Avoid hard-coding .cs extension

Author: jjonescz

src/NuGet.Core/NuGet.CommandLine.XPlat/Commands/Package/Update/PackageUpdateArgs.cs

@@ -24,5 +24,10 @@ internal record PackageUpdateArgs
         /// Path to a file with the XML content of the project (used for virtual projects).
         /// </summary>
         public string? ProjectContentFile { get; init; }
+
+        /// <summary>
+        /// For virtual projects (when <see cref="ProjectContentFile"/> is set), this is the original path to the entry-point file.
+        /// </summary>
+        public string? OriginalProject { get; init; }
     }
 }

src/NuGet.Core/NuGet.CommandLine.XPlat/Commands/Package/Update/PackageUpdateCommand.cs

@@ -64,6 +64,7 @@ internal static void Register(Command packageCommand, Option<bool> interactiveOp
             bool vulnerable = args.GetValue(vulnerableOption);
 
             var projectPath = project?.FullName ?? Environment.CurrentDirectory;
+            var originalProjectPath = projectPath;
             var projectContentFile = args.GetValue(projectContentFileOption)?.FullName;
             projectPath = MSBuildAPIUtility.ChangeProjectPath(projectPath, projectContentFile);
 
@@ -75,6 +76,7 @@ internal static void Register(Command packageCommand, Option<bool> interactiveOp
                 LogLevel = logLevel,
                 Vulnerable = vulnerable,
                 ProjectContentFile = projectContentFile,
+                OriginalProject = originalProjectPath,
             };
 
             return await action(commandArgs, cancellationToken);

src/NuGet.Core/NuGet.CommandLine.XPlat/Commands/Package/Update/PackageUpdateCommandRunner.cs

@@ -56,7 +56,7 @@ internal static async Task<int> Run(PackageUpdateArgs args, ILoggerWithColor log
 
         // 1. Get DGSpec for project/solution
         logger.LogVerbose(Strings.PackageUpdate_LoadingDGSpec);
-        var dgSpec = packageUpdateIO.GetDependencyGraphSpec(args.Project, args.ProjectContentFile);
+        var dgSpec = packageUpdateIO.GetDependencyGraphSpec(args.OriginalProject ?? args.Project, args.ProjectContentFile);
 
         if (dgSpec is null || dgSpec.Restore is null || dgSpec.Restore.Count == 0)
         {

src/NuGet.Core/NuGet.CommandLine.XPlat/Commands/Package/Update/PackageUpdateIO.cs

@@ -90,7 +90,7 @@ bool RunMsbuildTarget(string project, string tempFile, string? projectContentFil
             ProcessStartInfo processStartInfo = new ProcessStartInfo(dotnetPath)
             {
                 Arguments = $"build " +
-                $"\"{(projectContentFile is null ? project : Path.ChangeExtension(project, ".cs"))}\" " +
+                $"\"{project}\" " +
                 $"--no-restore " +
                 $"-target:GenerateRestoreGraphFile " +
                 $"-property:RestoreGraphOutputPath=\"{tempFile}\" " +