feat: add property path support

src/request.validation.tests/PropertyPathTests.cs

@@ -0,0 +1,76 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+using System.Text.Json;
+
+namespace Geekeey.Request.Validation.Tests;
+
+internal sealed class PropertyPathTests
+{
+	private static readonly JsonSerializerOptions CamelCaseJsonOptions = new()
+	{
+		PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+	};
+
+	[Test]
+	public async Task I_serialize_property_paths_using_the_json_naming_policy()
+	{
+		var problem = new Problem
+		{
+			PropertyPath = "Address.Street",
+			Message = "Street is required.",
+		};
+
+		var json = JsonSerializer.Serialize(problem, CamelCaseJsonOptions);
+
+		await Assert.That(json).IsEqualTo(/*lang=json,strict*/ """{"propertyPath":"address.street","severity":0,"message":"Street is required.","code":null,"attemptedValue":null}""");
+	}
+
+	[Test]
+	public async Task I_serialize_indexed_property_paths_using_the_json_naming_policy()
+	{
+		var problem = new Problem
+		{
+			PropertyPath = "Members[1].Name",
+			Message = "Member name is required.",
+		};
+
+		var json = JsonSerializer.Serialize(problem, CamelCaseJsonOptions);
+
+		await Assert.That(json).IsEqualTo(/*lang=json,strict*/ """{"propertyPath":"members[1].name","severity":0,"message":"Member name is required.","code":null,"attemptedValue":null}""");
+	}
+
+	[Test]
+	public async Task I_can_combine_property_paths_with_the_plus_operator()
+	{
+		var propertyPath = "Address" + (PropertyPath)"Street";
+
+		await Assert.That(propertyPath).IsEqualTo("Address.Street");
+	}
+
+	[Test]
+	public async Task I_can_combine_property_paths_with_the_plus_operator_when_one_side_is_empty()
+	{
+		var leftEmpty = "" + (PropertyPath)"Street";
+		var rightEmpty = (PropertyPath)"Address" + "";
+
+		await Assert.That(leftEmpty).IsEqualTo("Street");
+		await Assert.That(rightEmpty).IsEqualTo("Address");
+	}
+
+	[Test]
+	public async Task I_can_append_a_collection_index_with_the_plus_operator()
+	{
+		var propertyPath = (PropertyPath)"Members" + 1;
+
+		await Assert.That(propertyPath).IsEqualTo("Members[1]");
+	}
+
+	[Test]
+	public async Task I_can_append_a_collection_index_with_the_plus_operator_when_the_property_name_is_empty()
+	{
+		var propertyPath = (PropertyPath)"" + 1;
+
+		await Assert.That(propertyPath).IsEqualTo("[1]");
+	}
+}

src/request.validation.tests/RuleBuilderExtensionsTests.cs

@@ -311,7 +311,7 @@ internal sealed class RuleBuilderExtensionsTests
 			.Throws<ArgumentOutOfRangeException>();
 	}
 
-	private static async Task AssertSingleProblem(Validation validation, string propertyName, string message)
+	private static async Task AssertSingleProblem(Validation validation, string propertyPath, string message)
 	{
 		await Assert.That(validation.Problems).Count().IsEqualTo(1);
 
@@ -319,7 +319,7 @@ internal sealed class RuleBuilderExtensionsTests
 
 		using (Assert.Multiple())
 		{
-			await Assert.That(problem.PropertyName).IsEqualTo(propertyName);
+			await Assert.That(problem.PropertyPath).IsEqualTo(propertyPath);
 			await Assert.That(problem.Message).IsEqualTo(message);
 		}
 	}

src/request.validation.tests/ValidatorTests.cs

@@ -21,7 +21,7 @@ internal sealed class ValidatorTests
 
 		using (Assert.Multiple())
 		{
-			await Assert.That(problem.PropertyName).IsEqualTo(nameof(Person.Name));
+			await Assert.That(problem.PropertyPath).IsEqualTo(nameof(Person.Name));
 			await Assert.That(problem.Message).IsEqualTo("Name is required.");
 			await Assert.That(problem.Code).IsEqualTo("NAME_REQUIRED");
 			await Assert.That(problem.Severity).IsEqualTo(Severity.Warning);
@@ -58,7 +58,7 @@ internal sealed class ValidatorTests
 		});
 
 		await Assert.That(result.Problems).Count().IsEqualTo(1);
-		await Assert.That(result.Problems.Single().PropertyName).IsEqualTo("Address.Street");
+		await Assert.That(result.Problems.Single().PropertyPath).IsEqualTo("Address.Street");
 	}
 
