Extension method syntax on lambda expressions/delegates is not allowed.

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

@@ -159,6 +159,17 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 		{
 		}
 
+		public static Predicate<T> And<T>(this Predicate<T> filter1, Predicate<T> filter2)
+		{
+			if (filter1 == null) {
+				return filter2;
+			}
+			if (filter2 == null) {
+				return filter1;
+			}
+			return (T m) => filter1(m) && filter2(m);
+		}
+
 		public static Action<string> ExtensionMethodUnbound()
 		{
 			return Test;
@@ -174,6 +185,11 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			return ((string)null).Test;
 		}
 
+		public static Predicate<int> NoExtensionMethodOnLambda()
+		{
+			return And((int x) => x >= 0, (int x) => x <= 100);
+		}
+
 		public static object StaticMethod()
 		{
 			return new Func<Action>(ExtensionMethodBound);

ICSharpCode.Decompiler/CSharp/Transforms/IntroduceExtensionMethods.cs

@@ -162,6 +162,8 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 		public static bool CanTransformToExtensionMethodCall(CSharpResolver resolver, IMethod method,
 			IReadOnlyList<IType> typeArguments, ResolveResult target, ResolveResult[] arguments, string[] argumentNames)
 		{
+			if (target is LambdaResolveResult)
+				return false;
 			var rr = resolver.ResolveMemberAccess(target, method.Name, typeArguments, NameLookupMode.InvocationTarget) as MethodGroupResolveResult;
 			if (rr == null)
 				return false;