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

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

[Garreau, Alexandre]

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")

Yet backrefs are supported on the other side of the rule… is this
normal? why is that? I at least would like a confirmation ^^

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

[tomas]

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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?

> 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.

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

[Garreau, Alexandre]

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>”?

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

[tomas]

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

[Stefan Monnier]

Indeed, they don't support backrefs, because Gnus takes the regexp you
specify and embeds it into a larger regexp which also uses \(...\)
grouping, so you'd have to offset your backrefs by the proper number of
preceding \( in order for them to work right (and changes in Emacs/Gnus
can change this offset, of course, to make things more interesting).


        Stefan

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

[tomas]

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On Tue, Mar 20, 2018 at 04:20:41PM -0400, Stefan Monnier wrote:
> 
> Indeed, they don't support backrefs, because Gnus takes the regexp you
> specify and embeds it into a larger regexp which also uses \(...\)
> grouping, so you'd have to offset your backrefs by the proper number of
> preceding \( in order for them to work right (and changes in Emacs/Gnus
> can change this offset, of course, to make things more interesting).

Oh, good catch. Perhaps using explicitly numbered groups \(?NUM:...\)
might help here...

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

[Stefan Monnier]

> Oh, good catch. Perhaps using explicitly numbered groups \(?NUM:...\)
> might help here...

Right, but use large enough numbers to avoid conflict,


        Stefan