[net6] Fixes build issues from VS for Preview 7 (#12281)

* [net6] Adds missing custom linker steps when building from Windows

To share the definition of the custom steps we need to specify the right path to the `dotnet-linker.dll`.

When building from macOS `_XamarinSdkRootDirectoryOnMac` will have the same value as `_XamarinSdkRootDirectory` (which is the local Xamarin SDK dir), but from Windows the former will be the path to the Xamarin SDK on the connected Mac. Essentially this new property is agnostic from the platform from which the build is being executed, and will always return the path to the Xamarin SDK on macOS (either local or remote), so it can be used on scenarios like this one where we know the resource we need should always be referenced from macOS.

* [net6] Updates .NET SDK path for remote tasks execution

This path needs to be updated because VS (from Dev17 Preview 3+) will install through XMA the .NET SDK and the iOS SDK on macOS in a custom dir. This should be the preferred path when building from Windows if it does exist.

* Adds missing spaces to TaskRunner.cs

dotnet/Microsoft.iOS.Windows.Sdk/targets/Microsoft.iOS.Windows.Sdk.props

@@ -6,8 +6,8 @@
 
   <PropertyGroup>
     <_DotNetRootRemoteDirectory Condition="$(_DotNetRootRemoteDirectory) == ''">/usr/local/share/dotnet/</_DotNetRootRemoteDirectory>
-    <_XamarinSdkRemoteRootDirectory Condition="'$(_XamarinSdkRemoteRootDirectory)' == ''">$(_XamarinSdkRootDirectory.Replace('$(NetCoreRoot)', '$(_DotNetRootRemoteDirectory)'))</_XamarinSdkRemoteRootDirectory>
-    <_MlaunchPath Condition="'$(_MlaunchPath)' == ''">$(_XamarinSdkRemoteRootDirectory)tools/bin/mlaunch</_MlaunchPath>
+    <_XamarinSdkRootDirectoryOnMac Condition="'$(_XamarinSdkRootDirectory)' != ''">$(_XamarinSdkRootDirectory.Replace('$(NetCoreRoot)', '$(_DotNetRootRemoteDirectory)'))</_XamarinSdkRootDirectoryOnMac>
+    <_MlaunchPath Condition="'$(_MlaunchPath)' == ''">$(_XamarinSdkRootDirectoryOnMac)tools/bin/mlaunch</_MlaunchPath>
     <AfterMicrosoftNETSdkTargets>$(AfterMicrosoftNETSdkTargets);$(MSBuildThisFileDirectory)..\targets\Microsoft.iOS.Windows.Sdk.targets</AfterMicrosoftNETSdkTargets>
 
     <_XamarinSdkRootOnMac Condition="'$(_XamarinSdkRoot)' != ''">$(_XamarinSdkRoot.Replace('$(NetCoreRoot)', '$(_DotNetRootRemoteDirectory)'))</_XamarinSdkRootOnMac>

