elixir-lang/elixir — pull request #2240 by gmcabrita (2014-05-06 00:17:38+00:00)
Title: Improve compiler message when duplicated modules are detected

As per #2131.

Now when you `mix compile` a project with the following files,

foo.ex

defmodule Foo do
def foo do
42
end

end

bar.ex

defmodule Foo do
def foo do
42
end
end

You now get:

== Compilation error on file lib/foo.ex ==
** (CompileError) lib/foo.ex:1: cannot define module Foo because it is currently being defined in lib/bar.ex:1