Fix using NuGet package with different dependencies

#4182

Source/Tools/Flax.Build/Build/Builder.cs

@@ -520,7 +520,7 @@ namespace Flax.Build
             {
                 var doc = System.Xml.Linq.XDocument.Load(nuspecFile);
                 var root = (System.Xml.Linq.XElement)doc.FirstNode;
-                var metadataNode = root.Descendants().First(x => x.Name.LocalName== "metadata");
+                var metadataNode = root.Descendants().First(x => x.Name.LocalName == "metadata");
                 var dependenciesNode = metadataNode.Descendants().First(x => x.Name.LocalName == "dependencies");
                 var groupNode = dependenciesNode.Descendants().FirstOrDefault(x => x.Attribute("targetFramework")?.Value == package.Framework);
                 if (groupNode == null)
@@ -539,6 +539,10 @@ namespace Flax.Build
                     DeployNuGetPackage(nugetPath, targetBuildOptions, nugetFiles, new NugetPackage { Name = dependencyId, Version = dependencyVersion, Framework = package.Framework } );
                 }
             }
+            else
+            {
+                Log.Verbose($"Missing nuspec file '{nuspecFile}' for NuGet package '{package}'");
+            }
         }
     }
 }

Source/Tools/Flax.Build/Build/NativeCpp/BuildOptions.cs

@@ -130,6 +130,21 @@ namespace Flax.Build.NativeCpp
                 }
             }
 
+            // Fallback to netcore or netstandard if original directory
+            var fallbacks = new[]
+            {
+                "netcoreapp3.1",
+                "netcoreapp3.0",
+                "netstandard2.1",
+                "netstandard2.0",
+            };
+            foreach (var fallback in fallbacks)
+            {
+                libFolder = Path.Combine(nugetPath, Name, Version, "lib", fallback);
+                if (Directory.Exists(libFolder))
+                    return libFolder;
+            }
+
             Log.Error($"Missing NuGet package \"{Name}, {Version}, {Framework}\" (nuget: {nugetPath})");
             return string.Empty;
         }
@@ -157,6 +172,11 @@ namespace Flax.Build.NativeCpp
             }
             return dlls[0];
         }
+
+        public override string ToString()
+        {
+            return $"{Name}, {Version}, {Framework}";
+        }
     }
 
     /// <summary>