bug#69542: Feature request: making occur obey isearch-filter-predicate

[Gabriele Nicolardi]

> I think duplicating the whole body of functions is not better
> than using advice.
>

Until yesterday, I had no idea how to advise a function.

Now I'm experimenting with this code to obtain modified versions of occur and how-many that are sensitive to isearch-filter-predicate.

I'm not a programmer, so my code may not be very rigorous:

;; I need a copy of `re-search-forward' because it will be temporary adviced in
;; `how-many-ifp' and `occur-ifp' functions:
(defalias 're-search-forward-copy
  (symbol-function 're-search-forward)
  "Copy of `re-search-forward'")

(defun re-search-forward-ifp (REGEXP &optional BOUND NOERROR COUNT)
  "Modified version of `search-forward-regexp' that filters (skips) matches
according to `isearch-filter-predicate'."
  (let ((POINT (point)))
    (catch 'filtered
      (while (re-search-forward-copy REGEXP BOUND NOERROR COUNT)
        (let ((B (match-beginning 0))
              (E (match-end 0)))
          (when (funcall isearch-filter-predicate B E)
            (throw 'filtered (point)))))
      (goto-char POINT)
      nil)))
(defalias 'search-forward-regexp-ifp 're-search-forward-ifp)

(defun override-re-search-forward (orig-fun &rest args)
  "Temporary advice the `re-search-forward' function, overriding it with
`re-search-forward-ifp' to make it sensitive to `isearch-filter-predicate'"
  (unwind-protect
      (progn
        (advice-add 're-search-forward :override #'re-search-forward-ifp)
        (apply orig-fun args))
    (advice-remove 're-search-forward #'re-search-forward-ifp)))

(defalias 'how-many-ifp
  (symbol-function 'how-many)
  "Copy of the `how-many' function (to be) adviced to obey to
`isearch-filter-predicate'")
(defalias 'count-matches-ifp 'how-many-ifp)

(advice-add 'how-many-ifp :around #'override-re-search-forward)

(defalias 'occur-ifp
  (symbol-function 'occur)
  "Copy of the `occur' function (to be) adviced to obey to
 `isearch-filter-predicate'")

(advice-add 'occur-ifp :around #'override-re-search-forward)

The key is the `re-search-forward` function used in `how-many` and `occur` definition. If you make it sensible to `isearch-filter-predicate` also `how-many` and `occur` will be.

I don't know if advicing a function to advice a function inside it is a good idea but it seem to work (I need more tests).

Now I discovered how to build these functions I could be fine with my modified ones, but making this feature avaible (maybe not default) in the original functions could be a better idea.

>  An alternative would be to add a new variable
> 're-search-forward-function' and then to use it like
> '(funcall re-search-forward-function)'.
>

The idea of a new function seems good to me.