Incorrect coverage for statement lambda function

[driseley]

Coverlet appears to report incorrect coverage for anonymous statement lambda functions.

For the following class:

using System;
using System.IO;
using System.Text;

namespace DemoLibrary
{
	public class DemoClass
	{
		protected T WriteToStream<T>(Func<Stream, bool, T> getResultFunction)
		{
			using (var stream = new MemoryStream())
			{
				var result = getResultFunction(stream, false);
				stream.Close();
				Console.WriteLine(Encoding.Default.GetString(stream.ToArray()));
				return result;
			}
		}

		public bool WriteHelloWorldToStream(Stream stream , bool condition)
		{
			if (condition) stream.Write(Encoding.Default.GetBytes("Hello World"));
			else stream.Write(Encoding.Default.GetBytes("Goodbye World"));        
			return condition;
		}

		public bool InvokeFunction()
		{
			return WriteToStream((stream,condition) => WriteHelloWorldToStream(stream, condition));
		}

		public bool InvokeAnonymous()
		{
			return WriteToStream((stream, condition) =>
			{
				if (condition) stream.Write(Encoding.Default.GetBytes("Hello World"));
				else stream.Write(Encoding.Default.GetBytes("Goodbye World"));               
				return condition;
			}
			);
		}
	}
}

The following tests:

using DemoLibrary;
using System;
using System.IO;
using Xunit;

namespace DemoLibraryTests
{
	public class DemoClassTests
	{
		[Fact]
		public void InvokeFunction_Test()
		{
			DemoClass demoClass = new DemoClass();
			bool result = demoClass.InvokeFunction();
			Assert.False(result);
		}

		[Fact]
		public void InvokeAnonymous_Test()
		{
			DemoClass demoClass = new DemoClass();
			bool result = demoClass.InvokeAnonymous();
			Assert.False(result);
		}
	}
}

Report the following results:

Notice that the coverage for the InvokeAnonymous function shows all lines and all branches covered ( which clearly cannot be correct ). For the named function, the coverage is correct.

[driseley]

I have created an example project that demonstrates the issue:
https://github.com/driseley/coverlet-issue-343

[driseley]

Coverlet version 2.5.1, Project .Net Core 2.1

[tonerdo]

@driseley thanks for providing the repro project. @MarcoRossignoli when you do get some time can you take a look at this. You've got more experience with compiler generated code