[Xamarin.Android.Build.Tasks] <GenerateJavaStubs/> improvements (#2956)

I went through the `_GenerateJavaStubs` MSBuild target and the
`<GenerateJavaStubs/>` MSBuild task. There was an "easy" win to
improve incremental build performance. I also made a few other general
improvements to `<GenerateJavaStubs/>`.

~~ Inputs & Outputs ~~

`_GenerateJavaStubs` has `Inputs` of:

    Inputs="$(MSBuildAllProjects);@(_ResolvedAssemblies);$(_AndroidManifestAbs);$(_AndroidBuildPropertiesCache);@(_AndroidResourceDest)"

Lets say a NetStandard assembly changes, such as a XAML change in a
Xamarin.Forms app. In this case `_GenerateJavaStubs` does not actually
need to run again.

We can use `@(_ResolvedUserMonoAndroidAssemblies)` as an input instead
of `@(_ResolvedAssemblies)`.

This is the biggest win--to skip this target completely.

~~ selectedWhitelistAssemblies ~~

`ManifestDocument` had the concept of a "whitelist" assembly, which
currently consisted of a single assembly:

    internal static readonly string [] FrameworkAttributeLookupTargets = {"Mono.Android.GoogleMaps.dll"};

`Mono.Android.GoogleMaps.dll` no longer exists, so I was able to
remove a bit of code that still used that dead codepath.

~~ Typemaps ~~

Just a couple minor improvements here:

* Fixed the usage of the `[Obsolete]` constructor for
  `TypeNameMapGenerator`. Using a `(TaskLevel level, string value)`
  callback instead.
* I reused the `MemoryStream` and got rid of the `UpdateWhenChanged`
  method.

~~ Tests ~~

I updated the `IncrementalBuildTest.ProduceReferenceAssembly` test
quite a bit:

* The library project using `$(ProduceReferenceAssembly)` is now a
  NetStandard library.
* I check all the targets that should be skipped from now on.

I made a few changes in `Xamarin.ProjectTools` to clean things up:

* The `DotNetStandard` class should just define
  `Language=XamarinAndroidProjectLanguage.CSharp` by default.
* Added a `ShouldRestorePackageReferences` property for deciding if we
  pass `/restore` or not.
* The `DotNetStandard` class always needs to use `/restore`, even if
  there are no `PackageReferences`.
* I moved a couple methods from `DotNetXamarinProject` to
  `XamarinProject` so the `DotNetStandard` has them.

~~ Results ~~

Testing the Xamarin.Forms project in this repo. A fresh build I wasn't
able to see a noticeable improvement.

*However*, an incremental build with XAML-change:

    Before:
      861 ms  _GenerateJavaStubs                         1 calls
    After:
      n/a

The target is skipped now:

    _GenerateJavaStubs:
    Skipping target "_GenerateJavaStubs" because all output files are up-to-date with respect to the input files.

Overall this seems to be ~800ms better for incremental builds with
XAML changes.

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

@@ -2,12 +2,11 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.IO;
 using System.Linq;
-using System.Xml.Linq;
 using Microsoft.Build.Framework;
 using Microsoft.Build.Utilities;
-using MonoDroid.Utils;
 using Mono.Cecil;
 
 
@@ -104,14 +103,9 @@ void Run (DirectoryAssemblyResolver res)
 					res.SearchDirectories.Add (dir.ItemSpec);
 			}
 
-			var selectedWhitelistAssemblies = new List<string> ();
-
 			// Put every assembly we'll need in the resolver
 			foreach (var assembly in ResolvedAssemblies) {
-				var assemblyFullPath = Path.GetFullPath (assembly.ItemSpec);
-				res.Load (assemblyFullPath);
-				if (MonoAndroidHelper.FrameworkAttributeLookupTargets.Any (a => Path.GetFileName (assembly.ItemSpec) == a))
-					selectedWhitelistAssemblies.Add (assemblyFullPath);
+				res.Load (assembly.ItemSpec);
 			}
 
