Merge pull request #4001 from icsharpcode/fix/init-accessor-comment

Print the init-only marker after the set keyword again

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

@@ -254,6 +254,8 @@
     <None Include="TestCases\Ugly\NoFieldKeyword.Expected.cs" />
     <Compile Remove="TestCases\Ugly\NoForEachStatement.Expected.cs" />
     <None Include="TestCases\Ugly\NoForEachStatement.Expected.cs" />
+    <Compile Remove="TestCases\Ugly\NoInitAccessors.Expected.cs" />
+    <None Include="TestCases\Ugly\NoInitAccessors.Expected.cs" />
     <Compile Remove="TestCases\Ugly\NoLocalFunctions.Expected.cs" />
     <None Include="TestCases\Ugly\NoLocalFunctions.Expected.cs" />
     <Compile Remove="TestCases\Ugly\NoNewOfT.Expected.cs" />

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

@@ -0,0 +1,18 @@
+namespace ICSharpCode.Decompiler.Tests.TestCases.Ugly
+{
+	internal class NoInitAccessors
+	{
+		private string name;
+
+		public int AutoInit { get; set/*init*/; }
+
+		public string Name {
+			get {
+				return name;
+			}
+			set/*init*/ {
+				name = value;
+			}
+		}
+	}
+}

ICSharpCode.Decompiler.Tests/TestCases/Ugly/NoInitAccessors.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.
+
+namespace ICSharpCode.Decompiler.Tests.TestCases.Ugly
+{
+	internal class NoInitAccessors
+	{
+		private string name;
+
+		public int AutoInit { get; init; }
+
+		public string Name {
+			get {
+				return name;
+			}
+			init {
+				name = value;
+			}
+		}
+	}
+}

ICSharpCode.Decompiler.Tests/UglyTestRunner.cs

@@ -76,6 +76,15 @@ namespace ICSharpCode.Decompiler.Tests
 			CompilerOptions.Optimize | CompilerOptions.UseRoslynLatest,
 		});
 
+		// init accessors require C# 9 and the IsExternalInit marker, which .NET Framework 4.0 lacks
+		static readonly CompilerOptions[] initAccessorOptions = Tester.SupportedOnCurrentPlatform(new[]
+		{
+			CompilerOptions.UseRoslyn4_14_0,
+			CompilerOptions.Optimize | CompilerOptions.UseRoslyn4_14_0,
+			CompilerOptions.UseRoslynLatest,
+			CompilerOptions.Optimize | CompilerOptions.UseRoslynLatest,
+		});
+
 		// top-level statements require C# 9 and cannot target .NET Framework 4.0
 		static readonly CompilerOptions[] topLevelProgramOptions = Tester.SupportedOnCurrentPlatform(new[]
 		{
@@ -127,6 +136,12 @@ namespace ICSharpCode.Decompiler.Tests
 			});
 		}
 
+		[Test]
+		public async Task NoInitAccessors([ValueSource(nameof(initAccessorOptions))] CompilerOptions cscOptions)
+		{
+			await RunForLibrary(cscOptions: cscOptions, decompilerSettings: new DecompilerSettings(CSharp.LanguageVersion.CSharp8_0));
+		}
+
 		[Test]
 		public async Task NoForEachStatement([ValueSource(nameof(defaultOptions))] CompilerOptions cscOptions)
 		{

ICSharpCode.Decompiler/CSharp/OutputVisitor/CSharpOutputVisitor.cs

@@ -2295,6 +2295,12 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 				else
 				{
 					WriteKeyword("set");
+					if (accessor.IsInitOnly)
+					{
+						// The setter is init-only, but the output language version has no init accessor:
+						// mark the keyword, so that the difference is not lost silently.
+						writer.WriteComment(CommentType.MultiLine, "init");
+					}
 				}
 				style = policy.PropertySetBraceStyle;
 			}

ICSharpCode.Decompiler/CSharp/Syntax/TypeMembers/Accessor.cs

@@ -52,6 +52,16 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		public AccessorKind Kind { get; set; }
 
+		/// <summary>
+		/// True if the underlying setter is init-only. When <see cref="Kind"/> is not
+		/// <see cref="AccessorKind.Init"/>, because the output language version has no init accessors,
+		/// the accessor prints as "set" followed by an /*init*/ comment marking the difference.
+		/// Excluded from pattern matching: a pattern written for a setter has to match an init-only
+		/// setter just the same.
+		/// </summary>
+		[ExcludeFromMatch]
+		public bool IsInitOnly { get; set; }
+
 		// An accessor is printed as its keyword (get/set/init/add/remove), never an identifier, so it
 		// carries no name. The contract members are overridden to no-ops: shared decompiler code sets a
 		// name on every method-like entity (e.g. explicit interface implementations), which is irrelevant

ICSharpCode.Decompiler/CSharp/Syntax/TypeSystemAstBuilder.cs

@@ -228,7 +228,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		/// <summary>
 		/// Controls whether C# 9 "init;" accessors are supported.
-		/// If disabled, emits "set /*init*/;" instead.
+		/// If disabled, emits "set/*init*/;" instead.
 		/// </summary>
 		public bool SupportInitAccessors { get; set; }
 
@@ -2234,10 +2234,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 				accessorKind = AccessorKind.Init;
 			}
 			decl.Kind = accessorKind;
-			if (accessor.IsInitOnly && accessorKind != AccessorKind.Init)
-			{
-				decl.AddTrailingTrivia(new Comment("init", CommentType.MultiLine));
-			}
+			decl.IsInitOnly = accessor.IsInitOnly;
 			if (AddResolveResultAnnotations)
 			{
 				decl.AddAnnotation(new MemberResolveResult(null, accessor));