amnu3387

Getting Line Error on stack trace when "using" modules

I had a very large module (for my experience) with around 2k loc. I broke it down for organisational purposes, although I’m just “importing” these new modules into a main one. Now whenever I have an error that occurs in one of the modules being used I get the stack trace with the line where the module is imported, along with the function name and arity.

** (ArgumentError) could not put/update key nil on a nil value
    (elixir) lib/access.ex:371: Access.get_and_update/3
    (elixir) lib/kernel.ex:1880: Kernel.put_in/3
    (AetherWars) lib/aetherwars/duels/duels_processor.ex:12: AetherWars.Duels.Processor.decide_next_player/1
    (AetherWars) lib/aetherwars/duels/duels_processor.ex:11: AetherWars.Duels.Processor.pop_stack/4
    (AetherWars) lib/aetherwars/duels/duels_processor.ex:22: AetherWars.Duels.Processor.entry_point/4
    (AetherWars) web/channels/duel_channel.ex:25: AetherWars.DuelChannel.handle_in/3
    (phoenix) lib/phoenix/channel/server.ex:244: anonymous fn/4 in Phoenix.Channel.Server.handle_info/2
    (AetherWars) lib/aetherwars/endpoint.ex:1: AetherWars.Endpoint.instrument/4
    (stdlib) gen_server.erl:616: :gen_server.try_dispatch/4
    (stdlib) gen_server.erl:686: :gen_server.handle_msg/6
    (stdlib) proc_lib.erl:247: :proc_lib.init_p_do_apply/3

Sometimes this is all I need, but other times I have several different functions with the same arity pattern-matching on the head. Is there any way to be able to see in which line of the original module that has been used it occurs? (I guess since use when compiled basically places the code on the module calling it, it won’t be straightforward but perhaps there’s some easy work-around?)

You can see it becomes a bit problematic:

defmodule AetherWars.Duels.Processor do
  
  use AetherWars.Duels.Create
  use AetherWars.Duels.Utils
  use AetherWars.Duels.Payment
  use AetherWars.Duels.Legal
  use AetherWars.Duels.Messages
  use AetherWars.Duels.Strike
  use AetherWars.Duels.Guard
  use AetherWars.Duels.Stack
  use AetherWars.Duels.Turn
  use AetherWars.Duels.Manipulation
  use AetherWars.Duels.Battle
  alias AetherWars.Duels.Monitor
  ...
end

Any solution? Thanks

8 comments

#errors #tracing #stack

2 2662 8

2017-12-07 21:57:45 UTC

Marked As Solved

ericmj

Elixir Core Team

Generated code will use the stacktrace location of the caller. This is a good default for most macros since generated code should be kept to a minimum, the fact that you need the location of the generated code in the stacktrace is an indication that you are overusing it. Using use that expands to function definitions with the full implementation for composition is an anti-pattern.

If you do need the line information from the macros add location: :keep to the quoted code: quote location: :keep do ... end.

Post #4

Also Liked

benwilson512

Author of Craft GraphQL APIs in Elixir with Absinthe

Hey! Large modules can definitely be a pain, but this is not the way to solve them. Find boundaries, break those things out into dedicated modules, then just have them each call each other.

Post #2

amnu3387

@benwilson512 thanks for your input - and although I will probably end up doing that, I still think the error should be shown from its line on the used module and not the line where the use statement is (not sure how difficult it is to achieve in technical terms…).

Post #3

amnu3387

Thanks @ericmj - that indeed answers my question. I will nonetheless try organising my code in a different way, following ben’s and your advice - in my head - probably wrong - those functions would belong together in the same module, perhaps except messages and create, since they are all operations on the game state (but I will probably curse the future me about that choice).

Post #5

Last Post!

amnu3387

Besides my mental model when projecting this (and having to change function calls in so many places), nothing is wrong with calling functions where they’re located in the source code - I tend to do that usually ah. alias still implies calling the module name, and import I think I tried but then I would need to “import” things in multiple places - like in the sample, I would need to import “utils” & “legal” & “payment” and then in “payment” and “legal” probably import “utils” again, and so on, otherwise they would break.

Perhaps it’s just bad architecture but given that I’m creating it as I go and don’t have the whole engine yet designed/thought about…