Recognize field-backed properties when AutomaticProperties is off

ExpressionBuilder.ConvertField prints the C# 14 "field" keyword based on the
FieldKeyword setting alone, but PatternStatementTransform only entered the
property transform when AutomaticProperties was on. With FieldKeyword on and
AutomaticProperties off the backing-field declaration was therefore never
removed, and the output declared the backing field next to accessors already
written in terms of "field".

That output still compiles, which is what makes it dangerous: the keyword binds
to a second, freshly synthesized backing field while the declared one stays
unwritten, so the recompiled assembly has different storage than the input.
Only a CS0169 "field is never used" warning hints at it.

AutomaticProperties governs only whether trivial accessors collapse to
"get;"/"set;"; the declaration removal inside the transform is a separate step
that FieldKeyword alone is enough to justify. The entry gate now mirrors
CSharpDecompiler.MemberIsHidden, which already made the field's visibility
depend on either setting, with GetterOnlyAutomaticProperties vetoing the
getter-only case for both.

Assisted-by: Claude:claude-opus-5[1m]:Claude Code

ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj

@@ -264,6 +264,8 @@
     <None Include="TestCases\Ugly\AggressiveScalarReplacementOfAggregates.Expected.cs" />
     <Compile Remove="TestCases\Ugly\NoArrayInitializers.Expected.cs" />
     <None Include="TestCases\Ugly\NoArrayInitializers.Expected.cs" />
+    <Compile Remove="TestCases\Ugly\NoAutomaticProperties.Expected.cs" />
+    <None Include="TestCases\Ugly\NoAutomaticProperties.Expected.cs" />
     <Compile Remove="TestCases\Ugly\NoDecimalConstants.Expected.cs" />
     <None Include="TestCases\Ugly\NoDecimalConstants.Expected.cs" />
     <Compile Remove="TestCases\Ugly\NoExtensionMethods.Expected.cs" />

ICSharpCode.Decompiler.Tests/TestCases/Ugly/NoAutomaticProperties.Expected.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Runtime.CompilerServices;
+
+namespace ICSharpCode.Decompiler.Tests.TestCases.Ugly;
+
+internal class NoAutomaticProperties
+{
+	public int Plain {
+		[CompilerGenerated]
+		get {
+			return field;
+		}
+		[CompilerGenerated]
+		set {
+			field = value;
+		}
+	}
+
+	public int SemiAuto {
+		get {
+			return field;
+		}
+		set {
+			field = Math.Max(0, value);
+		}
+	}
+}

ICSharpCode.Decompiler.Tests/TestCases/Ugly/NoAutomaticProperties.cs

@@ -0,0 +1,36 @@
+// Copyright (c) 2026 Siegfried Pammer
+//
+// 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.Ugly
+{
+	internal class NoAutomaticProperties
+	{
+		public int Plain { get; set; }
+
+		public int SemiAuto {
+			get {
+				return field;
+			}
+			set {
+				field = Math.Max(0, value);
+			}
+		}
+	}
+}

ICSharpCode.Decompiler.Tests/UglyTestRunner.cs

@@ -128,6 +128,14 @@ namespace ICSharpCode.Decompiler.Tests
 			});
 		}
 
+		[Test]
+		public async Task NoAutomaticProperties([ValueSource(nameof(roslynLatestOnlyOptions))] CompilerOptions cscOptions)
+		{
+			await RunForLibrary(cscOptions: cscOptions, decompilerSettings: new DecompilerSettings {
+				AutomaticProperties = false
+			});
+		}
+
 		[Test]
 		public async Task NoFieldKeyword([ValueSource(nameof(roslynLatestOnlyOptions))] CompilerOptions cscOptions)
 		{

ICSharpCode.Decompiler/CSharp/Transforms/PatternStatementTransform.cs

@@ -111,7 +111,13 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 
 		public override AstNode VisitPropertyDeclaration(PropertyDeclaration propertyDeclaration)
 		{
-			if (context.Settings.AutomaticProperties
+			// Same rule as CSharpDecompiler.MemberIsHidden applies to the backing field: either
+			// setting on its own allows the field declaration to disappear, and
+			// GetterOnlyAutomaticProperties vetoes the getter-only case for both. Asking only
+			// about AutomaticProperties would skip the transform for a field-backed property
+			// while ExpressionBuilder.ConvertField has already printed "field" in its accessors,
+			// leaving the declaration and the keyword in the same output.
+			if ((context.Settings.AutomaticProperties || context.Settings.FieldKeyword)
 				&& (propertyDeclaration.Setter is not null || context.Settings.GetterOnlyAutomaticProperties))
 			{
 				AstNode? result = TransformAutomaticProperty(propertyDeclaration);