Re: Marking ! in virtual groups

[Matt Ford <matt@dancingfrog.co.uk>]

Goodness, I'm making a mess of this.  Okay, a simple test case.

Setting edebug over gnus-request-set-mark shows behaviour like so:

In a *nnimap* summary buffer marking an article with ! and then doing M-g
results in the action part of the function

(defun gnus-request-set-mark (group action)
  "Set marks on articles in the back end."
  (let ((gnus-command-method (gnus-find-method-for-group group)))
    (if (not (gnus-check-backend-function
	      'request-set-mark (car gnus-command-method)))
	action
      (funcall (gnus-get-function gnus-command-method 'request-set-mark)
	       (gnus-group-real-name group) action
	       (nth 1 gnus-command-method))
      (gnus-run-hook-with-args gnus-after-set-mark-hook group action))))

being

(((6507) add (tick)))

However in a *nnvirtual* summary buffer marking and article with ! and then doing M-g
results in the action being

((((1 . 6508)) add (read)))

so the passed action parameter is wrong.

I had a look at the M-g code and I reckon it's the function

(defun gnus-update-marks ()
  "Enter the various lists of marked articles into the newsgroup info list."
...

In particular its the section of this function that builds up the
delta-marks data structure used for changing the info.  It looks like this

...
	(when (and (gnus-check-backend-function
		    'request-set-mark gnus-newsgroup-name)
		   (not (gnus-article-unpropagatable-p (cdr type))))
	  (let* ((old (cdr (assq (cdr type) (gnus-info-marks info))))
		 ;; Don't do anything about marks for articles we
		 ;; didn't actually get any headers for.
... SNIP ...
	    (when add
	      (push (list add 'add (list (cdr type))) delta-marks))
	    (when del
	      ;; Don't delete marks from outside the active range.
	      ;; This shouldn't happen, but is a sanity check.
	      (setq del (gnus-sorted-range-intersection
			 (gnus-active gnus-newsgroup-name) del))
	      (push (list del 'del (list (cdr type))) delta-marks))))

Other functions that set marks seem to have a more sophisticated form
of checking that looks to iterate over the actual backends.  For example,

(defun gnus-request-set-mark (group action)
  "Set marks on articles in the back end."
  (let ((gnus-command-method (gnus-find-method-for-group group)))
    (if (not (gnus-check-backend-function
	      'request-set-mark (car gnus-command-method)))
	action
      (funcall (gnus-get-function gnus-command-method 'request-set-mark)
	       (gnus-group-real-name group) action
	       (nth 1 gnus-command-method))
      (gnus-run-hook-with-args gnus-after-set-mark-hook group action))))

I think this more advanced check could be used in gnus-update-marks
function for generating delta-marks over the "real" back-ends.
      
This is all at the very limit of my elisp and gnus so perhaps I've got
this horribly wrong. I'm very unsure of myself here.

Any help appreciated.
-- 
Matt