Add support for delegate type values through StringArgumentValue #259

src/Serilog.Settings.Configuration/Settings/Configuration/StringArgumentValue.cs

@@ -71,6 +71,43 @@ public object ConvertTo(Type toType, ResolutionContext resolutionContext)
                     TryParseStaticMemberAccessor(argumentValue, out var accessorTypeName, out var memberName))
                 {
                     var accessorType = Type.GetType(accessorTypeName, throwOnError: true);
+
+                    // if delegate, look for a method and then construct a delegate
+                    if (typeof(Delegate).IsAssignableFrom(toType) || typeof(MethodInfo) == toType)
+                    {
+                        var methodCandidates = accessorType.GetTypeInfo().DeclaredMethods
+                            .Where(x => x.Name == memberName)
+                            .Where(x => x.IsPublic)
+                            .Where(x => !x.IsGenericMethod)
+                            .Where(x => x.IsStatic)
+                            .ToList();
+
+                        if (methodCandidates.Count > 1 && typeof(Delegate).IsAssignableFrom(toType))
+                        {
+                            // filter possible method overloads
+
+                            var delegateSig = toType.GetMethod("Invoke");
+                            var delegateParameters = delegateSig!.GetParameters().Select(x => x.ParameterType);
+                            methodCandidates = methodCandidates
+                                .Where(x => x.ReturnType == delegateSig.ReturnType && x.GetParameters().Select(y => y.ParameterType).SequenceEqual(delegateParameters))
+                                .ToList();
+                        }
+
+                        var methodCandidate = methodCandidates.SingleOrDefault();
+
+                        if (methodCandidate != null)
+                        {
+                            if (typeof(MethodInfo) == toType)
+                            {
+                                return methodCandidate;
+                            }
+                            else
+                            {
+                                return methodCandidate.CreateDelegate(toType);
+                            }
+                        }
+                    }
+
                     // is there a public static property with that name ?
                     var publicStaticPropertyInfo = accessorType.GetTypeInfo().DeclaredProperties
                         .Where(x => x.Name == memberName)

test/Serilog.Settings.Configuration.Tests/StringArgumentValueTests.cs

@@ -99,6 +99,22 @@ public void StaticMembersAccessorsCanBeUsedForAbstractTypes(string input, Type t
             Assert.Equal(ConcreteImpl.Instance, actual);
         }
 
+        [Theory]
+        [InlineData("Serilog.Settings.Configuration.Tests.Support.ClassWithStaticAccessors::FuncIntParseField, Serilog.Settings.Configuration.Tests", typeof(Func<string, int>))]
+        [InlineData("Serilog.Settings.Configuration.Tests.Support.ClassWithStaticAccessors::NamedIntParseField, Serilog.Settings.Configuration.Tests", typeof(NamedIntParse))]
+        [InlineData("Serilog.Settings.Configuration.Tests.Support.ClassWithStaticAccessors::FuncIntParseProperty, Serilog.Settings.Configuration.Tests", typeof(Func<string, int>))]
+        [InlineData("Serilog.Settings.Configuration.Tests.Support.ClassWithStaticAccessors::NamedIntParseProperty, Serilog.Settings.Configuration.Tests", typeof(NamedIntParse))]
+        [InlineData("Serilog.Settings.Configuration.Tests.Support.ClassWithStaticAccessors::IntParseMethod, Serilog.Settings.Configuration.Tests", typeof(NamedIntParse))]
+        [InlineData("Serilog.Settings.Configuration.Tests.Support.ClassWithStaticAccessors::IntParseMethod, Serilog.Settings.Configuration.Tests", typeof(Func<string, int>))]
+        public void StaticMembersAccessorsCanBeUsedForDelegateTypes(string input, Type targetType)
+        {
+            var stringArgumentValue = new StringArgumentValue(input);
+
+            var actual = stringArgumentValue.ConvertTo(targetType, new ResolutionContext());
+
+            Assert.IsAssignableFrom(targetType, actual);
+        }
+
         [Theory]
         [InlineData("Serilog.Settings.Configuration.Tests.Support.ClassWithStaticAccessors::ConcreteClassProperty, Serilog.Settings.Configuration.Tests", typeof(AConcreteClass))]
         [InlineData("Serilog.Settings.Configuration.Tests.Support.ClassWithStaticAccessors::ConcreteClassField, Serilog.Settings.Configuration.Tests", typeof(AConcreteClass))]

test/Serilog.Settings.Configuration.Tests/Support/StaticAccessorClasses.cs

@@ -1,5 +1,9 @@
-namespace Serilog.Settings.Configuration.Tests.Support
+using System;
+
+namespace Serilog.Settings.Configuration.Tests.Support
 {
+    public delegate int NamedIntParse(string value);
+
     public interface IAmAnInterface
     {
     }
@@ -46,5 +50,13 @@ public class ClassWithStaticAccessors
 #pragma warning restore 169
         public IAmAnInterface InstanceInterfaceProperty => ConcreteImpl.Instance;
         public IAmAnInterface InstanceInterfaceField = ConcreteImpl.Instance;
+
+        public static Func<string, int> FuncIntParseField = int.Parse;
+        public static NamedIntParse NamedIntParseField = int.Parse;
+        public static Func<string, int> FuncIntParseProperty => int.Parse;
+        public static NamedIntParse NamedIntParseProperty => int.Parse;
+        public static int IntParseMethod(string value) => int.Parse(value);
+        public static int IntParseMethod(string value, string otherValue) => int.Parse(value); // will not be chosen, extra parameter
+        public static int IntParseMethod(object value) => throw new NotImplementedException(); // will not be chosen, wrong parameter type
     }
 }