Wrong coverage for await foreach with generic method (#1312)

Author: daveMueller

Documentation/Changelog.md

@@ -4,6 +4,11 @@ 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
+-Await foreach has wrong branch coverage when method is generic [#1210](https://github.com/coverlet-coverage/coverlet/issues/1210)
+
 ## Release date 2022-02-06
 ### Packages  
 coverlet.msbuild 3.1.2  

src/coverlet.core/Symbols/CecilSymbolHelper.cs

@@ -496,8 +496,11 @@ static bool CheckForAsyncEnumerator(List<Instruction> instructions, Instruction
                     (instructions[currentIndex - 2].OpCode == OpCodes.Ldarg ||
                      instructions[currentIndex - 2].OpCode == OpCodes.Ldarg_0) &&
                     instructions[currentIndex - 1].OpCode == OpCodes.Ldfld &&
-                    instructions[currentIndex - 1].Operand is FieldDefinition field &&
-                    IsCompilerGenerated(field) && field.FieldType.FullName.StartsWith("System.Collections.Generic.IAsyncEnumerator"))
+                    (
+                        (instructions[currentIndex - 1].Operand is FieldDefinition field && IsCompilerGenerated(field) && field.FieldType.FullName.StartsWith("System.Collections.Generic.IAsyncEnumerator")) ||
+                        (instructions[currentIndex - 1].Operand is FieldReference fieldRef && IsCompilerGenerated(fieldRef.Resolve()) && fieldRef.FieldType.FullName.StartsWith("System.Collections.Generic.IAsyncEnumerator"))
+                    )
+                )
                 {
                     return true;
                 }
@@ -538,8 +541,10 @@ static bool CheckIfExceptionThrown(List<Instruction> instructions, Instruction i
                 for (int i = currentIndex - 1; i >= minFieldIndex; --i)
                 {
                     if (instructions[i].OpCode == OpCodes.Ldfld &&
-                        instructions[i].Operand is FieldDefinition field &&
-                        IsCompilerGenerated(field) && field.FieldType.FullName == "System.Object")
+                        (
+                            (instructions[i].Operand is FieldDefinition field && IsCompilerGenerated(field) && field.FieldType.FullName == "System.Object") ||
+                            (instructions[i].Operand is FieldReference fieldRef && IsCompilerGenerated(fieldRef.Resolve()) && fieldRef.FieldType.FullName == "System.Object")
+                        ))
                     {
                         // We expect the call to GetResult() to be no more than four
                         // instructions before the loading of the field's value.

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

@@ -24,6 +24,7 @@ public void AsyncForeach()
                         int res = ((ValueTask<int>)instance.SumWithATwist(AsyncEnumerable.Range(1, 5))).GetAwaiter().GetResult();
                         res += ((ValueTask<int>)instance.Sum(AsyncEnumerable.Range(1, 3))).GetAwaiter().GetResult();
                         res += ((ValueTask<int>)instance.SumEmpty()).GetAwaiter().GetResult();
+                        ((ValueTask)instance.GenericAsyncForeach<object>(AsyncEnumerable.Range(1, 3))).GetAwaiter().GetResult();
 
                         return Task.CompletedTask;
                     }, persistPrepareResultToFile: pathSerialize[0]);
@@ -43,7 +44,9 @@ public void AsyncForeach()
                                     // Sum(IAsyncEnumerable<int>)
                                     (34, 1), (35, 1), (37, 9), (38, 3), (39, 3), (40, 3), (42, 1), (43, 1),
                                     // SumEmpty()
-                                    (47, 1), (48, 1), (50, 3), (51, 0), (52, 0), (53, 0), (55, 1), (56, 1)
+                                    (47, 1), (48, 1), (50, 3), (51, 0), (52, 0), (53, 0), (55, 1), (56, 1),
+                                    // GenericAsyncForeach
+                                    (59,1), (60, 9), (61, 3), (62, 3), (63, 3), (64, 1)
                                     )
                 .AssertBranchesCovered(BuildConfiguration.Debug,
                                        // SumWithATwist(IAsyncEnumerable<int>)
@@ -53,9 +56,10 @@ public void AsyncForeach()
                                        // SumEmpty()
                                        // If we never entered the loop, that's a branch not taken, which is
                                        // what we want to see.
-                                       (50, 0, 1), (50, 1, 0)
+                                       (50, 0, 1), (50, 1, 0),
+                                       (60, 0, 1), (60, 1, 3)
                                        )
-                .ExpectedTotalNumberOfBranches(BuildConfiguration.Debug, 4);
+                .ExpectedTotalNumberOfBranches(BuildConfiguration.Debug, 5);
             }
             finally
             {

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

@@ -54,5 +54,13 @@ async public ValueTask<int> SumEmpty()
 
             return sum;
         }
+
+        public async ValueTask GenericAsyncForeach<T>(IAsyncEnumerable<int> ints)
+        {
+            await foreach (int obj in ints)
+            {
+                await Task.Delay(1);
+            }
+        }
     }
 }