Add CombineLinkerXmlFiles task (#1234)

* Add CombineLinkerXmlFiles task

This task combines multiple linker xml files into a single, combined xml file.

* Fix formatting

src/ILLink.Tasks/CombineLinkerXmlFiles.cs

@@ -0,0 +1,50 @@
+using System.Xml;
+using System.Xml.Linq;
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+
+namespace ILLink.Tasks
+{
+	/// <summary>
+	/// Combines multiple linker xml files into a single xml file.
+	/// </summary>
+	public class CombineLinkerXmlFiles : Task
+	{
+		/// <summary>
+		/// The individual linker xml files that will be combined into one.
+		/// </summary>
+		[Required]
+		public ITaskItem[] LinkerXmlFiles { get; set; }
+
+		/// <summary>
+		/// The path to the file to generate.
+		/// </summary>
+		[Required]
+		public string CombinedLinkerXmlFile { get; set; }
+
+		public override bool Execute ()
+		{
+			var combined = new XElement ("linker");
+			foreach (var linkerXmlFile in LinkerXmlFiles) {
+				XDocument subFile = XDocument.Load (linkerXmlFile.ItemSpec);
+
+				foreach (var element in subFile.Root.Elements ()) {
+					combined.Add (element);
+				}
+			}
+
+			var xdoc = new XDocument (combined);
+
+			XmlWriterSettings xws = new XmlWriterSettings {
+				Indent = true,
+				OmitXmlDeclaration = true
+			};
+
+			using (XmlWriter xw = XmlWriter.Create (CombinedLinkerXmlFile, xws)) {
+				xdoc.Save (xw);
+			}
+
+			return true;
+		}
+	}
+}

src/ILLink.Tasks/ILLink.Tasks.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <!-- Keep these in sync with _ILLinkTasksTFM in Sdk.props. -->
     <!-- Keep the netcoreapp TFM in sync with the Mono.Linker.csproj condition below. -->
@@ -22,6 +22,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <Compile Include="CombineLinkerXmlFiles.cs" />
     <Compile Include="LinkTask.cs" />
     <Compile Include="CheckEmbeddedRootDescriptor.cs" />
     <Compile Include="CompareSizes.cs" />

test/ILLink.Tasks.Tests/CombineLinkerXmlFilesTests.cs

@@ -0,0 +1,66 @@
+using System.Xml.Linq;
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+using Xunit;
+
+namespace ILLink.Tasks.Tests
+{
+	public class CombineLinkerXmlFilesTests
+	{
+		[Fact]
+		public void TestCombineLinkerXmlFiles ()
+		{
+			CreateLinkerXml (
+				new XElement ("linker",
+					new XElement ("assembly",
+						new XAttribute ("fullname", "assembly1"),
+						new XElement ("type",
+							new XAttribute ("fullname", "Namespace1.Type1"),
+							new XAttribute ("required", "false")))),
+				"doc1.xml");
+
+			CreateLinkerXml (
+				new XElement ("linker",
+					new XElement ("assembly",
+						new XAttribute ("fullname", "assembly2"),
+						new XElement ("type",
+							new XAttribute ("fullname", "*"),
+							new XAttribute ("required", "true")))),
+				"doc2.xml");
+
+			var xmlFiles = new ITaskItem[] {
+				new TaskItem ("doc1.xml"),
+				new TaskItem ("doc2.xml"),
+			};
+
+			var combiner = new CombineLinkerXmlFiles () {
+				LinkerXmlFiles = xmlFiles,
+				CombinedLinkerXmlFile = "combined_output.xml"
+			};
+
+			Assert.True (combiner.Execute ());
+
+			XDocument combined = XDocument.Load ("combined_output.xml");
+
+			string expectedXml = new XElement ("linker",
+					new XElement ("assembly",
+						new XAttribute ("fullname", "assembly1"),
+						new XElement ("type",
+							new XAttribute ("fullname", "Namespace1.Type1"),
+							new XAttribute ("required", "false"))),
+					new XElement ("assembly",
+						new XAttribute ("fullname", "assembly2"),
+						new XElement ("type",
+							new XAttribute ("fullname", "*"),
+							new XAttribute ("required", "true")))).ToString ();
+			Assert.Equal (expectedXml, combined.Root.ToString ());
+		}
+
+		private static void CreateLinkerXml (XElement root, string path)
+		{
+			var doc = new XDocument ();
+			doc.Add (root);
+			doc.Save (path);
+		}
+	}
+}