 			// However we only want to look for JLO types in user code
@@ -234,7 +228,7 @@ void Run (DirectoryAssemblyResolver res)
 			manifest.NeedsInternet = NeedsInternet;
 			manifest.InstantRunEnabled = InstantRunEnabled;
 
-			var additionalProviders = manifest.Merge (all_java_types, selectedWhitelistAssemblies, ApplicationJavaClass, EmbedAssemblies, BundledWearApplicationName, MergedManifestDocuments);
+			var additionalProviders = manifest.Merge (all_java_types, ApplicationJavaClass, EmbedAssemblies, BundledWearApplicationName, MergedManifestDocuments);
 
 			using (var stream = new MemoryStream ()) {
 				manifest.Save (stream);
@@ -287,19 +281,17 @@ void SaveResource (string resource, string filename, string destDir, Func<string
 
 		void WriteTypeMappings (List<TypeDefinition> types)
 		{
-			using (var gen = UseSharedRuntime
-				? new TypeNameMapGenerator (types, Log.LogDebugMessage)
-			        : new TypeNameMapGenerator (ResolvedAssemblies.Select (p => p.ItemSpec), Log.LogDebugMessage)) {
-				UpdateWhenChanged (Path.Combine (OutputDirectory, "typemap.jm"), gen.WriteJavaToManaged);
-				UpdateWhenChanged (Path.Combine (OutputDirectory, "typemap.mj"), gen.WriteManagedToJava);
-			}
-		}
-
-		void UpdateWhenChanged (string path, Action<Stream> generator)
-		{
+			void logger (TraceLevel level, string value) => Log.LogDebugMessage (value);
+			TypeNameMapGenerator createTypeMapGenerator () => UseSharedRuntime ?
+				new TypeNameMapGenerator (types, logger) :
+				new TypeNameMapGenerator (ResolvedAssemblies.Select (p => p.ItemSpec), logger);
+			using (var gen = createTypeMapGenerator ())
 			using (var stream = new MemoryStream ()) {
-				generator (stream);
-				MonoAndroidHelper.CopyIfStreamChanged (stream, path);
+				gen.WriteJavaToManaged (stream);
+				MonoAndroidHelper.CopyIfStreamChanged (stream, Path.Combine (OutputDirectory, "typemap.jm"));
+				stream.SetLength (0); //Reuse the stream
+				gen.WriteManagedToJava (stream);
+				MonoAndroidHelper.CopyIfStreamChanged (stream, Path.Combine (OutputDirectory, "typemap.mj"));
 			}
 		}
 	}

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

@@ -481,8 +481,10 @@ public void ProduceReferenceAssembly ()
 			app.SetProperty ("AndroidUseSharedRuntime", false.ToString ());
 
 			int count = 0;
-			var lib = new XamarinAndroidLibraryProject {
+			var lib = new DotNetStandard {
 				ProjectName = "MyLibrary",
+				Sdk = "Microsoft.NET.Sdk",
+				TargetFramework = "netstandard2.0",
 				Sources = {
 					new BuildItem.Source ("Bar.cs") {
 						TextContent = () => "public class Bar { public Bar () { System.Console.WriteLine (" + count++ + "); } }"
@@ -503,8 +505,10 @@ public void ProduceReferenceAssembly ()
 				Assert.IsTrue (appBuilder.Build (app, doNotCleanupOnUpdate: true, saveProject: false), "second app build should have succeeded.");
 
 				var targetsShouldSkip = new [] {
-					//TODO: perhaps more targets will skip here eventually?
 					"CoreCompile",
+					"_BuildLibraryImportsCache",
+					"_ResolveLibraryProjectImports",
+					"_GenerateJavaStubs",
 				};
 				foreach (var target in targetsShouldSkip) {
 					Assert.IsTrue (appBuilder.Output.IsTargetSkipped (target), $"`{target}` should be skipped!");

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

@@ -341,7 +341,6 @@ public void CheckAppBundle ([Values (true, false)] bool isRelease)
 		public void NetStandardReferenceTest ()
 		{
 			var netStandardProject = new DotNetStandard () {
-				Language = XamarinAndroidProjectLanguage.CSharp,
 				ProjectName = "XamFormsSample",
 				ProjectGuid = Guid.NewGuid ().ToString (),
 				Sdk = "Microsoft.NET.Sdk",

