AbstractValidator.cs

#region License
// Copyright (c) .NET Foundation and contributors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// The latest version of this file can be found at https://github.com/FluentValidation/FluentValidation
#endregion

// ReSharper disable MemberCanBePrivate.Global
namespace FluentValidation;

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Threading;
using System.Threading.Tasks;
using Internal;
using Results;

/// <summary>
/// Base class for object validators.
/// </summary>
/// <typeparam name="T">The type of the object being validated</typeparam>
public abstract class AbstractValidator<T> : IValidator<T>, IEnumerable<IValidationRule> {
	internal TrackingCollection<IValidationRuleInternal<T>> Rules { get; } = new();
	private Func<CascadeMode> _classLevelCascadeMode = () => ValidatorOptions.Global.DefaultClassLevelCascadeMode;
	private Func<CascadeMode> _ruleLevelCascadeMode = () => ValidatorOptions.Global.DefaultRuleLevelCascadeMode;

#pragma warning disable 618
	/// <summary>
	/// <para>
	/// Gets a single <see cref="CascadeMode"/> mode value representing the default values of
	/// <see cref="AbstractValidator{T}.ClassLevelCascadeMode"/>
	/// and <see cref="AbstractValidator{T}.RuleLevelCascadeMode"/>., based on the same logic as used when setting
	/// this property as described below.
	/// </para>
	/// <para>
	/// Sets the values of <see cref="AbstractValidator{T}.ClassLevelCascadeMode"/>
	/// and <see cref="AbstractValidator{T}.RuleLevelCascadeMode"/>.
	/// </para>
	/// <para>
	/// If set to <see cref="FluentValidation.CascadeMode.Continue"/> or <see cref="FluentValidation.CascadeMode.Stop"/>, then both properties are set
	/// to that value.
	/// </para>
	/// <para>
	/// If set to the deprecated <see cref="FluentValidation.CascadeMode.StopOnFirstFailure"/>,
	/// then <see cref="AbstractValidator{T}.ClassLevelCascadeMode"/>
	/// is set to <see cref="FluentValidation.CascadeMode.Continue"/>, and <see cref="AbstractValidator{T}.RuleLevelCascadeMode"/>
	/// is set to <see cref="FluentValidation.CascadeMode.Stop"/>.
	/// This results in the same behaviour as before this property was deprecated.
	/// </para>
	/// </summary>
	[Obsolete($"Use {nameof(ClassLevelCascadeMode)} and/or {nameof(RuleLevelCascadeMode)} instead. " +
	          "CascadeMode will be removed in a future release. " +
	          "For more details, see https://docs.fluentvalidation.net/en/latest/cascade.html")]
	public CascadeMode CascadeMode {
		get {
			if (ClassLevelCascadeMode == RuleLevelCascadeMode) {
				return ClassLevelCascadeMode;
			}
			else if (ClassLevelCascadeMode == CascadeMode.Continue && RuleLevelCascadeMode == CascadeMode.Stop) {
				return CascadeMode.StopOnFirstFailure;
			}
			else {
				throw new Exception(
					$"There is no conversion to a single {nameof(CascadeMode)} value from the current combination of " +
					$"{nameof(ClassLevelCascadeMode)} and {nameof(RuleLevelCascadeMode)}. " +
					$"Please use these properties instead of the deprecated {nameof(CascadeMode)} going forward.");
			}
		}
		set {
			ClassLevelCascadeMode = value == CascadeMode.StopOnFirstFailure
				? CascadeMode.Continue
				: value;

			RuleLevelCascadeMode = value == CascadeMode.StopOnFirstFailure
				? CascadeMode.Stop
				: value;
		}
	}

	/// <summary>
	/// <para>
	/// Sets the cascade behaviour <i>in between</i> rules in this validator.
	/// This overrides the default value set in <see cref="ValidatorConfiguration.DefaultClassLevelCascadeMode"/>.
	/// </para>
	/// <para>
	/// If set to <see cref="FluentValidation.CascadeMode.Continue"/> then all rules in the class will execute regardless of failures.
	/// </para>
	/// <para>
	/// If set to <see cref="FluentValidation.CascadeMode.Stop"/> then execution of the validator will stop after any rule fails.
	/// </para>
	/// <para>
	/// Note that cascade behaviour <i>within</i> individual rules is controlled by
	/// <see cref="AbstractValidator{T}.RuleLevelCascadeMode"/>.
	/// </para>
	/// <para>
	/// This cannot be set to the deprecated <see cref="FluentValidation.CascadeMode.StopOnFirstFailure"/>.
	/// <see cref="FluentValidation.CascadeMode.StopOnFirstFailure"/>. Attempting to do so it will actually
	/// result in <see cref="FluentValidation.CascadeMode.Stop"/> being used.
	/// </para>
	/// </summary>
	public CascadeMode ClassLevelCascadeMode {
		get => _classLevelCascadeMode();
		set => _classLevelCascadeMode = value == CascadeMode.StopOnFirstFailure
			? () => CascadeMode.Stop
			: () => value;
	}

