[patch] Run occur command restricted to a region

[Tino Calancha <tino.calancha@gmail.com>]

Hi,

is it worth to have versions of `occur' restricting the
search to lines before (after) the current line?

Maybe there is already a way to do that, and i just ignore it.
I usually just i copy the region into a temporary buffer; then
i run `occur' there.

I just wrote a patch to show my point; it adds the following commands:
1) occur-backward: for lines before the current one.
2) occur-forward: for lines after the current one.
3) occur-in-region: for lines within the active region.

Not sure if we want to bind them to keys.
Tentatively, i have assigned `M-s b' and `M-s f' for
1) and 2) in the `search-map'.  That means, these bindings
are not available in all modes; OTOH command `occur' is in
the `global-map', so it's always available.

Any comment about this proposal?

Thanks,
Tino
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From 61097b346737aa1960da568c54fc2b9211e5fe5c Mon Sep 17 00:00:00 2001
From: Tino Calancha <tino.calancha@gmail.com>
Date: Thu, 29 Dec 2016 15:02:47 +0900
Subject: [PATCH] New commands: occur-forward, occur-backward, occur-in-region

* lisp/replace.el (occur-matches-threshold): New variable.
(occur-in-region, occur-forward, occur-backward): New commands.
* lisp/bindings.el (search-map): Bind occur-backward to 'M-s b'
and occur-forward to 'M-s f'.
---
 lisp/bindings.el |  2 ++
 lisp/replace.el  | 51 ++++++++++++++++++++++++++++++++++++++++++++++-----
 2 files changed, 48 insertions(+), 5 deletions(-)

diff --git a/lisp/bindings.el b/lisp/bindings.el
index c13f4b156a..4b1c88a3c5 100644
--- a/lisp/bindings.el
+++ b/lisp/bindings.el
@@ -928,6 +928,8 @@ search-map
 (define-key esc-map "s" search-map)
 
 (define-key search-map "o"    'occur)
+(define-key search-map "b"    'occur-backward)
+(define-key search-map "f"    'occur-forward)
 (define-key search-map "\M-w" 'eww-search-words)
 (define-key search-map "hr"   'highlight-regexp)
 (define-key search-map "hp"   'highlight-phrase)
diff --git a/lisp/replace.el b/lisp/replace.el
index a172174633..09e0bf1e1f 100644
--- a/lisp/replace.el
+++ b/lisp/replace.el
@@ -1322,11 +1322,12 @@ occur-excluded-properties
   :group 'matching
   :version "22.1")
 
-(defun occur-read-primary-args ()
-  (let* ((perform-collect (consp current-prefix-arg))
+(defun occur-read-primary-args (&optional where)
+  (let* ((str (if where (concat " " where) ""))
+         (perform-collect (consp current-prefix-arg))
          (regexp (read-regexp (if perform-collect
-                                  "Collect strings matching regexp"
-                                "List lines matching regexp")
+                                  (concat "Collect strings matching regexp" str)
+                                (concat "List lines matching regexp" str))
                               'regexp-history-last)))
     (list regexp
 	  (if perform-collect
@@ -1389,6 +1390,42 @@ occur
   (interactive (occur-read-primary-args))
   (occur-1 regexp nlines (list (current-buffer))))
 
+(defun occur-backward (regexp &optional nlines)
+    "Show all lines before current line containing a match for REGEXP.
+Each line is displayed with NLINES lines before and after, or -NLINES
+before if NLINES is negative.
+As `occur' but restricted to lines before the current one."
+  (interactive (occur-read-primary-args "backward"))
+  (narrow-to-region (point-min) (point))
+  (occur regexp nlines)
+  (widen))
+
+(defun occur-forward (regexp &optional nlines)
+  "Show all lines after current line containing a match for REGEXP.
+Each line is displayed with NLINES lines before and after, or -NLINES
+before if NLINES is negative.
+As `occur' but restricted to lines after the current one."
+  (interactive (occur-read-primary-args "forward"))
+  (let ((occur-matches-threshold
+         (line-number-at-pos (point))))
+    (narrow-to-region (point) (point-max))
+    (occur regexp nlines))
+  (widen))
+
+(defun occur-in-region (regexp &optional nlines)
+  "Show all lines in the active region containing a match for REGEXP.
+Each line is displayed with NLINES lines before and after, or -NLINES
+before if NLINES is negative.
+As `occur' but restricted to lines within the active region."
+  (interactive (occur-read-primary-args "in region"))
+  (unless (use-region-p)
+    (error "Region not active"))
+    (let ((occur-matches-threshold
+         (line-number-at-pos (region-beginning))))
+      (narrow-to-region (region-beginning) (region-end))
+      (occur regexp nlines))
+    (widen))
+
 (defvar ido-ignore-item-temp-list)
 
 (defun multi-occur (bufs regexp &optional nlines)
@@ -1539,6 +1576,9 @@ occur-1
             (set-buffer-modified-p nil)
             (run-hooks 'occur-hook)))))))
 
+;; Let binded in `occur-forward' and `occur-in-region'.
+(defvar occur-matches-threshold nil)
+
 (defun occur-engine (regexp buffers out-buf nlines case-fold
 			    title-face prefix-face match-face keep-props)
   (with-current-buffer out-buf
@@ -1551,7 +1591,8 @@ occur-engine
 	(when (buffer-live-p buf)
 	  (let ((lines 0)               ;; count of matching lines
 		(matches 0)             ;; count of matches
-		(curr-line 1)           ;; line count
+		(curr-line              ;; line count
+                 (or occur-matches-threshold 1))
 		(prev-line nil)         ;; line number of prev match endpt
 		(prev-after-lines nil)  ;; context lines of prev match
 		(matchbeg 0)
-- 
2.11.0

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
In GNU Emacs 26.0.50.1 (x86_64-pc-linux-gnu, GTK+ Version 3.22.5)
 of 2016-12-28
Repository revision: 112460da705c2a6716d7b6bc72501de0a3757259