Re: [PATCH] lisp/files.el: Add `file-name-set-extension`

["Colin Woodbury" <colin@fosskers.ca>]

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Hi Andreas (et al.),

After asking around, it seems like letting `string-trim` fail naturally is indeed the canonical thing to do here, especially since with `toggle-debug-on-error` we're able to get the full call-stack if we need it. I've altered the patch (see attached) accordingly. Thanks for your patience.

Cheers,
Colin

On Wed, 26 May 2021, at 10:39, Andreas Schwab wrote:
> That's exactly what should happen.
> 
> Andreas.
> 
> -- 
> Andreas Schwab, schwab@linux-m68k.org <mailto:schwab%40linux-m68k.org>
> GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
> "And now for something completely different."
> 

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diff --git a/lisp/files.el b/lisp/files.el
index 62e1702fdf..eed818e2fa 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -4889,6 +4889,15 @@ extension, the value is \"\"."
         (if period
             "")))))
 
+(defun file-name-set-extension (filename extension)
+  "Set the EXTENSION of a FILENAME.
+Consolidates leading/trailing dots so that either `foo' or `.foo'
+can be passed as an EXTENSION."
+  (let* ((patt "[ .]+")
+         (filename (string-trim-right filename patt))
+         (extension (string-trim-left extension patt)))
+    (concat (file-name-sans-extension filename) "." extension)))
+
 (defun file-name-base (&optional filename)
   "Return the base name of the FILENAME: no directory, no extension."
   (declare (advertised-calling-convention (filename) "27.1"))