bug#74132: 31.0.50; thing-at-pt, ffap and Github markdown

[Madhu <enometh@meer.net>]

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Consider the following text as is typically found on README.md

```
[![GitHub Releases Downloads](https://img.shields.io/github/downloads/raysan5/raylib/total)](https://github.com/raysan5/raylib/releases)
```

If the point is say at "r" at "raylib/releases", invoking
(ffap-url-at-point) fails.  this eventually calls
thing-at-point-bounds-of-url-at-point, which has hardcoded behaviour
to, skip over "allowed characters" backwards to find the beginning of
the bound. here it it finds the space character (in "Release
Downloads") and the whole thing fails.

This particular failure can be addressed by supplying the lim
paramater to the skip-chars-backward, as shown in the attached
patch.

does this look like a problem which ought to be solved? and is this
appropriate? (I was going to post on emacs-devel but decided to post
to the bug list instead) -- Best Regards, Madhu


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From 5971b7c10d7c38d540fdf278a0cd559c96b10ed2 Mon Sep 17 00:00:00 2001
From: Madhu <enometh@net.meer>
Date: Thu, 31 Oct 2024 15:40:42 +0530
Subject: [PATCH] lisp/thingatpt.el: recognize urls better in markdown text

* lisp/thingatpt.el: (thing-at-point-bounds-of-url-at-point): supply a
LIM when calling (skip-chars-backward allowed-chars), which is the
position where `thing-at-point-beginning-of-url-regexp' matches
backwards

problematic url e.g.
```
[![GitHub Releases Downloads](https://img.shields.io/github/downloads/raysan5/raylib/total)](https://github.com/raysan5/raylib/releases)
```
If the point is in the the second url, skip-chars-backwards goes to the
space (between s and D) and `ffap-url-at-point' eventually fails.
but if we supply a limit with a left anchor, we work around it.
---
 lisp/thingatpt.el | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/lisp/thingatpt.el b/lisp/thingatpt.el
index 3cfd3905701..0b8e28af5b9 100644
--- a/lisp/thingatpt.el
+++ b/lisp/thingatpt.el
@@ -502,9 +502,14 @@ thing-at-point-bounds-of-url-at-point
       (let* ((allowed-chars "--:=&?$+@-Z_[:alpha:]~#,%;*()!'[]")
 	     (skip-before "^[0-9a-zA-Z]")
 	     (skip-after  ":;.,!?'")
+             (hard-beg (and thing-at-point-beginning-of-url-regexp
+                            (save-excursion
+                              (re-search-backward
+                               thing-at-point-beginning-of-url-regexp nil t)
+                              (point))))
 	     (pt (point))
 	     (beg (save-excursion
-		    (skip-chars-backward allowed-chars)
+		    (skip-chars-backward allowed-chars hard-beg)
 		    (skip-chars-forward skip-before pt)
 		    (point)))
 	     (end (save-excursion
-- 
2.46.0.27.gfa3b914457