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Using a type defined in another module implies in compile-time dependency #5087

rranelli opened this issue Aug 3, 2016 · 3 comments


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@rranelli rranelli commented Aug 3, 2016


  • Elixir version (elixir -v): 1.3.2 & 1.2.6
  • Operating system: debian8 (jessie)

Current behavior

While debugging recompilation issues in my project I noticed that whenever we
add a reference to a type defined in another module in a typespec, the other
module is added as compile-time dependency.

For example, if we have something like this:

## type_a.ex
defmodule TypeA do
  @type t :: integer

## type_c.ex
defmodule TypeC do
  @type t :: integer

## type_b.ex
defmodule TypeB do
  @spec a() :: TypeA.t
  def a, do: ()

  @spec c() :: TypeC.t
  def c, do: ()

I will end up with the following dependency graph:

screenshot from 2016-08-03 13 55 08

This contributes to unnecessary re-compilation. Because of this, some "cycles"
appeared in my project and changing a particular file implied in the
recompilation of 200+ others. I ended up commenting all type declarations and
specs to workaround the issue.

I have been able to reproduce this behavior in both v1.3.2 and v1.2.6.

(I have created a repository to
exemplify the problem.)

Expected behavior

I have talked with @josevalim over IRC about this and it seems to him that this
behavior is a bug.

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@josevalim josevalim commented Aug 3, 2016

Thank you! We should fix this and backport it. :)

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Contributor Author

@rranelli rranelli commented Aug 3, 2016

If there is anything I can do to help, let me know 👍

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@ericentin ericentin commented Aug 3, 2016

@josevalim are you still taking a look at this like you were this morning? Happy to work on this if you would prefer to do stuff on GenStage or whatever.

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