Look at ApiConventionType attributes defined on base types

Fixes https://github.com/aspnet/AspNetCore/issues/4951

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

@@ -160,7 +160,7 @@ namespace Microsoft.AspNetCore.Mvc.Api.Analyzers
 
         internal static IReadOnlyList<ITypeSymbol> GetConventionTypes(in ApiControllerSymbolCache symbolCache, IMethodSymbol method)
         {
-            var attributes = method.ContainingType.GetAttributes(symbolCache.ApiConventionTypeAttribute).ToArray();
+            var attributes = method.ContainingType.GetAttributes(symbolCache.ApiConventionTypeAttribute, inherit: true).ToArray();
             if (attributes.Length == 0)
             {
                 attributes = method.ContainingAssembly.GetAttributes(symbolCache.ApiConventionTypeAttribute).ToArray();

src/Mvc/test/Mvc.Api.Analyzers.Test/SymbolApiResponseMetadataProviderTest.cs

@@ -290,6 +290,50 @@ namespace Microsoft.AspNetCore.Mvc.Api.Analyzers
                 });
         }
 
+        [Fact]
+        public async Task GetDeclaredResponseMetadata_ApiConventionTypeAttributeOnType_Works()
+        {
+            // Arrange
+            var type = typeof(GetDeclaredResponseMetadata_ApiConventionTypeAttributeOnType);
+            var compilation = await GetResponseMetadataCompilation();
+            var controller = compilation.GetTypeByMetadataName(type.FullName);
+            var method = (IMethodSymbol)controller.GetMembers().First();
+            var symbolCache = new ApiControllerSymbolCache(compilation);
+
+            // Act
+            var result = SymbolApiResponseMetadataProvider.GetDeclaredResponseMetadata(symbolCache, method);
+
+            // Assert
+            // We should expect 3 entries specified by DefaultApiConventions.Post
+            Assert.Collection(
+                result.OrderBy(r => r.StatusCode),
+                metadata => Assert.True(metadata.IsDefault),
+                metadata => Assert.Equal(201, metadata.StatusCode),
+                metadata => Assert.Equal(400, metadata.StatusCode));
+        }
+
+        [Fact]
+        public async Task GetDeclaredResponseMetadata_ApiConventionTypeAttributeOnBaseType_Works()
+        {
+            // Arrange
+            var type = typeof(GetDeclaredResponseMetadata_ApiConventionTypeAttributeOnBaseType);
+            var compilation = await GetResponseMetadataCompilation();
+            var controller = compilation.GetTypeByMetadataName(type.FullName);
+            var method = (IMethodSymbol)controller.GetMembers().First();
+            var symbolCache = new ApiControllerSymbolCache(compilation);
+
+            // Act
+            var result = SymbolApiResponseMetadataProvider.GetDeclaredResponseMetadata(symbolCache, method);
+
+            // Assert
+            // We should expect 3 entries specified by DefaultApiConventions.Post
+            Assert.Collection(
+                result.OrderBy(r => r.StatusCode),
+                metadata => Assert.True(metadata.IsDefault),
+                metadata => Assert.Equal(201, metadata.StatusCode),
+                metadata => Assert.Equal(400, metadata.StatusCode));
+        }
+
         [Fact]
         public Task GetStatusCode_ReturnsValueFromConstructor()
         {

src/Mvc/test/Mvc.Api.Analyzers.Test/TestFiles/SymbolApiResponseMetadataProviderTest/GetResponseMetadataTests.cs

@@ -90,4 +90,20 @@ namespace Microsoft.AspNetCore.Mvc.Api.Analyzers
             }
         }
     }
+
+    [ApiConventionType(typeof(DefaultApiConventions))]
+    public class GetDeclaredResponseMetadata_ApiConventionTypeAttributeOnType : Controller
+    {
+        public IActionResult Post(object model) => null;
+    }
+
+    [ApiConventionType(typeof(DefaultApiConventions))]
+    public class GetDeclaredResponseMetadata_ApiConventionTypeAttributeOnBaseTypeBase
+    {
+    }
+
+    public class GetDeclaredResponseMetadata_ApiConventionTypeAttributeOnBaseType : GetDeclaredResponseMetadata_ApiConventionTypeAttributeOnBaseTypeBase
+    {
+        public IActionResult Post(object model) => null;
+    }
 }