Intermittent :nofile error when deriving an `Any` protocol implementation.
Charles Lanahan
I'm cross-posting this to the Elixir forums and was discussing it on discord so I apologize if you see this twice.
I’m having a bit of an intermittent issue with deriving a protocol with an Any implementation and I’m not sure how to debug the issue or even reproduce consistently enough to file a bug so I thought I’d ask for suggestions here first.
I have a complex project where this appears. Unfortunately this project isn’t open source yet but hopefully soon as it would be much easier to share code to debug this weird issue. I have successfully implemented about 8 protocols so far (although none with deriving `Any`). I was creating a textbook Any protocol to derive from similar to https://hexdocs.pm/elixir/protocols.html#deriving .
At first this bug arose when I stuck a dbg() statement into the Any implementation in order to debug an issue I was getting. When I did this and tried to derive the protocol for a given module struct I’d get something similar to:
```
== Compilation error in file lib/kerilixir/KERI/events/receipt_event.ex ==
** (ArgumentError) could not load module Said.Saidifiable due to reason :nofile, cannot derive Said.Saidifiable for Kerilixir.Keri.ReceiptEvent
(elixir 1.19.5) lib/protocol.ex:331: Protocol.assert_protocol!/2
(elixir 1.19.5) lib/protocol.ex:1104: Protocol.derive/4
(stdlib 7.2) lists.erl:2641: :lists.foreach_1/2
(elixir 1.19.5) lib/protocol.ex:1097: Protocol.derive/3
lib/kerilixir/KERI/events/receipt_event.ex:22: (module)
```
When I removed the dbg() statement, removed the @derive from the struct, recompiled, added back the derive (without the dbg statement) the protocol would derive successfully. Adding the debug statement back would reproduce the error consistently.
Then somehow yesterday in fooling around with it I got the compilation and tests to pass with dbg() statement allowing me to troubleshoot the function call and fix the bug. Now when trying to derive this protocol for other structs I’m getting this error consistently again. At this point, I don’t have the dbg() calls anymore in the Any implementation but am still getting the :nofile error.
It seems like this is an issue in consolidation or compilation or something else that I don’t understand and so I’m reaching out for any ideas or even places to look in beginning to debug this. Its frustrating because the pattern of having a default protocol will work for most of these structs but then a few will be exceptions that will need custom implementations.
It did seem to happen with mix test more than mix compile but maybe that's all in my head. Now its just occurring over and over with mix compile.
I tried to create a simpler example of the file structure and test structure I’m running here (tests fail but not the :nofile error) but failed to reproduce my error in this simpler example. https://github.com/daidoji/simple_example
tl;dr something weird is happening in consolidation or compilation process and my protocol isn’t getting derived even though it should. Looking for ideas on how to troubleshoot this intermittent error.
José Valim
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Charles Lanahan
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