[msbuild] Fix how UnpackLibraryResources handles mscorlib.dll (and potentially other framework assemblies) (#1011)

Target _UnpackLibraryResources:
	Task "UnpackLibraryResources"
		Using task UnpackLibraryResources from Xamarin.MacDev.Tasks.UnpackLibraryResources, Xamarin.MacDev.Tasks, Version=1.0.6128.15885, Culture=neutral, PublicKeyToken=null
		UnpackLibraryResources Task
		  Prefix: monotouch
		  IntermediateOutputPath: obj/iPhone/Debug/
		  NoOverwrite:
		    obj/iPhone/Debug/ibtool-link/LaunchScreen.storyboardc/01J-lp-oVM-view-Ze5-6b-2t3.nib
		    obj/iPhone/Debug/ibtool-link/LaunchScreen.storyboardc/Info.plist
		    obj/iPhone/Debug/ibtool-link/LaunchScreen.storyboardc/UIViewController-01J-lp-oVM.nib
		    obj/iPhone/Debug/ibtool-link/Main.storyboardc/BYZ-38-t0r-view-8bC-Xf-vdC.nib
		    obj/iPhone/Debug/ibtool-link/Main.storyboardc/Info.plist
		    obj/iPhone/Debug/ibtool-link/Main.storyboardc/UIViewController-BYZ-38-t0r.nib
		  ReferencedLibraries:
		    /Users/poupou/git/xamarin/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/Current/lib/mono/Xamarin.iOS/System.dll
		    /Users/poupou/git/xamarin/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/Current/lib/mono/Xamarin.iOS/System.Xml.dll
		    /Users/poupou/git/xamarin/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/Current/lib/mono/Xamarin.iOS/System.Core.dll
		    /Users/poupou/git/xamarin/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/Current/lib/mono/Xamarin.iOS/Xamarin.iOS.dll
		    /Users/poupou/Downloads/LinkingTest-2/RMSDKWrapper/bin/Debug//RMSDKWrapper.dll
		    /Users/poupou/git/xamarin/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/Current/lib/mono/Xamarin.iOS//mscorlib.dll
		    /Users/poupou/git/xamarin/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/Current/lib/mono/Xamarin.iOS//mscorlib.dll
		  Skipping framework assembly: /Users/poupou/git/xamarin/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/Current/lib/mono/Xamarin.iOS/System.dll
		  Skipping framework assembly: /Users/poupou/git/xamarin/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/Current/lib/mono/Xamarin.iOS/System.Xml.dll
		  Skipping framework assembly: /Users/poupou/git/xamarin/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/Current/lib/mono/Xamarin.iOS/System.Core.dll
		  Skipping framework assembly: /Users/poupou/git/xamarin/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/Current/lib/mono/Xamarin.iOS/Xamarin.iOS.dll
		  Inspecting assembly: /Users/poupou/Downloads/LinkingTest-2/RMSDKWrapper/bin/Debug//RMSDKWrapper.dll
		  Inspecting assembly: /Users/poupou/git/xamarin/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/Current/lib/mono/Xamarin.iOS//mscorlib.dll
		  Inspecting assembly: /Users/poupou/git/xamarin/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/Current/lib/mono/Xamarin.iOS//mscorlib.dll
	Done executing task "UnpackLibraryResources"
	Done building target "_UnpackLibraryResources" in project "/Users/poupou/Downloads/LinkingTest-2/LinkingTest/LinkingTest.csproj".

The above log excerpt shows two issues:

1. mscorlib.dll is needlessly inspected as it's **not** considered a
   "framework" assembly.

   The current check was checking *how* it was resolved and not *where*
   it was resolved to. The later is the most important as it's possible
   for other assemblies to have direct paths references and we do not
   want to process them.

   This is fixed by comparing each assembly path with the (now) provided
   `TargetFrameworkDirectory`

2. mscorlib.dll is inspected twice

   That's because it's present two times in the task's input. That issue
   is upstream (not sure why) of the current task but it makes #1 twice
   as costly. The fix for #1 indirectly fix that too.

Future
------

It's worth investigating to move that logic into `mtouch`. The later must
already load all assemblies and is in charge of removing other embedded
data (e.g. native code from bindings) from the assemblies (so they are not
shipped both inside and outside the .dll in the final .app). This makes
this task seems extraneous work.

