Make output-file option required and enable nullable contexts

Set the output-file option as required in tests to ensure proper parsing. Added nullable context enforcement and enabled implicit usings in source generator tests for better code safety and modern language compatibility.

Author: arturcic

new-cli/GitVersion.Cli.Generator.Tests/SystemCommandlineGeneratorTests.cs

@@ -1,4 +1,4 @@
-using System.CommandLine;
+using System.CommandLine;
 using GitVersion.Infrastructure;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
@@ -69,7 +69,7 @@ public TestCommandImpl(TestCommand command)
     {
         OutputFileOption = new Option<string>("--output-file", [])
         {
-            Required = false,
+            Required = true,
             Description = "The output file",
         };
         Add(OutputFileOption);
@@ -81,7 +81,7 @@ Task<int> Run(ParseResult parseResult, CancellationToken cancellationToken)
         {
             var settings = new TestCommandSettings
             {
-                OutputFile = parseResult.GetValue(OutputFileOption),
+                OutputFile = parseResult.GetValue(OutputFileOption)!,
             };
             return command.InvokeAsync(settings, cancellationToken);
         }
@@ -174,6 +174,24 @@ public async Task ValidateGeneratedCommandImplementation()
             }
         };
 
+        sourceGeneratorTest.SolutionTransforms.Add(
+            // make sure the ImplicitUsage is enabled
+            (solution, projectId) =>
+            {
+                var project = solution.GetProject(projectId)!;
+
+                // Enable ImplicitUsings
+                var parseOptions = (CSharpParseOptions)project.ParseOptions!;
+                var compilationOptions = (CSharpCompilationOptions)project.CompilationOptions!;
+
+                // Enable implicit usings (same as `<ImplicitUsings>enable</ImplicitUsings>` in .csproj)
+                compilationOptions = compilationOptions.WithNullableContextOptions(NullableContextOptions.Enable);
+
+                return project
+                    .WithParseOptions(parseOptions.WithLanguageVersion(LanguageVersion.Latest))
+                    .WithCompilationOptions(compilationOptions)
+                    .Solution;
+            });
         await sourceGeneratorTest.RunAsync();
     }
 }