dotnet/targets/Xamarin.Shared.Sdk.props

@@ -14,8 +14,10 @@
 	<PropertyGroup>
 		<!-- Set to true when using the Microsoft.<platform>.Sdk NuGet. This is used by pre-existing/shared targets to tweak behavior depending on build system -->
 		<UsingAppleNETSdk>true</UsingAppleNETSdk>
-		<!-- This is the location of the Microsoft.<platform>.Sdk NuGet (/usr/local/share/dotnet/sdk/<version>/Sdks/Microsoft.[iOS/tvOS/watchOS/macOS].Sdk) -->
+		<!-- This is the location of the Microsoft.<platform>.Sdk NuGet (/usr/local/share/dotnet/sdk/<version>/Sdks/Microsoft.[iOS/tvOS/watchOS/macOS].Sdk) on the platform the build is running from (Mac or Win) -->
 		<_XamarinSdkRootDirectory>$([MSBuild]::NormalizePath('$(MSBuildThisFileDirectory)', '..'))\</_XamarinSdkRootDirectory>
+		<!-- This is the location of the Microsoft.<platform>.Sdk NuGet on macOS, this value will be overriden from Windows  -->
+		<_XamarinSdkRootDirectoryOnMac>$(_XamarinSdkRootDirectory)</_XamarinSdkRootDirectoryOnMac>
 		<_XamarinTaskAssembly Condition="'$(_PlatformName)' != 'macOS'">$(_XamarinSdkRootDirectory)\tools\msbuild\iOS\Xamarin.iOS.Tasks.dll</_XamarinTaskAssembly>
 		<_XamarinTaskAssembly Condition="'$(_PlatformName)' == 'macOS'">$(_XamarinSdkRootDirectory)\tools\msbuild\macOS\Xamarin.Mac.Tasks.dll</_XamarinTaskAssembly>
 		<SuppressTrimAnalysisWarnings Condition=" '$(SuppressTrimAnalysisWarnings)' == '' ">true</SuppressTrimAnalysisWarnings>

dotnet/targets/Xamarin.Shared.Sdk.targets

@@ -234,12 +234,6 @@
 		</CreateAppBundleDependsOn>
 	</PropertyGroup>
 
-	<!-- Linker -->
-	<PropertyGroup>
-		<_AdditionalTaskAssemblyDirectory>$(_XamarinSdkRootDirectory)tools/dotnet-linker/</_AdditionalTaskAssemblyDirectory>
-		<_AdditionalTaskAssembly>$(_AdditionalTaskAssemblyDirectory)dotnet-linker.dll</_AdditionalTaskAssembly>
-	</PropertyGroup>
-
 	<!-- PublishTrimmed must be calculated as part of a target because IsMacEnabled on Windows will be set after connecting to the Mac -->
 	<Target Name="_ComputePublishTrimmed">
 		<PropertyGroup>
@@ -431,6 +425,10 @@
 
 			<!-- We always want the linker to process debug symbols, even when building in Release mode, because the AOT compiler uses the managed debug symbols to output DWARF debugging symbols -->
 			<TrimmerRemoveSymbols Condition="'$(TrimmerRemoveSymbols)' == ''">false</TrimmerRemoveSymbols>
+
+			<!-- Linker -->
+			<_AdditionalTaskAssemblyDirectory>$(_XamarinSdkRootDirectoryOnMac)tools/dotnet-linker/</_AdditionalTaskAssemblyDirectory>
+			<_AdditionalTaskAssembly>$(_AdditionalTaskAssemblyDirectory)dotnet-linker.dll</_AdditionalTaskAssembly>
 		</PropertyGroup>
 
 		<ItemGroup>

msbuild/Messaging/Xamarin.Messaging.Build/TaskRunner.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.IO;
 using System.Linq;
 using System.Reflection;
 using Microsoft.Build.Utilities;
@@ -16,8 +17,15 @@ internal TaskRunner (ITaskSerializer serializer)
 		{
 			this.serializer = serializer;
 
+			var dotnetPath = Path.Combine (MessagingContext.GetXmaPath (), "SDKs", "dotnet", "dotnet");
+
+			//In case the XMA dotnet has not been installed yet
+			if (!File.Exists (dotnetPath)) {
+				dotnetPath = "/usr/local/share/dotnet/dotnet";
+			}
+
 			// TODO: Needed by the ILLinkTask, we need to add support for doing this from Windows
-			Environment.SetEnvironmentVariable ("DOTNET_HOST_PATH", "/usr/local/share/dotnet/dotnet");
+			Environment.SetEnvironmentVariable ("DOTNET_HOST_PATH", dotnetPath);
 		}
 
 		internal IEnumerable<Type> Tasks => tasks.AsReadOnly ();
@@ -48,4 +56,4 @@ public ExecuteTaskResult Execute (string taskName, string inputs)
 			return result;
 		}
 	}
-}
+}