Fix a bug in the state cache mechanism. Refactor this a bit.

cc-engine.el (c-parse-state-get-strategy): Remove the `cache-pos' element
from the return value.
(c-append-lower-brace-pair-to-state-cache): "Narrow" to end of buffer to
enable proper searching from beyond HERE.
Amend the test for detecting the sought brace pair.  Amend the value
written to the "brace desert cache" when the brace isn't found.
(c-remove-stale-state-cache): Rename `good-pos' to `start-point', and
several other variables analogously.
(c-remove-stale-state-cache-backwards): Change `cache-pos' from a
parameter to a locally calculated variable.
(c-parse-state-1): Change the calling conventions to the two defuns
involving `cache-pos'.

2 files changed, 73 insertions, 48 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index eee7700446a..49fbf0eb5b6 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,20 @@
+2013-01-23  Alan Mackenzie  <acm@muc.de>
+
+	Fix a bug in the state cache mechanism.  Refactor this a bit.
+
+	* progmodes/cc-engine.el (c-parse-state-get-strategy): Remove the
+	`cache-pos' element from the return value.
+	(c-append-lower-brace-pair-to-state-cache): "Narrow" to end of
+	buffer to enable proper searching from beyond HERE.  Amend the
+	test for detecting the sought brace pair.  Amend the value written
+	to the "brace desert cache" when the brace isn't found.
+	(c-remove-stale-state-cache): Rename `good-pos' to `start-point',
+	and several other variables analogously.
+	(c-remove-stale-state-cache-backwards): Change `cache-pos' from a
+	parameter to a locally calculated variable.
+	(c-parse-state-1): Change the calling conventions to the two
+	defuns involving `cache-pos'.
+
 2013-01-23  Chong Yidong  <cyd@gnu.org>
 
 	* xml.el (xml-entity-or-char-ref-re): Fix regexp.
diff --git a/lisp/progmodes/cc-engine.el b/lisp/progmodes/cc-engine.el
index 560b66bf3b0..1eac45d06e0 100644
--- a/lisp/progmodes/cc-engine.el
+++ b/lisp/progmodes/cc-engine.el
@@ -2545,14 +2545,12 @@ comment at the start of cc-engine.el for more info."
   ;;
   ;; The return value is a list, one of the following:
   ;;
-  ;; o - ('forward CACHE-POS START-POINT) - scan forward from START-POINT,
-  ;;                                        which is not less than CACHE-POS.
-  ;; o - ('backward CACHE-POS nil) - scan backwards (from HERE).
-  ;; o - ('BOD nil START-POINT) - scan forwards from START-POINT, which is at the
+  ;; o - ('forward START-POINT) - scan forward from START-POINT,
+  ;;	 which is not less than the highest position in `c-state-cache' below here.
+  ;; o - ('backward nil) - scan backwards (from HERE).
+  ;; o - ('BOD START-POINT) - scan forwards from START-POINT, which is at the
   ;;   top level.
-  ;; o - ('IN-LIT nil nil) - point is inside the literal containing point-min.
-  ;; , where CACHE-POS is the highest position recorded in `c-state-cache' at
-  ;; or below HERE.
+  ;; o - ('IN-LIT nil) - point is inside the literal containing point-min.
   (let ((cache-pos (c-get-cache-scan-pos here))	; highest position below HERE in cache (or 1)
 	BOD-pos		    ; position of 2nd BOD before HERE.
 	strategy	    ; 'forward, 'backward, 'BOD, or 'IN-LIT.
@@ -2590,7 +2588,6 @@ comment at the start of cc-engine.el for more info."
 
     (list
      strategy
-     (and (memq strategy '(forward backward)) cache-pos)
      (and (memq strategy '(forward BOD)) start-point))))
 
 
@@ -2657,7 +2654,8 @@ comment at the start of cc-engine.el for more info."
   ;; reduce the time wasted in repeated fruitless searches in brace deserts.
   (save-excursion
     (save-restriction
-      (let* (new-cons
+      (let* ((here (point-max))
+	     new-cons
 	     (cache-pos (c-state-cache-top-lparen)) ; might be nil.
 	     (macro-start-or-from
 	      (progn (goto-char from)
@@ -2692,6 +2690,7 @@ comment at the start of cc-engine.el for more info."
 		;; search bound, even though the algorithm below would skip
 		;; over the new paren pair.
 		(cache-lim (and cache-pos (< cache-pos from) cache-pos)))
+	    (widen)
 	    (narrow-to-region
 		(cond
 		 ((and desert-lim cache-lim)
@@ -2711,16 +2710,18 @@ comment at the start of cc-engine.el for more info."
 		  (while
 		      (and (setq ce (scan-lists bra -1 -1)) ; back past )/]/}; might signal
 			   (setq bra (scan-lists ce -1 1)) ; back past (/[/{; might signal
-			   (or (> ce upper-lim)
-			       (not (eq (char-after bra) ?\{))
-			       (and (goto-char bra)
-				    (c-beginning-of-macro)
-				    (< (point) macro-start-or-from))))))
+			   (or (> bra here) ;(> ce here)
+			       (and
+				(< ce here)
+				(or (not (eq (char-after bra) ?\{))
+				    (and (goto-char bra)
+					 (c-beginning-of-macro)
+					 (< (point) macro-start-or-from))))))))
 		(and ce (< ce bra)))
 	    (setq bra ce))	; If we just backed over an unbalanced closing
 					; brace, ignore it.
 
