Use MSBuildProjectExtensionsPath for RestoreOutputPath

src/NuGet.Clients/NuGet.CommandLine/Common/CommandLineResponseFile.cs

@@ -126,13 +126,13 @@ private static string[] SplitArgs(string unsplitArguments)
         {
             if (string.IsNullOrWhiteSpace(unsplitArguments))
             {
-                return new string[0];
+                return Array.Empty<string>();
             }
 
             var ptrToSplitArgs = CommandLineToArgvW(unsplitArguments, out int numberOfArgs);
             if (ptrToSplitArgs == IntPtr.Zero)
             {
-                return new string[0];
+                return Array.Empty<string>();
             }
 
             try

src/NuGet.Clients/NuGet.PackageManagement.VisualStudio/Projects/VsProjectAdapter.cs

@@ -278,7 +278,7 @@ public async Task<string[]> GetProjectTypeGuidsAsync()
                     return new string[] { _projectTypeGuid };
                 }
 
-                return new string[0];
+                return Array.Empty<string>();
             }
         }
 

src/NuGet.Clients/NuGet.VisualStudio.Common/VsHierarchyUtility.cs

@@ -104,7 +104,7 @@ public static string[] GetProjectTypeGuids(IVsHierarchy hierarchy, string defaul
                 return new[] { defaultType };
             }
 
-            return new string[0];
+            return Array.Empty<string>();
         }
 
         /// <summary>

src/NuGet.Clients/NuGetConsole.Host.PowerShell/UnsupportedHost.cs

@@ -46,7 +46,7 @@ public string ActivePackageSource
 
         public string[] GetPackageSources()
         {
-            return new string[0];
+            return Array.Empty<string>();
         }
 
         public string DefaultProject
@@ -60,7 +60,7 @@ public void SetDefaultProjectIndex(int index)
 
         public string[] GetAvailableProjects()
         {
-            return new string[0];
+            return Array.Empty<string>();
         }
 
         public void SetDefaultRunspace()

src/NuGet.Core/NuGet.Build.Tasks.Pack/NuGet.Build.Tasks.Pack.targets

@@ -148,7 +148,7 @@ Copyright (c) .NET Foundation. All rights reserved.
     </PropertyGroup>
     <PropertyGroup>
       <PackageOutputPath Condition=" '$(PackageOutputPath)' == '' ">$(OutputPath)</PackageOutputPath>
-      <RestoreOutputPath Condition=" '$(RestoreOutputPath)' == '' " >$(BaseIntermediateOutputPath)</RestoreOutputPath>
+      <RestoreOutputPath Condition=" '$(RestoreOutputPath)' == '' " >$(MSBuildProjectExtensionsPath)</RestoreOutputPath>
     </PropertyGroup>
 
     <ConvertToAbsolutePath Paths="$(NuspecOutputPath)">

src/NuGet.Core/NuGet.Build.Tasks/ErrorForMismatchRestoreOutputPathTask.cs

@@ -0,0 +1,31 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+using NuGet.Commands;
+
+namespace NuGet.Build.Tasks
+{
+    public class ErrorForMismatchRestoreOutputPathTask : Task
+    {
+        [Required]
+        public string RestoreOutputAbsolutePath { get; set; }
+
+        [Required]
+        public string MSBuildProjectExtensionsPath { get; set; }
+
+        public override bool Execute()
+        {
+            if (RestoreOutputAbsolutePath != MSBuildProjectExtensionsPath)
+            {
+                //  The RestoreOutputPath, which resolved to '{0}', did not match the MSBuildProjectExtensionsPath, which was '{1}'.  These properties must match in order for assets from NuGet restore to be applied correctly when building.
+                var log = new MSBuildLogger(Log);
+                var message = MSBuildRestoreUtility.GetErrorForRestoreOutputPathMismatch(RestoreOutputAbsolutePath, MSBuildProjectExtensionsPath);
+                log.Log(message);
+            }
+
+            return true;
+        }
+    }
+}

