fix exception filter

Author: MarcoRossignoli

src/coverlet.core/Symbols/CecilSymbolHelper.cs

@@ -42,6 +42,9 @@ public static List<BranchPoint> GetBranchPoints(MethodDefinition methodDefinitio
                         continue;
                     }
 
+                    if (BranchIsInGeneratedExceptionFilter(instruction, methodDefinition))
+                        continue;
+
                     if (BranchIsInGeneratedFinallyBlock(instruction, methodDefinition)) 
                         continue;
 
@@ -197,6 +200,35 @@ private static uint BuildPointsForSwitchCases(List<BranchPoint> list, BranchPoin
             return ordinal;
         }
 
+        private static bool BranchIsInGeneratedExceptionFilter(Instruction branchInstruction, MethodDefinition methodDefinition)
+        {
+            if (!methodDefinition.Body.HasExceptionHandlers)
+                return false;
+
+            // a generated filter block will have no sequence points in its range
+            var handlers = methodDefinition.Body.ExceptionHandlers
+                .Where(e => e.HandlerType == ExceptionHandlerType.Filter)
+                .ToList();
+
+            foreach (var exceptionHandler in handlers)
+            {
+                Instruction startFilter = exceptionHandler.FilterStart;
+                Instruction endFilter = startFilter;
+
+                while(endFilter.OpCode != OpCodes.Endfilter && endFilter != null)
+                {
+                    endFilter = endFilter.Next;
+                }
+
+                if(branchInstruction.Offset >= startFilter.Offset && branchInstruction.Offset <= endFilter.Offset)
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
         private static bool BranchIsInGeneratedFinallyBlock(Instruction branchInstruction, MethodDefinition methodDefinition)
         {
             if (!methodDefinition.Body.HasExceptionHandlers) 

test/coverlet.core.tests/Samples/Samples.cs

@@ -210,4 +210,31 @@ public string Method(string input)
             return input;
         }
     }
+
+    public class ExceptionFilter
+    {
+        public void Test()
+        {
+            try
+            {
+                int a = 0;
+                int b = 1;
+                int c = b / a;
+            }
+            catch (Exception ex) when (True() && False())
+            {
+                Console.WriteLine(ex.Message);
+            }
+        }
+
+        public bool True()
+        {
+            return true;
+        }
+
+        public bool False()
+        {
+            return false;
+        }
+    }
 }

test/coverlet.core.tests/Symbols/CecilSymbolHelperTests.cs

@@ -259,5 +259,17 @@ public void GetBranchPoints_IgnoresSwitchIn_GeneratedMoveNext()
             Assert.Empty(points);
 
         }
+
+        [Fact]
+        public void GetBranchPoints_ExceptionFilter()
+        {
+            // arrange
+            var type = _module.Types.First(x => x.FullName == typeof(ExceptionFilter).FullName);
+            var method = type.Methods.First(x => x.FullName.Contains($"::{nameof(ExceptionFilter.Test)}"));
+            // act
+            var points = CecilSymbolHelper.GetBranchPoints(method);
+            
+            Assert.Empty(points);
+        }
     }
 }