Issue #12944 has been updated by Eregon (Benoit Daloze).


It seems it is a compatibility issue.
For instance Thread.exclusive warning is now printed incorrectly:

~~~
$ ruby -ve 'def m; Thread.exclusive {}; end; m'
ruby 2.4.0p0 (2016-12-24 revision 57164) [x86_64-linux]
Thread.exclusive is deprecated, use Thread::Mutex
-e:1:in `m'
-e:1:in `<main>'

$ ruby -ve 'def m; Thread.exclusive {}; end; m'
ruby 2.5.0dev (2017-04-24 trunk 58466) [x86_64-linux]
Thread.exclusive is deprecated, use Thread::Mutex
["-e:1:in `m'", "-e:1:in `<main>'"]
~~~

The fix is easy:

~~~ diff
   def self.exclusive
-    warn "Thread.exclusive is deprecated, use Thread::Mutex", caller
+    warn "Thread.exclusive is deprecated, use Thread::Mutex", *caller
     MUTEX_FOR_THREAD_EXCLUSIVE.synchronize{
~~~

But this is not the only usage of warn + caller.
https://github.com/search?l=Ruby&p=2&q=warn+caller&type=Code&utf8=%E2%9C%93
I think it would be best to remain compatible and join("\n") #warn's arguments.

----------------------------------------
Feature #12944: Change Kernel#warn to call Warning.warn
https://bugs.ruby-lang.org/issues/12944#change-64454

* Author: jeremyevans0 (Jeremy Evans)
* Status: Closed
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
Currently, Kernel#warn is basically the same as $stderr.puts.  With the new Warning.warn support in ruby 2.4, it makes sense for Kernel#warn to call Warning.warn, otherwise you will not be able to use Warning.warn to filter/process warning messages generated by Kernel#warn.

The Kernel#warn API is different than the Warning.warn API, the attached patch tries to get similar behavior, but there are probably corner cases where the behavior is different.

---Files--------------------------------
0001-Change-Kernel-warn-to-call-Warning.warn.patch (1.88 KB)
0001-Change-Kernel-warn-to-call-Warning.warn.patch (1.89 KB)
0001-Change-Kernel-warn-to-call-Warning.warn.patch (2.36 KB)
0001-Change-Kernel-warn-to-call-Warning.warn.patch (2.3 KB)
0001-Change-Kernel-warn-to-call-Warning.warn.patch (3.23 KB)


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