src/NuGet.Core/NuGet.Build.Tasks/GetRestoreSettingsTask.cs

@@ -131,7 +131,7 @@ public override bool Execute()
                 // Sources
                 var currentSources = RestoreSettingsUtils.GetValue(
                     () => RestoreSourcesOverride?.Select(MSBuildRestoreUtility.FixSourcePath).Select(e => GetGlobalAbsolutePath(e)).ToArray(),
-                    () => MSBuildRestoreUtility.ContainsClearKeyword(RestoreSources) ? new string[0] : null,
+                    () => MSBuildRestoreUtility.ContainsClearKeyword(RestoreSources) ? Array.Empty<string>() : null,
                     () => RestoreSources?.Select(MSBuildRestoreUtility.FixSourcePath).Select(e => UriUtility.GetAbsolutePathFromFile(ProjectUniqueName, e)).ToArray(),
                     () => (new PackageSourceProvider(settings)).LoadPackageSources().Where(e => e.IsEnabled).Select(e => e.Source).ToArray());
 
@@ -148,7 +148,7 @@ public override bool Execute()
                 // Fallback folders
                 var currentFallbackFolders = RestoreSettingsUtils.GetValue(
                     () => RestoreFallbackFoldersOverride?.Select(e => GetGlobalAbsolutePath(e)).ToArray(),
-                    () => MSBuildRestoreUtility.ContainsClearKeyword(RestoreFallbackFolders) ? new string[0] : null,
+                    () => MSBuildRestoreUtility.ContainsClearKeyword(RestoreFallbackFolders) ? Array.Empty<string>() : null,
                     () => RestoreFallbackFolders?.Select(e => UriUtility.GetAbsolutePathFromFile(ProjectUniqueName, e)).ToArray(),
                     () => SettingsUtility.GetFallbackPackageFolders(settings).ToArray());
 

src/NuGet.Core/NuGet.Build.Tasks/NuGet.targets

@@ -93,6 +93,7 @@ Copyright (c) .NET Foundation. All rights reserved.
   <UsingTask TaskName="NuGet.Build.Tasks.GetRestoreSettingsTask" AssemblyFile="$(RestoreTaskAssemblyFile)" />
   <UsingTask TaskName="NuGet.Build.Tasks.WarnForInvalidProjectsTask" AssemblyFile="$(RestoreTaskAssemblyFile)" />
   <UsingTask TaskName="NuGet.Build.Tasks.GetReferenceNearestTargetFrameworkTask" AssemblyFile="$(RestoreTaskAssemblyFile)" />
+  <UsingTask TaskName="NuGet.Build.Tasks.ErrorForMismatchRestoreOutputPathTask" AssemblyFile="$(RestoreTaskAssemblyFile)" />
 
   <!--
     ============================================================
@@ -570,13 +571,19 @@ Copyright (c) .NET Foundation. All rights reserved.
 
     <!-- Determine the restore output path -->
     <PropertyGroup Condition=" '$(PackageReferenceCompatibleProjectStyle)' == 'true' OR '$(RestoreProjectStyle)' == 'ProjectJson' ">
-      <RestoreOutputPath Condition=" '$(RestoreOutputPath)' == '' " >$(BaseIntermediateOutputPath)</RestoreOutputPath>
+      <RestoreOutputPath Condition=" '$(RestoreOutputPath)' == '' " >$(MSBuildProjectExtensionsPath)</RestoreOutputPath>
     </PropertyGroup>
 
     <ConvertToAbsolutePath Paths="$(RestoreOutputPath)" Condition=" '$(PackageReferenceCompatibleProjectStyle)' == 'true' OR '$(RestoreProjectStyle)' == 'ProjectJson'">
       <Output TaskParameter="AbsolutePaths" PropertyName="RestoreOutputAbsolutePath" />
     </ConvertToAbsolutePath>
 
+    <ErrorForMismatchRestoreOutputPathTask
+      RestoreOutputAbsolutePath="$(RestoreOutputAbsolutePath)"
+      MSBuildProjectExtensionsPath="$(MSBuildProjectExtensionsPath)"
+      Condition=" '$(PackageReferenceCompatibleProjectStyle)' == 'true' OR '$(RestoreProjectStyle)' == 'ProjectJson'"
+      />
+
     <!--
       Determine project name for the assets file.
       Highest priority: PackageId

src/NuGet.Core/NuGet.Build.Tasks/WarnForInvalidProjectsTask.cs

@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
 using System.Linq;
 using Microsoft.Build.Framework;
 using Microsoft.Build.Utilities;
@@ -28,8 +29,8 @@ public override bool Execute()
             var log = new MSBuildLogger(Log);
 
