[Xamarin.Android.Build.Tasks] Use @(AndroidDefineConstants)

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

@@ -1,6 +1,7 @@
 // Copyright (C) 2011 Xamarin, Inc. All rights reserved.
 
 using System;
+using System.Collections.Generic;
 using System.Text;
 using System.Text.RegularExpressions;
 using Microsoft.Build.Framework;
@@ -16,21 +17,25 @@ public class GetAndroidDefineConstants : Task
 		public string ProductVersion         { get; set; }
 
 		[Output]
-		public string AndroidDefineConstants { get; set; }
+		public  ITaskItem[]     AndroidDefineConstants      { get; set; }
 
 		public override bool Execute ()
 		{
-			var sb = new StringBuilder ();
+			var constants = new List<ITaskItem> ();
 
 			if (!string.IsNullOrEmpty (ProductVersion)) {
-				sb.AppendFormat ("__XAMARIN_ANDROID_{0}__;", Regex.Replace (ProductVersion, "[^A-Za-z0-9]", "_"));
+				var version = Regex.Replace (ProductVersion, "[^A-Za-z0-9]", "_");
+				constants.Add (new TaskItem ($"__XAMARIN_ANDROID_{version}__"));
 			}
-			sb.Append ("__MOBILE__;__ANDROID__");
 
-			for (int i = 1; i <= AndroidApiLevel; ++i)
-				sb.Append (";__ANDROID_").Append (i).Append ("__");
+			constants.Add (new TaskItem ("__MOBILE__"));
+			constants.Add (new TaskItem ("__ANDROID__"));
 
-			AndroidDefineConstants = sb.ToString ();
+			for (int i = 1; i <= AndroidApiLevel; ++i) {
+				constants.Add (new TaskItem ($"__ANDROID_{i}__"));
+			}
+
+			AndroidDefineConstants = constants.ToArray ();
 
 			return true;
 		}

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

@@ -50,6 +50,29 @@ public void BuildBasicApplicationReleaseFSharp ()
 			}
 		}
 
+		[Test]
+		public void FSharpAppHasAndroidDefine ()
+		{
+			var proj = new XamarinAndroidApplicationProject () {
+				Language  = XamarinAndroidProjectLanguage.FSharp,
+			};
+			proj.Sources.Add (new BuildItem ("Compile", "IsAndroidDefined.fs") {
+				TextContent = () => @"
+module Xamarin.Android.Tests
+// conditional compilation; can we elicit a compile-time error?
+let x =
+#if __ANDROID__
+  42
+#endif  // __ANDROID__
+
+printf ""%d"" x
+",
+			});
+			using (var b = CreateApkBuilder ("temp/" + nameof (FSharpAppHasAndroidDefine))) {
+				Assert.IsTrue (b.Build (proj), "Build should have succeeded.");
+			}
+		}
+
 		[Test]
 		public void BuildApplicationAndClean ([Values (false, true)] bool isRelease)
 		{

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets

@@ -822,12 +822,12 @@ because xbuild doesn't support framework reference assemblies.
 
 	<!-- Get the defined constants for this API Level -->
 	<GetAndroidDefineConstants AndroidApiLevel="$(_SupportedApiLevel)" ProductVersion="$(MonoAndroidVersion)">
-		<Output TaskParameter="AndroidDefineConstants" PropertyName="AndroidDefineConstants" />
+		<Output TaskParameter="AndroidDefineConstants" ItemName="AndroidDefineConstants" />
 	</GetAndroidDefineConstants>
 
-	<CreateProperty Value="$(DefineConstants);$(AndroidDefineConstants)">
-		<Output TaskParameter="Value" PropertyName="DefineConstants" />
-	</CreateProperty>
+	<PropertyGroup>
+		<DefineConstants>$(DefineConstants);@(AndroidDefineConstants)</DefineConstants>
+	</PropertyGroup>
 </Target>
 
 <Target Name="AndroidPrepareForBuild" DependsOnTargets="$(_OnResolveMonoAndroidSdks)" />