Refactor filter descriptor type checks in SwaggerGen (#3125)

Introduce `IsAssignableTo` method in `FilterDescriptor` class to check if `FilterInstance` is an instance of a specified type or if the `Type` property is assignable to the specified type.

Author: iskandersierra

src/Swashbuckle.AspNetCore.SwaggerGen/DependencyInjection/ConfigureSwaggerGeneratorOptions.cs

@@ -36,51 +36,51 @@ public void Configure(SwaggerGeneratorOptions options)
 
             foreach (var filterDescriptor in _swaggerGenOptions.ParameterFilterDescriptors)
             {
-                if (filterDescriptor.Type.IsAssignableTo(typeof(IParameterFilter)))
+                if (filterDescriptor.IsAssignableTo(typeof(IParameterFilter)))
                 {
                     options.ParameterFilters.Add(GetOrCreateFilter<IParameterFilter>(filterDescriptor));
                 }
 
-                if (filterDescriptor.Type.IsAssignableTo(typeof(IParameterAsyncFilter)))
+                if (filterDescriptor.IsAssignableTo(typeof(IParameterAsyncFilter)))
                 {
                     options.ParameterAsyncFilters.Add(GetOrCreateFilter<IParameterAsyncFilter>(filterDescriptor));
                 }
             }
 
             foreach (var filterDescriptor in _swaggerGenOptions.RequestBodyFilterDescriptors)
             {
-                if (filterDescriptor.Type.IsAssignableTo(typeof(IRequestBodyFilter)))
+                if (filterDescriptor.IsAssignableTo(typeof(IRequestBodyFilter)))
                 {
                     options.RequestBodyFilters.Add(GetOrCreateFilter<IRequestBodyFilter>(filterDescriptor));
                 }
 
-                if (filterDescriptor.Type.IsAssignableTo(typeof(IRequestBodyAsyncFilter)))
+                if (filterDescriptor.IsAssignableTo(typeof(IRequestBodyAsyncFilter)))
                 {
                     options.RequestBodyAsyncFilters.Add(GetOrCreateFilter<IRequestBodyAsyncFilter>(filterDescriptor));
                 }
             }
 
             foreach (var filterDescriptor in _swaggerGenOptions.OperationFilterDescriptors)
             {
-                if (filterDescriptor.Type.IsAssignableTo(typeof(IOperationFilter)))
+                if (filterDescriptor.IsAssignableTo(typeof(IOperationFilter)))
                 {
                     options.OperationFilters.Add(GetOrCreateFilter<IOperationFilter>(filterDescriptor));
                 }
 
-                if (filterDescriptor.Type.IsAssignableTo(typeof(IOperationAsyncFilter)))
+                if (filterDescriptor.IsAssignableTo(typeof(IOperationAsyncFilter)))
                 {
                     options.OperationAsyncFilters.Add(GetOrCreateFilter<IOperationAsyncFilter>(filterDescriptor));
                 }
             }
 
             foreach (var filterDescriptor in _swaggerGenOptions.DocumentFilterDescriptors)
             {
-                if (filterDescriptor.Type.IsAssignableTo(typeof(IDocumentFilter)))
+                if (filterDescriptor.IsAssignableTo(typeof(IDocumentFilter)))
                 {
                     options.DocumentFilters.Add(GetOrCreateFilter<IDocumentFilter>(filterDescriptor));
                 }
 
-                if (filterDescriptor.Type.IsAssignableTo(typeof(IDocumentAsyncFilter)))
+                if (filterDescriptor.IsAssignableTo(typeof(IDocumentAsyncFilter)))
                 {
                     options.DocumentAsyncFilters.Add(GetOrCreateFilter<IDocumentAsyncFilter>(filterDescriptor));
                 }

src/Swashbuckle.AspNetCore.SwaggerGen/DependencyInjection/SwaggerGenOptions.cs

@@ -32,5 +32,11 @@ public class FilterDescriptor
         public object[] Arguments { get; set; }
 
         public object FilterInstance { get; set; }
+
+        internal bool IsAssignableTo(Type type)
+        {
+            return (FilterInstance != null && type.IsInstanceOfType(FilterInstance)) ||
+                   (Type != null && Type.IsAssignableTo(type));
+        }
     }
 }

test/Swashbuckle.AspNetCore.SwaggerGen.Test/ConfigureSwaggerGeneratorOptionsTests.cs

@@ -412,4 +412,31 @@ public static void AddingDocumentAsyncFilterTypes_WhenConfiguringOptions_Differe
         Assert.Equal(2, swaggerGeneratorOptions.DocumentAsyncFilters.Count);
         Assert.NotSame(swaggerGeneratorOptions.DocumentAsyncFilters.First(), swaggerGeneratorOptions.DocumentAsyncFilters.Last());
     }
+
+    [Fact]
+    public static void AddingFilterDescriptorWithFilterInstance_WhenConfiguringOptions_NoExceptionIsThrown()
+    {
+        var webhostingEnvironment = Substitute.For<IWebHostEnvironment>();
+        webhostingEnvironment.ApplicationName.Returns("Swashbuckle.AspNetCore.SwaggerGen.Test");
+
+        var options = new SwaggerGenOptions();
+        options.OperationFilterDescriptors.Add(
+            new FilterDescriptor()
+            {
+                Type = null,
+                FilterInstance = new TestOperationFilter(),
+            });
+
+        using var serviceProvider = new ServiceCollection().BuildServiceProvider();
+
+        var configureSwaggerGeneratorOptions = new ConfigureSwaggerGeneratorOptions(
+            Options.Create(options),
+            serviceProvider,
+            webhostingEnvironment);
+        var swaggerGeneratorOptions = new SwaggerGeneratorOptions();
+
+        configureSwaggerGeneratorOptions.Configure(swaggerGeneratorOptions);
+
+        Assert.Single(swaggerGeneratorOptions.OperationFilters);
+    }
 }