             // item -> string
-            var all = AllProjects?.Select(e => e.ItemSpec).ToArray() ?? new string[0];
-            var valid = ValidProjects?.Select(e => e.ItemSpec).ToArray() ?? new string[0];
+            var all = AllProjects?.Select(e => e.ItemSpec).ToArray() ?? Array.Empty<string>();
+            var valid = ValidProjects?.Select(e => e.ItemSpec).ToArray() ?? Array.Empty<string>();
 
             // log inputs
             BuildTasksUtility.LogInputParam(log, nameof(AllProjects), all);

src/NuGet.Core/NuGet.Commands/RestoreCommand/Utility/MSBuildRestoreUtility.cs

@@ -396,6 +396,15 @@ public static bool LogErrorForClearIfInvalid(IEnumerable<string> values, string
             return false;
         }
 
+        //  Log error NU1003
+        public static RestoreLogMessage GetErrorForRestoreOutputPathMismatch(string restoreOutputAbsolutePath, string msbuildProjectExtensionsPath)
+        {
+            var text = string.Format(CultureInfo.CurrentCulture, Strings.Error_RestoreOutputPathMismatch, restoreOutputAbsolutePath, msbuildProjectExtensionsPath);
+            var message = RestoreLogMessage.CreateError(NuGetLogCode.NU1503, text);
+
+            return message;
+        }
+
         /// <summary>
         /// Log warning NU1503
         /// </summary>

src/NuGet.Core/NuGet.Commands/Strings.resx

@@ -691,4 +691,7 @@ For more information, visit http://docs.nuget.org/docs/reference/command-line-re
   <data name="Error_InvalidDependencyVersionConstraints" xml:space="preserve">
     <value>Package version constraints for '{0}' return a version range that is empty.</value>
   </data>
+  <data name="Error_RestoreOutputPathMismatch" xml:space="preserve">
+    <value>The RestoreOutputPath, which resolved to '{0}', did not match the MSBuildProjectExtensionsPath, which was '{1}'.  These properties must match in order for assets from NuGet restore to be applied correctly when building.</value>
+  </data>
 </root>

src/NuGet.Core/NuGet.Common/Errors/NuGetLogCode.cs

@@ -4,7 +4,7 @@
 namespace NuGet.Common
 {
     /// <summary>
-    /// This enum is used to quantify NuGet error and wanring codes. 
+    /// This enum is used to quantify NuGet error and warning codes. 
     /// Format - NUxyzw where NU is the profix indicating NuGet and xyzw is a 4 digit code
     ///
     /// Numbers - xyzw
@@ -59,6 +59,11 @@ public enum NuGetLogCode
         /// </summary>
         NU1003 = 1003,
 
+        /// <summary>
+        /// RestoreOutputPath does not match MSBuildProjectExtensionsPath
+        /// </summary>
+        NU1004 = 1004,
+
         /// <summary>
         /// Unable to resolve package, generic message for unknown type constraints.
         /// </summary>

src/NuGet.Core/NuGet.Common/MsBuildStringUtility.cs

@@ -34,7 +34,7 @@ public static string[] Split(string s, params char[] chars)
                     .ToArray();
             }
 
-            return new string[0];
+            return Array.Empty<string>();
         }
 
         /// <summary>
@@ -59,7 +59,7 @@ public static string[] TrimAndExcludeNullOrEmpty(string[] strings)
         {
             if (strings == null)
             {
-                return new string[0];
+                return Array.Empty<string>();
             }
 
             return strings

src/NuGet.Core/NuGet.Packaging/TopologicalSortUtility.cs

@@ -141,7 +141,7 @@ private static void CalculateRelationships(ItemDependencyInfo[] packages, Dictio
         {
             foreach (var package in packages)
             {
-                var dependencies = package.DependencyIds ?? new string[0];
+                var dependencies = package.DependencyIds ?? Array.Empty<string>();
 
