Add support for binding record types

Author: pranavkm

src/Mvc/Mvc.Abstractions/src/ModelBinding/IPropertyFilterProvider.cs

@@ -12,6 +12,9 @@ public interface IPropertyFilterProvider
     {
         /// <summary>
         /// Gets a predicate which can determines which model properties should be bound by model binding.
+        /// <para>
+        /// This predicates are also applied to determine which parameters are bound when a model's constructor is bound.
+        /// </para>
         /// </summary>
         Func<ModelMetadata, bool> PropertyFilter { get; }
     }

src/Mvc/Mvc.Abstractions/src/ModelBinding/Metadata/ModelBindingMessageProvider.cs

@@ -43,31 +43,31 @@ public abstract class ModelBindingMessageProvider
         /// <summary>
         /// Error message the model binding system adds when <see cref="ModelError.Exception"/> is of type
         /// <see cref="FormatException"/> or <see cref="OverflowException"/>, value is known, and error is associated
-        /// with a property.
+        /// with a property or parameter.
         /// </summary>
         /// <value>Default <see cref="string"/> is "The value '{0}' is not valid for {1}.".</value>
         public virtual Func<string, string, string> AttemptedValueIsInvalidAccessor { get; } = default!;
 
         /// <summary>
         /// Error message the model binding system adds when <see cref="ModelError.Exception"/> is of type
         /// <see cref="FormatException"/> or <see cref="OverflowException"/>, value is known, and error is associated
-        /// with a collection element or action parameter.
+        /// with a collection element.
         /// </summary>
         /// <value>Default <see cref="string"/> is "The value '{0}' is not valid.".</value>
         public virtual Func<string, string> NonPropertyAttemptedValueIsInvalidAccessor { get; } = default!;
 
         /// <summary>
         /// Error message the model binding system adds when <see cref="ModelError.Exception"/> is of type
         /// <see cref="FormatException"/> or <see cref="OverflowException"/>, value is unknown, and error is associated
-        /// with a property.
+        /// with a property or parameter.
         /// </summary>
         /// <value>Default <see cref="string"/> is "The supplied value is invalid for {0}.".</value>
         public virtual Func<string, string> UnknownValueIsInvalidAccessor { get; } = default!;
 
         /// <summary>
         /// Error message the model binding system adds when <see cref="ModelError.Exception"/> is of type
         /// <see cref="FormatException"/> or <see cref="OverflowException"/>, value is unknown, and error is associated
-        /// with a collection element or action parameter.
+        /// with a collection element .
         /// </summary>
         /// <value>Default <see cref="string"/> is "The supplied value is invalid.".</value>
         public virtual Func<string> NonPropertyUnknownValueIsInvalidAccessor { get; } = default!;

src/Mvc/Mvc.Abstractions/src/ModelBinding/Metadata/ModelMetadataIdentity.cs

@@ -16,12 +16,14 @@ private ModelMetadataIdentity(
             Type modelType,
             string? name = null,
             Type? containerType = null,
-            object? fieldInfo = null)
+            object? fieldInfo = null,
+            ConstructorInfo? constructorInfo = null)
         {
             ModelType = modelType;
             Name = name;
             ContainerType = containerType;
             FieldInfo = fieldInfo;
+            ConstructorInfo = constructorInfo;
         }
 
         /// <summary>
@@ -130,6 +132,28 @@ public static ModelMetadataIdentity ForParameter(ParameterInfo parameter, Type m
             return new ModelMetadataIdentity(modelType, parameter.Name, fieldInfo: parameter);
         }
 
+        /// <summary>
+        /// Creates a <see cref="ModelMetadataIdentity"/> for the provided parameter with the specified
+        /// model type.
+        /// </summary>
+        /// <param name="constructor">The <see cref="ConstructorInfo" />.</param>
+        /// <param name="modelType">The model type.</param>
+        /// <returns>A <see cref="ModelMetadataIdentity"/>.</returns>
+        public static ModelMetadataIdentity ForConstructor(ConstructorInfo constructor, Type modelType)
+        {
+            if (constructor == null)
+            {
+                throw new ArgumentNullException(nameof(constructor));
+            }
+
+            if (modelType == null)
+            {
+                throw new ArgumentNullException(nameof(modelType));
+            }
+
+            return new ModelMetadataIdentity(modelType, constructor.Name, constructorInfo: constructor);
+        }
+
         /// <summary>
         /// Gets the <see cref="Type"/> defining the model property represented by the current
         /// instance, or <c>null</c> if the current instance does not represent a property.
@@ -152,6 +176,10 @@ public ModelMetadataKind MetadataKind
                 {
                     return ModelMetadataKind.Parameter;
                 }
+                else if (ConstructorInfo != null)
+                {
+                    return ModelMetadataKind.Constructor;
+                }
                 else if (ContainerType != null && Name != null)
                 {
                     return ModelMetadataKind.Property;
@@ -183,6 +211,12 @@ public ModelMetadataKind MetadataKind
         /// </summary>
         public PropertyInfo? PropertyInfo => FieldInfo as PropertyInfo;
 
