Fix coding systems used for X input methods

* doc/emacs/mule.texi (International): Refer to X Coding as
well.
(Communication Coding): Document that locale-coding-system is
not always used on X to decode keyboard input.
(X Coding): New node.
* etc/NEWS: Announce change to input method coding resolution.
* lisp/term/x-win.el (x-get-input-coding-system): New function.
* src/coding.c (syms_of_coding): Update doc string of
locale-coding-system.
* src/xfns.c (struct x_xim_text_conversion_data)
(x_xim_text_to_utf8_unix_1, x_xim_text_to_utf8_unix_2)
(x_xim_text_to_utf8_unix): Accept dpyinfo.  Use the coding
system specified inside if possible.
(xic_preedit_draw_callback): Pass dpyinfo.
* src/xterm.c (handle_one_xevent): Use XIM coding system for IM
input.
(xim_open_dpy): Try to determine the input method coding system.
(mark_xterm): Mark `xim_coding'.
(syms_of_xterm): New variable `x-input-coding-system'.
* src/xterm.h (struct x_display_info): New field `xim_coding'.
(FRAME_X_XIM_CODING): New macro.

1 files changed, 22 insertions, 0 deletions

diff --git a/lisp/term/x-win.el b/lisp/term/x-win.el
index 9d3e7803650..57c6b785e73 100644
--- a/lisp/term/x-win.el
+++ b/lisp/term/x-win.el
@@ -1613,6 +1613,28 @@ Users should not call this function; see `device-class' instead."
 (setq x-dnd-movement-function #'x-dnd-movement)
 (setq x-dnd-unsupported-drop-function #'x-dnd-handle-unsupported-drop)
 
+(defvar x-input-coding-function)
+
+(defun x-get-input-coding-system (x-locale)
+  "Return a coding system for the locale X-LOCALE.
+Return a coding system that is able to decode text sent with the
+X input method locale X-LOCALE, or nil if no coding system was
+found."
+  (if (equal x-locale "C")
+      ;; Treat the C locale specially, as it means "ascii" under X.
+      'ascii
+    (let ((locale (downcase x-locale)))
+      (or (locale-name-match locale locale-preferred-coding-systems)
+          (when locale
+            (if (string-match "\\.\\([^@]+\\)" locale)
+                (locale-charset-to-coding-system
+                 (match-string 1 locale))))
+          (let ((language-name
+                 (locale-name-match locale locale-language-names)))
+            (and (consp language-name) (cdr language-name)))))))
+
+(setq x-input-coding-function #'x-get-input-coding-system)
+
 (provide 'x-win)
 (provide 'term/x-win)