[perl #6893] \G with /h results in infinite loop in 5.6 and later

On Wed Apr 25 06:17:47 2001, jeff@yahoo-inc.com wrote:
> Hi.  The attached program behaves differently on 5.005 and
> 5.6.  The relevant part is the regular expression
> m#(\G|\n)([^\n]*)\n#gsx, which under 5.005 iterates through
> every line in the string, but under 5.6 gets stuck on the second
> line and loops forever.
> 
> I don't know if this was a bug in 5.005 that is now fixed, but
> I can't figure out why it doesn't work.

This bug persists in blead perl (v5.9.5).

The attached patch fixes the immediate issue, but results in 

  lib/Text/Balanced/t/extqlk.t

failing some tests so it cant be applied. The test part could be
converted to a TODO however and applied regardless.

I have to say that the way /g code is handled in pp_match doesnt make a
lot of sense to me, and some parts of it are IMO highly suspect. I dont
think anything outside of the regexe engine should be assigning to the
paren buffers, especially not without taking measures to undo the change
in the case of a failed match.

Anyway, im investigating further but assistance or advice would be welcome.

Also I am renaming the bug to more accurately describe the underlying issue.

Cheers,
Yves

• [ID 20010425.006] regexp difference between 5.005 and 5.6 by Jeff Jones
• [perl #6893] \G with /h results in infinite loop in 5.6 and later by yves orton via RT