                 foreach (var id in dependencies)
                 {

src/NuGet.Core/NuGet.ProjectModel/JsonPackageSpecReader.cs

@@ -346,8 +346,8 @@ private static PackOptions GetPackOptions(PackageSpec packageSpec, JObject rawPa
             }
             var owners = rawPackOptions["owners"];
             var tags = rawPackOptions["tags"];
-            packageSpec.Owners = owners == null ? new string[0] { } : owners.ValueAsArray<string>();
-            packageSpec.Tags = tags == null ? new string[0] { } : tags.ValueAsArray<string>();
+            packageSpec.Owners = owners == null ? Array.Empty<string>() : owners.ValueAsArray<string>();
+            packageSpec.Tags = tags == null ? Array.Empty<string>() : tags.ValueAsArray<string>();
             packageSpec.ProjectUrl = rawPackOptions.GetValue<string>("projectUrl");
             packageSpec.IconUrl = rawPackOptions.GetValue<string>("iconUrl");
             packageSpec.Summary = rawPackOptions.GetValue<string>("summary");

src/NuGet.Core/NuGet.ProjectModel/PackageSpec.cs

@@ -59,9 +59,9 @@ public NuGetVersion Version
 
         public string ReleaseNotes { get; set; }
 
-        public string[] Authors { get; set; } = new string[0];
+        public string[] Authors { get; set; } = Array.Empty<string>();
 
-        public string[] Owners { get; set; } = new string[0];
+        public string[] Owners { get; set; } = Array.Empty<string>();
 
         public string ProjectUrl { get; set; }
 
@@ -77,7 +77,7 @@ public NuGetVersion Version
 
         public BuildOptions BuildOptions { get; set; }
 
-        public string[] Tags { get; set; } = new string[0];
+        public string[] Tags { get; set; } = Array.Empty<string>();
 
         public IList<string> ContentFiles { get; set; } = new List<string>();
 

src/NuGet.Core/NuGet.Protocol/LegacyFeed/V2FeedPackageInfo.cs

@@ -48,8 +48,8 @@ public V2FeedPackageInfo(PackageIdentity identity, string title, string summary,
         {
             _summary = summary;
             _description = description;
-            _authors = authors == null ? new string[0] : authors.ToArray();
-            _owners = owners == null ? new string[0] : owners.ToArray();
+            _authors = authors == null ? Array.Empty<string>() : authors.ToArray();
+            _owners = owners == null ? Array.Empty<string>() : owners.ToArray();
             _iconUrl = iconUrl;
             _licenseUrl = licenseUrl;
             _projectUrl = projectUrl;

src/NuGet.Core/NuGet.Versioning/SemanticVersionFactory.cs

@@ -9,7 +9,7 @@ namespace NuGet.Versioning
     public partial class SemanticVersion
     {
         // Reusable set of empty release labels
-        internal static readonly string[] EmptyReleaseLabels = new string[0];
+        internal static readonly string[] EmptyReleaseLabels = Array.Empty<string>();
 
         /// <summary>
         /// Parses a SemVer string using strict SemVer rules.

test/NuGet.Core.Tests/NuGet.Build.Tasks.Pack.Test/PackTaskTests.cs

@@ -317,9 +317,9 @@ public void PackTask_MapsAllProperties()
             {
                 AssemblyName = "AssemblyName",
                 FrameworkAssemblyReferences = new ITaskItem[0],
-                Authors = new string[0],
-                AllowedOutputExtensionsInPackageBuildOutputFolder = new string[0],
-                AllowedOutputExtensionsInSymbolsPackageBuildOutputFolder = new string[0],
+                Authors = Array.Empty<string>(),
+                AllowedOutputExtensionsInPackageBuildOutputFolder = Array.Empty<string>(),
+                AllowedOutputExtensionsInSymbolsPackageBuildOutputFolder = Array.Empty<string>(),
                 BuildOutputFolder = "BuildOutputFolder",
                 ContentTargetFolders = new string[] { "ContentTargetFolders" } ,
                 ContinuePackingAfterGeneratingNuspec = true,
@@ -335,13 +335,13 @@ public void PackTask_MapsAllProperties()
                 MinClientVersion = "MinClientVersion",
                 NoPackageAnalysis = true,
                 NuspecOutputPath = "NuspecOutputPath",
-                NuspecProperties = new string[0],
+                NuspecProperties = Array.Empty<string>(),
                 PackItem = null, // This is asserted by other tests. It does not serialize well.
                 PackageFiles = new ITaskItem[0],
                 PackageFilesToExclude = new ITaskItem[0],
                 PackageId = "PackageId",
                 PackageOutputPath = "PackageOutputPath",
-                PackageTypes = new string[0],
+                PackageTypes = Array.Empty<string>(),
                 PackageVersion = "PackageVersion",
                 ProjectReferencesWithVersions = new ITaskItem[0],
                 ProjectUrl = "ProjectUrl",
@@ -353,8 +353,8 @@ public void PackTask_MapsAllProperties()
                 RequireLicenseAcceptance = true,
                 Serviceable = true,
                 SourceFiles = new ITaskItem[0],
-                Tags = new string[0],
-                TargetFrameworks = new string[0],
+                Tags = Array.Empty<string>(),
+                TargetFrameworks = Array.Empty<string>(),
                 BuildOutputInPackage = new ITaskItem[0],
                 TargetPathsToSymbols = new ITaskItem[0]
             };

