Fix #2177: PDB Generation is confused by enhanced using statements

ICSharpCode.Decompiler/CSharp/SequencePointBuilder.cs

@@ -112,21 +112,28 @@ namespace ICSharpCode.Decompiler.CSharp
 
 		public override void VisitBlockStatement(BlockStatement blockStatement)
 		{
-			ILInstruction blockContainer = blockStatement.Annotations.OfType<ILInstruction>().FirstOrDefault();
+			// enhanced using variables need special-casing here, because we omit the block syntax from the
+			// text output, so we cannot use positions of opening/closing braces here.
+			bool isEnhancedUsing = blockStatement.Parent is UsingStatement us && us.IsEnhanced;
+			if (!isEnhancedUsing)
+			{
+				var blockContainer = blockStatement.Annotation<BlockContainer>();
 				if (blockContainer != null)
 				{
 					StartSequencePoint(blockStatement.LBraceToken);
 					int intervalStart;
 					if (blockContainer.Parent is TryCatchHandler handler && !handler.ExceptionSpecifierILRange.IsEmpty)
 					{
-					// if this block container is part of a TryCatchHandler, do not steal the exception-specifier IL range
+						// if this block container is part of a TryCatchHandler, do not steal the
+						// exception-specifier IL range
 						intervalStart = handler.ExceptionSpecifierILRange.End;
 					}
 					else
 					{
 						intervalStart = blockContainer.StartILOffset;
 					}
-				// The end will be set to the first sequence point candidate location before the first statement of the function when the seqeunce point is adjusted
+					// The end will be set to the first sequence point candidate location before the first
+					// statement of the function when the seqeunce point is adjusted
 					int intervalEnd = intervalStart + 1;
 
 					Interval interval = new Interval(intervalStart, intervalEnd);
@@ -138,16 +145,18 @@ namespace ICSharpCode.Decompiler.CSharp
 				}
 				else
 				{
-				// Ideally, we'd be able to address this case. Blocks that are not the top-level function block have no ILInstruction annotations. It isn't clear to me how to determine the il range.
+					// Ideally, we'd be able to address this case. Blocks that are not the top-level function
+					// block have no ILInstruction annotations. It isn't clear to me how to determine the il range.
 					// For now, do not add the opening brace sequence in this case.
 				}
+			}
 
 			foreach (var stmt in blockStatement.Statements)
 			{
 				VisitAsSequencePoint(stmt);
 			}
 			var implicitReturn = blockStatement.Annotation<ImplicitReturnAnnotation>();
-			if (implicitReturn != null)
+			if (implicitReturn != null && !isEnhancedUsing)
 			{
 				StartSequencePoint(blockStatement.RBraceToken);
 				AddToSequencePoint(implicitReturn.Leave);
@@ -263,6 +272,9 @@ namespace ICSharpCode.Decompiler.CSharp
 			usingStatement.ResourceAcquisition.AcceptVisitor(this);
 			VisitAsSequencePoint(usingStatement.EmbeddedStatement);
 			AddToSequencePoint(usingStatement);
+			if (usingStatement.IsEnhanced)
+				EndSequencePoint(usingStatement.StartLocation, usingStatement.ResourceAcquisition.EndLocation);
+			else
 				EndSequencePoint(usingStatement.StartLocation, usingStatement.RParToken.EndLocation);
 		}