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Common/DotNetStandard.cs

@@ -7,7 +7,6 @@ namespace Xamarin.ProjectTools
 {
 	public class DotNetStandard : XamarinProject
 	{
-
 		public override string ProjectTypeGuid {
 			get {
 				return string.Empty;
@@ -20,7 +19,12 @@ public DotNetStandard ()
 			OtherBuildItems = new List<BuildItem> ();
 			SetProperty (CommonProperties, "DebugType", "full");
 			ItemGroupList.Add (Sources);
+			Language = XamarinAndroidProjectLanguage.CSharp;
 		}
+
+		// NetStandard projects always need to restore
+		public override bool ShouldRestorePackageReferences => true;
+
 		public string PackageTargetFallback {
 			get { return GetProperty ("PackageTargetFallback"); }
 			set { SetProperty ("PackageTargetFallback", value); }

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Common/DotNetXamarinProject.cs

@@ -72,11 +72,6 @@ public string IntermediateOutputPath {
 			set { SetProperty (ActiveConfigurationProperties, KnownProperties.IntermediateOutputPath, value); }
 		}
 
-		public BuildItem GetItem (string include)
-		{
-			return ItemGroupList.SelectMany (g => g).First (i => i.Include ().Equals (include, StringComparison.OrdinalIgnoreCase));
-		}
-
 		public void AddReferences (params string [] references)
 		{
 			foreach (var s in references)
@@ -89,12 +84,6 @@ public void AddSources (params string [] sources)
 				Sources.Add (new BuildItem.Source (s));
 		}
 
-		public void Touch (params string [] itemPaths)
-		{
-			foreach (var item in itemPaths)
-				GetItem (item).Timestamp = DateTimeOffset.UtcNow;
-		}
-
 		public virtual ProjectRootElement Construct ()
 		{
 			var root = ProjectRootElement.Create ();

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Common/ProjectBuilder.cs

@@ -73,7 +73,7 @@ public bool Build (XamarinProject project, bool doNotCleanupOnUpdate = false, st
 				project.NuGetRestore (Path.Combine (XABuildPaths.TestOutputDirectory, ProjectDirectory), PackagesDirectory);
 			}
 
-			bool result = BuildInternal (Path.Combine (ProjectDirectory, project.ProjectFilePath), Target, parameters, environmentVariables, restore: project.PackageReferences?.Count > 0);
+			bool result = BuildInternal (Path.Combine (ProjectDirectory, project.ProjectFilePath), Target, parameters, environmentVariables, restore: project.ShouldRestorePackageReferences);
 			built_before = true;
 
 			if (CleanupAfterSuccessfulBuild)

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Common/SolutionBuilder.cs

@@ -67,7 +67,7 @@ public void Save ()
 
 		public bool BuildProject(XamarinProject project, string target = "Build")
 		{
-			BuildSucceeded = BuildInternal(Path.Combine (SolutionPath, project.ProjectName, project.ProjectFilePath), target, restore: project.PackageReferences?.Count > 0);
+			BuildSucceeded = BuildInternal(Path.Combine (SolutionPath, project.ProjectName, project.ProjectFilePath), target, restore: project.ShouldRestorePackageReferences);
 			return BuildSucceeded;
 		}
 

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Common/XamarinProject.cs

@@ -31,6 +31,7 @@ public abstract class XamarinProject
 		public IList<Package> Packages { get; private set; }
 		public IList<BuildItem> References { get; private set; }
 		public IList<Package> PackageReferences { get; private set; }
+		public virtual bool ShouldRestorePackageReferences => PackageReferences?.Count > 0;
 		public IList<Import> Imports { get; private set; }
 		PropertyGroup common, debug, release;
 
@@ -120,6 +121,17 @@ public void SetProperty (IList<Property> group, string name, Func<string> value,
 			}
 		}
 