 	[Test]
@@ -87,7 +87,7 @@ internal sealed class ValidatorTests
 		});
 
 		await Assert.That(result.Problems).Count().IsEqualTo(1);
-		await Assert.That(result.Problems.Single().PropertyName).IsEqualTo("Members[1].Name");
+		await Assert.That(result.Problems.Single().PropertyPath).IsEqualTo("Members[1].Name");
 	}
 
 	[Test]
@@ -105,7 +105,7 @@ internal sealed class ValidatorTests
 
 		using (Assert.Multiple())
 		{
-			await Assert.That(problem.PropertyName).IsEqualTo("Address.Street");
+			await Assert.That(problem.PropertyPath).IsEqualTo("Address.Street");
 			await Assert.That(problem.Message).IsEqualTo("Value is required.");
 		}
 	}
@@ -124,7 +124,7 @@ internal sealed class ValidatorTests
 
 		using (Assert.Multiple())
 		{
-			await Assert.That(problem.PropertyName).IsEqualTo(nameof(Person.Name));
+			await Assert.That(problem.PropertyPath).IsEqualTo(nameof(Person.Name));
 			await Assert.That(problem.Message).IsEqualTo("Value is required.");
 		}
 	}
@@ -208,8 +208,8 @@ internal sealed class ValidatorTests
 		});
 
 		await Assert.That(result.Problems).Count().IsEqualTo(2);
-		await Assert.That(result.Problems[0].PropertyName).IsEqualTo("Members[0].Name");
-		await Assert.That(result.Problems[1].PropertyName).IsEqualTo("Members[2].Name");
+		await Assert.That(result.Problems[0].PropertyPath).IsEqualTo("Members[0].Name");
+		await Assert.That(result.Problems[1].PropertyPath).IsEqualTo("Members[2].Name");
 	}
 
 	[Test]
@@ -230,7 +230,7 @@ internal sealed class ValidatorTests
 		var result = validator.Validate(context);
 
 		await Assert.That(result.Problems).Count().IsEqualTo(1);
-		await Assert.That(result.Problems.Single().PropertyName).IsEqualTo("Address.Street");
+		await Assert.That(result.Problems.Single().PropertyPath).IsEqualTo("Address.Street");
 	}
 
 	[Test]

src/request.validation/Problem.cs

@@ -11,7 +11,7 @@ public record Problem
 	/// <summary>
 	/// The name of the property.
 	/// </summary>
-	public required string PropertyName { get; init; }
+	public required PropertyPath PropertyPath { get; init; }
 
 	/// <summary>
 	/// Custom severity level associated with the failure.