	/// <summary>
	/// <para>
	/// Sets the default cascade behaviour <i>within</i> each rule in this validator.
	/// </para>
	/// <para>
	/// This overrides the default value set in <see cref="ValidatorConfiguration.DefaultRuleLevelCascadeMode"/>.
	/// </para>
	/// <para>
	/// It can be further overridden for specific rules by calling
	/// <see cref="DefaultValidatorOptions.Cascade{T, TProperty}(IRuleBuilderInitial{T, TProperty}, FluentValidation.CascadeMode)"/>.
	/// <seealso cref="RuleBase{T, TProperty, TValue}.CascadeMode"/>.
	/// </para>
	/// <para>
	/// Note that cascade behaviour <i>between</i> rules is controlled by <see cref="AbstractValidator{T}.ClassLevelCascadeMode"/>.
	/// </para>
	/// <para>
	/// This cannot be set to the deprecated <see cref="FluentValidation.CascadeMode.StopOnFirstFailure"/>.
	/// <see cref="FluentValidation.CascadeMode.StopOnFirstFailure"/>. Attempting to do so it will actually
	/// result in <see cref="FluentValidation.CascadeMode.Stop"/> being used.
	/// </para>
	/// </summary>
	public CascadeMode RuleLevelCascadeMode {
		get => _ruleLevelCascadeMode();
		set => _ruleLevelCascadeMode = value == CascadeMode.StopOnFirstFailure
			? () => CascadeMode.Stop
			: () => value;
	}

#pragma warning restore 618
	ValidationResult IValidator.Validate(IValidationContext context) {
		context.Guard("Cannot pass null to Validate", nameof(context));
		return Validate(ValidationContext<T>.GetFromNonGenericContext(context));
	}

	Task<ValidationResult> IValidator.ValidateAsync(IValidationContext context, CancellationToken cancellation) {
		context.Guard("Cannot pass null to Validate", nameof(context));
		return ValidateAsync(ValidationContext<T>.GetFromNonGenericContext(context), cancellation);
	}

	/// <summary>
	/// Validates the specified instance
	/// </summary>
	/// <param name="instance">The object to validate</param>
	/// <returns>A ValidationResult object containing any validation failures</returns>
	public ValidationResult Validate(T instance)
		=> Validate(new ValidationContext<T>(instance, null, ValidatorOptions.Global.ValidatorSelectors.DefaultValidatorSelectorFactory()));

	/// <summary>
	/// Validates the specified instance asynchronously
	/// </summary>
	/// <param name="instance">The object to validate</param>
	/// <param name="cancellation">Cancellation token</param>
	/// <returns>A ValidationResult object containing any validation failures</returns>
	public Task<ValidationResult> ValidateAsync(T instance, CancellationToken cancellation = new())
		=> ValidateAsync(new ValidationContext<T>(instance, null, ValidatorOptions.Global.ValidatorSelectors.DefaultValidatorSelectorFactory()), cancellation);

	/// <summary>
	/// Validates the specified instance.
	/// </summary>
	/// <param name="context">Validation Context</param>
	/// <returns>A ValidationResult object containing any validation failures.</returns>
	public virtual ValidationResult Validate(ValidationContext<T> context) {
		if (context == null) throw new ArgumentNullException(nameof(context));

		// Note: Sync-over-async is OK in this scenario.
		// The use of the `useAsync` parameter ensures that no async code is
		// actually run, and we're using ValueTask
		// which is optimised for synchronous execution of tasks.
		// Unlike 'real' sync-over-async, we can never run into deadlocks as we're not actually invoking anything asynchronously.
		// See RuleComponent.ValidateAsync for the lowest level.
		// This technique is used by Microsoft within the .net runtime to avoid duplicate code paths for sync/async.
		// See https://www.thereformedprogrammer.net/using-valuetask-to-create-methods-that-can-work-as-sync-or-async/
		try {
			ValueTask<ValidationResult> completedValueTask
				= ValidateInternalAsync(context, useAsync: false, default);

