>
-  <Target Name="AfterBuild">
+  <ItemGroup>
+    <ApiCompatibilityReferenceFiles Include="../../external/xamarin-android-api-compatibility/reference/*.dll" />
+  </ItemGroup>
+  <Target Name="AfterBuild" Inputs="$(TargetPath);@(ApiCompatibilityFiles)" Outputs="$(IntermediateOutputPath)/CheckApiCompatibility.stamp">
     <CheckApiCompatibility
       ApiCompatPath="../../packages/Microsoft.DotNet.ApiCompat.5.0.0-beta.19554.1/tools/net472/"
       ApiLevel="$(AndroidFrameworkVersion)"
       LastStableApiLevel="$(AndroidLatestStableFrameworkVersion)"
       ApiCompatContractPath = "../../external/xamarin-android-api-compatibility/"
       TargetImplementationPath="$(OutputPath)"
       />
+      <Touch Files="$(IntermediateOutputPath)/CheckApiCompatibility.stamp" AlwaysCreate="True" />
+      <ItemGroup>
+        <FileWrites Include="$(IntermediateOutputPath)/CheckApiCompatibility.stamp" />
+      </ItemGroup>
   </Target>
 </Project>