Use IAsyncSwaggerProvider in CLI to support async filters

The CLI's `tofile` command previously resolved only `ISwaggerProvider`,
which uses the synchronous `GenerateOperation` path that skips
`IOperationAsyncFilter` registrations. This meant async operation
filters had no effect on CLI-generated swagger documents.

When available, the CLI now prefers `IAsyncSwaggerProvider.GetSwaggerAsync`
which invokes both async and sync filters, matching the runtime middleware
behavior.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: bt-Knodel

src/Swashbuckle.AspNetCore.Cli/Program.cs

@@ -62,12 +62,14 @@ public static int Main(string[] args)
 
             c.OnRun((namedArgs) =>
             {
-                SetupAndRetrieveSwaggerProviderAndOptions(namedArgs, out var swaggerProvider, out var swaggerOptions);
+                SetupAndRetrieveSwaggerProviderAndOptions(namedArgs, out var asyncSwaggerProvider, out var swaggerProvider, out var swaggerOptions);
                 var swaggerDocumentSerializer = swaggerOptions?.Value?.CustomDocumentSerializer;
-                var swagger = swaggerProvider.GetSwagger(
-                    namedArgs["swaggerdoc"],
-                    namedArgs.TryGetValue("--host", out var arg) ? arg : null,
-                    namedArgs.TryGetValue("--basepath", out var namedArg) ? namedArg : null);
+
+                var host = namedArgs.TryGetValue("--host", out var arg) ? arg : null;
+                var basePath = namedArgs.TryGetValue("--basepath", out var namedArg) ? namedArg : null;
+                var swagger = asyncSwaggerProvider != null
+                    ? asyncSwaggerProvider.GetSwaggerAsync(namedArgs["swaggerdoc"], host, basePath).GetAwaiter().GetResult()
+                    : swaggerProvider.GetSwagger(namedArgs["swaggerdoc"], host, basePath);
 
                 // 4) Serialize to specified output location or stdout
                 var outputPath = namedArgs.TryGetValue("--output", out var arg1)
@@ -150,7 +152,7 @@ public static int Main(string[] args)
             c.Option("--output", "");
             c.OnRun((namedArgs) =>
             {
-                SetupAndRetrieveSwaggerProviderAndOptions(namedArgs, out var swaggerProvider, out var swaggerOptions);
+                SetupAndRetrieveSwaggerProviderAndOptions(namedArgs, out _, out var swaggerProvider, out var swaggerOptions);
                 IList<string> docNames = [];
 
                 string outputPath = namedArgs.TryGetValue("--output", out var arg1)
@@ -189,7 +191,7 @@ public static int Main(string[] args)
         return runner.Run(args);
     }
 
-    private static void SetupAndRetrieveSwaggerProviderAndOptions(IDictionary<string, string> namedArgs, out ISwaggerProvider swaggerProvider, out IOptions<SwaggerOptions> swaggerOptions)
+    private static void SetupAndRetrieveSwaggerProviderAndOptions(IDictionary<string, string> namedArgs, out IAsyncSwaggerProvider asyncSwaggerProvider, out ISwaggerProvider swaggerProvider, out IOptions<SwaggerOptions> swaggerOptions)
     {
         // 1) Configure host with provided startupassembly
         var startupAssembly = AssemblyLoadContext.Default.LoadFromAssemblyPath(
@@ -199,6 +201,7 @@ private static void SetupAndRetrieveSwaggerProviderAndOptions(IDictionary<string
         var serviceProvider = GetServiceProvider(startupAssembly);
 
         // 3) Retrieve Swagger via configured provider
+        asyncSwaggerProvider = serviceProvider.GetService<IAsyncSwaggerProvider>();
         swaggerProvider = serviceProvider.GetRequiredService<ISwaggerProvider>();
         swaggerOptions = serviceProvider.GetService<IOptions<SwaggerOptions>>();
     }

test/Swashbuckle.AspNetCore.Cli.Test/ToolTests.cs

@@ -133,6 +133,26 @@ public static void Can_Generate_Swagger_Json_v3_OpenApiVersion()
         Assert.True(productsPath.TryGetProperty("post", out _));
     }
 
+    [Fact]
+    public static void Can_Generate_Swagger_Json_With_Async_Operation_Filters()
+    {
+        using var document = RunToJsonCommand((outputPath) =>
+        [
+            "tofile",
+            "--output",
+            outputPath,
+            Path.Combine(Directory.GetCurrentDirectory(), "Basic.dll"),
+            "v1"
+        ]);
+
+        // verify that async operation filter output is included
+        var paths = document.RootElement.GetProperty("paths");
+        var productsPath = paths.GetProperty("/products");
+        var postOp = productsPath.GetProperty("post");
+        Assert.True(postOp.TryGetProperty("x-async-filter", out var asyncFilterValue));
+        Assert.Equal("async-test", asyncFilterValue.GetString());
+    }
+
     [Fact]
     public static void Overwrites_Existing_File()
     {

test/WebSites/Basic/Startup.cs

@@ -27,6 +27,7 @@ public void ConfigureServices(IServiceCollection services)
             c.RequestBodyFilter<AssignRequestBodyVendorExtensions>();
 
             c.OperationFilter<AssignOperationVendorExtensions>();
+            c.OperationAsyncFilter<AssignOperationVendorExtensionsAsync>();
 
             c.SchemaFilter<ExamplesSchemaFilter>();
 

test/WebSites/Basic/Swagger/AssignOperationVendorExtensionsAsync.cs

@@ -0,0 +1,14 @@
+using Microsoft.OpenApi;
+using Swashbuckle.AspNetCore.SwaggerGen;
+
+namespace Basic.Swagger;
+
+public class AssignOperationVendorExtensionsAsync : IOperationAsyncFilter
+{
+    public Task ApplyAsync(OpenApiOperation operation, OperationFilterContext context, CancellationToken cancellationToken)
+    {
+        operation.Extensions ??= new Dictionary<string, IOpenApiExtension>();
+        operation.Extensions.Add("x-async-filter", new JsonNodeExtension("async-test"));
+        return Task.CompletedTask;
+    }
+}