-	  (if (and ce (< bra ce) (eq (char-after bra) ?\{))
+	  (if (and ce (< ce here) (< bra ce) (eq (char-after bra) ?\{))
 	      ;; We've found the desired brace-pair.
 	      (progn
 		(setq new-cons (cons bra (1+ ce)))
@@ -2734,7 +2735,11 @@ comment at the start of cc-engine.el for more info."
 		 (t (setq c-state-cache (cons new-cons c-state-cache)))))
 
 	    ;; We haven't found a brace pair.  Record this in the cache.
-	    (setq c-state-brace-pair-desert (cons cache-pos from))))))))
+	    (setq c-state-brace-pair-desert
+		  (cons (if (and ce (< bra ce) (> ce here)) ; {..} straddling HERE?
+			    bra
+			  (point-min))
+			(min here from)))))))))
 
 (defsubst c-state-push-any-brace-pair (bra+1 macro-start-or-here)
   ;; If BRA+1 is nil, do nothing.  Otherwise, BRA+1 is the buffer position
@@ -2852,19 +2857,19 @@ comment at the start of cc-engine.el for more info."
        (paren+1)
        (t from)))))
 
-(defun c-remove-stale-state-cache (good-pos pps-point)
+(defun c-remove-stale-state-cache (start-point pps-point)
   ;; Remove stale entries from the `c-cache-state', i.e. those which will
   ;; not be in it when it is amended for position (point-max).
   ;; Additionally, the "outermost" open-brace entry before (point-max)
   ;; will be converted to a cons if the matching close-brace is scanned.
   ;;
-  ;; GOOD-POS is a "maximal" "safe position" - there must be no open
-  ;; parens/braces/brackets between GOOD-POS and (point-max).
+  ;; START-POINT is a "maximal" "safe position" - there must be no open
+  ;; parens/braces/brackets between START-POINT and (point-max).
   ;;
   ;; As a second thing, calculate the result of parse-partial-sexp at
-  ;; PPS-POINT, w.r.t. GOOD-POS.  The motivation here is that
+  ;; PPS-POINT, w.r.t. START-POINT.  The motivation here is that
   ;; `c-state-cache-good-pos' may become PPS-POINT, but the caller may need to
-  ;; adjust it to get outside a string/comment.  (Sorry about this!  The code
+  ;; adjust it to get outside a string/comment.	 (Sorry about this!  The code
   ;; needs to be FAST).
   ;;
   ;; Return a list (GOOD-POS SCAN-BACK-POS PPS-STATE), where
@@ -2872,7 +2877,9 @@ comment at the start of cc-engine.el for more info."
   ;;   to be good (we aim for this to be as high as possible);
   ;; o - SCAN-BACK-POS, if not nil, indicates there may be a brace pair
   ;;   preceding POS which needs to be recorded in `c-state-cache'.  It is a
-  ;;   position to scan backwards from.
+  ;;   position to scan backwards from.  It is the position of the "{" of the
+  ;;   last element to be removed from `c-state-cache', when that elt is a
+  ;;   cons, otherwise nil.
   ;; o - PPS-STATE is the parse-partial-sexp state at PPS-POINT.
   (save-restriction
     (narrow-to-region 1 (point-max))
@@ -2882,21 +2889,21 @@ comment at the start of cc-engine.el for more info."
 		(goto-char (point-max))
 		(and (c-beginning-of-macro)
 		     (point))))
-	     (good-pos-actual-macro-start ; Start of macro containing good-pos
-					; or nil
-	      (and (< good-pos (point-max))
+	     (start-point-actual-macro-start ; Start of macro containing
+					     ; start-point or nil
+	      (and (< start-point (point-max))
 		   (save-excursion
-		     (goto-char good-pos)
+		     (goto-char start-point)
 		     (and (c-beginning-of-macro)
 			  (point)))))
-	     (good-pos-actual-macro-end	; End of this macro, (maybe
+	     (start-point-actual-macro-end ; End of this macro, (maybe
 					; (point-max)), or nil.
-	      (and good-pos-actual-macro-start
+	      (and start-point-actual-macro-start
 		   (save-excursion
-		     (goto-char good-pos-actual-macro-start)
+		     (goto-char start-point-actual-macro-start)
 		     (c-end-of-macro)
 		     (point))))
-	     pps-state 			; Will be 9 or 10 elements long.
+	     pps-state			; Will be 9 or 10 elements long.
 	     pos
 	     upper-lim	   ; ,beyond which `c-state-cache' entries are removed
 	     scan-back-pos
@@ -2926,15 +2933,15 @@ comment at the start of cc-engine.el for more info."
 	;; The next loop jumps forward out of a nested level of parens each
 	;; time round; the corresponding elements in `c-state-cache' are
 	;; removed.  `pos' is just after the brace-pair or the open paren at
-	;; (car c-state-cache).  There can be no open parens/braces/brackets
-	;; between `good-pos'/`good-pos-actual-macro-start' and (point-max),
+	;; (car c-state-cache).	 There can be no open parens/braces/brackets
+	;; between `start-point'/`start-point-actual-macro-start' and (point-max),
 	;; due to the interface spec to this function.
-	(setq pos (if (and good-pos-actual-macro-end
-			   (not (eq good-pos-actual-macro-start
+	(setq pos (if (and start-point-actual-macro-end
+			   (not (eq start-point-actual-macro-start
 				    in-macro-start)))
-		      (1+ good-pos-actual-macro-end) ; get outside the macro as
+		      (1+ start-point-actual-macro-end) ; get outside the macro as
 					; marked by a `category' text property.
-		    good-pos))
+		    start-point))
 	(goto-char pos)
 	(while (and c-state-cache
 		    (< (point) (point-max)))
@@ -2993,14 +3000,14 @@ comment at the start of cc-engine.el for more info."
 