Considering that my current test case, `RMSDKWrapper.dll`, is 1.3GB in
size it's easy to see that the extra load (which has nothing to be
extracted wrt resources*) is quite visible in build time.

>  3268.201 ms  UnpackLibraryResources                                  1 calls

* it has for bindings but that's already handled by mtouch

msbuild/Xamarin.Mac.Tasks/Xamarin.Mac.Common.targets

@@ -441,6 +441,7 @@ Copyright (C) 2014 Xamarin. All rights reserved.
 			Prefix="xammac"
 			NoOverwrite="@(_BundleResourceWithLogicalName)"
 			IntermediateOutputPath="$(IntermediateOutputPath)"
+			TargetFrameworkDirectory="$(TargetFrameworkDirectory)"
 			ReferencedLibraries="@(ResolvedFiles)">
 			<Output TaskParameter="BundleResourcesWithLogicalNames" ItemName="_BundleResourceWithLogicalName" />
 			<Output TaskParameter="BundleResourcesWithLogicalNames" ItemName="FileWrites" />

msbuild/Xamarin.MacDev.Tasks.Core/Tasks/UnpackLibraryResourcesTaskBase.cs

@@ -26,6 +26,9 @@ namespace Xamarin.MacDev.Tasks
 		[Required]
 		public ITaskItem[] ReferencedLibraries { get; set; }
 
+		[Required]
+		public ITaskItem[] TargetFrameworkDirectory { get; set; }
+
 		#endregion
 
 		#region Outputs
@@ -42,6 +45,7 @@ namespace Xamarin.MacDev.Tasks
 			Log.LogTaskProperty ("IntermediateOutputPath", IntermediateOutputPath);
 			Log.LogTaskProperty ("NoOverwrite", NoOverwrite);
 			Log.LogTaskProperty ("ReferencedLibraries", ReferencedLibraries);
+			Log.LogTaskProperty ("TargetFrameworkDirectory", TargetFrameworkDirectory);
 
 			// TODO: give each assembly its own intermediate output directory
 			// TODO: use list file to avoid re-extracting assemblies but allow FileWrites to work
@@ -49,7 +53,9 @@ namespace Xamarin.MacDev.Tasks
 			HashSet<string> ignore = null;
 
 			foreach (var asm in ReferencedLibraries) {
-				if (asm.GetMetadata ("ResolvedFrom") == "{TargetFrameworkDirectory}") {
+				// mscorlib.dll was not coming out with ResolvedFrom == {TargetFrameworkDirectory}
+				// and what we really care is where it comes from, not how it was resolved
+				if (IsFrameworkAssembly (asm)) {
 					Log.LogMessage (MessageImportance.Low, "  Skipping framework assembly: {0}", asm.ItemSpec);
 				} else {
 					var extracted = ExtractContentAssembly (asm.ItemSpec, IntermediateOutputPath);
@@ -83,6 +89,16 @@ namespace Xamarin.MacDev.Tasks
 			return !Log.HasLoggedErrors;
 		}
 
+		bool IsFrameworkAssembly (ITaskItem asm)
+		{
+			var asm_path = asm.GetMetadata ("FullPath");
+			foreach (var dir in TargetFrameworkDirectory) {
+				if (asm_path.StartsWith (dir.GetMetadata ("FullPath"), StringComparison.OrdinalIgnoreCase))
+					return true;
+			}
+			return false;
+		}
+
 		IEnumerable<ITaskItem> ExtractContentAssembly (string assembly, string intermediatePath)
 		{
 			Log.LogMessage (MessageImportance.Low, "  Inspecting assembly: {0}", assembly);

msbuild/Xamarin.iOS.Tasks.Core/Xamarin.iOS.Common.targets

@@ -543,6 +543,7 @@ Copyright (C) 2013-2016 Xamarin. All rights reserved.
 			Prefix="monotouch"
 			NoOverwrite="@(_BundleResourceWithLogicalName)"
 			IntermediateOutputPath="$(DeviceSpecificIntermediateOutputPath)"
+			TargetFrameworkDirectory="$(TargetFrameworkDirectory)"
 			ReferencedLibraries="@(ReferencePath);@(ReferenceDependencyPaths)">
 			<Output TaskParameter="BundleResourcesWithLogicalNames" ItemName="_BundleResourceWithLogicalName" />
 		</UnpackLibraryResources>