			// Sync tasks should always be completed.
			System.Diagnostics.Debug.Assert(completedValueTask.IsCompleted);

			// GetResult() will also bubble up any exceptions correctly.
			return completedValueTask.GetAwaiter().GetResult();
		}
		catch (AsyncValidatorInvokedSynchronouslyException) {
			// If we attempted to execute an async validator, re-create the exception with more useful info.
			bool wasInvokedByMvc = context.RootContextData.ContainsKey("InvokedByMvc");
			throw new AsyncValidatorInvokedSynchronouslyException(GetType(), wasInvokedByMvc);
		}
	}

	/// <summary>
	/// Validates the specified instance asynchronously.
	/// </summary>
	/// <param name="context">Validation Context</param>
	/// <param name="cancellation">Cancellation token</param>
	/// <returns>A ValidationResult object containing any validation failures.</returns>
	public virtual async Task<ValidationResult> ValidateAsync(ValidationContext<T> context, CancellationToken cancellation = new CancellationToken()) {
		if (context == null) throw new ArgumentNullException(nameof(context));
		context.IsAsync = true;
		return await ValidateInternalAsync(context, useAsync: true, cancellation);
	}

	private async ValueTask<ValidationResult> ValidateInternalAsync(ValidationContext<T> context, bool useAsync, CancellationToken cancellation) {
		var result = new ValidationResult(context.Failures);
		bool shouldContinue = PreValidate(context, result);

		if (!shouldContinue) {
			if (!result.IsValid && context.ThrowOnFailures) {
				RaiseValidationException(context, result);
			}

			return result;
		}

#pragma warning disable CS0618
		EnsureInstanceNotNull(context.InstanceToValidate);
#pragma warning restore CS0618

		int count = Rules.Count;

		// Performance: Use for loop rather than foreach to reduce allocations.
		for (int i = 0; i < count; i++) {
			cancellation.ThrowIfCancellationRequested();
			await Rules[i].ValidateAsync(context, useAsync, cancellation);

			if (ClassLevelCascadeMode == CascadeMode.Stop && result.Errors.Count > 0) {
				// Bail out if we're "failing-fast".
				// Check for > 0 rather than == 1 because a rule chain may have overridden the Stop behaviour to Continue
				// meaning that although the first rule failed, it actually generated 2 failures if there were 2 validators
				// in the chain.
				break;
			}
		}

		SetExecutedRuleSets(result, context);

		if (!result.IsValid && context.ThrowOnFailures) {
			RaiseValidationException(context, result);
		}

		return result;
	}

	private void SetExecutedRuleSets(ValidationResult result, ValidationContext<T> context) {
		if (context.RootContextData.TryGetValue("_FV_RuleSetsExecuted", out var obj) && obj is HashSet<string> set) {
			result.RuleSetsExecuted = set.ToArray();
		}
		else {
			result.RuleSetsExecuted = RulesetValidatorSelector.DefaultRuleSetNameInArray;
		}
	}

	/// <summary>
	/// Creates a <see cref="IValidatorDescriptor" /> that can be used to obtain metadata about the current validator.
	/// </summary>
	public virtual IValidatorDescriptor CreateDescriptor() => new ValidatorDescriptor<T>(Rules);

	bool IValidator.CanValidateInstancesOfType(Type type) {
		if (type == null) throw new ArgumentNullException(nameof(type));
		return typeof(T).IsAssignableFrom(type);
	}

	/// <summary>
	/// Defines a validation rule for a specific property.
	/// </summary>
	/// <example>
	/// RuleFor(x => x.Surname)...
	/// </example>
	/// <typeparam name="TProperty">The type of property being validated</typeparam>
	/// <param name="expression">The expression representing the property to validate</param>
	/// <returns>an IRuleBuilder instance on which validators can be defined</returns>
	public IRuleBuilderInitial<T, TProperty> RuleFor<TProperty>(Expression<Func<T, TProperty>> expression) {
		expression.Guard("Cannot pass null to RuleFor", nameof(expression));
		var rule = PropertyRule<T, TProperty>.Create(expression, () => RuleLevelCascadeMode);
		Rules.Add(rule);
		OnRuleAdded(rule);
		return new RuleBuilder<T, TProperty>(rule, this);
	}

