adding AddRuntimeOSTask

src/Microsoft.DotNet.Build.Tasks.TargetFramework.Sdk/src/AddRuntimeOSPropertyTask.cs

@@ -0,0 +1,46 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using Microsoft.Build.Construction;
+using Microsoft.Build.Framework;
+
+namespace Microsoft.DotNet.Build.Tasks.TargetFramework.Sdk
+{
+    public class GenerateRuntimeOSPropsFile : BuildTask
+    {
+        public  const string RuntimeOSProperty = "RuntimeOS";
+
+        [Required]
+        public string RuntimePropsFilePath {get ; set; }
+
+        public override bool Execute()
+        {
+            ProjectRootElement project = ProjectRootElement.Create();
+            CreateRuntimeIdentifier(project);
+            project.Save(RuntimePropsFilePath);
+            return !Log.HasLoggedErrors;
+        }
+
+        public void CreateRuntimeIdentifier(ProjectRootElement project)
+        {
+            var rid = PlatformAbstractions.RuntimeEnvironment.GetRuntimeIdentifier();
+            string[] ridParts = rid.Split('-');
+
+            if (ridParts.Length < 1)
+            {
+                throw new System.InvalidOperationException($"Unknown rid format {rid}.");
+            }
+
+            string osNameAndVersion = ridParts[0];
+
+            var propertyGroup = project.CreatePropertyGroupElement();
+            project.AppendChild(propertyGroup);
+
+            var runtimeProperty = propertyGroup.AddProperty(RuntimeOSProperty, $"{osNameAndVersion}");
+            runtimeProperty.Condition = $"'$({RuntimeOSProperty})' == ''";
+
+            Log.LogMessage($"Running on OS with RID {rid}, so defaulting RuntimeOS to '{osNameAndVersion}'");
+        }
+    }
+}

src/Microsoft.DotNet.Build.Tasks.TargetFramework.Sdk/src/build/Microsoft.DotNet.Build.Tasks.TargetFramework.Sdk.targets

@@ -3,6 +3,7 @@
   <UsingTask TaskName="ChooseBestP2PTargetFrameworkTask" AssemblyFile="$(DotNetBuildTasksTargetFrameworkSdkAssembly)"/>
   <UsingTask TaskName="ChooseBestTargetFrameworksTask" AssemblyFile="$(DotNetBuildTasksTargetFrameworkSdkAssembly)"/>
   <UsingTask TaskName="AddTargetFrameworksToProjectTask" AssemblyFile="$(DotNetBuildTasksTargetFrameworkSdkAssembly)"/>
+  <UsingTask TaskName="GenerateRuntimeOSPropsFile" AssemblyFile="$(DotNetBuildTasksTargetFrameworkSdkAssembly)"/>
 
   <PropertyGroup>
     <_OriginalTargetFrameworks>$(TargetFrameworks)</_OriginalTargetFrameworks>
@@ -116,4 +117,9 @@
       <PackageTargetFrameworks>@(PackageTargetFrameworksFinalList)</PackageTargetFrameworks>
     </PropertyGroup>
   </Target>
+
+  <Target Name="AddRuntimeOSProperty">
+    <GenerateRuntimeOSPropsFile RuntimePropsFilePath="$(RuntimePropsFile)" />
+  </Target>
+
 </Project>