[ruby-core:63156] [ruby-trunk - Bug #9943] [Open] Ruby 1.9.3 improperly reports unused variable warnings

Issue #9943 has been reported by Aaron Kromer.

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Bug #9943: Ruby 1.9.3 improperly reports unused variable warnings
https://bugs.ruby-lang.org/issues/9943

* Author: Aaron Kromer
* Status: Open
* Priority: Normal
* Assignee: 
* Category: core
* Target version: 
* ruby -v: ruby 1.9.3p547 (2014-05-14 revision 45962) [x86_64-darwin13.2.0]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN
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This is related to https://bugs.ruby-lang.org/issues/6693 and possibly https://bugs.ruby-lang.org/issues/7730.

Top-level unused variables prefixed with an underscore, _, do not report a warning. However, unused variables in methods or in required files which all report warnings.

The _only_ Ruby version which _incorrectly_ reports the warnings is 1.9.3. I've attached the simple scripts which demonstrate the issue.

~~~
$ ruby -v; ruby -w base_script.rb 
ruby 1.9.3p547 (2014-05-14 revision 45962) [x86_64-darwin13.2.0]
base_script.rb:2: warning: assigned but unused variable - _a
~/another_file.rb:2: warning: assigned but unused variable - _c
~/another_file.rb:6: warning: assigned but unused variable - _d
in required file
end of script
~~~

To confirm this was the only version, here is my output for all the versions I test:

~~~
$ rvm use 1.8.7; ruby -v; ruby -w base_script.rb 
Using ~/.rvm/gems/ruby-1.8.7-head
ruby 1.8.7 (2014-01-28 patchlevel 376) [i686-darwin13.2.0]
in required file
end of script

$ rvm use 1.9.2; ruby -v; ruby -w base_script.rb
Using ~/.rvm/gems/ruby-1.9.2-head
ruby 1.9.2p327 (2014-01-23 revision 44682) [x86_64-darwin13.2.0]
in required file
end of script

$ rvm use 1.9.3; ruby -v; ruby -w base_script.rb
Using ~/.rvm/gems/ruby-1.9.3-p547
ruby 1.9.3p547 (2014-05-14 revision 45962) [x86_64-darwin13.2.0]
base_script.rb:2: warning: assigned but unused variable - _a
~/another_file.rb:2: warning: assigned but unused variable - _c
~/another_file.rb:6: warning: assigned but unused variable - _d
in required file
end of script

$ rvm use 2.0.0; ruby -v; ruby -w base_script.rb
Using ~/.rvm/gems/ruby-2.0.0-p481
ruby 2.0.0p481 (2014-05-08 revision 45883) [x86_64-darwin13.1.0]
in required file
end of script

$ rvm use 2.1.2; ruby -v; ruby -w base_script.rb
Using ~/.rvm/gems/ruby-2.1.2
ruby 2.1.2p95 (2014-05-08 revision 45877) [x86_64-darwin13.0]
in required file
end of script
~~~


---Files--------------------------------
another_file.rb (131 Bytes)
base_script.rb (98 Bytes)


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