+        /// <summary>
+        /// Gets a descriptor for the constructor, or <c>null</c> if this instance
+        /// does not represent a constructor.
+        /// </summary>
+        public ConstructorInfo? ConstructorInfo { get; }
+
         /// <inheritdoc />
         public bool Equals(ModelMetadataIdentity other)
         {
@@ -191,7 +225,8 @@ public bool Equals(ModelMetadataIdentity other)
                 ModelType == other.ModelType &&
                 Name == other.Name &&
                 ParameterInfo == other.ParameterInfo && 
-                PropertyInfo == other.PropertyInfo;
+                PropertyInfo == other.PropertyInfo &&
+                ConstructorInfo == other.ConstructorInfo;
         }
 
         /// <inheritdoc />
@@ -210,6 +245,7 @@ public override int GetHashCode()
             hash.Add(Name, StringComparer.Ordinal);
             hash.Add(ParameterInfo);
             hash.Add(PropertyInfo);
+            hash.Add(ConstructorInfo);
             return hash.ToHashCode();
         }
     }

src/Mvc/Mvc.Abstractions/src/ModelBinding/Metadata/ModelMetadataKind.cs

@@ -22,5 +22,10 @@ public enum ModelMetadataKind
         /// Used for <see cref="ModelMetadata"/> for a parameter.
         /// </summary>
         Parameter,
+
+        /// <summary>
+        /// <see cref="ModelMetadata"/> for a constructor.
+        /// </summary>
+        Constructor,
     }
-}
+}

src/Mvc/Mvc.Abstractions/src/ModelBinding/ModelMetadata.cs

@@ -4,8 +4,10 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using System.Collections.ObjectModel;
 using System.ComponentModel;
 using System.Diagnostics;
+using System.Linq;
 using System.Reflection;
 using Microsoft.AspNetCore.Mvc.ModelBinding.Metadata;
 using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
@@ -24,7 +26,11 @@ public abstract class ModelMetadata : IEquatable<ModelMetadata?>, IModelMetadata
         /// </summary>
         public static readonly int DefaultOrder = 10000;
 
+        private static readonly IReadOnlyDictionary<ModelMetadata, ModelMetadata> EmptyParameterMapping = new Dictionary<ModelMetadata, ModelMetadata>(0);
+
         private int? _hashCode;
+        private IReadOnlyList<ModelMetadata>? _boundProperties;
+        private IReadOnlyDictionary<ModelMetadata, ModelMetadata>? _parameterMapping;
 
         /// <summary>
         /// Creates a new <see cref="ModelMetadata"/>.
@@ -83,7 +89,7 @@ public virtual ModelMetadata ContainerMetadata
         /// <summary>
         /// Gets the key for the current instance.
         /// </summary>
-        protected ModelMetadataIdentity Identity { get; }
+        protected internal ModelMetadataIdentity Identity { get; }
 
         /// <summary>
         /// Gets a collection of additional information about the model.
@@ -95,6 +101,94 @@ public virtual ModelMetadata ContainerMetadata
         /// </summary>
         public abstract ModelPropertyCollection Properties { get; }
 
