Package: emacs;
Reported by: Alan Mackenzie <acm <at> muc.de>
Date: Fri, 11 Mar 2016 15:13:02 UTC
Severity: normal
Done: Alan Mackenzie <acm <at> muc.de>
Bug is archived. No further changes may be made.
View this message in rfc822 format
From: Alan Mackenzie <acm <at> muc.de> To: Dmitry Gutov <dgutov <at> yandex.ru>, Philipp Stephani <p.stephani2 <at> gmail.com> Cc: John Wiegley <jwiegley <at> gmail.com>, 22983 <at> debbugs.gnu.org Subject: bug#22983: [ Patch ] Re: bug#22983: syntax-ppss returns wrong result. Date: Sun, 10 Sep 2017 11:36:26 +0000
Hello, Dmitry and Philipp.
On Sat, Sep 09, 2017 at 12:44:02 +0300, Dmitry Gutov wrote:
> Hi Alan,
> On 9/7/17 11:45 PM, Alan Mackenzie wrote:
> > The solution I propose is to introduce a second cache into syntax-ppss,
> > and this cache would be used whenever (not (eq (point-min) 1)).
> > Whenever point-min changes, and isn't 1, this second cached would be
> > calculated again from scratch.
Here is a patch implementing this. Comments about it would be welcome.
[ .... ]
> And since the API doesn't change, and the observable behavior doesn't
> either (in the vast majority of cases; probably all except the broken
> ones), we can refine this solution easily, or even swap it for something
> else, with little cost.
[ .... ]
> Caveats:
> - This solves the dependency on point-min, but does nothing about the
> dependency on the current syntax-table (which can change). I'm not
> necessarily suggesting we try to solve that now, though.
> - Before this change is pushed to master, or shortly after, I'd like to
> know that it actually fixed the problem Philipp experienced with
> python-mode, so we can revert 4fbd330. If it was caused by e.g.
> syntax-table changing, we've not improved much.
Philipp, any chance of you trying out python mode with this patch but
without 4fbd330?
diff --git a/lisp/emacs-lisp/syntax.el b/lisp/emacs-lisp/syntax.el
index d1d5176944..952ea8bb83 100644
--- a/lisp/emacs-lisp/syntax.el
+++ b/lisp/emacs-lisp/syntax.el
@@ -386,11 +386,103 @@ syntax-ppss-cache
(defvar-local syntax-ppss-last nil
"Cache of (LAST-POS . LAST-PPSS).")
-(defalias 'syntax-ppss-after-change-function 'syntax-ppss-flush-cache)
-(defun syntax-ppss-flush-cache (beg &rest ignored)
- "Flush the cache of `syntax-ppss' starting at position BEG."
- ;; Set syntax-propertize to refontify anything past beg.
- (setq syntax-propertize--done (min beg syntax-propertize--done))
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Several caches.
+;;
+;; Because `syntax-ppss' is equivalent to (parse-partial-sexp
+;; (POINT-MIN) x), we need either to empty the cache when we narrow
+;; the buffer, which is suboptimal, or we need to use several caches.
+;;
+;; The implementation which follows uses three caches, the current one
+;; (in `syntax-ppss-cache' and `syntax-ppss-last') and two inactive
+;; ones (in `syntax-ppss-{cache,last}-{wide,narrow}'), which store the
+;; former state of the active cache as it was used in widened and
+;; narrowed buffers respectively. There are also the variables
+;; `syntax-ppss-max-valid-{wide,narrow}' which hold the maximum
+;; position where the caches are valid, due to buffer changes.
+;;
+;; At the first call to `syntax-ppss' after a widening or narrowing of
+;; the buffer, the pertinent inactive cache is swapped into the
+;; current cache by calling `syntax-ppss-set-cache'. Note that there
+;; is currently just one inactive cache for narrowed buffers, so only
+;; one inactive narrowed cache can be stored at a time.
+;;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(defvar-local syntax-ppss-cache-wide nil
+ "Holds the value of `syntax-ppss-cache' for a widened buffer.")
+(defvar-local syntax-ppss-last-wide nil
+ "Holds the value of `syntax-ppss-last' for a widened buffer.")
+(defvar-local syntax-ppss-max-valid-wide most-positive-fixnum
+ "The buffer position after which `syntax-ppss-cache-wide' is invalid.")
+
+(defvar-local syntax-ppss-cache-narrow nil
+ "Holds the value of `syntax-ppss-cache' for a narrowed buffer.")
+(defvar-local syntax-ppss-last-narrow nil
+ "Holds the value of `syntax-ppss-last' for a narrowed buffer.")
+(defvar-local syntax-ppss-max-valid-narrow most-positive-fixnum
+ "The buffer position after which `syntax-ppss-cache-narrow' is invalid.")
