bug#22983: syntax-ppss returns wrong result.

[Dmitry Gutov <dgutov@yandex.ru>]

On 03/11/2016 05:15 PM, Alan Mackenzie wrote:

This patch should make ppss-0 and ppss-1 match:

diff --git a/lisp/emacs-lisp/syntax.el b/lisp/emacs-lisp/syntax.el
index e20a210..c1b9d84 100644
--- a/lisp/emacs-lisp/syntax.el
+++ b/lisp/emacs-lisp/syntax.el
@@ -371,6 +371,11 @@ syntax-ppss-max-span
  We try to make sure that cache entries are at least this far apart
  from each other, to avoid keeping too much useless info.")

+(defvar syntax-ppss-dont-widen nil
+  "If non-nil, `syntax-ppss' will work on the non-widened buffer.
+The code that uses this should create local bindings for
+`syntax-ppss-cache' and `syntax-ppss-last' too.")
+
  (defvar syntax-begin-function nil
    "Function to move back outside of any comment/string/paren.
  This function should move the cursor back to some syntactically safe
@@ -423,12 +428,21 @@ syntax-ppss
  in the returned list (counting from 0) cannot be relied upon.
  Point is at POS when this function returns.

+IF `syntax-ppss-dont-widen' is nil, the buffer is temporarily
+widened.
+
  It is necessary to call `syntax-ppss-flush-cache' explicitly if
  this function is called while `before-change-functions' is
  temporarily let-bound, or if the buffer is modified without
  running the hook."
    ;; Default values.
    (unless pos (setq pos (point)))
+  (save-restriction
+    (unless syntax-ppss-dont-widen
+      (widen))
+    (syntax-pps--at pos)))
+
+(defun syntax-ppss--at (pos)
    (syntax-propertize pos)
    ;;
    (let ((old-ppss (cdr syntax-ppss-last))