+        internal IReadOnlyList<ModelMetadata> BoundProperties
+        {
+            get
+            {
+                // An item may appear as both a constructor parameter and a property. For instance, in record types,
+                // each constructor parameter is also a settable property and will have the same name, possibly with a difference in case.
+                // Executing model binding on these parameters twice may have detrimental effects, such as duplicate validation entries,
+                // or failures if a model expects to be bound exactly ones.
+                // Consequently when a bound constructor is present, we only bind and validate the subset of properties whose names
+                // haven't appeared as parameters.
+                if (BoundConstructor is null)
+                {
+                    return Properties;
+                }
+
+                if (_boundProperties is null)
+                {
+                    var boundParameters = BoundConstructor.Parameters;
+                    var boundProperties = new List<ModelMetadata>();
+
+                    foreach (var metadata in Properties)
+                    {
+                        if (!boundParameters.Any(p =>
+                            string.Equals(p.ParameterName, metadata.PropertyName, StringComparison.OrdinalIgnoreCase)
+                            && p.ModelType == metadata.ModelType))
+                        {
+                            boundProperties.Add(metadata);
+                        }
+                    }
+
+                    _boundProperties = boundProperties;
+                }
+
+                return _boundProperties;
+            }
+        }
+
+        internal IReadOnlyDictionary<ModelMetadata, ModelMetadata> ParameterMapping
+        {
+            get
+            {
+                if (_parameterMapping != null)
+                {
+                    return _parameterMapping;
+                }
+
+                if (BoundConstructor is null)
+                {
+                    _parameterMapping = EmptyParameterMapping;
+                    return _parameterMapping;
+                }
+
+                var boundParameters = BoundConstructor.Parameters;
+                var parameterMapping = new Dictionary<ModelMetadata, ModelMetadata>();
+
+                foreach (var parameter in boundParameters)
+                {
+                    var property = Properties.FirstOrDefault(p =>
+                        string.Equals(p.Name, parameter.ParameterName, StringComparison.OrdinalIgnoreCase) &&
+                        p.ModelType == parameter.ModelType);
+
+                    if (property != null)
+                    {
+                        parameterMapping[parameter] = property;
+                    }
+                }
+
+                _parameterMapping = parameterMapping;
+                return _parameterMapping;
+            }
+        }
+
+        /// <summary>
+        /// Gets <see cref="ModelMetadata"/> instance for a constructor that is used during binding and validation.
+        /// <para>
+        /// A constructor is used during model binding and validation if it is the only constructor on the type,
+        /// is a parameterless constructor on a type with multiple constructors, or is a constructor with the
+        /// <c>ModelBindingConstructorAttribute</c>.
+        /// </para>
+        /// </summary>
+        public virtual ModelMetadata? BoundConstructor { get; }
+
+        /// <summary>
+        /// Gets the collection of <see cref="ModelMetadata"/> instances for a constructor's parameters.
+        /// This is only available when <see cref="MetadataKind"/> is <see cref="ModelMetadataKind.Constructor"/>.
+        /// </summary>
+        public abstract IReadOnlyList<ModelMetadata> Parameters { get; }
+
         /// <summary>
         /// Gets the name of a model if specified explicitly using <see cref="IModelNameProvider"/>.
         /// </summary>
@@ -401,6 +495,11 @@ public virtual ModelMetadata ContainerMetadata
         /// </summary>
         public abstract Action<object, object> PropertySetter { get; }
 
+        /// <summary>
+        /// Gets a delegate that invokes the constructor.
+        /// </summary>
+        public abstract Func<object[], object> ConstructorInvoker { get; }
+
         /// <summary>
         /// Gets a display name for the model.
         /// </summary>
@@ -500,6 +599,8 @@ private string DebuggerToString()
                     return $"ModelMetadata (Property: '{ContainerType!.Name}.{PropertyName}' Type: '{ModelType.Name}')";
                 case ModelMetadataKind.Type:
                     return $"ModelMetadata (Type: '{ModelType.Name}')";
+                case ModelMetadataKind.Constructor:
+                    return $"ModelMetadata (Constructor: '{ModelType.Name}')";
                 default:
                     return $"Unsupported MetadataKind '{MetadataKind}'.";
             }

src/Mvc/Mvc.Abstractions/src/ModelBinding/ModelMetadataProvider.cs

@@ -54,5 +54,16 @@ public virtual ModelMetadata GetMetadataForProperty(PropertyInfo propertyInfo, T
         {
             throw new NotSupportedException();
         }
+
+        /// <summary>
+        /// Supplies metadata describing a property.
+        /// </summary>
+        /// <param name="constructor">The <see cref="ConstructorInfo"/>.</param>
+        /// <param name="modelType">The type declaring the constructor.</param>
+        /// <returns>A <see cref="ModelMetadata"/> instance describing the <paramref name="constructor"/>.</returns>
+        public virtual ModelMetadata GetMetadataForConstructor(ConstructorInfo constructor, Type modelType)
+        {
+            throw new NotSupportedException();
+        }
     }
 }

