Preserve original NuGet framework string when determining dependency groups

Also add tests for empty dependency groups as they are supported by using the
special identifier/"file" `_._'.

Author: kzu

src/Build/NuGet.Build.Packaging.Tasks/CreatePackage.cs

@@ -110,14 +110,14 @@ where item.GetMetadata(MetadataName.Kind) == PackageItemKind.Dependency &&
 							   {
 								   Id = item.ItemSpec,
 								   Version = VersionRange.Parse(item.GetMetadata(MetadataName.Version)),
-								   TargetFramework = item.GetTargetFramework()
+								   TargetFramework = item.GetNuGetTargetFramework()
 							   };
 
 			manifest.Metadata.DependencyGroups = (from dependency in dependencies
 												  group dependency by dependency.TargetFramework into dependenciesByFramework
 												  select new PackageDependencyGroup
 												  (
-													  NuGetFramework.Parse(dependenciesByFramework.Key.GetShortFrameworkName() ?? PackagingConstants.AnyFramework),
+													  dependenciesByFramework.Key,
 													  (from dependency in dependenciesByFramework
 													   where dependency.Id != "_._"
 													   group dependency by dependency.Id into dependenciesById
@@ -253,7 +253,7 @@ class Dependency
 		{
 			public string Id { get; set; }
 
-			public FrameworkName TargetFramework { get; set; }
+			public NuGetFramework TargetFramework { get; set; }
 
 			public VersionRange Version { get; set; }
 		}

src/Build/NuGet.Build.Packaging.Tasks/Extensions.cs

@@ -58,6 +58,18 @@ public static Manifest GetManifest(this IPackageCoreReader packageReader)
 			}
 		}
 
+		public static NuGetFramework GetNuGetTargetFramework(this ITaskItem taskItem)
+		{
+			var metadataValue = taskItem.GetMetadata(MetadataName.TargetFramework);
+			if (string.IsNullOrEmpty(metadataValue))
+				metadataValue = taskItem.GetMetadata(MetadataName.TargetFrameworkMoniker);
+
+			if (!string.IsNullOrEmpty(metadataValue))
+				return NuGetFramework.Parse(metadataValue);
+			else
+				return NuGetFramework.AnyFramework;
+		}
+
 		public static FrameworkName GetTargetFramework(this ITaskItem taskItem)
 		{
 			var metadataValue = taskItem.GetMetadata(MetadataName.TargetFramework);

src/Build/NuGet.Build.Packaging.Tests/CreatePackageTests.cs

@@ -148,6 +148,62 @@ public void when_creating_package_with_simple_dependency_then_contains_dependenc
 			Assert.Equal("8.0.0", manifest.Metadata.DependencyGroups.First().Packages.First().VersionRange.MinVersion.ToString());
 		}
 
+		[Fact]
+		public void when_creating_package_with_empty_dependency_groups_then_succeeds()
+		{
+			task.Contents = new[]
+			{
+				new TaskItem(Path.GetTempFileName(), new Metadata
+				{
+					{ MetadataName.PackageId, task.Manifest.GetMetadata("Id") },
+					{ MetadataName.Kind, PackageItemKind.None },
+					{ MetadataName.PackagePath, "readme.txt" }
+				}),
+				new TaskItem("_._", new Metadata
+				{
+					{ MetadataName.PackageId, task.Manifest.GetMetadata("Id") },
+					{ MetadataName.Kind, PackageItemKind.Dependency },
+					{ MetadataName.Version, "*" },
+					{ MetadataName.TargetFramework, "net45" }
+				}),
+				new TaskItem("_._", new Metadata
+				{
+					{ MetadataName.PackageId, task.Manifest.GetMetadata("Id") },
+					{ MetadataName.Kind, PackageItemKind.Dependency },
+					{ MetadataName.Version, "*" },
+					{ MetadataName.TargetFramework, "win" }
+				}),
+				new TaskItem("_._", new Metadata
+				{
+					{ MetadataName.PackageId, task.Manifest.GetMetadata("Id") },
+					{ MetadataName.Kind, PackageItemKind.Dependency },
+					{ MetadataName.Version, "*" },
+					{ MetadataName.TargetFramework, "wpa" }
+				}),
+				new TaskItem("_._", new Metadata
+				{
+					{ MetadataName.PackageId, task.Manifest.GetMetadata("Id") },
+					{ MetadataName.Kind, PackageItemKind.Dependency },
+					{ MetadataName.Version, "*" },
+					{ MetadataName.TargetFramework, "MonoAndroid10" }
+				}),
+			};
+
+			var manifest = ExecuteTask();
+
+			Assert.NotNull(manifest);
+			Assert.Equal(4, manifest.Metadata.DependencyGroups.Count());
+			Assert.All(manifest.Metadata.DependencyGroups, d => Assert.Empty(d.Packages));
+
+			//Assert.Equal(NuGetFramework.Parse(".NETFramework,Version=v4.5"), manifest.Metadata.DependencyGroups.First().TargetFramework);
+			//Assert.Equal(1, manifest.Metadata.DependencyGroups.First().Packages.Count());
+			//Assert.Equal("Newtonsoft.Json", manifest.Metadata.DependencyGroups.First().Packages.First().Id);
+
+			//// We get a version range actually for the specified dependency, like [1.0.0,)
+			//Assert.Equal("8.0.0", manifest.Metadata.DependencyGroups.First().Packages.First().VersionRange.MinVersion.ToString());
+		}
+
+
 		[Fact]
 		public void when_creating_package_with_development_dependency_then_does_not_generate_dependency_group()
 		{