feat: Add diagnostics for source generators

Author: linkdotnet

docs/site/docs/extensions/bunit-generators.md

@@ -82,3 +82,11 @@ internal partial class ThirdPartyStub { }
 ```
 
 Current limitations of this approach is that he stubbed type is not allowed to be nested inside the test class.
+
+## Reported Diagnostics
+The generators will report a range of diagnostics to help understanding what issue is present. The following table shows the diagnostics that are reported.
+
+| Diagnostic ID | Error                                           | Severity | Description                                                                  |
+| ------------- | ----------------------------------------------- | -------- | ---------------------------------------------------------------------------- |
+| BUNIT0001     | Stubbing nested classes ({0}) is not supported. | Warning  | Types annotated with `ComponentStub` can not be nested inside another class. |
+| BUNIT0002     | Class ({0}) is not partial.                     | Warning  | Types annotated with `ComponentStub` must be partial.                        |

src/bunit.generators/Web.Stubs/AttributeStubGenerator/ComponentStubAttributeGenerator.cs

@@ -1,6 +1,7 @@
 using System.Linq;
 using System.Text;
 using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.Text;
 
@@ -49,6 +50,7 @@ private static StubClassInfo GetStubClassInfo(GeneratorAttributeSyntaxContext co
 			var namespaceName = stubbedType.ContainingNamespace.ToDisplayString();
 			var className = context.TargetSymbol.Name;
 			var visibility = context.TargetSymbol.DeclaredAccessibility.ToString().ToLower();
+			var isPartial = ((ClassDeclarationSyntax)context.TargetNode).Modifiers.Any(SyntaxKind.PartialKeyword);
 
 			var originalTypeToStub = attribute.AttributeClass?.TypeArguments.FirstOrDefault();
 			if (originalTypeToStub is null)
@@ -61,7 +63,9 @@ private static StubClassInfo GetStubClassInfo(GeneratorAttributeSyntaxContext co
 				ClassName = className,
 				Namespace = namespaceName,
 				TargetType = originalTypeToStub,
-				Visibility = visibility
+				Visibility = visibility,
+				IsNestedClass = context.TargetSymbol.ContainingType is not null,
+				IsPartial = isPartial,
 			};
 		}
 
@@ -70,6 +74,11 @@ private static StubClassInfo GetStubClassInfo(GeneratorAttributeSyntaxContext co
 
 	private static void Execute(StubClassInfo classInfo, SourceProductionContext context)
 	{
+		if (CheckDiagnostics(classInfo, context))
+		{
+			return;
+		}
+
 		var hasSomethingToStub = false;
 		var targetTypeSymbol = (INamedTypeSymbol)classInfo!.TargetType;
 		var sourceBuilder = new StringBuilder(1000);
@@ -97,11 +106,7 @@ private static void Execute(StubClassInfo classInfo, SourceProductionContext con
 			var propertyType = member.Type.ToDisplayString();
 			var propertyName = member.Name;
 
-			var isParameterAttribute = member.GetAttributes().Any(attr =>
-				attr.AttributeClass?.ToDisplayString() == "Microsoft.AspNetCore.Components.ParameterAttribute");
-			var attributeLine = isParameterAttribute
-				? "\t[global::Microsoft.AspNetCore.Components.Parameter]"
-				: "\t[global::Microsoft.AspNetCore.Components.CascadingParameter]";
+			var attributeLine = GetAttributeLineForMember(member);
 
 			sourceBuilder.AppendLine(attributeLine);
 			sourceBuilder.AppendLine($"\tpublic {propertyType} {propertyName} {{ get; set; }} = default!;");
@@ -113,6 +118,45 @@ private static void Execute(StubClassInfo classInfo, SourceProductionContext con
 		{
 			context.AddSource($"{classInfo.ClassName}.g.cs", sourceBuilder.ToString());
 		}
+
+		static string GetAttributeLineForMember(ISymbol member)
+		{
+			var isParameterAttribute = member.GetAttributes().Any(attr =>
+				attr.AttributeClass?.ToDisplayString() == "Microsoft.AspNetCore.Components.ParameterAttribute");
+			var attributeLine = isParameterAttribute
+				? "\t[global::Microsoft.AspNetCore.Components.Parameter]"
+				: "\t[global::Microsoft.AspNetCore.Components.CascadingParameter]";
+			return attributeLine;
+		}
+	}
+
+	private static bool CheckDiagnostics(StubClassInfo classInfo, SourceProductionContext context)
+	{
+		if (classInfo.IsNestedClass)
+		{
+			context.ReportDiagnostic(Diagnostic.Create(new DiagnosticDescriptor(
+					"BUNIT0001",
+					"Stubbing nested classes is not supported",
+					"Stubbing nested classes ({0}) is not supported.",
+					"Bunit", DiagnosticSeverity.Warning, true),
+				Location.None,
+				classInfo.TargetType.ToDisplayString()));
+			return true;
+		}
+
+		if (!classInfo.IsPartial)
+		{
+			context.ReportDiagnostic(Diagnostic.Create(new DiagnosticDescriptor(
+					"BUNIT0002",
+					"Stubbing non-partial classes is not supported",
+					"Class ({0}) is not partial.",
+					"Bunit", DiagnosticSeverity.Warning, true),
+				Location.None,
+				classInfo.TargetType.ToDisplayString()));
+			return true;
+		}
+
+		return false;
 	}
 }
 
@@ -122,4 +166,6 @@ internal sealed class StubClassInfo
 	public string Namespace { get; set; }
 	public ITypeSymbol TargetType { get; set; }
 	public string Visibility { get; set; }
+	public bool IsNestedClass { get; set; }
+	public bool IsPartial { get; set; }
 }

tests/bunit.generators.tests/Web.Stub/AddStubGeneratorTests.cs

@@ -64,6 +64,4 @@ public void Generated_stub_via_attribute_has_same_parameters()
 }
 
 [ComponentStub<ButtonComponent>]
-public partial class ButtonComponentStub
-{
-}
+public partial class ButtonComponentStub;