Recursive regex compile fails: (RegexpError) invalid group name <0> #4077
Description
Environment
$ jruby -v
jruby 9.1.2.0 (2.3.0) 2016-05-26 7357c8f Java HotSpot(TM) 64-Bit Server VM 25.40-b25 on 1.8.0_40-b26 +jit [darwin-x86_64]
$ uname -a
Darwin rnevell-lt.local 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
Test case
$ cat test.rb
re = /a\g<0>*z/
if "aaazzz".match(re)
puts "PASS"
else
puts "FAIL"
exit 1
end
Expected Behavior
MRI allows recursive regular expressions groups with the \g<0> group which is particularly useful to match balanced expressions (ie parenthesis).
Actual Behavior
Attempting to compile a regular expression with \g<0> in jruby results in:
SyntaxError: (RegexpError) invalid group name <0>: /a\g<0>*z/