src/request.validation/PropertyPath.cs

@@ -0,0 +1,169 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+using System.Text;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace Geekeey.Request.Validation;
+
+/// <summary>
+/// Represents a property path used by validation problems.
+/// </summary>
+[JsonConverter(typeof(PropertyPathJsonConverter))]
+public readonly struct PropertyPath : IEquatable<PropertyPath>
+{
+	/// <summary>
+	/// Creates a new property path.
+	/// </summary>
+	public PropertyPath(string value)
+	{
+		ArgumentNullException.ThrowIfNull(value);
+		Value = value;
+	}
+
+	/// <summary>
+	/// Gets the raw property path.
+	/// </summary>
+	public string Value { get; } = string.Empty;
+
+	/// <inheritdoc />
+	public override string ToString()
+	{
+		return Value;
+	}
+
+	/// <summary>
+	/// Converts a string into a property path.
+	/// </summary>
+	public static implicit operator PropertyPath(string value)
+	{
+		return new PropertyPath(value);
+	}
+
+	/// <summary>
+	/// Converts a property path into its string representation.
+	/// </summary>
+	public static implicit operator string(PropertyPath propertyPath)
+	{
+		return propertyPath.Value;
+	}
+
+	/// <inheritdoc />
+	public bool Equals(PropertyPath other)
+	{
+		return string.Equals(Value, other.Value, StringComparison.Ordinal);
+	}
+
+	/// <inheritdoc />
+	public override bool Equals(object? obj)
+	{
+		return obj is PropertyPath other && Equals(other);
+	}
+
+	/// <inheritdoc />
+	public override int GetHashCode()
+	{
+		return StringComparer.Ordinal.GetHashCode(Value ?? string.Empty);
+	}
+
+	/// <summary>
+	/// Compares two property paths for ordinal equality.
+	/// </summary>
+	public static bool operator ==(PropertyPath left, PropertyPath right)
+	{
+		return left.Equals(right);
+	}
+
+	/// <summary>
+	/// Compares two property paths for ordinal inequality.
+	/// </summary>
+	public static bool operator !=(PropertyPath left, PropertyPath right)
+	{
+		return !left.Equals(right);
+	}
+
+	/// <summary>
+	/// Combines two property paths using the same rules as nested validation paths.
+	/// </summary>
+	public static PropertyPath operator +(PropertyPath prefix, PropertyPath suffix)
+	{
+		if (prefix.Value is not { Length: > 0 })
+		{
+			return suffix;
+		}
+
+		if (suffix.Value is not { Length: > 0 })
+		{
+			return prefix;
+		}
+
+		return $"{prefix}.{suffix}";
+	}
+
+	/// <summary>
+	/// Appends a collection index to a property path.
+	/// </summary>
+	public static PropertyPath operator +(PropertyPath propertyPath, int index)
+	{
+		return propertyPath.Value is { Length: > 0 } ? $"{propertyPath}[{index}]" : $"[{index}]";
+	}
+
+	internal string ToJsonName(JsonNamingPolicy? namingPolicy)
+	{
+		var value = Value ?? string.Empty;
+		if (namingPolicy is null || value.Length is 0)
+		{
+			return value;
+		}
+
+		var builder = new StringBuilder(value.Length);
+		var first = true;
+
+		foreach (var range in value.AsSpan().Split('.'))
+		{
+			if (!first)
+			{
+				builder.Append('.');
+			}
+
+			var segment = value.AsSpan()[range];
+			if (segment.Length is not 0)
+			{
+				if (segment.IndexOf('[') is >= 0 and var x)
+				{
+					builder.Append(namingPolicy.ConvertName(segment[..x].ToString()));
+					builder.Append(segment[x..]);
+				}
+				else
+				{
+					builder.Append(namingPolicy.ConvertName(segment.ToString()));
+				}
+			}
+
+			first = false;
+		}
+
+		return builder.ToString();
+	}
+}
+
+internal sealed class PropertyPathJsonConverter : JsonConverter<PropertyPath>
+{
+	/// <inheritdoc />
+	public override PropertyPath Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+	{
+		if (reader.TokenType is JsonTokenType.String)
+		{
+			return new PropertyPath(reader.GetString()!);
+		}
+
+		throw new JsonException($"Expected {nameof(JsonTokenType.String)} but got {reader.TokenType}.");
+	}
+
+	/// <inheritdoc />
+	public override void Write(Utf8JsonWriter writer, PropertyPath value, JsonSerializerOptions options)
+	{
+		writer.WriteStringValue(value.ToJsonName(options.PropertyNamingPolicy));
+	}
+}

src/request.validation/Rule.cs

@@ -18,14 +18,14 @@ internal abstract record Rule<T, TProperty> : Rule
 {
 	protected Rule(Expression expression)
 	{
-		PropertyName = GetPropertyPath(expression);
+		PropertyPath = GetPropertyPath(expression);
 	}
 
-	public string PropertyName { get; }
+	public PropertyPath PropertyPath { get; }
 
 	public IReadOnlyList<IRuleStep<TProperty>> Steps { get; init; } = [];
 
-	private static string GetPropertyPath(Expression expression)
+	private static PropertyPath GetPropertyPath(Expression expression)
 	{
 		var members = new Stack<string>();
 
@@ -34,18 +34,15 @@ internal abstract record Rule<T, TProperty> : Rule
 		{
 			switch (current)
 			{
-				case LambdaExpression lambdaExpression:
-					current = lambdaExpression.Body;
+				case LambdaExpression expr:
+					current = expr.Body;
 					break;
-				case MemberExpression memberExpression:
-					members.Push(memberExpression.Member.Name);
-					current = memberExpression.Expression;
+				case MemberExpression expr:
+					members.Push(expr.Member.Name);
+					current = expr.Expression;
 					break;
-				case UnaryExpression
-				{
-					NodeType: ExpressionType.Convert or ExpressionType.ConvertChecked
-				} unaryExpression:
-					current = unaryExpression.Operand;
+				case UnaryExpression { NodeType: ExpressionType.Convert or ExpressionType.ConvertChecked } expr:
+					current = expr.Operand;
 					break;
 				case ParameterExpression:
 					current = null;
@@ -55,7 +52,7 @@ internal abstract record Rule<T, TProperty> : Rule
 			}
 		}
 
