Make occur handle multi-line matches cleanly with context.

http://lists.gnu.org/archive/html/emacs-devel/2010-03/msg01280.html

* replace.el (occur-accumulate-lines): Add optional arg `pt'.
(occur-engine): Add local variables `ret', `prev-after-lines',
`prev-lines'.  Use more arguments for `occur-context-lines'.
Set first elem of its returned list to `data', and the second elem
to `prev-after-lines'.  Don't print the separator line.
In the end, print remaining context after-lines.
(occur-context-lines): Add new arguments `begpt', `endpt',
`lines', `prev-lines', `prev-after-lines'.  Rewrite to combine
after-lines of the previous match with before-lines of the
current match and not overlap them.  Return a list with two
values: the output line and the list of context after-lines.

* search.texi (Other Repeating Search): Remove line that `occur'
can not handle multiline matches.

* occur-testsuite.el (occur-tests): Add tests for context lines.

1 files changed, 73 insertions, 17 deletions

diff --git a/lisp/replace.el b/lisp/replace.el
index a74da4b89b5..14a1869b4f9 100644
--- a/lisp/replace.el
+++ b/lisp/replace.el
@@ -1005,8 +1005,10 @@ which means to discard all text properties."
   :group 'matching
   :version "22.1")
 
-(defun occur-accumulate-lines (count &optional keep-props)
+(defun occur-accumulate-lines (count &optional keep-props pt)
   (save-excursion
+    (when pt
+      (goto-char pt))
     (let ((forwardp (> count 0))
           result beg end moved)
       (while (not (or (zerop count)
@@ -1189,12 +1191,15 @@ See also `multi-occur'."
         (when (buffer-live-p buf)
           (let ((matches 0)     ;; count of matched lines
                 (lines 1)       ;; line count
+                (prev-after-lines nil)  ;; context lines of prev match
+                (prev-lines nil)        ;; line number of prev match endpt
                 (matchbeg 0)
                 (origpt nil)
                 (begpt nil)
                 (endpt nil)
                 (marker nil)
                 (curstring "")
+                (ret nil)
                 (inhibit-field-text-motion t)
                 (headerpt (with-current-buffer out-buf (point))))
             (with-current-buffer buf
@@ -1271,14 +1276,17 @@ See also `multi-occur'."
                                 ;; The simple display style
                                 out-line
                               ;; The complex multi-line display style.
-                              (occur-context-lines out-line nlines keep-props)
-                              )))
+                              (setq ret (occur-context-lines
+                                         out-line nlines keep-props begpt endpt
+                                         lines prev-lines prev-after-lines))
+                              ;; Set first elem of the returned list to `data',
+                              ;; and the second elem to `prev-after-lines'.
+                              (setq prev-after-lines (nth 1 ret))
+                              (nth 0 ret))))
                       ;; Actually insert the match display data
                       (with-current-buffer out-buf
                         (let ((beg (point))
-                              (end (progn (insert data) (point))))
-                          (unless (= nlines 0)
-                            (insert "-------\n")))))
+                              (end (progn (insert data) (point)))))))
                     (goto-char endpt))
                   (if endpt
                       (progn
@@ -1289,7 +1297,13 @@ See also `multi-occur'."
                                        (if (and (bolp) (eolp)) 1 0)))
                         ;; On to the next match...
                         (forward-line 1))
-                    (goto-char (point-max))))))
+                    (goto-char (point-max)))
+                  (setq prev-lines (1- lines)))
+                ;; Flush remaining context after-lines.
+                (when prev-after-lines
+                  (with-current-buffer out-buf
+                    (insert (apply #'concat (occur-engine-add-prefix
+                                             prev-after-lines)))))))
             (when (not (zerop matches)) ;; is the count zero?
               (setq globalcount (+ globalcount matches))
               (with-current-buffer out-buf
@@ -1345,18 +1359,60 @@ See also `multi-occur'."
 ;; Generate context display for occur.
 ;; OUT-LINE is the line where the match is.
 ;; NLINES and KEEP-PROPS are args to occur-engine.
+;; LINES is line count of the current match,
+;; PREV-LINES is line count of the previous match,
+;; PREV-AFTER-LINES is a list of after-context lines of the previous match.
 ;; Generate a list of lines, add prefixes to all but OUT-LINE,
 ;; then concatenate them all together.
-(defun occur-context-lines (out-line nlines keep-props)
-  (apply #'concat
-         (nconc
-          (occur-engine-add-prefix
-           (nreverse (cdr (occur-accumulate-lines
-                           (- (1+ (abs nlines))) keep-props))))
-          (list out-line)
-          (if (> nlines 0)
-              (occur-engine-add-prefix
-               (cdr (occur-accumulate-lines (1+ nlines) keep-props)))))))
+(defun occur-context-lines (out-line nlines keep-props begpt endpt
+                                     lines prev-lines prev-after-lines)
+  ;; Find after- and before-context lines of the current match.
+  (let ((before-lines
+         (nreverse (cdr (occur-accumulate-lines
+                         (- (1+ (abs nlines))) keep-props begpt))))
+        (after-lines
+         (cdr (occur-accumulate-lines
+               (1+ nlines) keep-props endpt)))
+        separator)
+
+    ;; Combine after-lines of the previous match
+    ;; with before-lines of the current match.
+
+    (when prev-after-lines
+      ;; Don't overlap prev after-lines with current before-lines.
+      (if (>= (+ prev-lines (length prev-after-lines))
+              (- lines      (length before-lines)))
+          (setq prev-after-lines
+                (butlast prev-after-lines
+                         (- (length prev-after-lines)
+                            (- lines prev-lines (length before-lines) 1))))
+        ;; Separate non-overlapping context lines with a dashed line.
+        (setq separator "-------\n")))
+
+    (when prev-lines
+      ;; Don't overlap current before-lines with previous match line.
+      (if (<= (- lines (length before-lines))
+              prev-lines)
+          (setq before-lines
+                (nthcdr (- (length before-lines)
+                           (- lines prev-lines 1))
+                        before-lines))
+        ;; Separate non-overlapping before-context lines.
+        (unless (> nlines 0)
+          (setq separator "-------\n"))))
+
+    (list
+     ;; Return a list where the first element is the output line.
+     (apply #'concat
+            (append
+             (and prev-after-lines
+                  (occur-engine-add-prefix prev-after-lines))
+             (and separator (list separator))
+             (occur-engine-add-prefix before-lines)
+             (list out-line)))
+     ;; And the second element is the list of context after-lines.
+     (if (> nlines 0) after-lines))))
+
 
 ;; It would be nice to use \\[...], but there is no reasonable way
 ;; to make that display both SPC and Y.