I am trying to understand why transitive compile-time dependency is there, and what’s a good strategy to remove it. The mix app for example below is available here.

In a nutshell, I have these 3 modules:

# a.ex
defmodule A do
  import B, only: [valid_string: 1]

  def check(string) when valid_string(string), do: "OK"
end

# b.ex
defmodule B do
  defguard valid_string(string) when string in ~w(read write)

  def by_the_way do
    C.something()
  end
end

# c.ex
defmodule C do
  def something do
    IO.puts("Just passing by")
  end
end

Dependencies from this module form a what’s known as transitive compile-time dependency. This can be confirmed by running mix href command:

mix xref graph --label compile-connected

Output:

lib/a.ex
└── lib/b.ex (compile)

If I remove by_the_way function from module B, mix xref no longer reports a transitive compile-time dependency. Could someone explain to me why A transitively depends on C, even though A is only interested in importing the macro from B, and doesn’t really care about the function by_the_way or its implementation?

What’s a good strategy to remove such transitive compile time dependency? Is it like separating macros and functions in different modules?