FirstHalfCodeFix2.csx

[ExportCodeFixProvider(LanguageNames.CSharp, Name = nameof(Analyzer1CodeFixProvider)), Shared]
public class Analyzer1CodeFixProvider : CodeFixProvider
{
  ...
  
  public sealed override async Task RegisterCodeFixesAsync(CodeFixContext context)
  {
      var root = await context.Document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);

      // TODO: Replace the following code with your own analysis, generating a CodeAction for each fix to suggest
      var diagnostic = context.Diagnostics.First();
      var diagnosticSpan = diagnostic.Location.SourceSpan;

      // Find the type declaration identified by the diagnostic.
      var declaration = root.FindToken(diagnosticSpan.Start).Parent.AncestorsAndSelf().OfType<TypeDeclarationSyntax>().First();

      // Register a code action that will invoke the fix.
      context.RegisterCodeFix(
          CodeAction.Create(
              title: title,
              createChangedSolution: c => MakeUppercaseAsync(context.Document, declaration, c),
              equivalenceKey: title),
          diagnostic);
  }

  private async Task<Solution> MakeUppercaseAsync(Document document, TypeDeclarationSyntax typeDecl, CancellationToken cancellationToken)
  {
      // Compute new uppercase name.
      var identifierToken = typeDecl.Identifier;
      var newName = identifierToken.Text.ToUpperInvariant();

      // Get the symbol representing the type to be renamed.
      var semanticModel = await document.GetSemanticModelAsync(cancellationToken);
      var typeSymbol = semanticModel.GetDeclaredSymbol(typeDecl, cancellationToken);

      // Produce a new solution that has all references to that type renamed, including the declaration.
      var originalSolution = document.Project.Solution;
      var optionSet = originalSolution.Workspace.Options;
      var newSolution = await Renamer.RenameSymbolAsync(document.Project.Solution, typeSymbol, newName, optionSet, cancellationToken).ConfigureAwait(false);

      // Return the new solution with the now-uppercase type name.
      return newSolution;
  }
}