Improve support of nuget commands with file-based apps

src/Cli/Microsoft.DotNet.Cli.Definitions/Commands/Hidden/List/ListCommandDefinition.cs

@@ -20,7 +20,7 @@ public static Argument<string> CreateSlnOrProjectArgument(string name, string de
             Arity = ArgumentArity.ZeroOrOne
         }.DefaultToCurrentDirectory();
 
-    public readonly Argument<string> SlnOrProjectArgument = CreateSlnOrProjectArgument(CommandDefinitionStrings.SolutionOrProjectArgumentName, CommandDefinitionStrings.SolutionOrProjectArgumentDescription);
+    public readonly Argument<string> SlnOrProjectOrFileArgument = CreateSlnOrProjectArgument(CommandDefinitionStrings.SolutionOrProjectOrFileArgumentName, CommandDefinitionStrings.SolutionOrProjectOrFileArgumentDescription);
 
     public readonly ListPackageCommandDefinition PackageCommand = new();
     public readonly ListReferenceCommandDefinition ReferenceCommand = new();
@@ -31,7 +31,7 @@ public ListCommandDefinition()
         Hidden = true;
         this.DocsLink = Link;
 
-        Arguments.Add(SlnOrProjectArgument);
+        Arguments.Add(SlnOrProjectOrFileArgument);
         Subcommands.Add(PackageCommand);
         Subcommands.Add(ReferenceCommand);
     }

src/Cli/Microsoft.DotNet.Cli.Definitions/Commands/Hidden/List/ListPackageCommandDefinition.cs

@@ -12,6 +12,6 @@ internal sealed class ListPackageCommandDefinition() : PackageListCommandDefinit
 
     public ListCommandDefinition Parent => (ListCommandDefinition)Parents.Single();
 
-    public override string? GetFileOrDirectory(ParseResult parseResult)
-        => parseResult.GetValue(Parent.SlnOrProjectArgument);
+    public override Argument<string>? GetProjectOrFileArgument()
+        => Parent.SlnOrProjectOrFileArgument;
 }

src/Cli/Microsoft.DotNet.Cli.Definitions/Commands/Hidden/List/ListReferenceCommandDefinition.cs

@@ -19,7 +19,7 @@ public ListReferenceCommandDefinition() : base(Name)
     public ListCommandDefinition Parent => (ListCommandDefinition)Parents.Single();
 
     internal override string? GetFileOrDirectory(ParseResult parseResult)
-        => parseResult.GetValue(Parent.SlnOrProjectArgument);
+        => parseResult.GetValue(Parent.SlnOrProjectOrFileArgument);
 }
 
 internal abstract class ListReferenceCommandDefinitionBase : Command

src/Cli/Microsoft.DotNet.Cli.Definitions/Commands/Package/PackageListCommandDefinition.cs

@@ -6,20 +6,12 @@
 
 namespace Microsoft.DotNet.Cli.Commands.Package.List;
 
-internal sealed class PackageListCommandDefinition : PackageListCommandDefinitionBase
+internal sealed class PackageListCommandDefinition() : PackageListCommandDefinitionBase(Name)
 {
     public new const string Name = "list";
 
-    public readonly Option<string?> ProjectOption = PackageCommandDefinition.CreateProjectOption();
-
-    public PackageListCommandDefinition()
-        : base(Name)
-    {
-        Options.Add(ProjectOption);
-    }
-
-    public override string? GetFileOrDirectory(ParseResult parseResult)
-        => parseResult.GetValue(ProjectOption);
+    public override Argument<string>? GetProjectOrFileArgument()
+        => null;
 }
 
 internal abstract class PackageListCommandDefinitionBase : Command
@@ -110,6 +102,9 @@ internal abstract class PackageListCommandDefinitionBase : Command
         Description = CommandDefinitionStrings.CmdOutputVersionDescription
     }.ForwardAsSingle(o => $"--output-version:{o}");
 
+    public readonly Option<string?> ProjectOption = PackageCommandDefinition.CreateProjectOption();
+    public readonly Option<string?> FileOption = PackageCommandDefinition.CreateFileOption();
+
     public PackageListCommandDefinitionBase(string name)
         : base(name, CommandDefinitionStrings.PackageListAppFullName)
     {
@@ -128,9 +123,11 @@ public PackageListCommandDefinitionBase(string name)
         Options.Add(FormatOption);
         Options.Add(OutputVersionOption);
         Options.Add(NoRestore);
+        Options.Add(ProjectOption);
+        Options.Add(FileOption);
     }
 
-    public abstract string? GetFileOrDirectory(ParseResult parseResult);
+    public abstract Argument<string>? GetProjectOrFileArgument();
 
     public void EnforceOptionRules(ParseResult parseResult)
     {

src/Cli/dotnet/Commands/CliCommandStrings.resx

@@ -651,11 +651,6 @@ Tool '{1}' (version '{2}') was successfully installed. Entry is added to the man
   <data name="PackageRemoveSpecifyExactlyOnePackageReference" xml:space="preserve">
     <value>Specify only one package reference to remove.</value>
   </data>
-  <data name="DirectivesRemoved" xml:space="preserve">
-    <value>Removed '{0}' directives ({1}) for '{2}' from: {3}</value>
-    <comment>{0} is a directive kind (like '#:package'). {1} is number of removed directives.
-    {2} is directive key (e.g., package name). {3} is file path from which directives were removed.</comment>
-  </data>
   <data name="PackagesCommandNameCollisionConclusion" xml:space="preserve">
     <value>Command names conflict. Command names are case insensitive.
 {0}</value>

src/Cli/dotnet/Commands/NuGet/NuGetCommand.cs

@@ -6,19 +6,36 @@
 using System.CommandLine;
 using Microsoft.DotNet.Cli.Extensions;
 using Microsoft.DotNet.Cli.Utils;
+using Microsoft.DotNet.ProjectTools;
 
 namespace Microsoft.DotNet.Cli.Commands.NuGet;
 
