Allow ApiControlelrAttribute to be applied to assemblies

Fixes #7343

src/Microsoft.AspNetCore.Mvc.Api.Analyzers/ApiControllerFacts.cs

@@ -25,7 +25,8 @@ public static bool IsApiControllerAction(ApiControllerSymbolCache symbolCache, I
                 return false;
             }
 
-            if (!method.ContainingType.HasAttribute(symbolCache.IApiBehaviorMetadata, inherit: true))
+            if (!method.ContainingType.HasAttribute(symbolCache.IApiBehaviorMetadata, inherit: true) &&
+                !method.ContainingAssembly.HasAttribute(symbolCache.IApiBehaviorMetadata))
             {
                 return false;
             }

src/Microsoft.AspNetCore.Mvc.Core/ApiControllerAttribute.cs

@@ -2,16 +2,20 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using Microsoft.AspNetCore.Mvc.Internal;
 
 namespace Microsoft.AspNetCore.Mvc
 {
     /// <summary>
-    /// Indicates that a type and all derived types are used to serve HTTP API responses. The presence of
-    /// this attribute can be used to target conventions, filters and other behaviors based on the purpose
-    /// of the controller.
+    /// Indicates that a type and all derived types are used to serve HTTP API responses. 
+    /// <para>
+    /// Controllers decorated with this attribute are configured with features and behavior targeted at improving the
+    /// developer experience for building APIs.
+    /// </para>
+    /// <para>
+    /// When decorated on an assembly, all controllers in the assembly will be treated as controllers with API behavior.
+    /// </para>
     /// </summary>
-    [AttributeUsage(AttributeTargets.Class, AllowMultiple = false, Inherited = true)]
+    [AttributeUsage(AttributeTargets.Assembly | AttributeTargets.Class, AllowMultiple = false, Inherited = true)]
     public class ApiControllerAttribute : ControllerAttribute, IApiBehaviorMetadata
     {
     }

src/Microsoft.AspNetCore.Mvc.Core/Internal/ApiBehaviorApplicationModelProvider.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Reflection;
 using Microsoft.AspNetCore.Mvc.ApplicationModels;
 using Microsoft.AspNetCore.Mvc.Core;
 using Microsoft.AspNetCore.Mvc.Infrastructure;
@@ -55,7 +56,7 @@ public void OnProvidersExecuting(ApplicationModelProviderContext context)
         {
             foreach (var controllerModel in context.Result.Controllers)
             {
-                if (!controllerModel.Attributes.OfType<IApiBehaviorMetadata>().Any())
+                if (!IsApiController(controllerModel))
                 {
                     continue;
                 }
@@ -103,5 +104,17 @@ bool IsAttributeRouted(IList<SelectorModel> selectorModel)
                 return false;
             }
         }
+
+        private static bool IsApiController(ControllerModel controller)
+        {
+            if (controller.Attributes.OfType<IApiBehaviorMetadata>().Any())
+            {
+                return true;
+            }
+
+            var controllerAssembly = controller.ControllerType.Assembly;
+            var assemblyAttributes = controllerAssembly.GetCustomAttributes();
+            return assemblyAttributes.OfType<IApiBehaviorMetadata>().Any();
+        }
     }
 }

test/Mvc.Api.Analyzers.Test/ApiControllerFactsTest.cs

@@ -4,6 +4,7 @@
 using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Analyzer.Testing;
+using Microsoft.AspNetCore.Mvc.Api.Analyzers.TestFiles.ApiControllerFactsTest;
 using Microsoft.CodeAnalysis;
 using Xunit;
 
@@ -110,9 +111,25 @@ public async Task IsApiControllerAction_ReturnsTrue_ForValidActionMethods()
             Assert.True(result);
         }
 
-        private Task<Compilation> GetCompilation()
+        [Fact]
+        public async Task IsApiControllerAction_ReturnsTrue_IfAttributeIsDeclaredOnAssembly()
+        {
+            // Arrange
+            var compilation = await GetCompilation(nameof(IsApiControllerAction_ReturnsTrue_IfAttributeIsDeclaredOnAssembly));
+            var symbolCache = new ApiControllerSymbolCache(compilation);
+            var type = compilation.GetTypeByMetadataName(typeof(IsApiControllerAction_ReturnsTrue_IfAttributeIsDeclaredOnAssemblyController).FullName);
+            var method = (IMethodSymbol)type.GetMembers(nameof(IsApiControllerAction_ReturnsTrue_IfAttributeIsDeclaredOnAssemblyController.Action)).First();
+
+            // Act
+            var result = ApiControllerFacts.IsApiControllerAction(symbolCache, method);
+
+            // Assert
+            Assert.True(result);
+        }
+
+        private Task<Compilation> GetCompilation(string testFile = "TestFile")
         {
-            var testSource = MvcTestSource.Read(GetType().Name, "TestFile");
+            var testSource = MvcTestSource.Read(GetType().Name, testFile);
             var project = DiagnosticProject.Create(GetType().Assembly, new[] { testSource.Source });
 
             return project.GetCompilationAsync();

test/Mvc.Api.Analyzers.Test/TestFiles/ApiControllerFactsTest/IsApiControllerAction_ReturnsTrue_IfAttributeIsDeclaredOnAssembly.cs

@@ -0,0 +1,11 @@
+using Microsoft.AspNetCore.Mvc;
+
+[assembly: ApiController]
+
+namespace Microsoft.AspNetCore.Mvc.Api.Analyzers.TestFiles.ApiControllerFactsTest
+{
+    public class IsApiControllerAction_ReturnsTrue_IfAttributeIsDeclaredOnAssemblyController : ControllerBase
+    {
+        public IActionResult Action() => null;
+    }
+}