Automatically add using directive from code fixer

src/ComputeSharp.D2D1.CodeFixers/MissingPixelShaderDescriptorOnPixelShaderCodeFixer.cs

@@ -1,14 +1,15 @@
 using System.Collections.Immutable;
 using System.Composition;
+using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CodeActions;
 using Microsoft.CodeAnalysis.CodeFixes;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.Editing;
+using Microsoft.CodeAnalysis.Simplification;
 using Microsoft.CodeAnalysis.Text;
 using static ComputeSharp.SourceGeneration.Diagnostics.DiagnosticDescriptors;
-using static Microsoft.CodeAnalysis.CSharp.SyntaxFactory;
 
 namespace CommunityToolkit.Mvvm.CodeFixers;
 
@@ -43,7 +44,7 @@ public override async Task RegisterCodeFixesAsync(CodeFixContext context)
             context.RegisterCodeFix(
                 CodeAction.Create(
                     title: "Add [D2DGeneratedPixelShaderDescriptor] attribute",
-                    createChangedDocument: token => ChangeReturnType(context.Document, root, structDeclaration),
+                    createChangedDocument: token => ChangeReturnType(context.Document, root, structDeclaration, token),
                     equivalenceKey: "Add [D2DGeneratedPixelShaderDescriptor] attribute"),
                 diagnostic);
         }
@@ -55,9 +56,22 @@ public override async Task RegisterCodeFixesAsync(CodeFixContext context)
     /// <param name="document">The original document being fixed.</param>
     /// <param name="root">The original tree root belonging to the current document.</param>
     /// <param name="structDeclaration">The <see cref="StructDeclarationSyntax"/> to update.</param>
+    /// <param name="cancellationToken">The cancellation token for the operation.</param>
     /// <returns>An updated document with the applied code fix, and the return type of the method being <see cref="Task"/>.</returns>
-    private static Task<Document> ChangeReturnType(Document document, SyntaxNode root, StructDeclarationSyntax structDeclaration)
+    private static async Task<Document> ChangeReturnType(Document document, SyntaxNode root, StructDeclarationSyntax structDeclaration, CancellationToken cancellationToken)
     {
+        // Get the semantic model (bail if it's not available)
+        if (await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false) is not SemanticModel semanticModel)
+        {
+            return document;
+        }
+
+        // Also bail if we can't resolve the [D2DGeneratedPixelShaderDescriptor] attribute symbol (this should really never happen)
+        if (semanticModel.Compilation.GetTypeByMetadataName("ComputeSharp.D2D1.D2DGeneratedPixelShaderDescriptorAttribute") is not INamedTypeSymbol attributeSymbol)
+        {
+            return document;
+        }
+
         int index = 0;
 
         // Find the index to use to insert the attribute. We want to make it so that if the struct declaration
@@ -89,15 +103,16 @@ private static Task<Document> ChangeReturnType(Document document, SyntaxNode roo
             }
         }
 
-        // Create the attribute syntax for the new attribute
-        AttributeListSyntax newAttributeList = AttributeList(SingletonSeparatedList(Attribute(IdentifierName("D2DGeneratedPixelShaderDescriptor"))));
+        SyntaxGenerator syntaxGenerator = SyntaxGenerator.GetGenerator(document);
 
-        // Create a new syntax node with the new attribute
-        SyntaxNode typeSyntax = SyntaxGenerator.GetGenerator(document).InsertAttributes(structDeclaration, index, newAttributeList);
+        // Create the attribute syntax for the new attribute. Also annotate it
+        // to automatically add using directives to the document, if needed.
+        // Then create the attribute syntax and insert it at the right position.
+        SyntaxNode attributeTypeSyntax = syntaxGenerator.TypeExpression(attributeSymbol).WithAdditionalAnnotations(Simplifier.AddImportsAnnotation);
+        SyntaxNode attributeSyntax = syntaxGenerator.Attribute(attributeTypeSyntax);
+        SyntaxNode updatedStructDeclarationSyntax = syntaxGenerator.InsertAttributes(structDeclaration, index, attributeSyntax);
 
         // Replace the node in the document tree
-        Document updatedDocument = document.WithSyntaxRoot(root.ReplaceNode(structDeclaration, typeSyntax));
-
-        return Task.FromResult(updatedDocument);
+        return document.WithSyntaxRoot(root.ReplaceNode(structDeclaration, updatedStructDeclarationSyntax));
     }
 }