bug#49865: 28.0.50; Customize project-find-file without thing-at-pont

[Dmitry Gutov <dgutov@yandex.ru>]

Hi Lars,

On 04.08.2021 11:37, Lars Ingebrigtsen wrote:
> This reminded me that I've been meaning to add a thing-at-point target
> that is like `filename', but returns nil if the file named doesn't
> exist, so I've now done this in Emacs 28.
> 
> Perhaps project.el should use it here?

I don't know if it will be the best choice here.

First of all, we already have the hook file-name-at-point-functions, 
which is consulted by read-file-name--defaults. So one can already e.g. 
move point to some existing file name, press C-x C-f M-n and with the 
power of the ffap package have the file name inserted.

But when we're completing project-wide, there will also be references 
that are not relative to the current directory (and instead relate to 
some project-configured path). Like

#include "stuff/thingy.h"

or

require 'actor/abc'

...where the string is both not relative to the current dir and is 
missing the extension.

ffap actually includes support for this, like having

(require 'cl-lib)

be recognized as '.../lisp/emacs-lisp/cl-lib.el', but it only works for 
a limited set of languages, and OOTB only for Elisp (for all others you 
need to configure variables like ffap-c++-path).