test/NuGet.Core.Tests/NuGet.Build.Tasks.Test/GetRestoreSettingTaskTests.cs

@@ -42,7 +42,7 @@ public void GetRestoreSettingsTask_GetValueGetLastValue()
             RestoreSettingsUtils.GetValue(
                 () => null,
                 () => null,
-                () => new string[0]).ShouldBeEquivalentTo(new string[0]);
+                () => Array.Empty<string>()).ShouldBeEquivalentTo(Array.Empty<string>());
         }
 
         [Fact]

test/NuGet.Core.Tests/NuGet.PackageManagement.Test/InstallationCompatibilityTests.cs

@@ -361,7 +361,7 @@ public TestContext(string userPackageFolder = null)
                     .Returns(userPackageFolder);
                 NuGetPathContext
                     .Setup(x => x.FallbackPackageFolders)
-                    .Returns(new string[0]);
+                    .Returns(Array.Empty<string>());
 
                 NuspecReader
                     .Setup(p => p.GetIdentity())

test/NuGet.Core.Tests/NuGet.Packaging.Test/SigningTests/AttributeUtilityTests.cs

@@ -566,7 +566,7 @@ public void CreateNuGetPackageOwners_WhenPackageOwnersNull_Throws()
         public void CreateNuGetPackageOwners_WhenPackageOwnersEmpty_Throws()
         {
             var exception = Assert.Throws<ArgumentException>(
-                () => AttributeUtility.CreateNuGetPackageOwners(new string[0]));
+                () => AttributeUtility.CreateNuGetPackageOwners(Array.Empty<string>()));
 
             Assert.Equal("packageOwners", exception.ParamName);
             Assert.StartsWith("The argument cannot be null or empty.", exception.Message);

test/NuGet.Core.Tests/NuGet.Packaging.Test/SigningTests/NuGetPackageOwnersTests.cs

@@ -25,7 +25,7 @@ public void Constructor_WhenPackageOwnersNull_Throws()
         public void Constructor_WhenPackageOwnersEmpty_Throws()
         {
             var exception = Assert.Throws<ArgumentException>(
-                () => new NuGetPackageOwners(new string[0]));
+                () => new NuGetPackageOwners(Array.Empty<string>()));
 
             Assert.Equal("packageOwners", exception.ParamName);
             Assert.StartsWith("The argument cannot be null or empty.", exception.Message);

test/NuGet.Core.Tests/NuGet.Packaging.Test/SigningTests/SigningUtilityTests.cs

@@ -267,7 +267,7 @@ public void CreateSignedAttributes_RepositorySignPackageRequest_WhenPackageOwner
         public void CreateSignedAttributes_RepositorySignPackageRequest_WhenPackageOwnersEmpty_ReturnsAttributes()
         {
             var v3ServiceIndexUrl = new Uri("https://test.test", UriKind.Absolute);
-            var packageOwners = new string[0];
+            var packageOwners = Array.Empty<string>();
 
             using (var certificate = _fixture.GetDefaultCertificate())
             using (var request = CreateRequestRepository(certificate, v3ServiceIndexUrl, packageOwners))