Fix #1030 - Allow ParameterFilterAttribute to check if parameter can be resolved

src/Autofac/Features/AttributeFilters/KeyFilterAttribute.cs

@@ -26,6 +26,7 @@
 using System;
 using System.Diagnostics.CodeAnalysis;
 using System.Reflection;
+using Autofac.Core;
 
 namespace Autofac.Features.AttributeFilters
 {
@@ -136,5 +137,18 @@ public override object ResolveParameter(ParameterInfo parameter, IComponentConte
             context.TryResolveKeyed(Key, parameter.ParameterType, out value);
             return value;
         }
+
+        /// <summary>
+        /// Checks a constructor parameter can be resolved based on keyed service requirements.
+        /// </summary>
+        /// <param name="parameter">The specific parameter being resolved that is marked with this attribute.</param>
+        /// <param name="context">The component context under which the parameter is being resolved.</param>
+        /// <returns>true if parameter can be resolved; otherwise, false.</returns>
+        public override bool CanResolveParameter(ParameterInfo parameter, IComponentContext context)
+        {
+            if (parameter == null) throw new ArgumentNullException(nameof(parameter));
+            if (context == null) throw new ArgumentNullException(nameof(context));
+            return context.ComponentRegistry.IsRegistered(new KeyedService(Key, parameter.ParameterType));
+        }
     }
 }

src/Autofac/Features/AttributeFilters/MetadataFilterAttribute.cs

@@ -105,6 +105,8 @@ public sealed class MetadataFilterAttribute : ParameterFilterAttribute
 
         private static readonly MethodInfo FilterAllMethod = typeof(MetadataFilterAttribute).GetTypeInfo().GetDeclaredMethod(nameof(FilterAll));
 
+        private static readonly MethodInfo CanResolveMethod = typeof(MetadataFilterAttribute).GetTypeInfo().GetDeclaredMethod(nameof(CanResolve));
+
         /// <summary>
         /// Initializes a new instance of the <see cref="MetadataFilterAttribute"/> class.
         /// </summary>
@@ -165,6 +167,26 @@ public override object ResolveParameter(ParameterInfo parameter, IComponentConte
                 : FilterOneMethod.MakeGenericMethod(elementType).Invoke(null, new[] { context, Key, Value });
         }
 
+        /// <summary>
+        /// Checks a constructor parameter can be resolved based on metadata requirements.
+        /// </summary>
+        /// <param name="parameter">The specific parameter being resolved that is marked with this attribute.</param>
+        /// <param name="context">The component context under which the parameter is being resolved.</param>
+        /// <returns>true if parameter can be resolved; otherwise, false.</returns>
+        public override bool CanResolveParameter(ParameterInfo parameter, IComponentContext context)
+        {
+            if (parameter == null) throw new ArgumentNullException(nameof(parameter));
+            if (context == null) throw new ArgumentNullException(nameof(context));
+
+            // GetElementType currently is the effective equivalent of "Determine if the type
+            // is in IEnumerable and if it is, get the type being enumerated." This doesn't support
+            // the other relationship types like Lazy<T>, Func<T>, etc. If we need to add that,
+            // this is the place to do it.
+            var elementType = GetElementType(parameter.ParameterType);
+
+            return (bool)CanResolveMethod.MakeGenericMethod(elementType).Invoke(null, new[] { context, Key, Value });
+        }
+
         private static Type GetElementType(Type type)
         {
             return type.IsGenericEnumerableInterfaceType() ? type.GetTypeInfo().GenericTypeArguments[0] : type;
@@ -187,5 +209,12 @@ private static IEnumerable<T> FilterAll<T>(IComponentContext context, string met
                 .Select(m => m.Value.Value)
                 .ToArray();
         }
+
+        private static bool CanResolve<T>(IComponentContext context, string metadataKey, object metadataValue)
+        {
+            // Using Lazy<T> to ensure components that aren't actually used won't get activated.
+            return context.Resolve<IEnumerable<Meta<Lazy<T>>>>()
+                .Any(m => m.Metadata.ContainsKey(metadataKey) && metadataValue.Equals(m.Metadata[metadataKey]));
+        }
     }
 }

src/Autofac/Features/AttributeFilters/ParameterFilterAttribute.cs

@@ -63,5 +63,13 @@ public abstract class ParameterFilterAttribute : Attribute
         /// <param name="context">The component context under which the parameter is being resolved.</param>
         /// <returns>The instance of the object that should be used for the parameter value.</returns>
         public abstract object ResolveParameter(ParameterInfo parameter, IComponentContext context);
+
+        /// <summary>
+        /// Implemented in derived classes to check a specific parameter can be resolved.
+        /// </summary>
+        /// <param name="parameter">The specific parameter being resolved that is marked with this attribute.</param>
+        /// <param name="context">The component context under which the parameter is being resolved.</param>
+        /// <returns>true if parameter can be resolved; otherwise, false.</returns>
+        public abstract bool CanResolveParameter(ParameterInfo parameter, IComponentContext context);
     }
 }

