Allow empty folders for known v3 folders

src/Core/Authoring/PackageBuilder.cs

@@ -515,10 +515,13 @@ private void AddFiles(string basePath, string source, string destination, string
             if (_includeEmptyDirectories)
             {
                 // we only allow empty directories which are legit framework folders.
-                searchFiles.RemoveAll(file => file.TargetFramework == null &&
-                                              Path.GetFileName(file.TargetPath) == Constants.PackageEmptyFileName);
+                // Folders for nuget v3 should be included here also since this part of nuget.core is still used 
+                // by nuget.exe 3.3.0.
+                searchFiles.RemoveAll(file => file.TargetFramework == null
+                                             && Path.GetFileName(file.TargetPath) == Constants.PackageEmptyFileName
+                                             && !IsKnownV3Folder(file.TargetPath));
             }
-            
+
             ExcludeFiles(searchFiles, basePath, exclude);
 
             if (!PathResolver.IsWildcardSearch(source) && !PathResolver.IsDirectoryPath(source) && !searchFiles.Any())
@@ -531,6 +534,48 @@ private void AddFiles(string basePath, string source, string destination, string
             Files.AddRange(searchFiles);
         }
 
+        /// <summary>
+        /// Returns true if the path uses a known v3 folder root.
+        /// </summary>
+        private static bool IsKnownV3Folder(string targetPath)
+        {
+            if (targetPath != null)
+            {
+                var parts = targetPath.Split(
+                    new char[] { '\\', '/' },
+                    StringSplitOptions.RemoveEmptyEntries);
+
+                // exclude things in the root of the directory, this is not allowed
+                // for any of the v3 folders.
+                // example: an empty 'native' folder does not have a TxM and cannot be used.
+                if (parts.Length > 1)
+                {
+                    var topLevelDirectory = parts.FirstOrDefault();
+
+                    return KnownFoldersForV3.Any(folder =>
+                        folder.Equals(topLevelDirectory, StringComparison.OrdinalIgnoreCase));
+                }
+            }
+
+            return false;
+        }
+
+        /// <summary>
+        /// Folders used in NuGet v3 that are not used in NuGet.Core
+        /// </summary>
+        private static IEnumerable<string> KnownFoldersForV3
+        {
+            get
+            {
+                yield return "contentFiles";
+                yield return "ref";
+                yield return "runtimes";
+                yield return "native";
+                yield return "analyzers";
+                yield break;
+            }
+        }
+
         private static void ExcludeFiles(List<PhysicalPackageFile> searchFiles, string basePath, string exclude)
         {
             if (String.IsNullOrEmpty(exclude))

test/Core.Test/PackageBuilderTest.cs

@@ -17,6 +17,66 @@ namespace NuGet.Test
 {
     public class PackageBuilderTest
     {
+        [Fact]
+        public void CreatePackageWithEmptyFoldersForV3Folders()
+        {
+            // Arrange
+            PackageBuilder builder = new PackageBuilder()
+            {
+                Id = "A",
+                Version = new SemanticVersion("1.0"),
+                Description = "Descriptions",
+            };
+
+            builder.Authors.Add("testAuthor");
+
+            var dependencies = new List<PackageDependency>();
+            dependencies.Add(new PackageDependency("packageB", VersionUtility.ParseVersionSpec("1.0.0"), null, "z"));
+            dependencies.Add(new PackageDependency(
+                "packageC",
+                VersionUtility.ParseVersionSpec("1.0.0"),
+                "a,b,c",
+                "b,c"));
+
+            var set = new PackageDependencySet(null, dependencies);
+            builder.DependencySets.Add(set);
+
+            builder.Files.Add(CreatePackageFile(@"build\_._"));
+            builder.Files.Add(CreatePackageFile(@"content\_._"));
+            builder.Files.Add(CreatePackageFile(@"contentFiles\any\any\_._"));
+            builder.Files.Add(CreatePackageFile(@"lib\net45\_._"));
+            builder.Files.Add(CreatePackageFile(@"native\net45\_._"));
+            builder.Files.Add(CreatePackageFile(@"ref\net45\_._"));
+            builder.Files.Add(CreatePackageFile(@"runtimes\net45\_._"));
+            builder.Files.Add(CreatePackageFile(@"tools\_._"));
+
+            using (var ms = new MemoryStream())
+            {
+                // Act
+                builder.Save(ms);
+
+                ms.Seek(0, SeekOrigin.Begin);
+
+                var zip = new ZipPackage(ms);
+                var files = zip.GetFiles()
+                    .Select(file => file.Path)
+                    .Where(file => Path.GetFileName(file) == "_._")
+                    .OrderBy(s => s)
+                    .ToArray();
+
+                // Assert
+                Assert.Equal(8, files.Length);
+                Assert.Equal(@"build\_._", files[0]);
+                Assert.Equal(@"content\_._", files[1]);
+                Assert.Equal(@"contentFiles\any\any\_._", files[2]);
+                Assert.Equal(@"lib\net45\_._", files[3]);
+                Assert.Equal(@"native\net45\_._", files[4]);
+                Assert.Equal(@"ref\net45\_._", files[5]);
+                Assert.Equal(@"runtimes\net45\_._", files[6]);
+                Assert.Equal(@"tools\_._", files[7]);
+            }
+        }
+
         [Fact]
         public void CreatePackageWithNuspecIncludeExcludeAnyGroup()
         {