Fix #1919: Use unmapped IL offsets at the start of a catch-block for the 'exception specifier' sequence point.

ICSharpCode.Decompiler/CSharp/SequencePointBuilder.cs

@@ -113,7 +113,13 @@ namespace ICSharpCode.Decompiler.CSharp
 			ILInstruction blockContainer = blockStatement.Annotations.OfType<ILInstruction>().FirstOrDefault();
 			if (blockContainer != null) {
 				StartSequencePoint(blockStatement.LBraceToken);
-				int intervalStart = blockContainer.ILRanges.First().Start;
+				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
+					intervalStart = handler.ExceptionSpecifierILRange.End;
+				} else {
+					intervalStart = blockContainer.ILRanges.First().Start;
+				}
 				// 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; 
 
@@ -321,17 +327,20 @@ namespace ICSharpCode.Decompiler.CSharp
 
 		public override void VisitCatchClause(CatchClause catchClause)
 		{
+			StartSequencePoint(catchClause);
 			if (catchClause.Condition.IsNull) {
-				StartSequencePoint(catchClause.CatchToken);
-				var function = catchClause.Ancestors.OfType<ILFunction>().FirstOrDefault();
-				AddToSequencePointRaw(function, new[] { catchClause.Annotation<TryCatchHandler>().ExceptionSpecifierILRange });
-				EndSequencePoint(catchClause.CatchToken.StartLocation, catchClause.RParToken.IsNull ? catchClause.CatchToken.EndLocation : catchClause.RParToken.EndLocation);
+				var tryCatchHandler = catchClause.Annotation<TryCatchHandler>();
+				if (!tryCatchHandler.ExceptionSpecifierILRange.IsEmpty) {
+					StartSequencePoint(catchClause.CatchToken);
+					var function = tryCatchHandler.Ancestors.OfType<ILFunction>().FirstOrDefault();
+					AddToSequencePointRaw(function, new[] { tryCatchHandler.ExceptionSpecifierILRange });
+					EndSequencePoint(catchClause.CatchToken.StartLocation, catchClause.RParToken.IsNull ? catchClause.CatchToken.EndLocation : catchClause.RParToken.EndLocation);
+				}
 			} else {
 				StartSequencePoint(catchClause.WhenToken);
 				AddToSequencePoint(catchClause.Condition);
 				EndSequencePoint(catchClause.WhenToken.StartLocation, catchClause.CondRParToken.EndLocation);
 			}
-			StartSequencePoint(catchClause);
 			catchClause.Body.AcceptVisitor(this);
 			EndSequencePoint(catchClause.StartLocation, catchClause.EndLocation);
 		}

ICSharpCode.Decompiler/IL/Transforms/ExpressionTransforms.cs

@@ -17,10 +17,12 @@
 // DEALINGS IN THE SOFTWARE.
 
 using System;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
 using System.Linq.Expressions;
 using ICSharpCode.Decompiler.TypeSystem;
+using ICSharpCode.Decompiler.Util;
 
 namespace ICSharpCode.Decompiler.IL.Transforms
 {
@@ -711,6 +713,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// </summary>
 		void TransformCatchVariable(TryCatchHandler handler, Block entryPoint, bool isCatchBlock)
 		{
+			List<Interval> ilOffsets = null;
 			if (!handler.Variable.IsSingleDefinition || handler.Variable.LoadCount != 1)
 				return; // handle.Variable already has non-trivial uses
 			if (!entryPoint.Instructions[0].MatchStLoc(out var exceptionVar, out var exceptionSlotLoad)) {
@@ -720,6 +723,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					if (inlinedUnboxAny.Type.Equals(handler.Variable.Type)) {
 						context.Step("TransformCatchVariable - remove inlined UnboxAny", inlinedUnboxAny);
 						inlinedUnboxAny.ReplaceWith(inlinedUnboxAny.Argument);
+						(ilOffsets ?? (ilOffsets = new List<Interval>())).AddRange(inlinedUnboxAny.ILRanges);
 					}
 				}
 				return;
@@ -746,6 +750,11 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			exceptionVar.Kind = VariableKind.ExceptionLocal;
 			exceptionVar.Type = handler.Variable.Type;
 			handler.Variable = exceptionVar;
+			if (isCatchBlock) {
+				(ilOffsets ?? (ilOffsets = new List<Interval>())).AddRange(entryPoint.Instructions[0].Descendants.SelectMany(o => o.ILRanges));
+				foreach (var offset in ilOffsets)
+					handler.AddExceptionSpecifierILRange(offset);
+			}
 			entryPoint.Instructions.RemoveAt(0);
 		}