Process C# directives in file-based programs

src/Cli/dotnet/commands/dotnet-project/convert/ProjectConvertCommand.cs

@@ -3,7 +3,9 @@
 
 #nullable enable
 
+using System.Collections.Immutable;
 using System.CommandLine;
+using System.IO;
 using Microsoft.DotNet.Cli;
 using Microsoft.DotNet.Cli.Utils;
 using Microsoft.TemplateEngine.Cli.Commands;
@@ -35,13 +37,29 @@ public override int Execute()
             throw new GracefulException(LocalizableStrings.DirectoryAlreadyExists, targetDirectory);
         }
 
+        // Find directives (this can fail, so do this before creating the target directory).
+        var sourceFile = VirtualProjectBuildingCommand.CreateSourceFile(file);
+        var directives = VirtualProjectBuildingCommand.FindDirectives(sourceFile);
+
         Directory.CreateDirectory(targetDirectory);
 
-        string projectFile = Path.Join(targetDirectory, Path.GetFileNameWithoutExtension(file) + ".csproj");
-        string projectFileText = VirtualProjectBuildingCommand.GetNonVirtualProjectFileText();
-        File.WriteAllText(path: projectFile, contents: projectFileText);
+        var targetFile = Path.Join(targetDirectory, Path.GetFileName(file));
+
+        // If there were any directives, remove them from the file.
+        if (directives.Length != 0)
+        {
+            VirtualProjectBuildingCommand.RemoveDirectivesFromFile(directives, sourceFile.Text, targetFile);
+            File.Delete(file);
+        }
+        else
+        {
+            File.Move(file, targetFile);
+        }
 
-        File.Move(file, Path.Join(targetDirectory, Path.GetFileName(file)));
+        string projectFile = Path.Join(targetDirectory, Path.GetFileNameWithoutExtension(file) + ".csproj");
+        using var stream = File.Open(projectFile, FileMode.Create, FileAccess.Write);
+        using var writer = new StreamWriter(stream, Encoding.UTF8);
+        VirtualProjectBuildingCommand.WriteProjectFile(writer, directives);
 
         return 0;
     }

src/Cli/dotnet/commands/dotnet-run/LocalizableStrings.resx

@@ -244,4 +244,20 @@ Make the profile names distinct.</value>
   <data name="LaunchProfileDoesNotExist" xml:space="preserve">
     <value>A launch profile with the name '{0}' doesn't exist.</value>
   </data>
+  <data name="UnrecognizedDirective" xml:space="preserve">
+    <value>Unrecognized directive '{0}' at {1}.</value>
+    <comment>{0} is the directive name like 'package' or 'sdk', {1} is the file path and line number.</comment>
+  </data>
+  <data name="MissingDirectiveName" xml:space="preserve">
+    <value>Missing name of '{0}' at {1}.</value>
+    <comment>{0} is the directive name like 'package' or 'sdk', {1} is the file path and line number.</comment>
+  </data>
+  <data name="PropertyDirectiveMissingParts" xml:space="preserve">
+    <value>The property directive needs to have two parts separated by '=' like 'PropertyName=PropertyValue': {0}</value>
+    <comment>{0} is the file path and line number. {Locked="="}</comment>
+  </data>
+  <data name="PropertyDirectiveInvalidName" xml:space="preserve">
+    <value>Invalid property name at {0}. {1}</value>
+    <comment>{0} is the file path and line number. {1} is an inner exception message.</comment>
+  </data>
 </root>

src/Cli/dotnet/commands/dotnet-run/RunCommand.cs

@@ -110,7 +110,7 @@ public int Execute()
             projectFactory = new VirtualProjectBuildingCommand
             {
                 EntryPointFileFullPath = EntryPointFileFullPath,
-            }.CreateProjectInstance;
+            }.PrepareProjectInstance().CreateProjectInstance;
         }
 
         try