-		return string.Join(".", members);
+		return string.Join('.', members);
 	}
 
 	public override IEnumerable<Problem> Validate(ValidationContext context)
@@ -95,7 +92,7 @@ internal sealed record PropertyRule<T, TProperty> : Rule<T, TProperty>
 		}
 
 		var value = _accessor(instance);
-		return Steps.SelectMany(step => step.Validate(value, context, PropertyName, Code, Severity));
+		return Steps.SelectMany(step => step.Validate(value, context, PropertyPath, Code, Severity));
 	}
 }
 
@@ -123,11 +120,11 @@ internal sealed record CollectionRule<T, TElement> : Rule<T, TElement>
 		var index = 0;
 		foreach (var element in collection)
 		{
-			var propertyName = string.IsNullOrEmpty(PropertyName) ? $"[{index}]" : $"{PropertyName}[{index}]";
+			var propertyPath = PropertyPath + index;
 
 			foreach (var step in Steps)
 			{
-				foreach (var problem in step.Validate(element, context, propertyName, Code, Severity))
+				foreach (var problem in step.Validate(element, context, propertyPath, Code, Severity))
 				{
 					yield return problem;
 				}

src/request.validation/RuleStep.cs

@@ -5,7 +5,7 @@ namespace Geekeey.Request.Validation;
 
 internal interface IRuleStep<in TValue>
 {
-	IEnumerable<Problem> Validate(TValue value, ValidationContext context, string propertyPath, string? code, Severity severity);
+	IEnumerable<Problem> Validate(TValue value, ValidationContext context, PropertyPath propertyPath, string? code, Severity severity);
 }
 
 internal sealed record PredicateRuleStep<TValue> : IRuleStep<TValue>
@@ -19,7 +19,7 @@ internal sealed record PredicateRuleStep<TValue> : IRuleStep<TValue>
 		_message = message;
 	}
 
-	public IEnumerable<Problem> Validate(TValue value, ValidationContext context, string propertyPath, string? code, Severity severity)
+	public IEnumerable<Problem> Validate(TValue value, ValidationContext context, PropertyPath propertyPath, string? code, Severity severity)
 	{
 		if (_predicate(value))
 		{
@@ -28,7 +28,7 @@ internal sealed record PredicateRuleStep<TValue> : IRuleStep<TValue>
 
 		yield return new Problem
 		{
-			PropertyName = propertyPath,
+			PropertyPath = propertyPath,
 			Message = _message,
 			Code = code,
 			Severity = severity,
@@ -46,7 +46,7 @@ internal sealed record ValidatorRuleStep<TValue> : IRuleStep<TValue>
 		_resolver = resolver;
 	}
 
-	public IEnumerable<Problem> Validate(TValue value, ValidationContext context, string propertyPath, string? code, Severity severity)
+	public IEnumerable<Problem> Validate(TValue value, ValidationContext context, PropertyPath propertyPath, string? code, Severity severity)
 	{
 		if (value is null)
 		{
@@ -58,22 +58,7 @@ internal sealed record ValidatorRuleStep<TValue> : IRuleStep<TValue>
 
 		foreach (var problem in validation.Problems)
 		{
-			yield return problem with { PropertyName = AppendPropertyPath(propertyPath, problem.PropertyName) };
+			yield return problem with { PropertyPath = propertyPath + problem.PropertyPath };
 		}
 	}
-
-	private static string AppendPropertyPath(string prefix, string suffix)
-	{
-		if (string.IsNullOrEmpty(prefix))
-		{
-			return suffix;
-		}
-
-		if (string.IsNullOrEmpty(suffix))
-		{
-			return prefix;
-		}
-
-		return $"{prefix}.{suffix}";
-	}
 }

src/request.validation/package-readme.md

@@ -77,7 +77,7 @@ var validation = validator.Validate(new CreateUserRequest(
 
 foreach (var problem in validation.Problems)
 {
-  Console.WriteLine($"{problem.PropertyName}: {problem.Message}");
+  Console.WriteLine($"{problem.PropertyPath}: {problem.Message}");
 }
 ```