Fix IncludeNuGetResolvedAssets to handle packages in nuget fallback directory correctly (#28150)

build/Targets/VisualStudio.targets

@@ -65,16 +65,25 @@
           by the NuGet build task. -->
 
   <Target Name="IncludeNuGetResolvedAssets" DependsOnTargets="ResolvePackageDependenciesForBuild" Condition="'@(NuGetPackageToIncludeInVsix)' != ''">
-    <FindNuGetAssetsForVsix
-      NuGetPackageRoot="$(NuGetPackageRoot)"
-      ReferenceCopyLocalPaths="@(ReferenceCopyLocalPaths)"
-      NuGetPackageToIncludeInVsix="@(NuGetPackageToIncludeInVsix)">
 
-      <Output TaskParameter="NuGetAssetsToIncludeInVsix" ItemName="NuGetAssetsToIncludeInVsix" />
-    </FindNuGetAssetsForVsix>
+    <!-- Calculate a list of packages ReferenceCopyLocalPaths originate from whose content should not be included in the VSIX -->
+    <ItemGroup>
+      <_ExcludedPackageId Include="@(ReferenceCopyLocalPaths->'%(NuGetPackageId)')" />
+      <_ExcludedPackageId Remove="@(NuGetPackageToIncludeInVsix)"/>
+    </ItemGroup>
+
+    <!-- Build a list assets to include in the VSIX keyed by package id -->
+    <ItemGroup>
+      <_AssetsByPackageId Include="@(ReferenceCopyLocalPaths->'%(NuGetPackageId)')">
+        <Path>%(ReferenceCopyLocalPaths.Identity)</Path>
+      </_AssetsByPackageId>
+
+      <_AssetsByPackageId Remove="@(_ExcludedPackageId)" />
+    </ItemGroup>
 
+    <!-- Include the assets in the VSIX -->
     <ItemGroup>
-      <VSIXCopyLocalReferenceSourceItem Include="@(NuGetAssetsToIncludeInVsix)">
+      <VSIXCopyLocalReferenceSourceItem Include="@(_AssetsByPackageId->'%(Path)')">
         <ForceIncludeInVsix>true</ForceIncludeInVsix>
         <Private>true</Private>
       </VSIXCopyLocalReferenceSourceItem>

src/Tools/BuildUtil/FindNuGetAssetsForVsix.cs

-using System;
-using System.Collections.Generic;
-using System.IO;
-using System.Linq;
-using Microsoft.Build.Framework;
-using Microsoft.Build.Utilities;
-
-#pragma warning disable CA1819 // CA1819: Properties should not return arrays 
-
-namespace Roslyn.MSBuild.Util
-{
-    /// <summary>
-    /// This task will filter down the elements in the ReferenceLocalCopyPaths item group to 
-    /// just the items in the set of NuGet packages we are interested in.
-    /// </summary>
-    public sealed class FindNuGetAssetsForVsix : Task
-    {
-        [Required]
-        public string NuGetPackageRoot { get; set; }
-
-        [Required]
-        public ITaskItem[] ReferenceCopyLocalPaths { get; set; }
-
-        [Required]
-        public ITaskItem[] NuGetPackageToIncludeInVsix { get; set; }
-
-        [Output]
-        public ITaskItem[] NuGetAssetsToIncludeInVsix { get; set; }
-
-        public FindNuGetAssetsForVsix()
-        {
-
-        }
-
-        public override bool Execute()
-        {
-            var nugetDirs = new List<string>();
-            foreach (var item in NuGetPackageToIncludeInVsix)
-            {
-                var nugetDir = NormalizePath(Path.Combine(NuGetPackageRoot, item.ItemSpec));
-                nugetDirs.Add(nugetDir);
-            }
-
-            var assets = new List<ITaskItem>();
-            foreach (var path in ReferenceCopyLocalPaths)
-            {
-                var itemPath = NormalizePath(path.ItemSpec);
-                if (nugetDirs.Any(x => itemPath.StartsWith(x, StringComparison.OrdinalIgnoreCase)))
-                {
-                    assets.Add(path);
-                }
-            }
-
-            NuGetAssetsToIncludeInVsix = assets.ToArray();
-            return true;
-        }
-
-        private static string NormalizePath(string path) => path.Replace('/', '\\').TrimEnd('\\');
-    }
-}