test: harden content enricher policy generation

src/PatternKit.Generators/Messaging/ContentEnricherGenerator.cs

@@ -85,6 +85,12 @@ private static void Generate(SourceProductionContext context, INamedTypeSymbol t
             return;
         }
 
+        if (!IsKnownPolicy(defaultPolicy))
+        {
+            context.ReportDiagnostic(Diagnostic.Create(InvalidConfiguration, node.Identifier.GetLocation(), type.Name, $"default policy '{defaultPolicy}' is not supported"));
+            return;
+        }
+
         var steps = type.GetMembers().OfType<IMethodSymbol>()
             .Select(method => (Method: method, Attribute: method.GetAttributes().FirstOrDefault(static attr => attr.AttributeClass?.ToDisplayString() == StepAttributeName)))
             .Where(static item => item.Attribute is not null)
@@ -107,6 +113,12 @@ private static void Generate(SourceProductionContext context, INamedTypeSymbol t
                 return;
             }
 
+            if (!IsKnownPolicy(step.Policy))
+            {
+                context.ReportDiagnostic(Diagnostic.Create(InvalidConfiguration, step.Method.Locations.FirstOrDefault(), type.Name, $"step '{step.Name}' policy '{step.Policy}' is not supported"));
+                return;
+            }
+
             if (step.Policy == "UseDefault")
             {
                 if (string.IsNullOrWhiteSpace(step.DefaultFactoryName))
@@ -225,6 +237,9 @@ private static bool IsValueTaskOfPayload(ITypeSymbol type, ITypeSymbol payloadTy
     private static int? GetNamedInt(AttributeData attribute, string name)
         => attribute.NamedArguments.FirstOrDefault(kv => kv.Key == name).Value.Value as int?;
 
+    private static bool IsKnownPolicy(string policy)
+        => policy is "Throw" or "Skip" or "UseDefault";
+
     private static string Escape(string value) => value.Replace("\\", "\\\\").Replace("\"", "\\\"");
 
     private static string GetAccessibility(Accessibility accessibility)

test/PatternKit.Generators.Tests/ContentEnricherGeneratorTests.cs

@@ -259,6 +259,52 @@ public static partial class Host;
         ScenarioExpect.Equal("PKMCE004", diagnostic.Id);
     }
 
+    [Scenario("Reports diagnostic for invalid default content enricher policy")]
+    [Fact]
+    public void ReportsDiagnosticForInvalidDefaultContentEnricherPolicy()
+    {
+        var source = """
+            using PatternKit.Generators.Messaging;
+
+            namespace Demo;
+
+            [GenerateContentEnricher(typeof(string), DefaultPolicy = (ContentEnrichmentErrorPolicy)99)]
+            public static partial class Host;
+            """;
+
+        var diagnostic = RunAndGetSingleDiagnostic(source, nameof(ReportsDiagnosticForInvalidDefaultContentEnricherPolicy));
+
+        ScenarioExpect.Equal("PKMCE004", diagnostic.Id);
+        ScenarioExpect.Contains("default policy '99' is not supported", diagnostic.GetMessage());
+    }
+
+    [Scenario("Reports diagnostic for invalid content enricher step policy")]
+    [Fact]
+    public void ReportsDiagnosticForInvalidContentEnricherStepPolicy()
+    {
+        var source = """
+            using System.Threading;
+            using System.Threading.Tasks;
+            using PatternKit.Generators.Messaging;
+            using PatternKit.Messaging;
+
+            namespace Demo;
+
+            [GenerateContentEnricher(typeof(string))]
+            public static partial class Host
+            {
+                [ContentEnrichmentStep("invalid", Policy = (ContentEnrichmentErrorPolicy)99)]
+                private static ValueTask<string> Add(string payload, MessageContext context, CancellationToken cancellationToken)
+                    => ValueTask.FromResult(payload);
+            }
+            """;
+
+        var diagnostic = RunAndGetSingleDiagnostic(source, nameof(ReportsDiagnosticForInvalidContentEnricherStepPolicy));
+
+        ScenarioExpect.Equal("PKMCE004", diagnostic.Id);
+        ScenarioExpect.Contains("step 'invalid' policy '99' is not supported", diagnostic.GetMessage());
+    }
+
     [Scenario("Reports diagnostic for invalid default content enricher factory")]
     [Fact]
     public void ReportsDiagnosticForInvalidDefaultContentEnricherFactory()