Fix duplicated files in folder content and contentFiles

src/NuGetForUnity/Editor/NugetPackageInstaller.cs

@@ -166,6 +166,10 @@ private static bool Install([NotNull] INugetPackage package, bool refreshAssets,
                     // unzip the package
                     using (var zip = ZipFile.OpenRead(cachedPackagePath))
                     {
+                        // check if nuget package has contentFiles folder
+                        const string contentFilesDirectoryName = "contentFiles/";
+                        var hasContentFilesFolder = zip.Entries.Any(entry => entry.FullName.StartsWith(contentFilesDirectoryName, StringComparison.Ordinal));
+
                         var libs = new Dictionary<string, List<ZipArchiveEntry>>();
                         var csFiles = new Dictionary<string, List<ZipArchiveEntry>>();
                         var anyFiles = new Dictionary<string, List<ZipArchiveEntry>>();
@@ -179,7 +183,7 @@ private static bool Install([NotNull] INugetPackage package, bool refreshAssets,
                                 continue;
                             }
 
-                            if (PackageContentManager.ShouldSkipUnpackingOnPath(entryFullName))
+                            if (PackageContentManager.ShouldSkipUnpackingOnPath(entryFullName, hasContentFilesFolder))
                             {
                                 continue;
                             }
@@ -206,7 +210,6 @@ private static bool Install([NotNull] INugetPackage package, bool refreshAssets,
 
                             // in case this is a source code package, we want to collect all its entries that have 'cs' or 'any' set as language
                             // and their frameworks so we can get the best framework later
-                            const string contentFilesDirectoryName = "contentFiles/";
                             if (entryFullName.StartsWith(contentFilesDirectoryName, StringComparison.Ordinal))
                             {
                                 // Folder structure for source code packages:

src/NuGetForUnity/Editor/PackageContentManager.cs

@@ -109,8 +109,12 @@ internal static void CleanInstallationDirectory([NotNull] INugetPackageIdentifie
         ///     The path of the file inside the .nupkg it is relative starting from the package route. It always uses '/' as a slash on all
         ///     platforms.
         /// </param>
+        /// <param name="hasContentFilesFolder">
+        ///     The package has contentfiles folder, we need to omit content folder it exist. Because some nuget package has both folder to
+        ///     to support old version and new version of nuget.
+        /// </param>
         /// <returns>True if the file can be skipped, is not needed.</returns>
-        internal static bool ShouldSkipUnpackingOnPath([NotNull] string path)
+        internal static bool ShouldSkipUnpackingOnPath([NotNull] string path, bool hasContentFilesFolder)
         {
             if (path.EndsWith("/"))
             {
@@ -120,6 +124,12 @@ internal static bool ShouldSkipUnpackingOnPath([NotNull] string path)
                 return true;
             }
 
+            // skip content folder when it has contentFiles folder
+            if (hasContentFilesFolder && (path.StartsWith("content/", StringComparison.Ordinal) || path.Contains("/content/")))
+            {
+                return true;
+            }
+
             // skip directories & files that NuGet normally deletes
             if (path.StartsWith("_rels/", StringComparison.Ordinal) || path.Contains("/_rels/"))
             {