Fix false negative with "/p:MergeWith" async/await branches

src/coverlet.core/Coverage.cs

@@ -132,7 +132,7 @@ public CoverageResult GetCoverageResult()
                                 if (methods.TryGetValue(branch.Method, out Method method))
                                 {
                                     method.Branches.Add(new BranchInfo
-                                    { Line = branch.Number, Hits = branch.Hits, Offset = branch.Offset, EndOffset = branch.EndOffset, Path = branch.Path, Ordinal = branch.Ordinal, IsAsyncStateMachineBranch = branch.IsAsyncStateMachineBranch }
+                                    { Line = branch.Number, Hits = branch.Hits, Offset = branch.Offset, EndOffset = branch.EndOffset, Path = branch.Path, Ordinal = branch.Ordinal }
                                     );
                                 }
                                 else
@@ -168,7 +168,7 @@ public CoverageResult GetCoverageResult()
                 InstrumentationHelper.RestoreOriginalModule(result.ModulePath, _identifier);
             }
 
-            var coverageResult = new CoverageResult { Identifier = _identifier, Modules = modules };
+            var coverageResult = new CoverageResult { Identifier = _identifier, Modules = modules, InstrumentedResults = _results };
 
             if (!string.IsNullOrEmpty(_mergeWith) && !string.IsNullOrWhiteSpace(_mergeWith) && File.Exists(_mergeWith))
             {
@@ -239,7 +239,7 @@ private void CalculateCoverage()
                     foreach (var branch in document.Value.Branches)
                     {
                         //if one branch is covered we search the other one only if it's not covered
-                        if (branch.Value.IsAsyncStateMachineBranch && branch.Value.Method.EndsWith("::MoveNext()") && branch.Value.Hits > 0)
+                        if (IsAsyncStateMachineMethod(branch.Value.Method) && branch.Value.Hits > 0)
                         {
                             foreach (var moveNextBranch in document.Value.Branches)
                             {
@@ -260,6 +260,18 @@ private void CalculateCoverage()
             }
         }
 
+        private bool IsAsyncStateMachineMethod(string method)
+        {
+            foreach (var instrumentationResult in _results)
+            {
+                if (instrumentationResult.AsyncMachineStateMethod.Contains(method))
+                {
+                    return true;
+                }
+            }
+            return false;
+        }
+
         private string GetSourceLinkUrl(Dictionary<string, string> sourceLinkDocuments, string document)
         {
             if (sourceLinkDocuments.TryGetValue(document, out string url))

src/coverlet.core/CoverageResult.cs

@@ -3,6 +3,7 @@
 using System.IO;
 using System.Linq;
 using Coverlet.Core.Enums;
+using Coverlet.Core.Instrumentation;
 using Coverlet.Core.Symbols;
 
 namespace Coverlet.Core
@@ -15,7 +16,6 @@ public class BranchInfo
         public int Path { get; set; }
         public uint Ordinal { get; set; }
         public int Hits { get; set; }
-        public bool IsAsyncStateMachineBranch { get; set; }
     }
 
     public class Lines : SortedDictionary<int, int> { }
@@ -41,6 +41,7 @@ public class CoverageResult
     {
         public string Identifier;
         public Modules Modules;
+        internal List<InstrumenterResult> InstrumentedResults;
 
         internal CoverageResult() { }
 
@@ -121,7 +122,7 @@ internal void Merge(Modules modules)
                         {
                             foreach (var branch in method.Value.Branches)
                             {
-                                if (branch.IsAsyncStateMachineBranch && method.Key.EndsWith("::MoveNext()") && branch.Hits > 0)
+                                if (IsAsyncStateMachineMethod(method.Key))
                                 {
                                     foreach (var moveNextBranch in method.Value.Branches)
                                     {
@@ -142,6 +143,18 @@ internal void Merge(Modules modules)
             }
         }
 
+        private bool IsAsyncStateMachineMethod(string method)
+        {
+            foreach (var instrumentedResult in InstrumentedResults)
+            {
+                if (instrumentedResult.AsyncMachineStateMethod.Contains(method))
+                {
+                    return true;
+                }
+            }
+            return false;
+        }
+
         public ThresholdTypeFlags GetThresholdTypesBelowThreshold(CoverageSummary summary, double threshold, ThresholdTypeFlags thresholdTypes, ThresholdStatistic thresholdStat)
         {
             var thresholdTypeFlags = ThresholdTypeFlags.None;

src/coverlet.core/Instrumentation/Instrumenter.cs

@@ -30,6 +30,7 @@ internal class Instrumenter
         private ILProcessor _customTrackerClassConstructorIl;
         private TypeDefinition _customTrackerTypeDef;
         private MethodReference _customTrackerRecordHitMethod;
+        private List<string> _asyncMachineStateMethod;
 
         public Instrumenter(string module, string identifier, string[] excludeFilters, string[] includeFilters, string[] excludedFiles, string[] excludedAttributes)
         {
@@ -59,6 +60,8 @@ public InstrumenterResult Instrument()
 
             InstrumentModule();
 
+            _result.AsyncMachineStateMethod = _asyncMachineStateMethod == null ? Array.Empty<string>() : _asyncMachineStateMethod.ToArray();
+
             return _result;
         }
 
@@ -326,6 +329,7 @@ private Instruction AddInstrumentationCode(MethodDefinition method, ILProcessor
 
             var key = (branchPoint.StartLine, (int)branchPoint.Ordinal);
             if (!document.Branches.ContainsKey(key))
+            { 
                 document.Branches.Add(key,
                     new Branch
                     {
@@ -335,11 +339,24 @@ private Instruction AddInstrumentationCode(MethodDefinition method, ILProcessor
                         Offset = branchPoint.Offset,
                         EndOffset = branchPoint.EndOffset,
                         Path = branchPoint.Path,
-                        Ordinal = branchPoint.Ordinal,
-                        IsAsyncStateMachineBranch = IsAsyncStateMachineBranch(method.DeclaringType, method)
+                        Ordinal = branchPoint.Ordinal
                     }
                 );
 
+                if (IsAsyncStateMachineBranch(method.DeclaringType, method))
+                {
+                    if (_asyncMachineStateMethod == null)
+                    {
+                        _asyncMachineStateMethod = new List<string>();
+                    }
+
+                    if (!_asyncMachineStateMethod.Contains(method.FullName))
+                    {
+                        _asyncMachineStateMethod.Add(method.FullName);
+                    }
+                }
+            }
+
             var entry = (true, document.Index, branchPoint.StartLine, (int)branchPoint.Ordinal);
             _result.HitCandidates.Add(entry);
 

src/coverlet.core/Instrumentation/InstrumenterResult.cs

@@ -16,7 +16,6 @@ internal class Branch : Line
         public int EndOffset;
         public int Path;
         public uint Ordinal;
-        public bool IsAsyncStateMachineBranch;
     }
 
     internal class Document
@@ -42,6 +41,7 @@ public InstrumenterResult()
         }
 
         public string Module;
+        public string[] AsyncMachineStateMethod;
         public string HitsFilePath;
         public string ModulePath;
         public string SourceLink;