add trimming of published output based on sharedfx

Any dependencies which **exactly** match the version requested in the
graph originating at the `type: platform` dependency (if any) are
trimmed from the publish output

TestAssets/TestProjects/PortableTests/PortableAppWithIntentionalManagedDowngrade/Program.cs

@@ -0,0 +1,12 @@
+using System;
+
+namespace PortableApp
+{
+    public static class Program
+    {
+        public static void Main(string[] args)
+        {
+            Console.WriteLine("Hello, World!");
+        }
+    }
+}

TestAssets/TestProjects/PortableTests/PortableAppWithIntentionalManagedDowngrade/project.json

@@ -0,0 +1,21 @@
+{
+  "compilationOptions": {
+    "emitEntryPoint": true
+  },
+  "dependencies": {},
+  "frameworks": {
+    "netstandard1.5": {
+      "imports": [
+        "dnxcore50",
+        "portable-net45+win8"
+      ],
+      "dependencies": {
+        "Microsoft.NETCore.App": {
+          "type": "platform",
+          "version": "1.0.0-rc2-23925"
+        },
+        "System.Linq": "4.0.0"
+      }
+    }
+  }
+}

src/dotnet/commands/dotnet-publish/PublishCommand.cs

@@ -14,6 +14,8 @@ using Microsoft.Extensions.PlatformAbstractions;
 using Microsoft.DotNet.Files;
 using Microsoft.DotNet.Tools.Common;
 using Microsoft.DotNet.ProjectModel.Utilities;
+using Microsoft.DotNet.ProjectModel.Graph;
+using NuGet.Versioning;
 
 namespace Microsoft.DotNet.Tools.Publish
 {
@@ -153,7 +155,14 @@ namespace Microsoft.DotNet.Tools.Publish
             var exporter = context.CreateExporter(configuration);
 
             var isPortable = string.IsNullOrEmpty(context.RuntimeIdentifier);
-            foreach (var export in exporter.GetAllExports())
+
+            // Collect all exports and organize them
+            var exports = exporter.GetAllExports()
+                .Where(e => e.Library.Identity.Type.Equals(LibraryType.Package))
+                .ToDictionary(e => e.Library.Identity.Name);
+            var collectExclusionList = isPortable ? GetExclusionList(context, exports) : new HashSet<string>();
+
+            foreach (var export in exporter.GetAllExports().Where(e => !collectExclusionList.Contains(e.Library.Identity.Name)))
             {
                 Reporter.Verbose.WriteLine($"Publishing {export.Library.Identity.ToString().Green().Bold()} ...");
 
@@ -198,6 +207,40 @@ namespace Microsoft.DotNet.Tools.Publish
             return true;
         }
 
+        private HashSet<string> GetExclusionList(ProjectContext context, Dictionary<string, LibraryExport> exports)
+        {
+            var exclusionList = new HashSet<string>();
+            var redistPackages = context.RootProject.Dependencies
+                .Where(r => r.Type.Equals(LibraryDependencyType.Platform))
+                .ToList();
+            if (redistPackages.Count == 0)
+            {
+                return exclusionList;
+            }
+            else if (redistPackages.Count > 1)
+            {
+                throw new InvalidOperationException("Multiple packages with type: \"platform\" were specified!");
+            }
+            var redistExport = exports[redistPackages[0].Name];
+
+            exclusionList.Add(redistExport.Library.Identity.Name);
+            CollectDependencies(exports, redistExport.Library.Dependencies, exclusionList);
+            return exclusionList;
+        }
+
+        private void CollectDependencies(Dictionary<string, LibraryExport> exports, IEnumerable<LibraryRange> dependencies, HashSet<string> exclusionList)
+        {
+            foreach (var dependency in dependencies)
+            {
+                var export = exports[dependency.Name];
+                if(export.Library.Identity.Version.Equals(dependency.VersionRange.MinVersion))
+                {
+                    exclusionList.Add(export.Library.Identity.Name);
+                    CollectDependencies(exports, export.Library.Dependencies, exclusionList);
+                }
+            }
+        }
+
         private static void PublishRefs(LibraryExport export, string outputPath)
         {
             var refsPath = Path.Combine(outputPath, "refs");

test/dotnet-publish.Tests/PublishPortableTests.cs

@@ -36,6 +36,9 @@ namespace Microsoft.DotNet.Tools.Publish.Tests
                 "PortableAppWithNative.deps.json"
             });
 
+            // Prior to `type:platform` trimming, this would have been published.
+            publishDir.Should().NotHaveFile("System.Linq.dll");
+
             var runtimesOutput = publishDir.Sub("runtimes");
 
             runtimesOutput.Should().Exist();
@@ -50,5 +53,26 @@ namespace Microsoft.DotNet.Tools.Publish.Tests
                 nativeDir.Should().HaveFile(output.Item2);
             }
         }
+
+        [Fact]
+        public void PortableAppWithIntentionalDowngradePublishesDowngradedManagedCode()
+        {
+            var testInstance = TestAssetsManager.CreateTestInstance("PortableTests")
+                .WithLockFiles();
+
+            var publishCommand = new PublishCommand(Path.Combine(testInstance.TestRoot, "PortableAppWithIntentionalManagedDowngrade"));
+            var publishResult = publishCommand.Execute();
+
+            publishResult.Should().Pass();
+
+            var publishDir = publishCommand.GetOutputDirectory(portable: true);
+            publishDir.Should().HaveFiles(new[]
+            {
+                "PortableAppWithIntentionalManagedDowngrade.dll",
+                "PortableAppWithIntentionalManagedDowngrade.deps",
+                "PortableAppWithIntentionalManagedDowngrade.deps.json",
+                "System.Linq.dll"
+            });
+        }
     }
 }