3

Generator/MySourceGenerator.cs

@@ -6,16 +6,11 @@ namespace MySourceGenerator {
 	[Generator]
 	public class MySourceGenerator : ISourceGenerator {
 		public void Execute(GeneratorExecutionContext context) {
-			var sb = new StringBuilder();
-			sb.AppendLine("using System;");
-			sb.AppendLine("namespace Generated;");
-			sb.AppendLine("public static class HelloWorld {");
-			sb.AppendLine("	public static string SayHello() {");
-			sb.AppendLine("		return \"Hello World!!!\";");
-			sb.AppendLine("	}");
-			sb.AppendLine("}");
-
-			context.AddSource("HelleWorld.generated", SourceText.From(sb.ToString(), Encoding.UTF8));
+			var template = context.AdditionalFiles.Where(static file => file.Path.EndsWith("HelloWorld.template.cs")).First().GetText()?.ToString();
+			if (template == null) {
+				return;
+			}
+			context.AddSource("HelleWorld.generated", SourceText.From(template, Encoding.UTF8));
 		}
 
 		public void Initialize(GeneratorInitializationContext context) {

Source/Source.csproj

@@ -6,6 +6,8 @@
 
 	<ItemGroup>
 		<ProjectReference Include="..\Generator\Generator.csproj" OutputItemType="Analyzer" ReferenceOutputAssembly="false" />
+		<Compile Remove="*/*.template.cs" />
+		<AdditionalFiles Include="*/*.template.cs" />
 	</ItemGroup>
 
 </Project>

Source/templates/HelloWorld.template.cs

@@ -0,0 +1,7 @@
+namespace Generated;
+
+public static class HelloWorld {
+	public static string SayHello() {
+		return "Hello World!!!";
+	}
+}