	/// <summary>
	/// Defines a validation rule for a specify property and transform it to a different type.
	/// </summary>
	/// <example>
	/// Transform(x => x.OrderNumber, to: orderNumber => orderNumber.ToString())...
	/// </example>
	/// <typeparam name="TProperty">The type of property being validated</typeparam>
	/// <typeparam name="TTransformed">The type after the transformer has been applied</typeparam>
	/// <param name="from">The expression representing the property to transform</param>
	/// <param name="to">Function to transform the property value into a different type</param>
	/// <returns>an IRuleBuilder instance on which validators can be defined</returns>
	[Obsolete("The Transform method is deprecated and will be removed in FluentValidation 12. We recommend using a computed property on your model instead. For details see https://github.com/FluentValidation/FluentValidation/issues/2072")]
	public IRuleBuilderInitial<T, TTransformed> Transform<TProperty, TTransformed>(Expression<Func<T, TProperty>> from, Func<TProperty, TTransformed> to) {
		from.Guard("Cannot pass null to Transform", nameof(from));
		var rule = PropertyRule<T, TTransformed>.Create(from, to, () => RuleLevelCascadeMode);
		Rules.Add(rule);
		OnRuleAdded(rule);
		return new RuleBuilder<T, TTransformed>(rule, this);
	}

	/// <summary>
	/// Defines a validation rule for a specify property and transform it to a different type.
	/// </summary>
	/// <example>
	/// Transform(x => x.OrderNumber, to: orderNumber => orderNumber.ToString())...
	/// </example>
	/// <typeparam name="TProperty">The type of property being validated</typeparam>
	/// <typeparam name="TTransformed">The type after the transformer has been applied</typeparam>
	/// <param name="from">The expression representing the property to transform</param>
	/// <param name="to">Function to transform the property value into a different type</param>
	/// <returns>an IRuleBuilder instance on which validators can be defined</returns>
	[Obsolete("The Transform method is deprecated and will be removed in FluentValidation 12. We recommend using a computed property on your model instead. For details see https://github.com/FluentValidation/FluentValidation/issues/2072")]
	public IRuleBuilderInitial<T, TTransformed> Transform<TProperty, TTransformed>(Expression<Func<T, TProperty>> from, Func<T, TProperty, TTransformed> to) {
		from.Guard("Cannot pass null to Transform", nameof(from));
		var rule = PropertyRule<T, TTransformed>.Create(from, to, () => RuleLevelCascadeMode);
		Rules.Add(rule);
		OnRuleAdded(rule);
		return new RuleBuilder<T, TTransformed>(rule, this);
	}


	/// <summary>
	/// Invokes a rule for each item in the collection.
	/// </summary>
	/// <typeparam name="TElement">Type of property</typeparam>
	/// <param name="expression">Expression representing the collection to validate</param>
	/// <returns>An IRuleBuilder instance on which validators can be defined</returns>
	public IRuleBuilderInitialCollection<T, TElement> RuleForEach<TElement>(Expression<Func<T, IEnumerable<TElement>>> expression) {
		expression.Guard("Cannot pass null to RuleForEach", nameof(expression));
		var rule = CollectionPropertyRule<T, TElement>.Create(expression, () => RuleLevelCascadeMode);
		Rules.Add(rule);
		OnRuleAdded(rule);
		return new RuleBuilder<T, TElement>(rule, this);
	}

	/// <summary>
	/// Invokes a rule for each item in the collection, transforming the element from one type to another.
	/// </summary>
	/// <typeparam name="TElement">Type of property</typeparam>
	/// <typeparam name="TTransformed">The type after the transformer has been applied</typeparam>
	/// <param name="expression">Expression representing the collection to validate</param>
	/// <param name="to">Function to transform the collection element into a different type</param>
	/// <returns>An IRuleBuilder instance on which validators can be defined</returns>
	[Obsolete("The TransformForEach method is deprecated and will be removed in FluentValidation 12. We recommend using a computed property on your model instead. For details see https://github.com/FluentValidation/FluentValidation/issues/2072")]
	public IRuleBuilderInitialCollection<T, TTransformed> TransformForEach<TElement, TTransformed>(Expression<Func<T, IEnumerable<TElement>>> expression, Func<TElement, TTransformed> to) {
		expression.Guard("Cannot pass null to RuleForEach", nameof(expression));
		var rule = CollectionPropertyRule<T, TTransformed>.CreateTransformed(expression, to, () => RuleLevelCascadeMode);
		Rules.Add(rule);
		OnRuleAdded(rule);
		return new RuleBuilder<T, TTransformed>(rule, this);
	}

