Issue #16345 has been updated by Eregon (Benoit Daloze).


The above also shows we should avoid multiple calls to rb_warn* for a single logical warning.
E.g., `warning: The last argument is used as the keyword parameter` and `warning: for method defined here` should be part of a single (multi-line) String sent to `Warning.warn`.
That's anyway much better for other kinds of filtering with `Warning.warn`.

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Feature #16345: Don't emit deprecation warnings by default.
https://bugs.ruby-lang.org/issues/16345#change-82839

* Author: akr (Akira Tanaka)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
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We propose that Ruby doesn't emit deprecation warnings by default.

Deprecation warnings are only useful during development for updating Ruby version.
They are not useful during development with current Ruby.
It is especially frustrating when deprecated warnings are generated in gems.
Also, deprecation warnings are totally useless in production environment.

So, we want to emit deprecation warnings only in useful situations.

We propose a command line argument `-W:deprecated` (or `--warning=deprecated`)
and the following methods to enable/disable deprecation warnings.

```ruby
Warning.disable(:deprecated)
Warning.enable(:deprecated)
Warning.enabled?(:deprecated)
```

Currently we don't propose a method to generate a deprecation warning
because currently our main intent is to disable deprecation warnings for 
keyword arguments, and the warnings are generated in C level.

Background:

We talked about keyword arguments during a developer meeting (2019-11-12).
https://bugs.ruby-lang.org/issues/16333
We expect many deprecation warnings to be generated in Ruby 2.7.
They are not useful except for development for Ruby transition, and
they may block transition to Ruby 2.7.

So, we have consensus to disable deprecation warnings by default.
Our design is intentionally minimum because we need this feature for Ruby 2.7.

We chose `Warning.disable(:deprecated)` instead of
re-defining `Warning.warn` in order to avoid string object generation.

Of course, we expect to extend this feature:
Ruby-level deprecation warning generation,
warnings other than deprecation, 
file-based restriction of warning generation, etc.
But this issue doesn't contain them.




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