Fix #3091: extension methods named "Add" were skipping some checks in AccessPathElement.IsMethodApplicable.

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

@@ -34,6 +34,10 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty.InitializerTests
 		public static void Add<T>(this IList<KeyValuePair<string, string>> collection, string key, T value, Func<T, string> convert = null)
 		{
 		}
+
+		public static void Add(this TestCases collection, string key)
+		{
+		}
 	}
 
 	public class TestCases
@@ -1104,6 +1108,14 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty.InitializerTests
 			Console.WriteLine(customList);
 		}
 
+		public static TestCases NoCollectionInitializerBecauseOfMissingIEnumerable()
+		{
+			TestCases testCases = new TestCases();
+			testCases.Add("int");
+			testCases.Add("string");
+			return testCases;
+		}
+
 		public static void CollectionInitializerWithParamsMethod()
 		{
 			X(Y(), new CustomList<int> { { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 } });

ICSharpCode.Decompiler/IL/Transforms/TransformCollectionAndObjectInitializers.cs

@@ -439,8 +439,12 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			if (!"Add".Equals(method.Name, StringComparison.Ordinal) || arguments.Count == 0)
 				return false;
 			if (method.IsExtensionMethod)
-				return settings?.ExtensionMethodsInCollectionInitializers != false
+			{
-					&& CSharp.Transforms.IntroduceExtensionMethods.CanTransformToExtensionMethodCall(method, resolveContext, ignoreTypeArguments: true);
+				if (settings?.ExtensionMethodsInCollectionInitializers == false)
+					return false;
+				if (!CSharp.Transforms.IntroduceExtensionMethods.CanTransformToExtensionMethodCall(method, resolveContext, ignoreTypeArguments: true))
+					return false;
+			}
 			var targetType = GetReturnTypeFromInstruction(arguments[0]) ?? rootType;
 			if (targetType == null)
 				return false;