Support collections as constructor arguments

Author: ChristofferGersen

src/Serilog.Settings.Configuration/Settings/Configuration/ObjectArgumentValue.cs

@@ -79,9 +79,7 @@ bool TryCreateContainer([NotNullWhen(true)] out object? result)
             if (toType.GetConstructor(Type.EmptyTypes) == null)
                 return false;
 
-            // https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/object-and-collection-initializers#collection-initializers
-            var addMethod = toType.GetMethods().FirstOrDefault(m => !m.IsStatic && m.Name == "Add" && m.GetParameters().Length == 1 && m.GetParameters()[0].ParameterType == elementType);
-            if (addMethod == null)
+            if (!HasAddMethod(toType, elementType, out var addMethod))
                 return false;
 
             var configurationElements = _section.GetChildren().ToArray();
@@ -203,7 +201,42 @@ static bool TryBindToCtorArgument(object value, Type type, ResolutionContext res
                 }
                 else if (s.GetChildren().Any())
                 {
-                    if (TryBuildCtorExpression(s, type, resolutionContext, out var ctorExpression))
+                    var elementType = type.GetElementType();
+                    if (elementType is not null)
+                    {
+                        var elements = new List<Expression>();
+                        foreach (var element in s.GetChildren())
+                        {
+                            if (TryBindToCtorArgument(element, elementType, resolutionContext, out var elementExpression))
+                            {
+                                elements.Add(elementExpression);
+                            }
+                            else
+                            {
+                                return false;
+                            }
+                        }
+                        argumentExpression = Expression.NewArrayInit(elementType, elements);
+                        return true;
+                    }
+                    else if (IsContainer(type, out elementType) && type.GetConstructor(Type.EmptyTypes) is not null && HasAddMethod(type, elementType, out var addMethod))
+                    {
+                        var elements = new List<Expression>();
+                        foreach (var element in s.GetChildren())
+                        {
+                            if (TryBindToCtorArgument(element, elementType, resolutionContext, out var elementExpression))
+                            {
+                                elements.Add(elementExpression);
+                            }
+                            else
+                            {
+                                return false;
+                            }
+                        }
+                        argumentExpression = Expression.ListInit(Expression.New(type), addMethod, elements);
+                        return true;
+                    }
+                    else if (TryBuildCtorExpression(s, type, resolutionContext, out var ctorExpression))
                     {
                         argumentExpression = ctorExpression;
                         return true;
@@ -235,4 +268,11 @@ static bool IsContainer(Type type, [NotNullWhen(true)] out Type? elementType)
 
         return false;
     }
+
+    static bool HasAddMethod(Type type, Type elementType, [NotNullWhen(true)] out MethodInfo? addMethod)
+    {
+        // https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/object-and-collection-initializers#collection-initializers
+        addMethod = type.GetMethods().FirstOrDefault(m => !m.IsStatic && m.Name == "Add" && m.GetParameters().Length == 1 && m.GetParameters()[0].ParameterType == elementType);
+        return addMethod is not null;
+    }
 }

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

@@ -1,4 +1,6 @@
 using Microsoft.Extensions.Configuration;
+using System.Collections;
+using System.Linq.Expressions;
 
 // ReSharper disable UnusedMember.Local
 // ReSharper disable UnusedParameter.Local
@@ -24,6 +26,9 @@ public ObjectArgumentValueTests()
     [InlineData("case_4", typeof(F), "new F(\"paramType\", new E(1, 2, 3, 4))")]
     [InlineData("case_5", typeof(G), "new G()")]
     [InlineData("case_6", typeof(G), "new G(3, 4)")]
+    [InlineData("case_7", typeof(H), "new H(new [] {\"1\", \"2\"})")]
+    [InlineData("case_8", typeof(H), "new H(new [] {new D(), new I()})")]
+    [InlineData("case_9", typeof(H), "new H(new J`1() {Void Add(C)(new D()), Void Add(C)(new I())})")]
     public void ShouldBindToConstructorArguments(string caseSection, Type targetType, string expectedExpression)
     {
         var testSection = _config.GetSection(caseSection);
@@ -32,6 +37,19 @@ public void ShouldBindToConstructorArguments(string caseSection, Type targetType
         Assert.Equal(expectedExpression, ctorExpression.ToString());
     }
 
+    [Fact]
+    public void ShouldBindToConstructorContainerArguments()
+    {
+        var testSection = _config.GetSection("case_9");
+
+        Assert.True(ObjectArgumentValue.TryBuildCtorExpression(testSection, typeof(H), new(), out var ctorExpression));
+        var instance = Expression.Lambda<Func<H>>(ctorExpression).Compile()();
+        Assert.IsType<J<C>>(instance.Collection);
+        Assert.Collection(instance.Collection,
+            first => Assert.IsType<D>(first),
+            second => Assert.IsType<I>(second));
+    }
+
     class A
     {
         public A(int a, TimeSpan b, Uri c, string d = "d") { }
@@ -64,4 +82,34 @@ class G
         public G() { }
         public G(int a = 1, int b = 2) { }
     }
+
+    class H
+    {
+        public J<C>? Collection { get; }
+
+        public H(params string[] strings) { }
+        public H(C[] array) { }
+        public H(J<C> collection) { Collection = collection; }
+    }
+
+    class I : C { }
+
+    class J<T> : IEnumerable<T>
+    {
+        private List<T> list = new();
+        public void Add(T value)
+        {
+            list.Add(value);
+        }
+
+        public IEnumerator<T> GetEnumerator()
+        {
+            return list.GetEnumerator();
+        }
+
+        IEnumerator IEnumerable.GetEnumerator()
+        {
+            return list.GetEnumerator();
+        }
+    }
 }

test/Serilog.Settings.Configuration.Tests/ObjectArgumentValueTests.json

@@ -40,5 +40,31 @@
   "case_6": {
     "a": 3,
     "b": 4
+  },
+
+  "case_7": {
+    "strings": [ "1", "2" ]
+  },
+
+  "case_8": {
+    "array": [
+      {
+        "type": "Serilog.Settings.Configuration.Tests.ObjectArgumentValueTests+D, Serilog.Settings.Configuration.Tests"
+      },
+      {
+        "type": "Serilog.Settings.Configuration.Tests.ObjectArgumentValueTests+I, Serilog.Settings.Configuration.Tests"
+      }
+    ]
+  },
+
+  "case_9": {
+    "collection": [
+      {
+        "type": "Serilog.Settings.Configuration.Tests.ObjectArgumentValueTests+D, Serilog.Settings.Configuration.Tests"
+      },
+      {
+        "type": "Serilog.Settings.Configuration.Tests.ObjectArgumentValueTests+I, Serilog.Settings.Configuration.Tests"
+      }
+    ]
   }
 }