Deprecate Transform and TransformForEach.

docs/index.rst

@@ -110,7 +110,6 @@ Example
 
   dependentrules
   inheritance
-  transform
   advanced
 
 .. _aspnet-docs:

docs/transform.md

@@ -1,5 +1,10 @@
 # Transforming Values
 
+```eval_rst
+.. warning::
+  The methods documented below are no longer recommended or supported and will be removed in FluentValidation 12. We instead recommend using computed properties on your model if you need to perform a transformation. For details please see `this GitHub issue <https://github.com/FluentValidation/FluentValidation/issues/2072>`_
+```
+
 As of FluentValidation 9.5, you can apply a transformation to a property value prior to validation being performed against it. For example, if you have property of type `string` that actually contains numeric input, you could apply a transformation to convert the string value to a number.
 
 
@@ -23,17 +28,4 @@ int? StringToNullableInt(string value)
 
 This syntax is available in FluentValidation 9.5 and newer.
 
-There is also a `TransformForEach` method available, which performs the transformation against each item in a collection.
-
-
-## Transforming Values (9.0 - 9.4)
-
-Prior to FluentValidation 9.5, you can use the `Transform` method after a call to `RuleFor` to achieve the same result.
-
-```csharp
-RuleFor(x => x.SomeStringProperty)
-    .Transform(value => int.TryParse(value, out int val) ? (int?) val : null)
-    .GreaterThan(10);
-```
-
-This `Transform` method is marked as obsolete as of FluentValidation 9.5 and is removed in FluentValidation 10.0. In newer versions of FluentValidation the transformation should be applied by calling `Transform` as the first method in the chain (see above).
+There is also a `TransformForEach` method available, which performs the transformation against each item in a collection.

src/FluentValidation.Tests/TransformTests.cs

@@ -23,6 +23,8 @@ namespace FluentValidation.Tests;
 using System.Threading.Tasks;
 using Xunit;
 
+#pragma warning disable CS0618
+
 public class TransformTests {
 	[Fact]
 	public void Transforms_property_value() {

src/FluentValidation/AbstractValidator.cs

@@ -298,6 +298,7 @@ ValueTask<ValidationResult> completedValueTask
 	/// <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);
@@ -316,6 +317,7 @@ ValueTask<ValidationResult> completedValueTask
 	/// <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);
@@ -345,6 +347,7 @@ ValueTask<ValidationResult> completedValueTask
 	/// <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);
@@ -360,6 +363,7 @@ ValueTask<ValidationResult> completedValueTask
 	/// <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);