[O] Bug: Capture template file source variant support in Customize [8.3.4 (8.3.4-47-gaf853d-elpa @ /home/phil/.emacs.d/elpa/org-20160502/)]

[Phil Hudson]

Remember to cover the basics, that is, what you expected to happen and
what in fact did happen.  You don't know how to make a good report?  See

     http://orgmode.org/manual/Feedback.html#Feedback

Your bug report will be posted to the Org-mode mailing list.
------------------------------------------------------------------------

Expected: When using the Customize interface to create/edit an Org
capture template, we expect to be able to specify a file to write the
captured item into using (according to the documentation) any one of:
  * a literal filename
  * a function
  * a variable
  * a form
But the Customize UI supports only the first of these. The attached
patch adds Customize support for the other three variants, in the proper
order (increasing generality/decreasing specificity).

Note that using Lisp to specify a capture template's target file using a
function, variable or sexp *does* work fine and as documented, except
that thereafter Customize fails to present the resulting variable
correctly; it reverts to showing the alist as one Lisp form. This patch
simply "catches up" the Customize UI with what Org can do and is
documented as doing.

As a workaround, I fell back on using the alternative 'function' target
specification method. That is, it's an alternative to 'file'; not to be
confused with the 'function' sub-method of 'file'. It took some rooting
around in source code for me to understand exactly what this function
has to do. It has to visit a file and optionally move point. Overkill
for my initial requirement, which was simply to produce a date-including
filename, but I made it work*, rather than lose the Customize UI. Anyway,
the documentation was too vague, and this patch also fixes that.

I have signed the FSF papers.  

* pending your acceptance of this patch, at which point I can revert to
  the simpler filename-producing function I wanted to use initially.
  
-- 
Phil Hudson                   http://hudson-it.ddns.net
@UWascalWabbit                 PGP/GnuPG ID: 0x887DCA63


--- org-20160502/org-capture.el 2016-05-07 10:18:26.000000000 +0100
+++ org.patched/org-capture.el  2016-05-04 11:54:23.000000000 +0100
@@ -157,8 +157,8 @@
                 File to the entry that is currently being clocked
 
              (function function-finding-location)
-                Most general way, write your own function to find both
-                file and location
+                Most general way: write your own function which both visits the
+                file and moves point to the right location.
 
 template     The template for creating the capture item.  If you leave this
              empty, an appropriate default template will be used.  See below
@@ -299,7 +299,11 @@
                  (choice :tag "Target location"
                          (list :tag "File"
                                (const :format "" file)
-                               (file :tag "  File"))
+                  (choice :tag "  Filename"
+                    (file :tag "  Literal")
+                    (function :tag "  Function")
+                    (variable :tag "  Variable")
+                    (sexp :tag "  Form")))
                          (list :tag "ID"
                                (const :format "" id)
                                (string :tag "  ID"))