Problem accessing Linq methods (extension methods of IQueryable) inside isolated code

[wfrohmberg]

I belive this problem was already issued before in original tonerdo/pose (tonerdo/pose#11) but I think it remained unaddressed. The problem occures when I want to access e.g. standard collection as queryable from inside of the isolated code e.g.:

internal class Program
{
     public static IQueryable<int> GetInts()
     {
         return null;
     }
     static void Main(string[] args)
     {
         List<int> ints = new List<int>();
         ints.Add(1);
         var getIntsShim = Pose.Shim.Replace(() => Program.GetInts())
             .With(() => ints.AsQueryable());
         Pose.PoseContext.Isolate(() =>
         {
             Console.WriteLine(Program.GetInts().Count());
         }, getIntsShim);
         Console.ReadLine();
     }
}

Isolated code seemed to get null (or at least perceives obtained object as a null).

[Miista]

I have looked at it, and it seems that the issue is caused by the call to get_Provider which is placed when a method is executed against an IQueryable. Will investigate further.

UPDATE: I have added tests to verify that we can indeed shim extensions methods. We can. The problem then lies with how the call to get_Provider is rewritten.

UPDATE: Yep. This is caused by an explicit interface implementation. We can fix this by looking up the method from the interface map associated with the type. Then we also need to update how we find the matching shim.

[Miista]

@wfrohmberg I pushed a fix for this to the associated branch. This fixes being unable to resolve explicit interface members.

Unfortunately, this is not the whole story. Once I got past the explicit interface, I ran into another problem.

There are the following methods on arrays:

• GetEnumerator
• CopyTo
• get_Count (Count property)
• get_Item (indexer)
• set_Item (indexer)
• Add
• Contains
• get_IsReadOnly (IsReadOnly property)
• Clear
• IndexOf
• Insert
• Remove
• RemoveAt

However, those methods do not actually exist on array. Arrays in C# "implement" IList, IReadOnlyCollection, and IEnumerable via something called SZArrayHelper. This is a special, magic class which the compiler and the runtime use to make it seem like arrays actually implement the mentioned interfaces. However, that's not true.

This means that when we attempt to devirtualize a method during a rewrite, the method does not exist on the type nor is it implemented via explicit interface.

More info can be found here: https://stackoverflow.com/a/11164210 and https://stackoverflow.com/questions/19914523/mystery-behind-system-array

I will investigate some more and see if there is a solution.

[BigDLA]

Hello, I had simular problem, so I tried using commit https://github.com/Miista/pose/tree/54-problem-accessing-linq-methods-extension-methods-of-iqueryable-inside-isolated-code if it solves problem for us as well. Unfortunatelly I think I ran into simular issue with GetHashCode on IEqualityComparer, as with array methods mentioned above. The situation is this:

• There is a public static method SomeMethod(IOurInterface type) returning IOurInterface.
• Inside the method there is call Collection.TryGetValue(type, out IOurInterfaceret), where Collection property is private static readonly ConcurrentDictionary<string, ConcurrentDictionary<IOurInterface, IOurInterface>>.
• TryGetValue calls GetHashCode.
• StubHelper.DeVirtualizeMethod then looks for GetHashCode on IOurInterface, where it doesn´t exist, and in GetExplicitlyImplementedMethod it ends in InvalidOperationException because interfaceType is null.

[Miista]

@BigDLA Can you put together a small example?

[BigDLA]

I´ll try, but its quite extensive complicated legacy code, so far I wasnt able to replicate it elsewhere. But I will give it another go. :D

[BigDLA]

I beleve I managed to reproduce it: https://github.com/BigDLA/PoseDemo.git, just run the console and it should fail when lolObject.LolMethod() is called in isolated code (specifically on line var foo = CollectionClass.SomeStaticMethod(a))

[Miista]

@BigDLA I got past the InvalidOperationException. There are no exceptions. Please see below image.

However, the key doesn't seem to be in the dictionary any longer. I'm sure this is somehow caused by the rewrite.

UPDATE: I was able to get it working successfully if I simply forward calls to ConcurrentDictionary<,> (that is, not rewrite them).

I believe this might be a valid way forward given that ConcurrentDictionary<,> is intended to be used in highly parallel situations.

That said, there seems to be a problem on .NET 6, 7, and 8 with regards to how the IL is rewritten. Most tests fail with "Common Language Runtime detected an invalid program." I'm tracking this is #55

[Miista]

@BigDLA It should be fixed in the latest commit on the associated branch. Please verify.

[BigDLA]

@Miista It looks like it fixed the reported problem, thank you for the swift reaction. However, I seem to have another problem further down the road, but having trouble pinpointing it. Do you have any tips if it is possible to somehow debug the emmited code?

[Miista]

@BigDLA Unfortunately, there is no way to set breakpoints in the emitted code.

You can define a TRACE constant in the Pose project and any project using it directly. This will output the IL for the code under isolation; not the IL being emitted, however.

Putting Console.WriteLines should work, however primitive it might be.

Can you tell me more about the issue?