C# 14 extensions: Add initial test case

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

@@ -8,7 +8,7 @@
 
   <PropertyGroup>
     <TargetFramework>net10.0-windows</TargetFramework>
-    <LangVersion>13</LangVersion>
+    <LangVersion>preview</LangVersion>
     <RuntimeIdentifier Condition="$(IsWindowsX64) == true">win-x64</RuntimeIdentifier>
     <RuntimeIdentifier Condition="$(IsWindowsARM64) == true">win-arm64</RuntimeIdentifier>
 
@@ -146,6 +146,7 @@
     <Compile Include="TestCases\ILPretty\Issue3442.cs" />
     <Compile Include="TestCases\ILPretty\Issue3466.cs" />
     <Compile Include="TestCases\ILPretty\Issue3524.cs" />
+    <Compile Include="TestCases\Pretty\ExtensionProperties.cs" />
     <None Include="TestCases\ILPretty\Issue3504.cs" />
     <Compile Include="TestCases\ILPretty\MonoFixed.cs" />
     <Compile Include="TestCases\Pretty\Comparisons.cs" />

ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs

@@ -527,6 +527,12 @@ namespace ICSharpCode.Decompiler.Tests
 			await RunForLibrary(cscOptions: cscOptions | CompilerOptions.NullableEnable);
 		}
 
+		[Test]
+		public async Task ExtensionProperties([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/ExtensionProperties.cs

@@ -0,0 +1,38 @@
+using System.Collections.Generic;
+using System.Linq;
+
+namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
+{
+	internal static class ExtensionProperties
+	{
+		extension<T>(ICollection<T> collection) where T : notnull
+		{
+			public bool IsEmpty => collection.Count == 0;
+
+			public int Test {
+				get {
+					return 42;
+				}
+				set {
+				}
+			}
+
+			public void AddIfNotNull(T item)
+			{
+				if (item != null)
+				{
+					collection.Add(item);
+				}
+			}
+
+			public T2 Cast<T2>(int index) where T2 : T
+			{
+				return (T2)(object)collection.ElementAt(index);
+			}
+
+			public static void StaticExtension()
+			{
+			}
+		}
+	}
+}