Implement field keyword support for semi-auto properties in C# 14

Co-authored-by: christophwille <344208+christophwille@users.noreply.github.com>

ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs

@@ -565,6 +565,12 @@ namespace ICSharpCode.Decompiler.Tests
 			await RunForLibrary(cscOptions: cscOptions | CompilerOptions.Preview);
 		}
 
+		[Test]
+		public async Task SemiAutoProperties([ValueSource(nameof(roslyn4OrNewerOptions))] CompilerOptions cscOptions)
+		{
+			await RunForLibrary(cscOptions: cscOptions | CompilerOptions.Preview);
+		}
+
 		[Test]
 		public async Task NullPropagation([ValueSource(nameof(roslynOnlyOptions))] CompilerOptions cscOptions)
 		{

ICSharpCode.Decompiler.Tests/TestCases/Pretty/SemiAutoProperties.cs

@@ -0,0 +1,76 @@
+// Copyright (c) AlphaSierraPapa for the SharpDevelop Team
+// 
+// Permission is hereby granted, free of charge, to any person obtaining a copy of this
+// software and associated documentation files (the "Software"), to deal in the Software
+// without restriction, including without limitation the rights to use, copy, modify, merge,
+// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
+// to whom the Software is furnished to do so, subject to the following conditions:
+// 
+// The above copyright notice and this permission notice shall be included in all copies or
+// substantial portions of the Software.
+// 
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
+// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+using System;
+
+namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
+{
+	internal class SemiAutoProperties
+	{
+		// Semi-auto property with validation in setter
+		public int ValidatedProperty {
+			get => field;
+			set {
+				if (value < 0)
+				{
+					throw new ArgumentOutOfRangeException();
+				}
+				field = value;
+			}
+		}
+
+		// Semi-auto property with lazy initialization
+		public string LazyProperty {
+			get {
+				if (field == null)
+				{
+					field = "default";
+				}
+				return field;
+			}
+			set => field = value;
+		}
+
+		// Semi-auto property with notification
+		public int NotifyProperty {
+			get => field;
+			set {
+				if (field != value)
+				{
+					field = value;
+					OnPropertyChanged();
+				}
+			}
+		}
+
+		// Getter-only semi-auto property with initialization
+		public int ReadOnlyWithInit {
+			get {
+				if (field == 0)
+				{
+					field = 42;
+				}
+				return field;
+			}
+		}
+
+		private void OnPropertyChanged()
+		{
+		}
+	}
+}

ICSharpCode.Decompiler/CSharp/Transforms/PatternStatementTransform.cs

@@ -111,7 +111,14 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 				if (result != null)
 					return result;
 			}
-			return base.VisitPropertyDeclaration(propertyDeclaration);
+			// First visit children (accessor bodies) before potentially transforming to semi-auto property
+			var visitedNode = base.VisitPropertyDeclaration(propertyDeclaration);
+			// After visiting children, check if we should transform to semi-auto property
+			if (context.Settings.SemiAutoProperties && context.Settings.AutomaticProperties)
+			{
+				TransformSemiAutoProperty(propertyDeclaration);
+			}
+			return visitedNode;
 		}
 
 		public override AstNode VisitCustomEventDeclaration(CustomEventDeclaration eventDeclaration)
@@ -660,6 +667,50 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			return null;
 		}
 