src/Autofac/Features/AttributeFilters/RegistrationExtensions.cs

@@ -66,7 +66,11 @@ public static IRegistrationBuilder<TLimit, TReflectionActivatorData, TRegistrati
             if (builder == null) throw new ArgumentNullException(nameof(builder));
 
             return builder.WithParameter(
-                (p, c) => p.GetCustomAttributes<ParameterFilterAttribute>(true).Any(),
+                (p, c) =>
+                {
+                    var filter = p.GetCustomAttributes<ParameterFilterAttribute>(true).FirstOrDefault();
+                    return filter != null && filter.CanResolveParameter(p, c);
+                },
                 (p, c) =>
                 {
                     var filter = p.GetCustomAttributes<ParameterFilterAttribute>(true).First();

test/Autofac.Test/Features/AttributeFilters/WithAttributeFilterTestFixture.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using Autofac.Core;
 using Autofac.Features.AttributeFilters;
 using Autofac.Features.Metadata;
 using Autofac.Features.OwnedInstances;
@@ -80,6 +81,9 @@ public void KeyFilterIsAppliedOnConstructorDependencyMultiple()
             builder.RegisterType<ToolWindowAdapter>()
                 .Keyed<IAdapter>("Other");
 
+            builder.RegisterType<ConsoleLogger>()
+                .Keyed<ILogger>("Solution");
+
             builder.RegisterType<SolutionExplorerKeyed>()
                 .WithAttributeFiltering();
 
@@ -266,6 +270,10 @@ public void MetadataFilterIsAppliedOnConstructorDependencyMultiple()
                 .WithMetadata<AdapterMetadata>(m => m.For(am => am.Target, "Other"))
                 .As<IAdapter>();
 
+            builder.RegisterType<ConsoleLogger>()
+                .WithMetadata("LoggerName", "Solution")
+                .As<ILogger>();
+
             builder.RegisterType<SolutionExplorerMetadata>().WithAttributeFiltering();
 
             var container = builder.Build();
@@ -299,6 +307,10 @@ public void ComponentsThatAreNotUsedDoNotGetActivated()
                 .As<IAdapter>()
                 .OnActivating(h => adapterActivationCount++);
 
+            builder.RegisterType<ConsoleLogger>()
+                .WithMetadata("LoggerName", "Solution")
+                .As<ILogger>();
+
             builder.RegisterType<SolutionExplorerMetadata>()
                 .WithAttributeFiltering();
 
@@ -309,6 +321,32 @@ public void ComponentsThatAreNotUsedDoNotGetActivated()
             Assert.Equal(2, adapterActivationCount);
         }
 
+        [Fact]
+        public void RequiredParameterWithKeyFilterCanNotBeResolvedWhenNotRegister()
+        {
+            var builder = new ContainerBuilder();
+
+            builder.RegisterType<RequiredParameterWithKeyFilter>()
+              .WithAttributeFiltering()
+              .As<RequiredParameterWithKeyFilter>();
+
+            Assert.Throws<DependencyResolutionException>(() => builder.Build().Resolve<RequiredParameterWithKeyFilter>());
+        }
+
+        [Fact]
+        public void OptionalParameterWithKeyFilterCanBeResolvedBySpecifiedDefaultValue()
+        {
+            var builder = new ContainerBuilder();
+
+            builder.RegisterType<OptionalParameterWithKeyFilter>()
+              .WithAttributeFiltering()
+              .As<OptionalParameterWithKeyFilter>();
+
+            var instance = builder.Build().Resolve<OptionalParameterWithKeyFilter>();
+
+            Assert.Equal(15, instance.Parameter);
+        }
+
         public interface ILogger
         {
         }
@@ -454,5 +492,25 @@ public class AdapterMetadata
         public class EmptyMetadata
         {
         }
+
+        public class RequiredParameterWithKeyFilter
+        {
+            public int Parameter { get; set; }
+
+            public RequiredParameterWithKeyFilter([KeyFilter(0)] int parameter)
+            {
+                Parameter = parameter;
+            }
+        }
+
+        public class OptionalParameterWithKeyFilter
+        {
+            public int Parameter { get; set; }
+
+            public OptionalParameterWithKeyFilter([KeyFilter(0)] int parameter = 15)
+            {
+                Parameter = parameter;
+            }
+        }
     }
 }