Fix missing metadata for AsParameters parameter when using RDG. (#48822)

Author: mitchdenny

src/Http/Http.Extensions/gen/StaticRouteHandlerModel/StaticRouteHandlerModel.Emitter.cs

@@ -228,10 +228,10 @@ private static void EmitCallsToMetadataProvidersForParameters(this Endpoint endp
                     ProcessParameter(innerParameter, codeWriter);
                 }
             }
-            else
-            {
-                ProcessParameter(parameter, codeWriter);
-            }
+
+            // Even if a parameter is decorated with the AsParameters attribute, we still need
+            // to fetch metadata on the parameter itself (as well as the properties).
+            ProcessParameter(parameter, codeWriter);
         }
 
         static void ProcessParameter(EndpointParameter parameter, CodeWriter codeWriter)

src/Http/Http.Extensions/test/RequestDelegateFactoryTests.cs

@@ -2501,29 +2501,6 @@ public void Create_CombinesDefaultMetadata_AndMetadataFromParameterTypesImplemen
         Assert.Contains(result.EndpointMetadata, m => m is CustomEndpointMetadata { Source: MetadataSource.Parameter });
     }
 
-    [Fact]
-    public void Create_CombinesPropertiesAsParameterMetadata_AndTopLevelParameter()
-    {
-        // Arrange
-        var @delegate = ([AsParameters] AddsCustomParameterMetadata param1) => new CountsDefaultEndpointMetadataResult();
-        var options = new RequestDelegateFactoryOptions
-        {
-            EndpointBuilder = CreateEndpointBuilder(new List<object>
-            {
-                new CustomEndpointMetadata { Source = MetadataSource.Caller }
-            }),
-        };
-
-        // Act
-        var result = RequestDelegateFactory.Create(@delegate, options);
-
-        // Assert
-        Assert.Contains(result.EndpointMetadata, m => m is CustomEndpointMetadata { Source: MetadataSource.Parameter });
-        Assert.Contains(result.EndpointMetadata, m => m is ParameterNameMetadata { Name: "param1" });
-        Assert.Contains(result.EndpointMetadata, m => m is CustomEndpointMetadata { Source: MetadataSource.Property });
-        Assert.Contains(result.EndpointMetadata, m => m is ParameterNameMetadata { Name: nameof(AddsCustomParameterMetadata.Data) });
-    }
-
     [Fact]
     public void Create_CombinesAllMetadata_InCorrectOrder()
     {

src/Http/Http.Extensions/test/RequestDelegateGenerator/RequestDelegateCreationTests.Metadata.cs

@@ -520,4 +520,23 @@ m is not Attribute2 &&
             // Entry-specific metadata added after a call to InferMetadata
             m => Assert.True(m is CustomEndpointMetadata { Source: MetadataSource.Caller }));
     }
+
+    [Fact]
+    public async Task Create_CombinesPropertiesAsParameterMetadata_AndTopLevelParameter()
+    {
+        // Arrange
+        var (_, compilation) = await RunGeneratorAsync("""
+app.MapPost("/test/pattern", ([AsParameters] AddsCustomParameterMetadata param1) => new CountsDefaultEndpointMetadataPoco())
+   .WithMetadata(new CustomEndpointMetadata { Source = MetadataSource.Caller });
+""");
+
+        // Act
+        var endpoint = GetEndpointFromCompilation(compilation);
+
+        // Assert
+        Assert.Contains(endpoint.Metadata, m => m is CustomEndpointMetadata { Source: MetadataSource.Parameter });
+        Assert.Contains(endpoint.Metadata, m => m is ParameterNameMetadata { Name: "param1" });
+        Assert.Contains(endpoint.Metadata, m => m is CustomEndpointMetadata { Source: MetadataSource.Property });
+        Assert.Contains(endpoint.Metadata, m => m is ParameterNameMetadata { Name: nameof(AddsCustomParameterMetadata.Data) });
+    }
 }