-public class NuGetCommand
+internal class NuGetCommand
 {
-    public static int Run(string[] args)
+    public static int Run(string[] args, bool isFileBasedApp = false)
     {
-        return Run(args, new NuGetCommandRunner());
+        return Run(args, isFileBasedApp
+            ? new InProcessNuGetCommandRunner(NuGetVirtualProjectBuilder.Instance)
+            : new NuGetCommandRunner());
     }
 
     public static int Run(ParseResult parseResult)
     {
-        return Run(parseResult.GetArguments(), new NuGetCommandRunner());
+        ICommandRunner runner;
+
+        if (parseResult.CommandResult.Command.Name == "why"
+            && parseResult.CommandResult.Command.Arguments.FirstOrDefault() is Argument<string> pathArg
+            && parseResult.GetValue(pathArg) is { } path
+            && VirtualProjectBuilder.IsValidEntryPointPath(path))
+        {
+            runner = new InProcessNuGetCommandRunner(NuGetVirtualProjectBuilder.Instance);
+        }
+        else
+        {
+            runner = new NuGetCommandRunner();
+        }
+
+        return Run(parseResult.GetArguments(), runner);
     }
 
     public static int Run(string[] args, ICommandRunner nugetCommandRunner)
@@ -43,11 +60,28 @@ private class NuGetCommandRunner : ICommandRunner
         public int Run(string[] args)
         {
             var nugetApp = new NuGetForwardingApp(args);
-            nugetApp.WithEnvironmentVariable("DOTNET_HOST_PATH", GetDotnetPath());
+            nugetApp.WithEnvironmentVariable(EnvironmentVariableNames.DOTNET_HOST_PATH, GetDotnetPath());
             return nugetApp.Execute();
         }
     }
 
+    private class InProcessNuGetCommandRunner(NuGetVirtualProjectBuilder virtualProjectBuilder) : ICommandRunner
+    {
+        public int Run(string[] args)
+        {
+            var originalDotNetHostPath = Environment.GetEnvironmentVariable(EnvironmentVariableNames.DOTNET_HOST_PATH);
+            Environment.SetEnvironmentVariable(EnvironmentVariableNames.DOTNET_HOST_PATH, GetDotnetPath());
+            try
+            {
+                return global::NuGet.CommandLine.XPlat.Program.Run(args, virtualProjectBuilder);
+            }
+            finally
+            {
+                Environment.SetEnvironmentVariable(EnvironmentVariableNames.DOTNET_HOST_PATH, originalDotNetHostPath);
+            }
+        }
+    }
+
     private static string GetDotnetPath()
     {
         return new Muxer().MuxerPath;

src/Cli/dotnet/Commands/NuGet/NuGetVirtualProjectBuilder.cs

@@ -0,0 +1,47 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.Build.Construction;
+using Microsoft.Build.Evaluation;
+using Microsoft.DotNet.Cli.Commands.Package;
+using Microsoft.DotNet.Cli.Commands.Run;
+using Microsoft.DotNet.FileBasedPrograms;
+using Microsoft.DotNet.ProjectTools;
+using NuGet.CommandLine.XPlat;
+
+namespace Microsoft.DotNet.Cli.Commands.NuGet;
+
+internal sealed class NuGetVirtualProjectBuilder : IVirtualProjectBuilder
+{
+    public static NuGetVirtualProjectBuilder Instance => field ??= new();
+
+    private NuGetVirtualProjectBuilder() { }
+
+    public bool IsValidEntryPointPath(string entryPointFilePath) => VirtualProjectBuilder.IsValidEntryPointPath(entryPointFilePath);
+
+    public string GetVirtualProjectPath(string entryPointFilePath) => VirtualProjectBuilder.GetVirtualProjectPath(entryPointFilePath);
+
+    public ProjectRootElement CreateProjectRootElement(string entryPointFilePath, ProjectCollection projectCollection)
+    {
+        if (!Path.IsPathFullyQualified(entryPointFilePath))
+        {
+            throw new ArgumentException($"'{entryPointFilePath}' is not a fully qualified path.", paramName: nameof(entryPointFilePath));
+        }
+
+        var builder = new VirtualProjectBuilder(entryPointFilePath, VirtualProjectBuildingCommand.TargetFramework);
+
+        builder.CreateProjectInstance(
+            projectCollection,
+            ErrorReporters.IgnoringReporter,
+            project: out _,
+            out var projectRootElement,
+            evaluatedDirectives: out _);
+
+        return projectRootElement;
+    }
+
+    public void SaveProject(string entryPointFilePath, ProjectRootElement projectRootElement)
+    {
+        VirtualProjectPackageReflector.ReflectChangesToDirectives(projectRootElement, entryPointFilePath);
+    }
+}