+		/// <summary>
+		/// Transforms a property that uses the backing field into a semi-auto property
+		/// by removing the backing field declaration. The field keyword replacements
+		/// are already done in ReplaceBackingFieldUsage during child visiting.
+		/// </summary>
+		void TransformSemiAutoProperty(PropertyDeclaration propertyDeclaration)
+		{
+			IProperty property = propertyDeclaration.GetSymbol() as IProperty;
+			if (property == null)
+				return;
+			// Check if any accessor body contains the 'field' keyword (which was transformed from backing field)
+			bool usesFieldKeyword = false;
+			foreach (var accessor in new[] { propertyDeclaration.Getter, propertyDeclaration.Setter })
+			{
+				if (accessor.IsNull || accessor.Body.IsNull)
+					continue;
+				usesFieldKeyword |= accessor.Body.Descendants.OfType<Identifier>()
+					.Any(id => id.Name == "field");
+			}
+			if (!usesFieldKeyword)
+				return;
+			// Find and remove the backing field declaration
+			string backingFieldName = "<" + property.Name + ">k__BackingField";
+			var fieldDecl = propertyDeclaration.Parent?.Children.OfType<FieldDeclaration>()
+				.FirstOrDefault(fd => {
+					var field = fd.GetSymbol() as IField;
+					return field != null && field.Name == backingFieldName
+						&& field.IsCompilerGenerated()
+						&& field.DeclaringTypeDefinition == property.DeclaringTypeDefinition;
+				});
+			if (fieldDecl != null)
+			{
+				fieldDecl.Remove();
+				// Move field attributes to the property with [field: ...] target
+				CSharpDecompiler.RemoveAttribute(fieldDecl, KnownAttribute.CompilerGenerated);
+				CSharpDecompiler.RemoveAttribute(fieldDecl, KnownAttribute.DebuggerBrowsable);
+				foreach (var section in fieldDecl.Attributes)
+				{
+					section.AttributeTarget = "field";
+					propertyDeclaration.Attributes.Add(section.Detach());
+				}
+			}
+		}
+
 		void RemoveCompilerGeneratedAttribute(AstNodeCollection<AttributeSection> attributeSections)
 		{
 			RemoveCompilerGeneratedAttribute(attributeSections, "System.Runtime.CompilerServices.CompilerGeneratedAttribute");
@@ -743,15 +794,26 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 				var parent = identifier.Parent;
 				var mrr = parent.Annotation<MemberResolveResult>();
 				var field = mrr?.Member as IField;
-				if (field != null && IsBackingFieldOfAutomaticProperty(field, out var property)
-					&& CanTransformToAutomaticProperty(property, !(field.IsCompilerGenerated() && field.Name == "_" + property.Name))
-					&& currentMethod.AccessorOwner != property)
+				if (field != null && IsBackingFieldOfAutomaticProperty(field, out var property))
 				{
-					if (!property.CanSet && !context.Settings.GetterOnlyAutomaticProperties)
+					if (currentMethod?.AccessorOwner == property)
+					{
+						// We're inside this property's accessor - use the field keyword if enabled
+						if (context.Settings.SemiAutoProperties)
+						{
+							return Identifier.Create("field");
+						}
 						return null;
-					parent.RemoveAnnotations<MemberResolveResult>();
-					parent.AddAnnotation(new MemberResolveResult(mrr.TargetResult, property));
-					return Identifier.Create(property.Name);
+					}
+					// Outside of property accessor - check if we can replace with property name
+					if (CanTransformToAutomaticProperty(property, !(field.IsCompilerGenerated() && field.Name == "_" + property.Name)))
+					{
+						if (!property.CanSet && !context.Settings.GetterOnlyAutomaticProperties)
+							return null;
+						parent.RemoveAnnotations<MemberResolveResult>();
+						parent.AddAnnotation(new MemberResolveResult(mrr.TargetResult, property));
+						return Identifier.Create(property.Name);
+					}
 				}
 			}
 			return null;

ICSharpCode.Decompiler/DecompilerSettings.cs

@@ -175,12 +175,13 @@ namespace ICSharpCode.Decompiler
 			if (languageVersion < CSharp.LanguageVersion.CSharp14_0)
 			{
 				extensionMembers = false;
+				semiAutoProperties = false;
 			}
 		}
 
 		public CSharp.LanguageVersion GetMinimumRequiredVersion()
 		{
-			if (extensionMembers)
+			if (extensionMembers || semiAutoProperties)
 				return CSharp.LanguageVersion.CSharp14_0;
 			if (paramsCollections)
 				return CSharp.LanguageVersion.CSharp13_0;
@@ -2179,6 +2180,24 @@ namespace ICSharpCode.Decompiler
 			}
 		}
 
+		bool semiAutoProperties = true;
+
+		/// <summary>
+		/// Gets/Sets whether C# 14.0 semi-auto properties using the <c>field</c> keyword should be used.
+		/// </summary>
+		[Category("C# 14.0 / VS 202x.yy")]
+		[Description("DecompilerSettings.SemiAutoProperties")]
+		public bool SemiAutoProperties {
+			get { return semiAutoProperties; }
+			set {
+				if (semiAutoProperties != value)
+				{
+					semiAutoProperties = value;
+					OnPropertyChanged();
+				}
+			}
+		}
+
 		bool separateLocalVariableDeclarations = false;
 
 		/// <summary>

ILSpy/Properties/Resources.Designer.cs

@@ -1361,6 +1361,15 @@ namespace ICSharpCode.ILSpy.Properties {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Use &apos;field&apos; keyword in semi-auto properties.
+        /// </summary>
+        public static string DecompilerSettings_SemiAutoProperties {
+            get {
+                return ResourceManager.GetString("DecompilerSettings.SemiAutoProperties", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Separate local variable declarations and initializers (int x = 5; -&gt; int x; x = 5;), if possible.
         /// </summary>

ILSpy/Properties/Resources.resx

@@ -474,6 +474,9 @@ Are you sure you want to continue?</value>
   <data name="DecompilerSettings.ScopedRef" xml:space="preserve">
     <value>'scoped' lifetime annotation</value>
   </data>
+  <data name="DecompilerSettings.SemiAutoProperties" xml:space="preserve">
+    <value>Use 'field' keyword in semi-auto properties</value>
+  </data>
   <data name="DecompilerSettings.SeparateLocalVariableDeclarations" xml:space="preserve">
     <value>Separate local variable declarations and initializers (int x = 5; -&gt; int x; x = 5;), if possible</value>
   </data>