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Subject: |
27.0.91; Using syntax-ppss-flush-cache in syntax-propertize-function infloops |
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Date: |
Tue, 12 May 2020 02:32:37 +0300 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 |
In theory, syntax-propertize-function implementations shouldn't change
buffer syntax the way that would affect the current syntax-ppss cache.
Or if they do, they should clear the cache accordingly.
Unfortunately, using syntax-ppss-flush-cache for that purpose doesn't
work: it makes Emacs infloop.
To reproduce, apply this patch:
diff --git a/lisp/progmodes/js.el b/lisp/progmodes/js.el
index 5ec3e94275..efe38049ab 100644
--- a/lisp/progmodes/js.el
+++ b/lisp/progmodes/js.el
@@ -2362,6 +2362,7 @@ js-syntax-propertize
(eval-when-compile (append "=({[,:;"
'(nil))))))
(put-text-property (match-beginning 1) (match-end 1)
'syntax-table (string-to-syntax "\"/"))
+ (syntax-ppss-flush-cache (match-beginning 0))
(js-syntax-propertize-regexp end)))))
("\`\(#\)!" (1 "< b"))
("<" (0 (ignore
and then edit a file with js-mode containing
a = /xyz/
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--- Begin Message ---
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Subject: |
Re: bug#41195: 27.0.91; Using syntax-ppss-flush-cache in syntax-propertize-function infloops |
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Date: |
Tue, 12 May 2020 16:55:18 -0400 |
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User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) |
Version: 28.1
> In theory, syntax-propertize-function implementations shouldn't change
> buffer syntax the way that would affect the current syntax-ppss cache.
> Or if they do, they should clear the cache accordingly.
> Unfortunately, using syntax-ppss-flush-cache for that purpose doesn't
> work: it makes Emacs infloop.
I thought at first that the fix should go into `emacs-27`, but then you
correctly pointed out that the docstring of `syntax-propertize-function`
warned that `syntax-ppss-flush-cache` should not be called, so this bug
is really a known and documented limitation.
But indeed, it's a limitation that we should lift, so I installed the
patch below into `master`.
Stefan
diff --git a/lisp/emacs-lisp/syntax.el b/lisp/emacs-lisp/syntax.el
index 3294378754a..46dc8d9ade8 100644
--- a/lisp/emacs-lisp/syntax.el
+++ b/lisp/emacs-lisp/syntax.el
@@ -63,9 +63,10 @@ syntax-propertize-function
cannot be handled just by the buffer's syntax-table.
The specified function may call `syntax-ppss' on any position
-before END, but it should not call `syntax-ppss-flush-cache',
-which means that it should not call `syntax-ppss' on some
-position and later modify the buffer on some earlier position.")
+before END, but if it calls `syntax-ppss' on some
+position and later modifies the buffer on some earlier position,
+then it is its responsability to call `syntax-ppss-flush-cache' to flush
+the now obsolete ppss info from the cache.")
(defvar syntax-propertize-chunk-size 500)
@@ -320,6 +321,11 @@ syntax-propertize-via-font-lock
(defvar-local syntax-ppss-table nil
"Syntax-table to use during `syntax-ppss', if any.")
+(defvar-local syntax-propertize--inhibit-flush nil
+ "If non-nil, `syntax-ppss-flush-cache' only flushes the ppss cache.
+Otherwise it flushes both the ppss cache and the properties
+set by `syntax-propertize'")
+
(defun syntax-propertize (pos)
"Ensure that syntax-table properties are set until POS (a buffer point)."
(when (< syntax-propertize--done pos)
@@ -375,8 +381,13 @@ syntax-propertize
;; (message "syntax-propertizing from %s to %s" start end)
(remove-text-properties start end
'(syntax-table nil syntax-multiline nil))
- ;; Avoid recursion!
- (let ((syntax-propertize--done most-positive-fixnum))
+ ;; Make sure we only let-bind it buffer-locally.
+ (make-local-variable 'syntax-propertize--inhibit-flush)
+ ;; Let-bind `syntax-propertize--done' to avoid infinite
recursion!
+ (let ((syntax-propertize--done most-positive-fixnum)
+ ;; Let `syntax-propertize-function' call
+ ;; `syntax-ppss-flush-cache' without worries.
+ (syntax-propertize--inhibit-flush t))
(funcall syntax-propertize-function start end)))))))))
;;; Link syntax-propertize with syntax.c.
@@ -455,7 +466,8 @@ 'syntax-ppss-after-change-function
(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))
+ (unless syntax-propertize--inhibit-flush
+ (setq syntax-propertize--done (min beg syntax-propertize--done)))
;; Flush invalid cache entries.
(dolist (cell (list syntax-ppss-wide syntax-ppss-narrow))
(pcase cell
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