bug#15803: default-file-name-coding-system: utf-8 better than latin-1 these days?

[Lars Ingebrigtsen <larsi@gnus.org>]

Glenn Morris <rgm@gnu.org> writes:

> utf-8 is the sensible, "modern" (ie, non-ancient) default.
> If there is no reason to use latin-1, Emacs should use utf-8.
> I'm not claiming it's critical.
>
> Take it or leave it, as you wish.

That was the final message in the thread.  Glenn's patch from six years
ago no longer applied, so I've respun it for Emacs 28 now (included
below).

Glenn's arguments make sense to me, but I'm not a domain expert here.
Does anybody object to applying this patch to Emacs 28?

diff --git a/doc/emacs/mule.texi b/doc/emacs/mule.texi
index 6eff0ca0d2..b78019020a 100644
--- a/doc/emacs/mule.texi
+++ b/doc/emacs/mule.texi
@@ -1215,11 +1215,8 @@ File Name Coding
 
   If @code{file-name-coding-system} is @code{nil}, Emacs uses a
 default coding system determined by the selected language environment,
-and stored in the @code{default-file-name-coding-system} variable.
-@c FIXME?  Is this correct?  What is the "default language environment"?
-In the default language environment, non-@acronym{ASCII} characters in
-file names are not encoded specially; they appear in the file system
-using the internal Emacs representation.
+and stored in the @code{default-file-name-coding-system} variable
+(normally UTF-8).
 
 @cindex file-name encoding, MS-Windows
 @vindex w32-unicode-filenames
diff --git a/lisp/international/mule-cmds.el b/lisp/international/mule-cmds.el
index ccc8ac9f9e..e3155dfc52 100644
--- a/lisp/international/mule-cmds.el
+++ b/lisp/international/mule-cmds.el
@@ -1799,13 +1799,11 @@ reset-language-environment
    'raw-text)
 
   (set-default-coding-systems nil)
-  (setq default-sendmail-coding-system 'iso-latin-1)
-  ;; On Darwin systems, this should be utf-8-unix, but when this file is loaded
-  ;; that is not yet defined, so we set it in set-locale-environment instead.
-  ;; [Actually, it seems to work fine to use utf-8-unix here, and not just
-  ;; on Darwin.  The previous comment seems to be outdated?
-  ;; See patch at https://debbugs.gnu.org/15803 ]
-  (setq default-file-name-coding-system 'iso-latin-1-unix)
+  (setq default-sendmail-coding-system 'utf-8)
+  (setq default-file-name-coding-system (if (memq system-type
+                                                  '(window-nt ms-dos))
+                                            'iso-latin-1-unix
+                                          'utf-8-unix))
   ;; Preserve eol-type from existing default-process-coding-systems.
   ;; On non-unix-like systems in particular, these may have been set
   ;; carefully by the user, or by the startup code, to deal with the
@@ -1821,8 +1819,10 @@ reset-language-environment
 	(input-coding
 	 (condition-case nil
 	     (coding-system-change-text-conversion
-	      (cdr default-process-coding-system) 'iso-latin-1)
-	   (coding-system-error 'iso-latin-1))))
+	      (cdr default-process-coding-system)
+	      (if (memq system-type '(window-nt ms-dos)) 'iso-latin-1 'utf-8))
+	   (coding-system-error
+	    (if (memq system-type '(window-nt ms-dos)) 'iso-latin-1 'utf-8)))))
     (setq default-process-coding-system
 	  (cons output-coding input-coding)))
 
diff --git a/lisp/mail/sendmail.el b/lisp/mail/sendmail.el
index dd6eecbfd0..7610939e57 100644
--- a/lisp/mail/sendmail.el
+++ b/lisp/mail/sendmail.el
@@ -975,7 +975,7 @@ sendmail-coding-system
 See also the function `select-message-coding-system'.")
 
 ;;;###autoload
-(defvar default-sendmail-coding-system 'iso-latin-1
+(defvar default-sendmail-coding-system 'utf-8
   "Default coding system for encoding the outgoing mail.
 This variable is used only when `sendmail-coding-system' is nil.
 
diff --git a/lisp/mh-e/mh-comp.el b/lisp/mh-e/mh-comp.el
index f7e30bfbb3..8a69adbb75 100644
--- a/lisp/mh-e/mh-comp.el
+++ b/lisp/mh-e/mh-comp.el
@@ -305,6 +305,7 @@ mh-send-letter
   (let ((draft-buffer (current-buffer))
         (file-name buffer-file-name)
         (config mh-previous-window-config)
+        ;; FIXME this is subtly different to select-message-coding-system.
         (coding-system-for-write
          (if (fboundp 'select-message-coding-system)
              (select-message-coding-system) ; Emacs has this since at least 21.1
@@ -318,7 +319,7 @@ mh-send-letter
              (or (and (boundp 'sendmail-coding-system) sendmail-coding-system)
                  (and (default-boundp 'buffer-file-coding-system)
                       (default-value 'buffer-file-coding-system))
-                 'iso-latin-1)))))
+                 'utf-8)))))
     ;; Older versions of spost do not support -msgid and -mime.
     (unless mh-send-uses-spost-flag
       ;; Adding a Message-ID field looks good, makes it easier to search for

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no