Generate empty dependency groups for target frameworks with libraries but no defined dependencies. (#137)

* Create test to ensure empty dependency groups are created for framework targets used in library files.

* Added code to create empty dependency groups when a file targets a framework and the framework has no defined dependencies.

Author: williamb1024

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

@@ -114,22 +114,33 @@ where item.GetMetadata(MetadataName.Kind) == PackageItemKind.Dependency &&
 								   Version = VersionRange.Parse(item.GetMetadata(MetadataName.Version)),
 								   TargetFramework = item.GetNuGetTargetFramework()
 							   };
-			
-			manifest.Metadata.DependencyGroups = (from dependency in dependencies
-												  group dependency by dependency.TargetFramework into dependenciesByFramework
-												  select new PackageDependencyGroup
-												  (
-													  dependenciesByFramework.Key,
-													  (from dependency in dependenciesByFramework
-													   where dependency.Id != "_._"
-													   group dependency by dependency.Id into dependenciesById
-													   select new PackageDependency
-													   (
-														  dependenciesById.Key,
-														  dependenciesById.Select(x => x.Version)
-														  .Aggregate(AggregateVersions)
-													   )).ToList()
-												 )).ToList();
+
+			var definedDependencyGroups = (from dependency in dependencies
+										   group dependency by dependency.TargetFramework into dependenciesByFramework
+										   select new PackageDependencyGroup
+										   (
+											   dependenciesByFramework.Key,
+											   (from dependency in dependenciesByFramework
+												where dependency.Id != "_._"
+												group dependency by dependency.Id into dependenciesById
+												select new PackageDependency
+												 (
+													 dependenciesById.Key,
+													 dependenciesById.Select(x => x.Version)
+													 .Aggregate(AggregateVersions)
+												 )).ToList()
+										   )).ToDictionary(p => p.TargetFramework.GetFrameworkString());
+
+			// include frameworks referenced by libraries, but without dependencies..
+			foreach (var targetFramework in (from item in Contents
+											 where item.GetMetadata(MetadataName.Kind) == PackageItemKind.Lib &&
+												   !"all".Equals(item.GetMetadata(MetadataName.PrivateAssets), StringComparison.OrdinalIgnoreCase)
+											 select item.GetNuGetTargetFramework()))
+				if (!definedDependencyGroups.ContainsKey(targetFramework.GetFrameworkString()))
+					definedDependencyGroups.Add(targetFramework.GetFrameworkString(),
+												new PackageDependencyGroup(targetFramework, Array.Empty<PackageDependency>()));
+
+			manifest.Metadata.DependencyGroups = definedDependencyGroups.Values;
 		}
 
 		void AddFiles(Manifest manifest)

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

@@ -283,6 +283,47 @@ public void when_creating_package_with_empty_dependency_groups_then_succeeds()
 			Assert.All(manifest.Metadata.DependencyGroups, d => Assert.Empty(d.Packages));
 		}
 
+		[Fact]
+		public void when_creating_package_with_multiple_target_frameworks_generates_empty_dependency_groups()
+		{
+			task.Contents = new[]
+			{
+				new TaskItem(Path.GetTempFileName(), new Metadata
+				{
+					{ MetadataName.PackageId, task.Manifest.GetMetadata("Id") },
+					{ MetadataName.PackagePath, "lib\\net35\\library.dll" },
+					{ MetadataName.Kind, PackageItemKind.Lib },
+					{ MetadataName.TargetFramework, "net35" }
+				}),
+				new TaskItem(Path.GetTempFileName(), new Metadata
+				{
+					{ MetadataName.PackageId, task.Manifest.GetMetadata("Id") },
+					{ MetadataName.PackagePath, "lib\\net40\\library.dll" },
+					{ MetadataName.Kind, PackageItemKind.Lib },
+					{ MetadataName.TargetFramework, "net40" }
+				}),
+				new TaskItem(Path.GetTempFileName(), new Metadata
+				{
+					{ MetadataName.PackageId, task.Manifest.GetMetadata("Id") },
+					{ MetadataName.PackagePath, "lib\\net45\\library.dll" },
+					{ MetadataName.Kind, PackageItemKind.Lib },
+					{ MetadataName.TargetFramework, "net45" }
+				})
+			};
+
+			var manifest = ExecuteTask();
+
+			HashSet<string> requiredFrameworks = new HashSet<string>()
+			{
+				"net35",
+				"net40",
+				"net45"
+			};
+
+			Assert.NotNull(manifest);
+			Assert.Equal(3, manifest.Metadata.DependencyGroups.Count());
+		}
+
 		[Fact]
 		public void when_creating_package_with_development_dependency_then_does_not_generate_dependency_group()
 		{