bug#24057: 25.1.50; ffap interprets comments beginning with "//" as file path

[Kaushal Modi <kaushal.modi@gmail.com>]

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Hi Noam,

Thanks for the detailed review. My comments are inline below.

Also I have attached a new patch re-based to the current master, and
applying all your suggestions.

On Thu, Mar 16, 2017 at 10:09 PM <npostavs@users.sourceforge.net> wrote:

> Kaushal Modi <kaushal.modi@gmail.com> writes:
>
> > * lisp/ffap.el (ffap-string-at-point): If the point is in a comment,
> > ensure that the returned string does not contain the comment start
> > characters (especially for major modes that have '//' as comment start
> > characters).
> >
>
> Why is there a blank line here?
>

Is it is convention to not format the commit summaries into multiple
paragraphs? I reread
http://git.savannah.gnu.org/cgit/emacs.git/plain/CONTRIBUTE but didn't find
any mention on that. But I have removed that newline from the patch that I
attach with this email.


> > Otherwise, in a major mode like c-mode, with `ido-mode' enabled and
> > `ido-use-filename-at-point' set to `guess', doing "C-x C-f" on a "//foo"
> > comment will initiate an attempt to access a path "//foo" (Bug#24057).
> > ---
>
> > +    ;; (message "ffap-string-at-point dbg: beg = %d end = %d" beg end)
>
> This can be removed.
>

Understood, the patch was still not in final stages.. The attached patch
does not have any debug statements.


> > +           ;; Check if END character is part of a comment.
> > +           (save-excursion
> > +             (goto-char end)
> > +             (nth 4 (syntax-ppss))))
>
> This could be just (nth 4 (syntax-ppss end)).
>

Thanks. TIL that syntax-ppss as POS as optional arg. Also retaining the
save-excursion as you correct yourself in the followup email.


> > +      (save-excursion
> > +        ;; Increment BEG till point at BEG is in a comment too.
> > +        ;; (nth 4 (syntax-ppss)) will be null for comment start
> > +        ;; characters (for example, for the "//" characters in
> > +        ;; `c-mode' line comments).
> > +        (setq beg (catch 'break
> > +                    (while (< beg-new end)
> > +                      (goto-char beg-new)
> > +                      (if (nth 4 (syntax-ppss)) ; in a comment
> > +                          (throw 'break beg-new)
> > +                        (setq beg-new (1+ beg-new))))
> > +                    end)))) ; Set BEG to END if no throw happens
>
> This could be just
>
>     ;; Move BEG to beginning of comment (after the comment start
>     ;; characters), or END, whichever comes first.
>     (let ((state (syntax-ppss beg)))
>       (unless (nth 4 state)
>         (parse-partial-sexp beg end nil nil state t)
>         (setq beg (point))))
>

Thanks! I did not know about parse-partial-sexp. Here too, I need to retain
the save-excursion, else the point will move after the comment start chars
if it is at the BOL in c-mode on a line like

    //tmp



> > +    ;; (message "ffap-string-at-point dbg: beg = %d beg-new = %d"
> > +    ;;          beg beg-new)
>
> > +    ;; (message "ffap-string-at-point dbg: ffap-string-at-point = %S"
> > +    ;;          ffap-string-at-point)
>
> These can be removed.
>

Done!

Review review the attached. Thanks!
-- 

Kaushal Modi

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From eda7a96b66f6937e094b0d76364c6711984db254 Mon Sep 17 00:00:00 2001
From: Kaushal Modi <kaushal.modi@gmail.com>
Date: Fri, 17 Mar 2017 18:03:23 -0400
Subject: [PATCH] Do not include comment start chars in ffap string

* lisp/ffap.el (ffap-string-at-point): If the point is in a comment,
ensure that the returned string does not contain the comment start
characters (especially for major modes that have '//' as comment start
characters). Otherwise, in a major mode like c-mode, with `ido-mode'
enabled and `ido-use-filename-at-point' set to `guess', doing "C-x
C-f" on a "//foo" comment will initiate an attempt to access a path
"//foo" (Bug#24057).

Co-authored-by: Noam Postavsky <npostavs@gmail.com>
---
 lisp/ffap.el | 41 ++++++++++++++++++++++++++++++++++++++---
 1 file changed, 38 insertions(+), 3 deletions(-)

diff --git a/lisp/ffap.el b/lisp/ffap.el
index d7222bfb68..a15083f4fa 100644
--- a/lisp/ffap.el
+++ b/lisp/ffap.el
@@ -1110,32 +1110,67 @@ ffap-string-at-point
 
 (defun ffap-string-at-point (&optional mode)
   "Return a string of characters from around point.
+
 MODE (defaults to value of `major-mode') is a symbol used to look up
 string syntax parameters in `ffap-string-at-point-mode-alist'.
+
 If MODE is not found, we use `file' instead of MODE.
+
 If the region is active, return a string from the region.
-Set the variable `ffap-string-at-point' and the variable
+
+If the point is in a comment, ensure that the returned string does not
+contain the comment start characters (especially for major modes that
+have '//' as comment start characters).
+
+Set the variables `ffap-string-at-point' and
 `ffap-string-at-point-region'.
+
 When the region is active and larger than `ffap-max-region-length',
 return an empty string, and set `ffap-string-at-point-region' to '(1 1)."
   (let* ((args
 	  (cdr
 	   (or (assq (or mode major-mode) ffap-string-at-point-mode-alist)
 	       (assq 'file ffap-string-at-point-mode-alist))))
+         (region-selected (use-region-p))
 	 (pt (point))
-	 (beg (if (use-region-p)
+         (beg (if region-selected
 		  (region-beginning)
 		(save-excursion
 		  (skip-chars-backward (car args))
 		  (skip-chars-forward (nth 1 args) pt)
 		  (point))))
-	 (end (if (use-region-p)
+         (end (if region-selected
 		  (region-end)
 		(save-excursion
 		  (skip-chars-forward (car args))
 		  (skip-chars-backward (nth 2 args) pt)
 		  (point))))
          (region-len (- (max beg end) (min beg end))))
+
+    ;; If the initial characters of the to-be-returned string are the
+    ;; current major mode's comment starter characters, *and* are
+    ;; not part of a comment, remove those from the returned string
+    ;; (Bug#24057).
+    ;; Example comments in `c-mode' (which considers lines beginning
+    ;; with "//" as comments):
+    ;;  //tmp - This is a comment. It does not contain any path reference.
+    ;;  ///tmp - This is a comment. The "/tmp" portion in that is a path.
+    ;;  ////tmp - This is a comment. The "//tmp" portion in that is a path.
+    (when (and
+           ;; Proceed if no region is selected by the user.
+           (null region-selected)
+           ;; Check if END character is part of a comment.
+           (save-excursion
+             (nth 4 (syntax-ppss end))))
+      ;; Move BEG to beginning of comment (after the comment start
+      ;; characters), or END, whichever comes first.
+      (save-excursion
+        (let ((state (syntax-ppss beg)))
+          ;; (nth 4 (syntax-ppss)) will be nil for comment start chars
+          (unless (nth 4 state)
+            (parse-partial-sexp beg end nil nil state :commentstop)
+            (setq beg (point))))))
+
     (if (and (natnump ffap-max-region-length)
              (< region-len ffap-max-region-length)) ; Bug#25243.
         (setf ffap-string-at-point-region (list beg end)
-- 
2.11.0