+		public BuildItem GetItem (string include)
+		{
+			return ItemGroupList.SelectMany (g => g).First (i => i.Include ().Equals (include, StringComparison.OrdinalIgnoreCase));
+		}
+
+		public void Touch (params string [] itemPaths)
+		{
+			foreach (var item in itemPaths)
+				GetItem (item).Timestamp = DateTimeOffset.UtcNow;
+		}
+
 		string project_file_path;
 		public string ProjectFilePath {
 			get { return project_file_path ?? ProjectName + Language.DefaultProjectExtension; }

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

@@ -224,7 +224,7 @@ void ReorderActivityAliases (XElement app)
 			}
 		}
 
-		public IList<string> Merge (List<TypeDefinition> subclasses, List<string> selectedWhitelistAssemblies, string applicationClass, bool embed, string bundledWearApplicationName, IEnumerable<string> mergedManifestDocuments)
+		public IList<string> Merge (List<TypeDefinition> subclasses, string applicationClass, bool embed, string bundledWearApplicationName, IEnumerable<string> mergedManifestDocuments)
 		{
 			string applicationName  = ApplicationName;
 
@@ -244,7 +244,7 @@ public IList<string> Merge (List<TypeDefinition> subclasses, List<string> select
 			if (manifest.Attribute (androidNs + "versionName") == null)
 				manifest.SetAttributeValue (androidNs + "versionName", "1.0");
 
-			app = CreateApplicationElement (manifest, applicationClass, subclasses, selectedWhitelistAssemblies);
+			app = CreateApplicationElement (manifest, applicationClass, subclasses);
 
 			if (app.Attribute (androidNs + "label") == null && applicationName != null)
 				app.SetAttributeValue (androidNs + "label", applicationName);
@@ -399,12 +399,12 @@ public IList<string> Merge (List<TypeDefinition> subclasses, List<string> select
 			}
 
 			AddInstrumentations (manifest, subclasses, targetSdkVersionValue);
-			AddPermissions (app, selectedWhitelistAssemblies);
-			AddPermissionGroups (app, selectedWhitelistAssemblies);
-			AddPermissionTrees (app, selectedWhitelistAssemblies);
-			AddUsesPermissions (app, selectedWhitelistAssemblies);
-			AddUsesFeatures (app, selectedWhitelistAssemblies);
-			AddSupportsGLTextures (app, selectedWhitelistAssemblies);
+			AddPermissions (app);
+			AddPermissionGroups (app);
+			AddPermissionTrees (app);
+			AddUsesPermissions (app);
+			AddUsesFeatures (app);
+			AddSupportsGLTextures (app);
 
 			ReorderActivityAliases (app);
 			ReorderElements (app);
@@ -508,7 +508,7 @@ Func<TypeDefinition, string, int, XElement> GetGenerator (TypeDefinition type)
 			return null;
 		}
 
-		XElement CreateApplicationElement (XElement manifest, string applicationClass, List<TypeDefinition> subclasses, List<string> selectedWhitelistAssemblies)
+		XElement CreateApplicationElement (XElement manifest, string applicationClass, List<TypeDefinition> subclasses)
 		{
 			var application = manifest.Descendants ("application").FirstOrDefault ();
 
@@ -521,10 +521,10 @@ XElement CreateApplicationElement (XElement manifest, string applicationClass, L
 					.Where (attr => attr != null)
 					.ToList ();
 			var usesLibraryAttr = 
-				Assemblies.Concat (selectedWhitelistAssemblies).SelectMany (path => UsesLibraryAttribute.FromCustomAttributeProvider (Resolver.GetAssembly (path)))
+				Assemblies.SelectMany (path => UsesLibraryAttribute.FromCustomAttributeProvider (Resolver.GetAssembly (path)))
 				.Where (attr => attr != null);
 			var usesConfigurationAttr =
-				Assemblies.Concat (selectedWhitelistAssemblies).SelectMany (path => UsesConfigurationAttribute.FromCustomAttributeProvider (Resolver.GetAssembly (path)))
+				Assemblies.SelectMany (path => UsesConfigurationAttribute.FromCustomAttributeProvider (Resolver.GetAssembly (path)))
 				.Where (attr => attr != null);
 			if (assemblyAttr.Count > 1)
 				throw new InvalidOperationException ("There can be only one [assembly:Application] attribute defined.");
@@ -772,54 +772,42 @@ public void AddFastDeployPermissions ()
 				app.AddBeforeSelf (new XElement ("uses-permission", new XAttribute (attName, permReadExternalStorage)));
 		}
 
