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

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

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Here a git formatted patch .. it's an optimized, generic version of the
snippet in my previous email. It's now "/" agnostic.

Here's the new table of expected values of ffap-string-at-point:
(x indicates the (point))

|-----------------------------------+---------------------------------|
| Example string in `c-mode' buffer | Returned `ffap-string-at-point' |
|-----------------------------------+---------------------------------|
| x//tmp                            | "tmp"                           |
| //xtmp                            | "tmp"                           |
| x///tmp                           | "/tmp"                          |
| //x/tmp                           | "/tmp"                          |
| x////tmp                          | "//tmp"                         |
| ////xtmp                          | "//tmp"                         |
| x// //tmp                         | ""                              |
| // x/tmp                          | "/tmp"                          |
| // x//tmp                         | "//tmp"                         |
|-----------------------------------+---------------------------------|

===== Patch follows

From 5e000cebb993a8cdccdf5e67f6b0eb66b4a267d8 Mon Sep 17 00:00:00 2001
From: Kaushal Modi <kaushal.modi@gmail.com>
Date: Mon, 25 Jul 2016 16:08:50 -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 | 87
+++++++++++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 65 insertions(+), 22 deletions(-)

diff --git a/lisp/ffap.el b/lisp/ffap.el
index 7013e6e..8708a17 100644
--- a/lisp/ffap.el
+++ b/lisp/ffap.el
@@ -1097,33 +1097,76 @@ 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 region is active,return a string from the 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))))
+         (end (if region-selected
+                  (region-end)
+                (save-excursion
+                  (skip-chars-forward (car args))
+                  (skip-chars-backward (nth 2 args) pt)
+                  (point))))
+         (beg-new beg))
+    ;; (message "ffap-string-at-point dbg: beg = %d end = %d" 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
+             (goto-char end)
+             (nth 4 (syntax-ppss))))
+      (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
+    ;; (message "ffap-string-at-point dbg: beg = %d beg-new = %d"
+    ;;          beg beg-new)
     (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)))
+    ;; (message "ffap-string-at-point dbg: ffap-string-at-point = %S"
+    ;;          ffap-string-at-point)
+    ffap-string-at-point))

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

-- 

Kaushal Modi

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