[erlang-questions] Deprecation warnings: OTP20 and OTP21 compatible code

[Loïc Hoguin]

On 06/06/2018 01:18 PM, Fred Hebert wrote:
> On 06/06, Loïc Hoguin wrote:
>> It's worth noting that you did not have an issue with Cowboy, Ranch 
>> and friends. That's because the default policy in Erlang.mk is to NOT 
>> use warnings_as_errors for dependencies (and as a result this option 
>> is not included in the generated rebar.config).
>>
>> This saves a lot of headaches. erlang:get_stacktrace/0 is notable in 
>> how widely used it is but issues with warnings_as_error have always 
>> existed for as long as I've been doing Erlang. Tools should really 
>> have a saner default policy for this. The build shouldn't break for 
>> your users just because a new warning was introduced.
>>
> 
> Rebar3 leaves the warnings that libs put for themselves there.
> 
> There's a PR currently going about adding a 'del' override, which would 
> let someone remove the option by specifying:
> 
> {overrides, [
>     {del, [
>         {erl_opts, [warning_as_errors]}
>     ]}
> ]}
> 
> and would let you instantly remove the option from all dependencies 
> rather than having to go through the override pattern Jesper has shown 
> here.
> 
> If/Once merged, it would help address the problem. I'm a bit hesitant to 
> go and disable some options _by default_ when library authors have set 
> them there for a reason.

They have a reason of course: this option is great during development. 
Everyone should use it.

Building as a dependency is a different context though and having your 
dependencies break every time there's a new OTP version is not the best 
user experience. I suppose Rebar3 has a way to have stricter compilation 
profiles for use during development, but I haven't seen much use of 
that. So it falls down to each dependency's user to fix those issues, 
and that's a problem.

It being a default may or may not be a good idea, I don't know. All I do 
know is that nobody complained and nobody asked for an option to disable 
that behavior so I think it's good enough for now. It's one less problem 
to worry about. Rebar has more users and with a different mindset so the 
same may not apply.

-- 
Loïc Hoguin
https://ninenines.eu