-		void AddPermissions (XElement application, List<string> selectedWhitelistAssemblies)
+		void AddPermissions (XElement application)
 		{
-			// Look in user assemblies + whitelist (like Maps)
-			var check_assemblies = Assemblies.Union (selectedWhitelistAssemblies);
-
 			var assemblyAttrs = 
-				check_assemblies.SelectMany (path => PermissionAttribute.FromCustomAttributeProvider (Resolver.GetAssembly (path)));
+				Assemblies.SelectMany (path => PermissionAttribute.FromCustomAttributeProvider (Resolver.GetAssembly (path)));
 			// Add unique permissions to the manifest
 			foreach (var pa in assemblyAttrs.Distinct (new PermissionAttribute.PermissionAttributeComparer ()))
 				if (!application.Parent.Descendants ("permission").Any (x => (string)x.Attribute (attName) == pa.Name))
 					application.AddBeforeSelf (pa.ToElement (PackageName));
 		}
 
-		void AddPermissionGroups (XElement application, List<string> selectedWhitelistAssemblies)
+		void AddPermissionGroups (XElement application)
 		{
-			// Look in user assemblies + whitelist (like Maps)
-			var check_assemblies = Assemblies.Union (selectedWhitelistAssemblies);
-
 			var assemblyAttrs = 
-				check_assemblies.SelectMany (path => PermissionGroupAttribute.FromCustomAttributeProvider (Resolver.GetAssembly (path)));
+				Assemblies.SelectMany (path => PermissionGroupAttribute.FromCustomAttributeProvider (Resolver.GetAssembly (path)));
 
 			// Add unique permissionGroups to the manifest
 			foreach (var pga in assemblyAttrs.Distinct (new PermissionGroupAttribute.PermissionGroupAttributeComparer ()))
 				if (!application.Parent.Descendants ("permissionGroup").Any (x => (string)x.Attribute (attName) == pga.Name))
 					application.AddBeforeSelf (pga.ToElement (PackageName));
 		}
 
-		void AddPermissionTrees (XElement application, List<string> selectedWhitelistAssemblies)
+		void AddPermissionTrees (XElement application)
 		{
-			// Look in user assemblies + whitelist (like Maps)
-			var check_assemblies = Assemblies.Union (selectedWhitelistAssemblies);
-
-			var assemblyAttrs = 
-				check_assemblies.SelectMany (path => PermissionTreeAttribute.FromCustomAttributeProvider (Resolver.GetAssembly (path)));
+			var assemblyAttrs =
+				Assemblies.SelectMany (path => PermissionTreeAttribute.FromCustomAttributeProvider (Resolver.GetAssembly (path)));
 
 			// Add unique permissionGroups to the manifest
 			foreach (var pta in assemblyAttrs.Distinct (new PermissionTreeAttribute.PermissionTreeAttributeComparer ()))
 				if (!application.Parent.Descendants ("permissionTree").Any (x => (string)x.Attribute (attName) == pta.Name))
 					application.AddBeforeSelf (pta.ToElement (PackageName));
 		}
 
-		void AddUsesPermissions (XElement application, List<string> selectedWhitelistAssemblies)
+		void AddUsesPermissions (XElement application)
 		{
-			// Look in user assemblies + whitelist (like Maps)
-			var check_assemblies = Assemblies.Union (selectedWhitelistAssemblies);
-
-			var assemblyAttrs = 
-				check_assemblies.SelectMany (path => UsesPermissionAttribute.FromCustomAttributeProvider (Resolver.GetAssembly (path)));
+			var assemblyAttrs =
+				Assemblies.SelectMany (path => UsesPermissionAttribute.FromCustomAttributeProvider (Resolver.GetAssembly (path)));
 