+
+(defvar-local syntax-ppss-narrow-point-min 1
+ "Value of `point-min' for which the stored \"narrow\" cache is valid.")
+
+(defvar-local syntax-ppss-supremum most-positive-fixnum
+ "Lowest change position since previous restriction change.")
+
+(defvar-local syntax-ppss-cache-point-min 1
+ "Value of `point-min' for which the current cache is valid.")
+
+(defun syntax-ppss-set-cache ()
+ "Swap in and out the cache pertinent to the new point-min."
+ (unless (eq (point-min) syntax-ppss-cache-point-min)
+ ;; Update the stored `...max-valid' values.
+ (setq syntax-ppss-max-valid-wide
+ (if (eq syntax-ppss-cache-point-min 1)
+ (or (caar syntax-ppss-cache)
+ 1)
+ (min syntax-ppss-max-valid-wide syntax-ppss-supremum)))
+ (setq syntax-ppss-max-valid-narrow
+ (if (eq syntax-ppss-cache-point-min syntax-ppss-narrow-point-min)
+ (or (caar syntax-ppss-cache)
+ syntax-ppss-cache-point-min)
+ (min syntax-ppss-max-valid-narrow syntax-ppss-supremum)))
+ (setq syntax-ppss-supremum most-positive-fixnum)
+
+ ;; Store away the current values of the cache.
+ (cond
+ ((eq syntax-ppss-cache-point-min 1)
+ (setq syntax-ppss-cache-wide syntax-ppss-cache
+ syntax-ppss-last-wide syntax-ppss-last))
+ ((eq syntax-ppss-cache-point-min syntax-ppss-narrow-point-min)
+ (setq syntax-ppss-cache-narrow syntax-ppss-cache
+ syntax-ppss-last-narrow syntax-ppss-last))
+ (syntax-ppss-cache
+ (setq syntax-ppss-narrow-point-min syntax-ppss-cache-point-min
+ syntax-ppss-cache-narrow syntax-ppss-cache
+ syntax-ppss-last-narrow syntax-ppss-last))
+ (t nil))
+
+ ;; Restore/initialize the cache for the new point-min.
+ (cond
+ ((eq (point-min) 1)
+ (setq syntax-ppss-cache syntax-ppss-cache-wide
+ syntax-ppss-last syntax-ppss-last-wide)
+ (save-restriction
+ (widen)
+ (syntax-ppss-invalidate-cache syntax-ppss-max-valid-wide)))
+ ((eq (point-min) syntax-ppss-narrow-point-min)
+ (setq syntax-ppss-cache syntax-ppss-cache-narrow
+ syntax-ppss-last syntax-ppss-last-narrow)
+ (save-restriction
+ (widen)
+ (syntax-ppss-invalidate-cache syntax-ppss-max-valid-narrow)))
+ (t
+ (setq syntax-ppss-cache nil
+ syntax-ppss-last nil)))
+ (setq syntax-ppss-cache-point-min (point-min))))
+
+(defun syntax-ppss-invalidate-cache (beg &rest ignored)
+ "Invalidate the cache of `syntax-ppss' starting at position BEG."
;; Flush invalid cache entries.
(while (and syntax-ppss-cache (> (caar syntax-ppss-cache) beg))
(setq syntax-ppss-cache (cdr syntax-ppss-cache)))
@@ -411,6 +503,16 @@ syntax-ppss-flush-cache
;; (remove-hook 'before-change-functions 'syntax-ppss-flush-cache t))
)
+;; Retain the following two for compatibility reasons.
+(defalias 'syntax-ppss-after-change-function 'syntax-ppss-flush-cache)
+(defun syntax-ppss-flush-cache (beg &rest ignored)
+ "Flush the `syntax-ppss' caches and set `syntax-propertize--done'."
+ (setq syntax-ppss-supremum (min beg syntax-ppss-supremum))
+ ;; Ensure the appropriate cache is active.
+ (syntax-ppss-set-cache)
+ (setq syntax-propertize--done (min beg syntax-propertize--done))
+ (syntax-ppss-invalidate-cache beg ignored))
+
(defvar syntax-ppss-stats
[(0 . 0.0) (0 . 0.0) (0 . 0.0) (0 . 0.0) (0 . 0.0) (1 . 2500.0)])
(defun syntax-ppss-stats ()
@@ -434,6 +536,8 @@ syntax-ppss
this function is called while `before-change-functions' is
temporarily let-bound, or if the buffer is modified without
running the hook."
+ ;; Ensure the appropriate cache is active.
+ (syntax-ppss-set-cache)
;; Default values.
(unless pos (setq pos (point)))
(syntax-propertize pos)
> All the best,
> Dmitry.
--
Alan Mackenzie (Nuremberg, Germany).
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1994-97 Ian Jackson.