bug#64128: regexp parser zero-width assertion bugs

[Paul Eggert]

On 2023-06-17 13:07, Mattias Engdegård wrote:
> 17 juni 2023 kl. 20.44 skrev Stefan Monnier <monnier@iro.umontreal.ca>:
>
> > I think the behavior that makes most sense is to signal an error when
> > compiling the regexp.
>
> Clearly, but some behaviour needs to be preserved for compatibility.
> Regexps like "^*" aren't uncommon. Can it be generalised in a useful way?

doc/lispref/searching.texi says that "*" is treated as an ordinary 
character if it is in a context where its special meaning makes no 
sense, giving "*foo" as an example. If we break with this tradition by 
making "\b*" an error instead of being equivalent to "\b\*", we should 
update that part of the manual.

One possible way forward is to update doc/lispref/searching.texi to 
specify what we want. Then we can modify the code to match the updated 
documentation.

In my experience, modifying the doc is often the hard part, so I took a 
crack at that in the draft proposed patch, which I have not installed.

Comments?

0001-Document-that-b-etc-are-now-invalid-regexps.patch
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