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Re: Perl 5.18 and Regexp::Grammars

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Karl Williamson
June 28, 2013 04:43
Re: Perl 5.18 and Regexp::Grammars
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On 06/27/2013 06:22 PM, Dave Mitchell wrote:
> I can reduce the failure to the following code:
>      m{(?&foo){0}(?<foo>)}
> which SEGVs during compilation. 'git blame' blames Karl.
> (which is not to say that there aren't other SEGing issues, which might
> involve code blocks, but this first SEGV is innocent of them).
> Karl, is this something you can deal with?
> v5.17.7.0-60-g3018b82
> 3018b823898645e44b8c37c70ac5c6302b031381 is the first bad commit
> commit 3018b823898645e44b8c37c70ac5c6302b031381

I believe I have found the problem.  I mistakenly combined what should 
have been two commits in this one, and the commit message doesn't even 
mention the one at fault.

What appears to be going on is that


is getting replaced by a NOTHING node, which is an optimization we 
agreed to on p5p.  Thus it doesn't set up 'foo', and so the reference to 
it is NULL, which segfaults when dereferenced.

Suggestions as to how to proceed are welcome.  Obviously, we could 
remove the optimization.  Or apply it when what is being replaced is one 
of certain node types, or has some characteristic, like width.  I 
haven't looked into this at all.

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