Merge pull request #3969 from sailro/fix-null-conditional-query-syntax

Keep null-conditional LINQ chains in method syntax

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

@@ -44,6 +44,20 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 
 	public class QueryExpressions
 	{
+		public class MaybeHolder
+		{
+			public Maybe<int> Value;
+
+#if CS60
+			public Maybe<int> this[int index] => default(Maybe<int>);
+#endif
+
+			public Func<Maybe<int>> Factory()
+			{
+				return () => default(Maybe<int>);
+			}
+		}
+
 		public class HbmParam
 		{
 			public string Name { get; set; }
@@ -217,6 +231,21 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 		{
 			return arglist?.OrderByDescending((string f) => f.Length).ThenBy((string f) => f.ToLower()).ToList();
 		}
+
+		public Maybe<string>? NullConditionalValueTypeQuery(MaybeHolder holder)
+		{
+			return holder?.Value.Where((int value) => value > 0).Select((int value) => value.ToString());
+		}
+
+		public Maybe<string>? NullConditionalNestedInvocationQuery(MaybeHolder holder)
+		{
+			return holder?.Factory()().Where((int value) => value > 0).Select((int value) => value.ToString());
+		}
+
+		public Maybe<string>? NullConditionalIndexerQuery(MaybeHolder holder)
+		{
+			return holder?[0].Where((int value) => value > 0).Select((int value) => value.ToString());
+		}
 #endif
 
 		public static IEnumerable<char> Issue1310a(bool test)

ICSharpCode.Decompiler/CSharp/Transforms/IntroduceQueryExpressions.cs

@@ -377,10 +377,13 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			}
 		}
 
-		bool IsNullConditional(Expression target)
-		{
-			return target is UnaryOperatorExpression uoe && uoe.Operator == UnaryOperatorType.NullConditional;
-		}
+		bool IsNullConditional(Expression target) => target switch {
+			UnaryOperatorExpression { Operator: UnaryOperatorType.NullConditional } => true,
+			MemberReferenceExpression member => IsNullConditional(member.Target),
+			InvocationExpression invocation => IsNullConditional(invocation.Target),
+			IndexerExpression { Target: { } indexerTarget } => IsNullConditional(indexerTarget),
+			_ => false
+		};
 
 		/// <summary>
 		/// This fixes #437: Decompilation of query expression loses material parentheses