bug#32510: acknowledged by developer (control message for bug #32510)

[Dmitry Gutov <dgutov@yandex.ru>]

On 14.07.2019 8:21, Eli Zaretskii wrote:
>> From: Ludovic Brenta <ludovic@ludovic-brenta.org>
>> Date: Sat, 13 Jul 2019 21:34:26 +0200
>>
>> This bug report states that a useful functionality of find-tag is *not*
>> provided by its official replacement, xref-find-definitions.  This is a
>> regression.  Just because you think this missing functionality should be
>> provided elsewhere is not a good reason to close this bug without
>> providing any solution.
> 
> With the patch below, you should be able to have what you want if you
> add tag-partial-file-name-match-p to the list in

Finally got around to reviewing it...

> diff --git a/lisp/progmodes/etags.el b/lisp/progmodes/etags.el
> index 7bf5753..b092c63 100644
> --- a/lisp/progmodes/etags.el
> +++ b/lisp/progmodes/etags.el
> @@ -2070,13 +2070,16 @@ etags--xref-find-definitions
>                 (beginning-of-line)
>                 (pcase-let* ((tag-info (etags-snarf-tag))
>                              (`(,hint ,line . _) tag-info))
> -                (unless (eq hint t) ; hint==t if we are in a filename line
> +                (unless (and (eq hint t) ; we are in a filename line
> +                             (not (eq order-fun
> +                                      'tag-partial-file-name-match-p)))

First, I was thinking we shouldn't check for the exact order-fun value 
(because others could be used, too) and replace it with something like

                               (save-excursion
                                (forward-line 0)
                                (forward-char -2)
                                (not (looking-at "\f\n")))

But then, I'm not sure why that check is there in the first place (the 
order functions make sure not to match the wrong like). Maybe because 
the code inside couldn't handle hint=t? So if it does now, the (unless 
...) conditional can be removed.

>                     (let* ((file (file-of-tag))
>                            (mark-key (cons file line)))
>                       (unless (gethash mark-key marks)
>                         (let ((loc (xref-make-etags-location
>                                     tag-info (expand-file-name file))))
> -                        (push (xref-make hint loc) xrefs)
> +                        (push (xref-make (if (eq hint t) pattern hint) loc)
> +                               xrefs)

I'm not sure using pattern as a hint works well. How about we say 
something like "(file name match)" instead? Or you could pick a better 
wording. The full proposed patch is below.

I see that it doesn't work exactly perfectly, e.g. moving point within 
the quotes in

   #include "composite.h"

and pressing M-. brings up three matches (composite.c, composite.h and 
composite.el), whereas only one of them is correct, but find-tag 
probably has the same problem anyway. Maybe CC Mode should set up 
find-tag-default-function to return the full file name when inside 
#include statements.

diff --git a/lisp/progmodes/etags.el b/lisp/progmodes/etags.el
index 7bf575340e..a052ad2ce5 100644
--- a/lisp/progmodes/etags.el
+++ b/lisp/progmodes/etags.el
@@ -2070,14 +2070,15 @@ etags--xref-find-definitions
                (beginning-of-line)
                (pcase-let* ((tag-info (etags-snarf-tag))
                             (`(,hint ,line . _) tag-info))
-                (unless (eq hint t) ; hint==t if we are in a filename line
-                  (let* ((file (file-of-tag))
-                         (mark-key (cons file line)))
-                    (unless (gethash mark-key marks)
-                      (let ((loc (xref-make-etags-location
-                                  tag-info (expand-file-name file))))
-                        (push (xref-make hint loc) xrefs)
-                        (puthash mark-key t marks)))))))))))
+                (let* ((file (file-of-tag))
+                       (mark-key (cons file line)))
+                  (unless (gethash mark-key marks)
+                    (let ((loc (xref-make-etags-location
+                                tag-info (expand-file-name file))))
+                      (push (xref-make (if (eq hint t) "(filename 
match)" hint)
+                                       loc)
+                            xrefs)
+                      (puthash mark-key t marks))))))))))
      (nreverse xrefs)))

  (defclass xref-etags-location (xref-location)