skip generated branches for method group

Author: daveMueller

Documentation/Changelog.md

@@ -7,6 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## Unreleased
 
 ### Fixed
+-Fix .NET 7 Method Group branch coverage issue [#1447](https://github.com/coverlet-coverage/coverlet/issues/1447)
 -Fix ExcludeFromCodeCoverage does not exclude method in a partial class [#1548](https://github.com/coverlet-coverage/coverlet/issues/1548) 
 -Fix ExcludeFromCodeCoverage does not exclude F# task [#1547](https://github.com/coverlet-coverage/coverlet/issues/1547) 
 -Fix issues where ExcludeFromCodeCoverage ignored [#1431](https://github.com/coverlet-coverage/coverlet/issues/1431)

src/coverlet.core/Symbols/CecilSymbolHelper.cs

@@ -6,7 +6,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Runtime.CompilerServices;
-
+using System.Text.RegularExpressions;
 using Coverlet.Core.Abstractions;
 using Coverlet.Core.Extensions;
 
@@ -251,6 +251,46 @@ Lambda cached field pattern
       return false;
     }
 
+    private static bool SkipDelegateCacheField(Instruction instruction)
+    {
+      /*
+          Delegate cached field pattern (e.g. method groups)
+
+          IL_0001: ldc.i4.1
+          IL_0002: newarr       [System.Runtime]System.Int32
+          IL_0007: dup
+          IL_0008: ldc.i4.0
+          IL_0009: ldc.i4.1
+          IL_000a: stelem.i4
+          IL_000b: ldsfld       class [System.Runtime]System.Func`2<int32, int32> Coverlet.Core.Samples.Tests.Issue_1447/'<>O'::'<0>__Map'
+          IL_0010: dup
+          IL_0011: brtrue.s     IL_0026 -> CHECK IF CACHED FIELD IS NULL OR JUMP TO DELEGATE USAGE
+
+          IL_0013: pop
+          IL_0014: ldnull
+          IL_0015: ldftn        int32 Coverlet.Core.Samples.Tests.Issue_1447::Map(int32)
+          IL_001b: newobj       instance void class [System.Runtime]System.Func`2<int32, int32>::.ctor(object, native int)
+          IL_0020: dup
+          IL_0021: stsfld       class [System.Runtime]System.Func`2<int32, int32> Coverlet.Core.Samples.Tests.Issue_1447/'<>O'::'<0>__Map'
+
+          (USE DELEGATE FIELD)
+          IL_0026: call         class [System.Runtime]System.Collections.Generic.IEnumerable`1<!!1> [System.Linq]System.Linq.Enumerable::Select<int32, int32>(class [System.Runtime] System.Collections.Generic.IEnumerable`1<!!0>, class [System.Runtime] System.Func`2<!!0, !!1>)
+       */
+
+      Instruction current = instruction.Previous;
+      for (int instructionBefore = 2; instructionBefore > 0 && current.Previous != null; current = current.Previous, instructionBefore--)
+      {
+        if (current.OpCode == OpCodes.Ldsfld && current.Operand is FieldDefinition fd &&
+            // https://github.com/dotnet/roslyn/blob/main/src/Compilers/CSharp/Portable/Symbols/Synthesized/GeneratedNames.cs#L513
+            Regex.IsMatch(fd.Name, "^<\\d+>__") &&
+            IsCompilerGenerated(fd))
+        {
+          return true;
+        }
+      }
+      return false;
+    }
+
     private static bool SkipGeneratedBranchForExceptionRethrown(List<Instruction> instructions, Instruction instruction)
     {
       /* 
@@ -984,7 +1024,7 @@ public IReadOnlyList<BranchPoint> GetBranchPoints(MethodDefinition methodDefinit
             continue;
           }
 
-          if (SkipLambdaCachedField(instruction))
+          if (SkipLambdaCachedField(instruction) || SkipDelegateCacheField(instruction))
           {
             continue;
           }

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

@@ -20,9 +20,9 @@ public void Lambda_Issue343()
         {
           CoveragePrepareResult coveragePrepareResult = await TestInstrumentationHelper.Run<Lambda_Issue343>(async instance =>
                   {
-              instance.InvokeAnonymous_Test();
-              await (Task<bool>)instance.InvokeAnonymousAsync_Test();
-            }, persistPrepareResultToFile: pathSerialize[0]);
+                    instance.InvokeAnonymous_Test();
+                    await (Task<bool>)instance.InvokeAnonymousAsync_Test();
+                  }, persistPrepareResultToFile: pathSerialize[0]);
           return 0;
         }, new string[] { path });
 
@@ -53,8 +53,8 @@ public void AsyncAwait_Issue_730()
         {
           CoveragePrepareResult coveragePrepareResult = await TestInstrumentationHelper.Run<Issue_730>(async instance =>
                   {
-              await (Task)instance.Invoke();
-            },
+                    await (Task)instance.Invoke();
+                  },
                   persistPrepareResultToFile: pathSerialize[0]);
 
           return 0;
@@ -81,9 +81,9 @@ public void Lambda_Issue760()
         {
           CoveragePrepareResult coveragePrepareResult = await TestInstrumentationHelper.Run<Issue_760>(async instance =>
                   {
-              await (Task)instance.If();
-              await (Task)instance.Foreach();
-            },
+                    await (Task)instance.If();
+                    await (Task)instance.Foreach();
+                  },
                   persistPrepareResultToFile: pathSerialize[0]);
 
           return 0;
@@ -134,5 +134,35 @@ public void Issue_1056()
         File.Delete(path);
       }
     }
+
+    [Fact]
+    public void Issue_1447()
+    {
+      string path = Path.GetTempFileName();
+      try
+      {
+        FunctionExecutor.Run(async (string[] pathSerialize) =>
+        {
+          CoveragePrepareResult coveragePrepareResult = await TestInstrumentationHelper.Run<Issue_1447>(instance =>
+            {
+              instance.Query1();
+              instance.Query2();
+              return Task.CompletedTask;
+            },
+            persistPrepareResultToFile: pathSerialize[0]);
+
+          return 0;
+        }, new string[] { path });
+
+        TestInstrumentationHelper.GetCoverageResult(path).GenerateReport(show: true)
+          .Document("Instrumentation.Lambda.cs")
+          .AssertLinesCovered((138, 1), (143, 1))
+          .ExpectedTotalNumberOfBranches(0);
+      }
+      finally
+      {
+        File.Delete(path);
+      }
+    }
   }
 }

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

@@ -130,4 +130,19 @@ private static object Do2(System.Func<object, object> func)
 
         public void WriteLine(string str) { }
     }
+
+    public class Issue_1447
+    {
+        public System.Collections.Generic.IEnumerable<int> Query1()
+        {
+            return new[] { 1 }.Select(Map);
+        }
+
+        public System.Collections.Generic.IEnumerable<int> Query2()
+        {
+            return new[] { 1 }.Select(Map);
+        }
+
+        private static int Map(int row) => row + 1;
+    }
 }