bug#24822: 25.1; [PATCH] Support remapping control X keysym

[Vasilij Schneidermann <v.schneidermann@gmail.com>]

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> Changes should always be documented in NEWS.  NEWS.25 describes
> changes in Emacs 25.x for Emacs 26 and higher, so it's never relevant.

Thanks, I've added it to the "Changes in Emacs 26.1" section.
 
> Did you look into the Emacs manual, to see if it also needs an update?

I've updated the existing manual entry now as well.

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From 1533124a83c82e60418669d3dcc83c38adfe3fa7 Mon Sep 17 00:00:00 2001
From: Vasilij Schneidermann <v.schneidermann@gmail.com>
Date: Sun, 30 Oct 2016 01:29:18 +0200
Subject: [PATCH] Support remapping control X keysym

---
 doc/lispref/os.texi | 10 ++++++----
 etc/NEWS            |  5 +++++
 src/xterm.c         | 43 +++++++++++++++++++++++++++++--------------
 3 files changed, 40 insertions(+), 18 deletions(-)

diff --git a/doc/lispref/os.texi b/doc/lispref/os.texi
index 277abb1..97b086c 100644
--- a/doc/lispref/os.texi
+++ b/doc/lispref/os.texi
@@ -2254,14 +2254,16 @@ The variable is always local to the current terminal, and cannot be
 buffer-local.  @xref{Multiple Terminals}.
 @end defvar
 
-You can specify which keysyms Emacs should use for the Meta, Alt, Hyper, and Super modifiers by setting these variables:
+You can specify which keysyms Emacs should use for the Control, Meta,
+Alt, Hyper, and Super modifiers by setting these variables:
 
-@defvar x-alt-keysym
+@defvar x-ctrl-keysym
+@defvarx x-alt-keysym
 @defvarx x-meta-keysym
 @defvarx x-hyper-keysym
 @defvarx x-super-keysym
-The name of the keysym that should stand for the Alt modifier
-(respectively, for Meta, Hyper, and Super).  For example, here is
+The name of the keysym that should stand for the Control modifier
+(respectively, for Alt, Meta, Hyper, and Super).  For example, here is
 how to swap the Meta and Alt modifiers within Emacs:
 @lisp
 (setq x-alt-keysym 'meta)
diff --git a/etc/NEWS b/etc/NEWS
index e29dfe2..a773e92 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -233,6 +233,11 @@ questions, with a handy way to display help texts.
 all call stack frames in a Lisp backtrace buffer as lists.  Both
 debug.el and edebug.el have been updated to heed to this variable.
 
++++
+** The new variable `x-ctrl-keysym` has been added to the existing
+roster of X keysyms.  It can be used in combination with another
+variable of this kind to swap modifiers in Emacs.
+
 \f
 * Editing Changes in Emacs 26.1
 
diff --git a/src/xterm.c b/src/xterm.c
index f0dd0ca..0a420cd 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -4701,12 +4701,15 @@ x_find_modifier_meanings (struct x_display_info *dpyinfo)
 int
 x_x_to_emacs_modifiers (struct x_display_info *dpyinfo, int state)
 {
+  int mod_ctrl = ctrl_modifier;
   int mod_meta = meta_modifier;
   int mod_alt  = alt_modifier;
   int mod_hyper = hyper_modifier;
   int mod_super = super_modifier;
   Lisp_Object tem;
 
+  tem = Fget (Vx_ctrl_keysym, Qmodifier_value);
+  if (INTEGERP (tem)) mod_ctrl = XINT (tem) & INT_MAX;
   tem = Fget (Vx_alt_keysym, Qmodifier_value);
   if (INTEGERP (tem)) mod_alt = XINT (tem) & INT_MAX;
   tem = Fget (Vx_meta_keysym, Qmodifier_value);
@@ -4717,7 +4720,7 @@ x_x_to_emacs_modifiers (struct x_display_info *dpyinfo, int state)
   if (INTEGERP (tem)) mod_super = XINT (tem) & INT_MAX;
 
   return (  ((state & (ShiftMask | dpyinfo->shift_lock_mask)) ? shift_modifier : 0)
-            | ((state & ControlMask)			? ctrl_modifier	: 0)
+            | ((state & ControlMask)			? mod_ctrl	: 0)
             | ((state & dpyinfo->meta_mod_mask)		? mod_meta	: 0)
             | ((state & dpyinfo->alt_mod_mask)		? mod_alt	: 0)
             | ((state & dpyinfo->super_mod_mask)	? mod_super	: 0)
@@ -4727,6 +4730,7 @@ x_x_to_emacs_modifiers (struct x_display_info *dpyinfo, int state)
 static int
 x_emacs_to_x_modifiers (struct x_display_info *dpyinfo, EMACS_INT state)
 {
+  EMACS_INT mod_ctrl = ctrl_modifier;
   EMACS_INT mod_meta = meta_modifier;
   EMACS_INT mod_alt  = alt_modifier;
   EMACS_INT mod_hyper = hyper_modifier;
@@ -4734,6 +4738,8 @@ x_emacs_to_x_modifiers (struct x_display_info *dpyinfo, EMACS_INT state)
 
   Lisp_Object tem;
 
+  tem = Fget (Vx_ctrl_keysym, Qmodifier_value);
+  if (INTEGERP (tem)) mod_ctrl = XINT (tem);
   tem = Fget (Vx_alt_keysym, