From bdf48e5a4765ef731df63acfceab9c841cb05dcc Mon Sep 17 00:00:00 2001 From: Siegfried Pammer Date: Fri, 28 Aug 2026 21:25:18 +0200 Subject: [PATCH] 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.csproj | 2 ++ .../Ugly/NoAutomaticProperties.Expected.cs | 27 ++++++++++++++ .../TestCases/Ugly/NoAutomaticProperties.cs | 36 +++++++++++++++++++ .../UglyTestRunner.cs | 8 +++++ .../Transforms/PatternStatementTransform.cs | 8 ++++- 5 files changed, 80 insertions(+), 1 deletion(-) create mode 100644 ICSharpCode.Decompiler.Tests/TestCases/Ugly/NoAutomaticProperties.Expected.cs create mode 100644 ICSharpCode.Decompiler.Tests/TestCases/Ugly/NoAutomaticProperties.cs diff --git a/ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj b/ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj index 714454f75..2d8758138 100644 --- a/ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj +++ b/ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj @@ -264,6 +264,8 @@ + + diff --git a/ICSharpCode.Decompiler.Tests/TestCases/Ugly/NoAutomaticProperties.Expected.cs b/ICSharpCode.Decompiler.Tests/TestCases/Ugly/NoAutomaticProperties.Expected.cs new file mode 100644 index 000000000..4b11c8101 --- /dev/null +++ b/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); + } + } +} diff --git a/ICSharpCode.Decompiler.Tests/TestCases/Ugly/NoAutomaticProperties.cs b/ICSharpCode.Decompiler.Tests/TestCases/Ugly/NoAutomaticProperties.cs new file mode 100644 index 000000000..752d8b9ad --- /dev/null +++ b/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); + } + } + } +} diff --git a/ICSharpCode.Decompiler.Tests/UglyTestRunner.cs b/ICSharpCode.Decompiler.Tests/UglyTestRunner.cs index c89807843..5db43d283 100644 --- a/ICSharpCode.Decompiler.Tests/UglyTestRunner.cs +++ b/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) { diff --git a/ICSharpCode.Decompiler/CSharp/Transforms/PatternStatementTransform.cs b/ICSharpCode.Decompiler/CSharp/Transforms/PatternStatementTransform.cs index 2f4adf6e4..e9bff79c0 100644 --- a/ICSharpCode.Decompiler/CSharp/Transforms/PatternStatementTransform.cs +++ b/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);