bug#35693: The prompt for find-file becomes a ~ instead of ~/

[Katsumi Yamaoka <yamaoka@jpl.org>]

On Sun, 12 May 2019 10:27:01 +0800, 積丹尼 wrote:
> M-x gnus
> C-x C-f
> The prompt for find-file becomes a ~ instead of ~/

`C-x C-f' invokes `find-file-at-point' because of `ffap-bindings'.

> It turns out because since one uses ffap-bindings
> and the cursor is now resting after a ":", the find-file prompt is
> affected.
> OK it is not a gnus bug, but most commonly seen when using gnus...

Yes, it's not a Gnus bug.  That happens when performing `C-x C-f'
just after the colon in the group line like this:

	123: nnfoo:bar

There ffap grabs a string "123:", recognizes it as a colon separated
paths list, and extracts a path where the cursor is, that is "".
That *path* string is used to create a prompt string by way of:

(abbreviate-file-name (expand-file-name ""))

It returns "~" because you are in the home directory.  That is why
you are prompted with "~" instead of "~/".

There would be many ways to solve it, though I'm not sure what is
the best.  Here are two of them (based on ffap.el in the trunk):

1. (ffap-file-at-point): Don't recognize "" as a path name.
--- ffap.el~	2019-05-12 21:20:25.967974700 +0000
+++ ffap.el	2019-05-14 05:51:47.038159300 +0000
@@ -1326,6 +1326,7 @@
 	 ;; If it contains a colon, get rid of it (and return if exists)
 	 ((and (string-match path-separator name)
 	       (setq name (ffap-string-at-point 'nocolon))
+	       (> (length name) 0)
 	       (ffap-file-exists-string name)))
 	 ;; File does not exist, try the alist:
 	 ((let ((alist ffap-alist) tem try case-fold-search)

2. (ffap-file-exists-string): Don't recognize "" as a file name.
--- ffap.el~	2019-05-12 21:20:25.967974700 +0000
+++ ffap.el	2019-05-14 05:51:47.038159300 +0000
@@ -513,7 +513,7 @@
 name may have a suffix added from `ffap-compression-suffixes'.
 The optional NOMODIFY argument suppresses the extra search."
   (cond
-   ((not file) nil)			; quietly reject nil
+   ((zerop (length file)) nil)		; quietly reject nil and ""
    ((file-exists-p file) file)		; try unmodified first
    ;; three reasons to suppress search:
    (nomodify nil)

Regards,