src/Mvc/Mvc.Abstractions/src/ModelBinding/ModelStateDictionary.cs

@@ -9,6 +9,7 @@
 using System.Runtime.CompilerServices;
 using Microsoft.AspNetCore.Mvc.Abstractions;
 using Microsoft.AspNetCore.Mvc.Formatters;
+using Microsoft.AspNetCore.Mvc.ModelBinding.Metadata;
 using Microsoft.Extensions.Primitives;
 
 namespace Microsoft.AspNetCore.Mvc.ModelBinding
@@ -298,7 +299,9 @@ public bool TryAddModelError(string key, Exception exception, ModelMetadata meta
                 // "The value '' is not valid." (when no value was provided, not even an empty string) and
                 // "The supplied value is invalid for Int32." (when error is for an element or parameter).
                 var messageProvider = metadata.ModelBindingMessageProvider;
-                var name = metadata.DisplayName ?? metadata.PropertyName;
+
+                var name = metadata.DisplayName ?? 
+                    ((metadata.MetadataKind == ModelMetadataKind.Parameter) ? metadata.ParameterName : metadata.PropertyName);
                 string errorMessage;
                 if (entry == null && name == null)
                 {

src/Mvc/Mvc.Abstractions/test/ModelBinding/BindingInfoTest.cs

@@ -83,7 +83,7 @@ public void GetBindingInfo_WithAttributesAndModelMetadata_UsesValuesFromBindingI
             // Arrange
             var attributes = new object[]
             {
-                new ModelBinderAttribute { BinderType = typeof(ComplexTypeModelBinder), Name = "Test" },
+                new ModelBinderAttribute { BinderType = typeof(ComplexObjectModelBinder), Name = "Test" },
             };
             var modelType = typeof(Guid);
             var provider = new TestModelMetadataProvider();
@@ -100,7 +100,7 @@ public void GetBindingInfo_WithAttributesAndModelMetadata_UsesValuesFromBindingI
 
             // Assert
             Assert.NotNull(bindingInfo);
-            Assert.Same(typeof(ComplexTypeModelBinder), bindingInfo.BinderType);
+            Assert.Same(typeof(ComplexObjectModelBinder), bindingInfo.BinderType);
             Assert.Same("Test", bindingInfo.BinderModelName);
         }
 
@@ -110,7 +110,7 @@ public void GetBindingInfo_WithAttributesAndModelMetadata_UsesBinderNameFromMode
             // Arrange
             var attributes = new object[]
             {
-                new ModelBinderAttribute(typeof(ComplexTypeModelBinder)),
+                new ModelBinderAttribute(typeof(ComplexObjectModelBinder)),
                 new ControllerAttribute(),
                 new BindNeverAttribute(),
             };
@@ -129,7 +129,7 @@ public void GetBindingInfo_WithAttributesAndModelMetadata_UsesBinderNameFromMode
 
             // Assert
             Assert.NotNull(bindingInfo);
-            Assert.Same(typeof(ComplexTypeModelBinder), bindingInfo.BinderType);
+            Assert.Same(typeof(ComplexObjectModelBinder), bindingInfo.BinderType);
             Assert.Same("Different", bindingInfo.BinderModelName);
             Assert.Same(BindingSource.Custom, bindingInfo.BindingSource);
         }
@@ -143,7 +143,7 @@ public void GetBindingInfo_WithAttributesAndModelMetadata_UsesModelBinderFromMod
             var provider = new TestModelMetadataProvider();
             provider.ForType(modelType).BindingDetails(metadata =>
             {
-                metadata.BinderType = typeof(ComplexTypeModelBinder);
+                metadata.BinderType = typeof(ComplexObjectModelBinder);
             });
             var modelMetadata = provider.GetMetadataForType(modelType);
 
@@ -152,7 +152,7 @@ public void GetBindingInfo_WithAttributesAndModelMetadata_UsesModelBinderFromMod
 
             // Assert
             Assert.NotNull(bindingInfo);
-            Assert.Same(typeof(ComplexTypeModelBinder), bindingInfo.BinderType);
+            Assert.Same(typeof(ComplexObjectModelBinder), bindingInfo.BinderType);
         }
 
         [Fact]
@@ -187,7 +187,7 @@ public void GetBindingInfo_WithAttributesAndModelMetadata_UsesPropertyPredicateP
             // Arrange
             var attributes = new object[]
             {
-                new ModelBinderAttribute(typeof(ComplexTypeModelBinder)),
+                new ModelBinderAttribute(typeof(ComplexObjectModelBinder)),
                 new ControllerAttribute(),
                 new BindNeverAttribute(),
             };