Re: Capture template and elisp expression

[Nick Dokos <nicholas.dokos@hp.com>]

Rainer M Krug <r.m.krug@gmail.com> wrote:

> 
> Hi
> 
> I want to use a Capture Template to record changes to files under
> version control. Everything works as expected, but I would like to
> include the current revision in the template.
> 
> Therefore I tried the following:
> 
> * %T %? at %a by Rainer M Krug, email: Rainer@krugs.de
> %(vc-working-revision buffer-file-name)
> 
> for the template, but I get an error:
> 
> **** <2011-01-06 Thu 13:06>  at
> [[file:~/Documents/Projects/BiocontrolAndAlienDynamics/nonSpatialAcacia/trunc/R/nsa.org::*Finalise][Finalise]]
> by Rainer M Krug, email: Rainer@krugs.de %![Error: (wrong-type-argument
> stringp nil)]
> 
> Any idea how I could get the revision of the org file from which the
> Capture has been initiated (here
> ~/Documents/Projects/BiocontrolAndAlienDynamics/nonSpatialAcacia/trunc/R/nsa.org
> )?
> 

There are a few problems: the evaluation of the sexp happens in the
capture buffer where buffer-file-name returns nil. Even if you could
get the file name, vc-working-revision would return nil on a file that
is not VC-registered and the template would barf.

Those are easy problems to solve but there is another one that seems
insurmountable (with current code): my original thought was to use the
%a escape to pass the link to a lisp function, extract the file name
from it[fn:1] and run vc-working-revision on it (with appropriate safeguards
to catch non-VC files), something like this:

"* %T %? at %a by Rainer M Krug, email: Rainer@krugs.de        %(rk-custom-function-to-get-vc-revision \"%a\")"

However, this fails because at the time that %(sexp) constructs are
expanded, simple %a etc. constructs have not been expanded yet, so what
the function above gets is a literal "%a": the subtitution sequence is

            ;; %[] Insert contents of a file.

            ...

            ;; %() embedded elisp

            ...

            ;; Simple %-escapes

(see lisp/org-capture.el, lines 1181-1229 or so).

Moreover, this sequence was different and was changed deliberately (see
the thread http://thread.gmane.org/gmane.emacs.orgmode/27649), so if it
is changed back, Sebastion Rose will not be happy :-)

So it seems there is no way to pass values from the capture context to a
lisp function in the capture template, but maybe I'm missing something.

Thanks,
Nick

Footnotes:
[fn:1] Is there an easier way to get the filename of the file I was
visiting when I initiated the capture? If not, should there be? Perhaps
a %f escape?