	/// <summary>
	/// Invokes a rule for each item in the collection, transforming the element from one type to another.
	/// </summary>
	/// <typeparam name="TElement">Type of property</typeparam>
	/// <typeparam name="TTransformed">The type after the transformer has been applied</typeparam>
	/// <param name="expression">Expression representing the collection to validate</param>
	/// <param name="to">Function to transform the collection element into a different type</param>
	/// <returns>An IRuleBuilder instance on which validators can be defined</returns>
	[Obsolete("The TransformForEach method is deprecated and will be removed in FluentValidation 12. We recommend using a computed property on your model instead. For details see https://github.com/FluentValidation/FluentValidation/issues/2072")]
	public IRuleBuilderInitialCollection<T, TTransformed> TransformForEach<TElement, TTransformed>(Expression<Func<T, IEnumerable<TElement>>> expression, Func<T, TElement, TTransformed> to) {
		expression.Guard("Cannot pass null to RuleForEach", nameof(expression));
		var rule = CollectionPropertyRule<T, TTransformed>.CreateTransformed(expression, to, () => RuleLevelCascadeMode);
		Rules.Add(rule);
		OnRuleAdded(rule);
		return new RuleBuilder<T, TTransformed>(rule, this);
	}

	/// <summary>
	/// Defines a RuleSet that can be used to group together several validators.
	/// </summary>
	/// <param name="ruleSetName">The name of the ruleset.</param>
	/// <param name="action">Action that encapsulates the rules in the ruleset.</param>
	public void RuleSet(string ruleSetName, Action action) {
		ruleSetName.Guard("A name must be specified when calling RuleSet.", nameof(ruleSetName));
		action.Guard("A ruleset definition must be specified when calling RuleSet.", nameof(action));

		var ruleSetNames = ruleSetName.Split(',', ';')
			.Select(x => x.Trim())
			.ToArray();

		using (Rules.OnItemAdded(r => r.RuleSets = ruleSetNames)) {
			action();
		}
	}

	/// <summary>
	/// Defines a condition that applies to several rules
	/// </summary>
	/// <param name="predicate">The condition that should apply to multiple rules</param>
	/// <param name="action">Action that encapsulates the rules.</param>
	/// <returns></returns>
	public IConditionBuilder When(Func<T, bool> predicate, Action action)
		=> When((x, _) => predicate(x), action);

	/// <summary>
	/// Defines a condition that applies to several rules
	/// </summary>
	/// <param name="predicate">The condition that should apply to multiple rules</param>
	/// <param name="action">Action that encapsulates the rules.</param>
	/// <returns></returns>
	public IConditionBuilder When(Func<T, ValidationContext<T>, bool> predicate, Action action)
		=> new ConditionBuilder<T>(Rules).When(predicate, action);

	/// <summary>
	/// Defines an inverse condition that applies to several rules
	/// </summary>
	/// <param name="predicate">The condition that should be applied to multiple rules</param>
	/// <param name="action">Action that encapsulates the rules</param>
	public IConditionBuilder Unless(Func<T, bool> predicate, Action action)
		=> Unless((x, _) => predicate(x), action);

	/// <summary>
	/// Defines an inverse condition that applies to several rules
	/// </summary>
	/// <param name="predicate">The condition that should be applied to multiple rules</param>
	/// <param name="action">Action that encapsulates the rules</param>
	public IConditionBuilder Unless(Func<T, ValidationContext<T>, bool> predicate, Action action)
		=> new ConditionBuilder<T>(Rules).Unless(predicate, action);

	/// <summary>
	/// Defines an asynchronous condition that applies to several rules
	/// </summary>
	/// <param name="predicate">The asynchronous condition that should apply to multiple rules</param>
	/// <param name="action">Action that encapsulates the rules.</param>
	/// <returns></returns>
	public IConditionBuilder WhenAsync(Func<T, CancellationToken, Task<bool>> predicate, Action action)
		=> WhenAsync((x, _, cancel) => predicate(x, cancel), action);