 	(list pos scan-back-pos pps-state)))))
 
-(defun c-remove-stale-state-cache-backwards (here cache-pos)
+(defun c-remove-stale-state-cache-backwards (here)
   ;; Strip stale elements of `c-state-cache' by moving backwards through the
   ;; buffer, and inform the caller of the scenario detected.
   ;;
   ;; HERE is the position we're setting `c-state-cache' for.
-  ;; CACHE-POS is just after the latest recorded position in `c-state-cache'
-  ;;   before HERE, or a position at or near point-min which isn't in a
-  ;;   literal.
+  ;; CACHE-POS (a locally bound variable) is just after the latest recorded
+  ;;   position in `c-state-cache' before HERE, or a position at or near
+  ;;   point-min which isn't in a literal.
   ;;
   ;; This function must only be called only when (> `c-state-cache-good-pos'
   ;; HERE).  Usually the gap between CACHE-POS and HERE is large.  It is thus
@@ -3023,10 +3030,11 @@ comment at the start of cc-engine.el for more info."
   ;; The comments in this defun use "paren" to mean parenthesis or square
   ;; bracket (as contrasted with a brace), and "(" and ")" likewise.
   ;;
-  ;;    .   {..} (..) (..)  ( .. {   }  ) (...)    ( ....          .  ..)
-  ;;    |                   |       |   |     |                    |
-  ;;    CP                  E      here D     C                   good
-  (let ((pos c-state-cache-good-pos)
+  ;;	.   {..} (..) (..)  ( .. {   }	) (...)	   ( ....	   .  ..)
+  ;;	|		    |	    |	|     |			   |
+  ;;	CP		    E	   here D     C			  good
+  (let ((cache-pos (c-get-cache-scan-pos here))	; highest position below HERE in cache (or 1)
+	(pos c-state-cache-good-pos)
 	pa ren	       ; positions of "(" and ")"
 	dropped-cons ; whether the last element dropped from `c-state-cache'
 		     ; was a cons (representing a brace-pair)
@@ -3263,7 +3271,8 @@ comment at the start of cc-engine.el for more info."
 	 cache-pos	     ; highest position below HERE already existing in
 			     ; cache (or 1).
 	 good-pos
-	 start-point
+	 start-point ; (when scanning forward) a place below HERE where there
+		     ; are no open parens/braces between it and HERE.
 	 bopl-state
 	 res
 	 scan-backward-pos scan-forward-p) ; used for 'backward.
@@ -3274,8 +3283,7 @@ comment at the start of cc-engine.el for more info."
     ;; Strategy?
     (setq res (c-parse-state-get-strategy here c-state-cache-good-pos)
 	  strategy (car res)
-	  cache-pos (cadr res)
-	  start-point (nth 2 res))
+	  start-point (cadr res))
 
     (when (eq strategy 'BOD)
       (setq c-state-cache nil
@@ -3302,7 +3310,7 @@ comment at the start of cc-engine.el for more info."
 		good-pos)))
 
        ((eq strategy 'backward)
-	(setq res (c-remove-stale-state-cache-backwards here cache-pos)
+	(setq res (c-remove-stale-state-cache-backwards here)
 	      good-pos (car res)
 	      scan-backward-pos (cadr res)
 	      scan-forward-p (car (cddr res)))