bug#64128: regexp parser zero-width assertion bugs

[Mattias Engdegård]

19 juni 2023 kl. 22.08 skrev Stefan Monnier <monnier@iro.umontreal.ca>:

> Hmm... maybe it's less wrong, but I'd rather make it behave like
> AB\(\b\)*C, which is, I'd argue, even less wrong.

I agree, and you are probably right that it's safe to do that.

> Or maybe make it signal an error: I can't imagine that the current
> behavior is used by very much code at all, seeing how it's so
> seriously non-intuitive.

That might be even better if we can get away with it.

19 juni 2023 kl. 22.40 skrev Paul Eggert <eggert@cs.ucla.edu>:

> In other words, how about if we change the groups from your list:
> 
> Group A: ^ $ \` \' \b \B
> Group B: \< \> \_< \_> \=
> 
> to this:
> 
> Group A: ^ \`
> Group B: $ \' \b \B \< \> \_< \_> \=
> 
> where "*" is ordinary after Group A, and special after Group B and there is 
> no other squirrelly behavior. And similarly for the other repetition 
> operators.

Sounds fine, with the option to go full error on group B if we agree that 
that's even better.

> Attached is a proposed doc change for this, which I have not installed.

Thank you, it has been incorporated in the attached patch which follows your 
suggestions above.

Your previous regexp doc updates are most appreciated. I still think the whole 
chapter needs a reform from the sheer weight of organic growth over the years. 
In particular, the division between "regexp special" and "regexp backslash" is 
purely syntactical, not semantic, and groups things in the wrong way.

0001-Straighten-regexp-postfix-operator-after-zero-width-.patch
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