gnus-shorten-url: Improve and avoid args-out-of-range error

'gnus-shorten-url' (used by 'gnus-summary-browse-url') ignored
fragment identifiers and didn't check substring bounds, in some cases
leading to runtime errors, e.g.:

  (gnus-shorten-url "https://some.url.with/path/and#also_a_long_target" 40)
  ;; => Lisp error: (args-out-of-range "/path/and" -18 nil)

This commit makes it account for #fragments and fixes faulty string
computation, reusing existing helper function.  (bug#39980)

* lisp/vc/ediff-init.el (ediff-truncate-string-left): Rename to
'string-truncate-left' and move...
* lisp/emacs-lisp/subr-x.el (string-truncate-left):  ...here.
All callers changed.
* lisp/gnus/gnus-sum.el (gnus-shorten-url): Fix args-out-of-range
error, don't drop #fragments, use 'string-truncate-left'.

1 files changed, 7 insertions, 7 deletions

diff --git a/lisp/gnus/gnus-sum.el b/lisp/gnus/gnus-sum.el
index a47e6576230..6f367692ddd 100644
--- a/lisp/gnus/gnus-sum.el
+++ b/lisp/gnus/gnus-sum.el
@@ -9494,15 +9494,15 @@ The 1st element is the button named by `gnus-collect-urls-primary-text'."
     (delete-dups urls)))
 
 (defun gnus-shorten-url (url max)
-  "Return an excerpt from URL."
+  "Return an excerpt from URL not exceeding MAX characters."
   (if (<= (length url) max)
       url
-    (let ((parsed (url-generic-parse-url url)))
-      (concat (url-host parsed)
-	      "..."
-	      (substring (url-filename parsed)
-			 (- (length (url-filename parsed))
-			    (max (- max (length (url-host parsed))) 0)))))))
+    (let* ((parsed (url-generic-parse-url url))
+           (host (url-host parsed))
+           (rest (concat (url-filename parsed)
+                         (when-let ((target (url-target parsed)))
+                           (concat "#" target)))))
+      (concat host (string-truncate-left rest (- max (length host)))))))
 
 (defun gnus-summary-browse-url (&optional external)
   "Scan the current article body for links, and offer to browse them.