File.dirname interprets backslashes as path separators on Mac OS X

[dlovellrw]

Environment

~/> ruby -v
jruby 1.7.21 (1.9.3p551) 2015-07-07 a741a82 on Java HotSpot(TM) 64-Bit Server VM 1.8.0_31-b13 +jit [darwin-x86_64]
~> uname -a
Darwin 15.6.0 Darwin Kernel Version 15.6.0: Thu Jun 23 18:25:34 PDT 2016; root:xnu-3248.60.10~1/RELEASE_X86_64 x86_64

Expected Behavior

~> ruby -v
ruby 1.9.3p551 (2014-11-13 revision 48407) [x86_64-darwin15.6.0]
~> irb
irb(main):001:0> path = 'this/path/has/filename\that\contains\backslashes'
=> "this/path/has/filename\\that\\contains\\backslashes"
irb(main):002:0> File.dirname path
=> "this/path/has"
irb(main):003:0>

~> ruby -v
ruby 2.2.4p230 (2015-12-16 revision 53155) [x86_64-darwin15]
~> irb
irb(main):001:0> path = 'this/path/has/filename\that\contains\backslashes'
=> "this/path/has/filename\\that\\contains\\backslashes"
irb(main):002:0> File.dirname path
=> "this/path/has"
irb(main):003:0>

Actual Behavior

~> ruby -v
jruby 1.7.21 (1.9.3p551) 2015-07-07 a741a82 on Java HotSpot(TM) 64-Bit Server VM 1.8.0_31-b13 +jit [darwin-x86_64]
~> irb
irb(main):001:0> path = 'this/path/has/filename\that\contains\backslashes'
=> "this/path/has/filename\\that\\contains\\backslashes"
irb(main):002:0> File.dirname path
=> "this/path/has/filename\\that\\contains"
irb(main):003:0>

~> ruby -v
jruby 9.1.2.0 (2.3.0) 2016-05-26 7357c8f Java HotSpot(TM) 64-Bit Server VM 25.31-b07 on 1.8.0_31-b13 +jit [darwin-x86_64]
~> irb
irb(main):001:0>  path = 'this/path/has/filename\that\contains\backslashes'
=> "this/path/has/filename\\that\\contains\\backslashes"
irb(main):002:0>  File.dirname path
=> "this/path/has/filename\\that\\contains"
irb(main):003:0>

Additional Information

The code in RubyFile.java uses hard-coded path separator values, e.g. line 724 if (endChar == '/' || endChar == '\\') {, rather than system dependent constants, such as Java File.separator.

[headius]

Shouldn't be a hard one to write a patch for...only use \ on platforms where that's the path separator. Anyone care to try a PR?