	/// <summary>
	/// Defines an asynchronous condition that applies to several rules
	/// </summary>
	/// <param name="predicate">The asynchronous condition that should apply to multiple rules</param>
	/// <param name="action">Action that encapsulates the rules.</param>
	/// <returns></returns>
	public IConditionBuilder WhenAsync(Func<T, ValidationContext<T>, CancellationToken, Task<bool>> predicate, Action action)
		=> new AsyncConditionBuilder<T>(Rules).WhenAsync(predicate, action);

	/// <summary>
	/// Defines an inverse asynchronous condition that applies to several rules
	/// </summary>
	/// <param name="predicate">The asynchronous condition that should be applied to multiple rules</param>
	/// <param name="action">Action that encapsulates the rules</param>
	public IConditionBuilder UnlessAsync(Func<T, CancellationToken, Task<bool>> predicate, Action action)
		=> UnlessAsync((x, _, cancel) => predicate(x, cancel), action);

	/// <summary>
	/// Defines an inverse asynchronous condition that applies to several rules
	/// </summary>
	/// <param name="predicate">The asynchronous condition that should be applied to multiple rules</param>
	/// <param name="action">Action that encapsulates the rules</param>
	public IConditionBuilder UnlessAsync(Func<T, ValidationContext<T>, CancellationToken, Task<bool>> predicate, Action action)
		=> new AsyncConditionBuilder<T>(Rules).UnlessAsync(predicate, action);

	/// <summary>
	/// Includes the rules from the specified validator
	/// </summary>
	public void Include(IValidator<T> rulesToInclude) {
		rulesToInclude.Guard("Cannot pass null to Include", nameof(rulesToInclude));
		var rule = IncludeRule<T>.Create(rulesToInclude, () => RuleLevelCascadeMode);
		Rules.Add(rule);
		OnRuleAdded(rule);
	}

	/// <summary>
	/// Includes the rules from the specified validator
	/// </summary>
	public void Include<TValidator>(Func<T, TValidator> rulesToInclude) where TValidator : IValidator<T> {
		rulesToInclude.Guard("Cannot pass null to Include", nameof(rulesToInclude));
		var rule = IncludeRule<T>.Create(rulesToInclude, () => RuleLevelCascadeMode);
		Rules.Add(rule);
		OnRuleAdded(rule);
	}

	/// <summary>
	/// Returns an enumerator that iterates through the collection of validation rules.
	/// </summary>
	/// <returns>
	/// A <see cref="T:System.Collections.Generic.IEnumerator`1"/> that can be used to iterate through the collection.
	/// </returns>
	/// <filterpriority>1</filterpriority>
	public IEnumerator<IValidationRule> GetEnumerator() => Rules.GetEnumerator();

	IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();

	/// <summary>
	/// Throws an exception if the instance being validated is null.
	/// </summary>
	/// <param name="instanceToValidate"></param>
	[Obsolete("Overriding the EnsureInstanceNotNull method to prevent FluentValidation for throwing an exception for null root models is no longer supported or recommended. The ability to override this method will be removed in FluentValidation 12. For details, see https://github.com/FluentValidation/FluentValidation/issues/2069")]
	protected virtual void EnsureInstanceNotNull(object instanceToValidate)
		=> instanceToValidate.Guard("Cannot pass null model to Validate.", nameof(instanceToValidate));

	/// <summary>
	/// Determines if validation should occur and provides a means to modify the context and ValidationResult prior to execution.
	/// If this method returns false, then the ValidationResult is immediately returned from Validate/ValidateAsync.
	/// </summary>
	/// <param name="context"></param>
	/// <param name="result"></param>
	/// <returns></returns>
	protected virtual bool PreValidate(ValidationContext<T> context, ValidationResult result) => true;

	/// <summary>
	/// Throws a ValidationException. This method will only be called if the validator has been configured
	/// to throw exceptions if validation fails. The default behaviour is not to throw an exception.
	/// </summary>
	/// <param name="context"></param>
	/// <param name="result"></param>
	/// <exception cref="ValidationException"></exception>
	protected virtual void RaiseValidationException(ValidationContext<T> context, ValidationResult result)
		=> throw new ValidationException(result.Errors);

	/// <summary>
	/// This method is invoked when a rule has been created (via RuleFor/RuleForEach) and has been added to the validator.
	/// You can override this method to provide customizations to all rule instances.
	/// </summary>
	/// <param name="rule"></param>
	protected virtual void OnRuleAdded(IValidationRule<T> rule) { }
}