Re: Gnus nnmail-split-fancy regexps can’t support backrefs inside themselves?

[tomas@tuxteam.de]

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On Mon, Mar 19, 2018 at 01:57:07PM +0100, Garreau, Alexandre wrote:
> Le 17/03/2018 à 09h25, tomas@tuxteam.de a écrit :
> > On Fri, Mar 16, 2018 at 08:15:59PM +0100, Garreau, Alexandre wrote:
> >> If I use a rule with a match regexp including a backreference inside the
> >> variable nnmail-split-fancy, it doesn’t match anything anymore:
> >> ("list-id" ".*<\\(gcc\\)-\\(help\\).\\1.\\(gnu\\)\\.org>.*" "lists.\\3.\\1.\\2")
> >
> > What are you trying to match? The above will match "gcc-help#gcc#gnu.org
> > (where '#' stands here for any character). This looks strange to me (what
> > is the use of \\(...\\) for a constant match? \1 will always (in the case
> > of a match, that is) be "gcc", \2 always "help" and \3 always "gnu".
> >
> > Is that really your intention? What are you trying to match?
> 
> Yes, and sorry (for the .), indeed I did correct this since, it is now
> ".*<\\(gcc\\)-\\(help\\)\\.gcc\\.\\(gnu\\)\\.org>.*". As the variable
> I’m talking about and the car of the list I’m talking about show, I’m
> trying to match the list-id mail header of the gcc-help mailing list,
> which contains “<gcc-help.gcc.gnu.org>”, but I reuse the words “gnu”,
> “gcc” and help in the group name I’m splitting this in
> (“lists.gnu.gcc.help”), so I group these names, so that later I can
> better factorise with other splitting rules. For maintainance and
> factorisations reasons, I’d also like to write “gcc” only once here,
> except it seems gnus/mail-split stops to match anything as soon as I
> include backrefs in the searching regexp.
> 
> >> Yet backrefs are supported on the other side of the rule… is this
> >> normal? why is that? I at least would like a confirmation ^^
> >
> > Yes, backreferences should work OK.
> 
> So why isn’t this regexp matching any line containing
> “<gcc-help.gcc.gnu.org>”?

By this you mean the one from your original mail, the one above,
i.e. ".*<\\(gcc\\)-\\(help\\).\\1.\\(gnu\\)\\.org>.*"?

For me, it matches:

  (string-match
    ".*<\\(gcc\\)-\\(help\\).\\1.\\(gnu\\)\\.org>.*"
    "<gcc-help.gcc.gnu.org>")

(returns 0, which is the start index. All is well).

Escaping the dots matches too, btw.

Cheers
- -- t
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