Get the backing field of an auto-property and vice versa (this only works for auto-props generated by C# compiler, and is not as good as Mono.Reflection.GetBackingField)

AutoPropertyExtensions.cs

using System;
using System.Reflection;
using System.Runtime.CompilerServices;
using System.Text.RegularExpressions;

public static class AutoPropertyExtensions {
	const String Prefix = "<";
	const String Suffix = ">k__BackingField";

	private static String GetBackingFieldName(String propertyName) => $"{Prefix}{propertyName}{Suffix}";

	private static String GetAutoPropertyName(String fieldName) {
		var match = Regex.Match(fieldName, $"{Prefix}(.+?){Suffix}");
		return match.Success ? match.Groups[1].Value : null;
	}

	public static Boolean IsAnAutoProperty(this PropertyInfo propertyInfo) => propertyInfo.GetBackingField() != null;

	public static Boolean IsBackingFieldOfAnAutoProperty(this FieldInfo propertyInfo) => propertyInfo.GetAutoProperty() != null;

	public static FieldInfo GetBackingField(this PropertyInfo propertyInfo) {
		if (propertyInfo == null)
			throw new ArgumentNullException(nameof(propertyInfo));
		if (!propertyInfo.CanRead || !propertyInfo.GetGetMethod(nonPublic: true).IsDefined(typeof(CompilerGeneratedAttribute), inherit: true))
			return null;
		var backingFieldName = GetBackingFieldName(propertyInfo.Name);
		var backingField = propertyInfo.DeclaringType?.GetField(backingFieldName, BindingFlags.Instance | BindingFlags.NonPublic);
		if (backingField == null)
			return null;
		if (!backingField.IsDefined(typeof(CompilerGeneratedAttribute), inherit: true))
			return null;
		return backingField;
	}

	public static PropertyInfo GetAutoProperty(this FieldInfo fieldInfo) {
		if (fieldInfo == null)
			throw new ArgumentNullException(nameof(fieldInfo));
		if (!fieldInfo.IsDefined(typeof(CompilerGeneratedAttribute), inherit: true))
			return null;
		var autoPropertyName = GetAutoPropertyName(fieldInfo.Name);
		if (autoPropertyName == null)
			return null;
		var autoProperty = fieldInfo.DeclaringType?.GetProperty(autoPropertyName);
		if (autoProperty == null)
			return null;
		if (!autoProperty.CanRead || !autoProperty.GetGetMethod(nonPublic: true).IsDefined(typeof(CompilerGeneratedAttribute), inherit: true))
			return null;
		return autoProperty;
	}
}