Branch coverage issue with several awaits (#1201)

Branch coverage issue with several awaits

Author: daveMueller

Documentation/Changelog.md

@@ -4,6 +4,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+
+### Fixed  
+-Fix branch coverage issue for il switch [#1177](https://github.com/coverlet-coverage/coverlet/issues/1177)
+-Fix branch coverage with using statement and several awaits[#1176](https://github.com/coverlet-coverage/coverlet/issues/1176)
+
 ## Release date 2021-07-19
 ### Packages  
 coverlet.msbuild 3.1.0  

src/coverlet.core/Symbols/CecilSymbolHelper.cs

@@ -124,8 +124,8 @@ private static bool SkipMoveNextPrologueBranches(Instruction instruction)
                    If method is a generated MoveNext we'll skip first branches (could be a switch or a series of branches) 
                    that check state machine value to jump to correct state (for instance after a true async call)
                    Check if it's a Cond_Branch on state machine current value int num = <>1__state;
-                   We are on branch OpCode so we need to go back by max 2 operation to reach ldloc.0 the load of "num"
-                   Max 2 because we handle following patterns
+                   We are on branch OpCode so we need to go back by max 3 operation to reach ldloc.0 the load of "num"
+                   Max 3 because we handle following patterns
 
                     Swich
 
@@ -168,7 +168,7 @@ so we know that current branch are checking that field and we're not interested
             */
 
             Instruction current = instruction.Previous;
-            for (int instructionBefore = 2; instructionBefore > 0 && current.Previous != null; current = current.Previous, instructionBefore--)
+            for (int instructionBefore = 3; instructionBefore > 0 && current.Previous != null; current = current.Previous, instructionBefore--)
             {
                 if (
                         (current.OpCode == OpCodes.Ldloc && current.Operand is VariableDefinition vo && vo.Index == 0) ||
@@ -1446,4 +1446,4 @@ public int Compare(Instruction x, Instruction y)
             }
         }
     }
-}
+}

test/coverlet.core.tests/Coverage/CoverageTests.AsyncAwait.cs

@@ -1,4 +1,5 @@
 using System.IO;
+using System.Linq;
 using System.Threading.Tasks;
 
 using Coverlet.Core.Samples.Tests;
@@ -125,5 +126,33 @@ public void AsyncAwait_Issue_669_2()
                 File.Delete(path);
             }
         }
+
+        [Fact]
+        public void AsyncAwait_Issue_1177()
+        {
+            string path = Path.GetTempFileName();
+            try
+            {
+                FunctionExecutor.Run(async (string[] pathSerialize) =>
+                {
+                    CoveragePrepareResult coveragePrepareResult = await TestInstrumentationHelper.Run<Issue_1177>(instance =>
+                        {
+                            ((Task)instance.Test()).ConfigureAwait(false).GetAwaiter().GetResult();
+                            return Task.CompletedTask;
+                        },
+                        persistPrepareResultToFile: pathSerialize[0]);
+
+                    return 0;
+                }, new string[] { path });
+
+                var document = TestInstrumentationHelper.GetCoverageResult(path).Document("Instrumentation.AsyncAwait.cs");
+                document.AssertLinesCovered(BuildConfiguration.Debug, (133, 1), (134, 1), (135, 1), (136, 1), (137, 1));
+                Assert.DoesNotContain(document.Branches, x => x.Key.Line == 134);
+            }
+            finally
+            {
+                File.Delete(path);
+            }
+        }
     }
 }

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

@@ -125,4 +125,16 @@ public interface IService
             Task Process(string cat);
         }
     }
+
+    public class Issue_1177
+    {
+        async public Task Test()
+        {
+            await Task.CompletedTask;
+            using var _ = new System.IO.MemoryStream();
+            await Task.CompletedTask;
+            await Task.CompletedTask;
+            await Task.CompletedTask;
+        }
+    }
 }