warning: System.stacktrace/0 outside of rescue/catch clauses is deprecated. If you want to support only Elixir v1.7+, you must access __STACKTRACE__ inside a rescue/catch. If you want to support earlier Elixir versions, move System.stacktrace/0 inside a rescue/catch
lib/plug/conn/wrapper_error.ex:23
The function in plug that causes the warning is deprecated. You will see the warning during compile time, but unless you cann that deprecated function nothing bad should happen.
The offending function and code though can’t be removed or fixed without a breakling change and therefore can’t be happen before Plug 2.0.