 			// Add unique permissions to the manifest
 			foreach (var upa in assemblyAttrs.Distinct (new UsesPermissionAttribute.UsesPermissionComparer ()))
@@ -841,13 +829,10 @@ void AddUsesLibraries (XElement application, IEnumerable<UsesLibraryAttribute> l
 					application.Add (ula.ToElement (PackageName));
 		}
 
-		void AddUsesFeatures (XElement application, List<string> selectedWhitelistAssemblies)
+		void AddUsesFeatures (XElement application)
 		{
-			// Look in user assemblies + whitelist (like Maps)
-			var check_assemblies = Assemblies.Union (selectedWhitelistAssemblies);
-
-			var assemblyAttrs = 
-				check_assemblies.SelectMany (path => UsesFeatureAttribute.FromCustomAttributeProvider (Resolver.GetAssembly (path)));
+			var assemblyAttrs =
+				Assemblies.SelectMany (path => UsesFeatureAttribute.FromCustomAttributeProvider (Resolver.GetAssembly (path)));
 
 			// Add unique features by Name or glESVersion to the manifest
 			foreach (var feature in assemblyAttrs) {
@@ -865,13 +850,10 @@ void AddUsesFeatures (XElement application, List<string> selectedWhitelistAssemb
 			}
 		}
 
-		void AddSupportsGLTextures (XElement application, List<string> selectedWhitelistAssemblies)
+		void AddSupportsGLTextures (XElement application)
 		{
-			// Look in user assemblies + whitelist (like Maps)
-			var check_assemblies = Assemblies.Union (selectedWhitelistAssemblies);
-
-			var assemblyAttrs = 
-				check_assemblies.SelectMany (path => SupportsGLTextureAttribute.FromCustomAttributeProvider (Resolver.GetAssembly (path)));
+			var assemblyAttrs =
+				Assemblies.SelectMany (path => SupportsGLTextureAttribute.FromCustomAttributeProvider (Resolver.GetAssembly (path)));
 
 			// Add unique items by Name to the manifest
 			foreach (var feature in assemblyAttrs) {

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

@@ -495,7 +495,6 @@ internal static IEnumerable<string> GetFrameworkAssembliesToTreatAsUserAssemblie
 		}
 #endif
 
-		internal static readonly string [] FrameworkAttributeLookupTargets = {"Mono.Android.GoogleMaps.dll"};
 		internal static readonly string [] FrameworkEmbeddedJarLookupTargets = {
 			"Mono.Android.Support.v13.dll",
 			"Mono.Android.Support.v4.dll",
@@ -507,7 +506,6 @@ internal static IEnumerable<string> GetFrameworkAssembliesToTreatAsUserAssemblie
 		};
 		// MUST BE SORTED CASE-INSENSITIVE
 		internal static readonly string[] FrameworkAssembliesToTreatAsUserAssemblies = {
-			"Mono.Android.GoogleMaps.dll",
 			"Mono.Android.Support.v13.dll",
 			"Mono.Android.Support.v4.dll",
 			"Xamarin.Android.NUnitLite.dll",

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

@@ -2245,7 +2245,7 @@ because xbuild doesn't support framework reference assemblies.
 
 <Target Name="_GenerateJavaStubs"
   DependsOnTargets="_SetLatestTargetFrameworkVersion;_PrepareAssemblies;$(_AfterPrepareAssemblies)"
-  Inputs="$(MSBuildAllProjects);@(_ResolvedAssemblies);$(_AndroidManifestAbs);$(_AndroidBuildPropertiesCache);@(_AndroidResourceDest)"
+  Inputs="$(MSBuildAllProjects);@(_ResolvedUserMonoAndroidAssemblies);$(_AndroidManifestAbs);$(_AndroidBuildPropertiesCache);@(_AndroidResourceDest)"
   Outputs="$(_AndroidStampDirectory)_GenerateJavaStubs.stamp">
   <GenerateJavaStubs
     ResolvedAssemblies="@(_ResolvedAssemblies)"