Use Kernel#warn for deprecations

[etiennebarrie]

That makes it possible to override Warning.warn starting with Ruby 2.5.0

See more at https://bugs.ruby-lang.org/issues/12299

[etiennebarrie]

This only applies to deprecations, if you're interested I can look at implementing this for the mocking warnings as well.
There were no tests for Mocha::Deprecation so I didn't add one specifically but I think it could be done even if it changes a global, because the tests don't run in parallel.

[floehopper]

I've only had a chance to read this very quickly and I'm not sure I understand. Can you give some example code demonstrating the problem you are trying to solve?

[etiennebarrie]

Using $stderr.puts does not respect the Ruby conventions which allow to set -W0 to silence warnings:

$ ruby -W0 -e 'warn "warning: not shown"'
# no output
$ ruby -e 'warn "warning: shown"'
warning: shown

https://idiosyncratic-ruby.com/3-ruby-can-you-speak-louder.html#command-line-options-for-debug-modes
https://mislav.net/2011/06/ruby-verbose-mode/

Using Kernel#warn gets us this feature for free, so we could remove Mocha::Deprecation.mode and change $VERBOSE directly in DeprecationDisabler.disable_deprecations.

---

Additionally, since Ruby 2.5.0, Kernel#warn calls Warning.warn in verbose mode, which lets you override it as described in feature 12299: https://bugs.ruby-lang.org/issues/12299

$ ruby -W0 -e 'def Warning.warn(warning) super("warning: #{warning}") end' -e 'warn "not shown"'
# no output
$ ruby -e 'def Warning.warn(warning) super("warning: #{warning}") end' -e 'warn "shown"'
warning: shown

I don't know if it's a good idea really, but my use case is to raise for warnings in CI/dev in a Rails app:

unless Rails.env.production?
  def Warning.warn(warning)
    raise warning
  end
end

[etiennebarrie]

Fixed in 196970a. Thanks!

[floehopper]

@etiennebarrie Oh, cool! Sorry for not responding sooner and thanks for noticing the (accidental!) fix. I'll try to get a release including the fix shipped in the not too distant future.

[etiennebarrie]

No problem. Thank you for your work!