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

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

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I am copying the last 3 committers on this section of the code to review
this patch.

Patch follows:

From a9e94ba5789d2b1d524120efecd3f9ab9af641cc Mon Sep 17 00:00:00 2001
From: Kaushal Modi <kaushal.modi@gmail.com>
Date: Fri, 22 Jul 2016 18:58:29 -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).
---
 lisp/ffap.el | 63
++++++++++++++++++++++++++++++++++++++++--------------------
 1 file changed, 42 insertions(+), 21 deletions(-)

diff --git a/lisp/ffap.el b/lisp/ffap.el
index 7013e6e..ba62012 100644
--- a/lisp/ffap.el
+++ b/lisp/ffap.el
@@ -1097,33 +1097,54 @@ 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.
-Sets the variable `ffap-string-at-point' and the variable
-`ffap-string-at-point-region'."
+
+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).
+
+Sets variables `ffap-string-at-point' and `ffap-string-at-point-region'. "
   (let* ((args
-  (cdr
-   (or (assq (or mode major-mode) ffap-string-at-point-mode-alist)
-       (assq 'file ffap-string-at-point-mode-alist))))
- (pt (point))
- (beg (if (use-region-p)
-  (region-beginning)
- (save-excursion
-  (skip-chars-backward (car args))
-  (skip-chars-forward (nth 1 args) pt)
-  (point))))
- (end (if (use-region-p)
-  (region-end)
- (save-excursion
-  (skip-chars-forward (car args))
-  (skip-chars-backward (nth 2 args) pt)
-  (point)))))
+          (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 region-selected
+                  (region-beginning)
+                (save-excursion
+                  (skip-chars-backward (car args))
+                  (skip-chars-forward (nth 1 args) pt)
+                  (point))))
+         ;; If point is in a comment like "//abc" (in `c-mode'), and a
+         ;; region is not selected, return the position of 'a'.
+         (comment-start-pos (unless region-selected
+                              (save-excursion
+                                (goto-char beg)
+                                (comment-search-forward
+                                 (line-end-position) :noerror)
+                                (point))))
+         (end (if region-selected
+                  (region-end)
+                (save-excursion
+                  (skip-chars-forward (car args))
+                  (skip-chars-backward (nth 2 args) pt)
+                  (point)))))
+    (when (and comment-start-pos
+               (> end comment-start-pos))
+      (setq beg comment-start-pos))
+    ;; (message "comment-start-pos = %d end = %d beg = %d"
+    ;;          comment-start-pos end beg)
     (setq ffap-string-at-point
-  (buffer-substring-no-properties
-   (setcar ffap-string-at-point-region beg)
-   (setcar (cdr ffap-string-at-point-region) end)))))
+          (buffer-substring-no-properties
+           (setcar ffap-string-at-point-region beg)
+           (setcar (cdr ffap-string-at-point-region) end)))))

 (defun ffap-string-around ()
   ;; Sometimes useful to decide how to treat a string.
-- 
2.9.2

-- 

Kaushal Modi

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