Fix for missing ReactiveUI using statement in generated code (#6)

Change test namespace to non ReactiveUI add using

src/ReactiveUI.SourceGenerators.Execute/Program.cs

@@ -8,8 +8,10 @@
 using System.Reactive.Linq;
 using System.Runtime.Serialization;
 using System.Text.Json.Serialization;
+using ReactiveUI;
+using ReactiveUI.SourceGenerators;
 
-namespace ReactiveUI.SourceGenerators.Test;
+namespace SGReactiveUI.SourceGenerators.Test;
 
 #pragma warning disable SA1402 // File may only contain a single type
 #pragma warning disable SA1649 // File name should match first type name

src/ReactiveUI.SourceGenerators/Reactive/ReactiveGenerator.cs

@@ -6,9 +6,11 @@
 using System.Collections.Immutable;
 using System.Linq;
 using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using ReactiveUI.SourceGenerators.Extensions;
 using ReactiveUI.SourceGenerators.Models;
+using static Microsoft.CodeAnalysis.CSharp.SyntaxFactory;
 
 namespace ReactiveUI.SourceGenerators;
 
@@ -67,7 +69,15 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
                 .ToImmutableArray();
 
             // Insert all members into the same partial type declaration
-            var compilationUnit = item.Key.GetCompilationUnit(memberDeclarations);
+            var compilationUnit = item.Key.GetCompilationUnit(memberDeclarations)
+                .WithLeadingTrivia(TriviaList(
+                    Comment("using ReactiveUI;"),
+                    CarriageReturn,
+                    Comment("// <auto-generated/>"),
+                    Trivia(PragmaWarningDirectiveTrivia(Token(SyntaxKind.DisableKeyword), true)),
+                    Trivia(NullableDirectiveTrivia(Token(SyntaxKind.EnableKeyword), true)),
+                    CarriageReturn))
+                .NormalizeWhitespace();
             context.AddSource($"{item.Key.FilenameHint}.Properties.g.cs", compilationUnit);
         });
     }