CompareAttribute.cs

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using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Globalization;
using System.Reflection;
 
namespace System.ComponentModel.DataAnnotations;
 
[AttributeUsage(AttributeTargets.Property, AllowMultiple = false)]
public class CompareAttribute : ValidationAttribute
{
    public string OtherProperty { get; }
 
    public string? OtherPropertyDisplayName { get; internal set; }
 
    public override bool RequiresValidationContext => true;
 
    [RequiresUnreferencedCode("The property referenced by 'otherProperty' may be trimmed. Ensure it is preserved.")]
    public CompareAttribute(string otherProperty)
        : base(System.SR.CompareAttribute_MustMatch)
    {
        OtherProperty = otherProperty ?? throw new ArgumentNullException("otherProperty");
    }
 
    public override string FormatErrorMessage(string name)
    {
        return string.Format(CultureInfo.CurrentCulture, base.ErrorMessageString, name, OtherPropertyDisplayName ?? OtherProperty);
    }
 
    [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2072:UnrecognizedReflectionPattern", Justification = "The ctor is marked with RequiresUnreferencedCode informing the caller to preserve the other property.")]
    protected override ValidationResult? IsValid(object? value, ValidationContext validationContext)
    {
        PropertyInfo runtimeProperty = validationContext.ObjectType.GetRuntimeProperty(OtherProperty);
        if (runtimeProperty == null)
        {
            return new ValidationResult(System.SR.Format(System.SR.CompareAttribute_UnknownProperty, OtherProperty));
        }
        if (runtimeProperty.GetIndexParameters().Length != 0)
        {
            throw new ArgumentException(System.SR.Format(System.SR.Common_PropertyNotFound, validationContext.ObjectType.FullName, OtherProperty));
        }
        object value2 = runtimeProperty.GetValue(validationContext.ObjectInstance, null);
        if (!object.Equals(value, value2))
        {
            if (OtherPropertyDisplayName == null)
            {
                OtherPropertyDisplayName = GetDisplayNameForProperty(runtimeProperty);
            }
            string[] memberNames = ((validationContext.MemberName == null) ? null : new string[1] { validationContext.MemberName });
            return new ValidationResult(FormatErrorMessage(validationContext.DisplayName), memberNames);
        }
        return null;
    }
 
    private string GetDisplayNameForProperty(PropertyInfo property)
    {
        IEnumerable<Attribute> customAttributes = CustomAttributeExtensions.GetCustomAttributes(property, inherit: true);
        foreach (Attribute item in customAttributes)
        {
            if (item is DisplayAttribute displayAttribute)
            {
                return displayAttribute.GetName();
            }
        }
        return OtherProperty;
    }
}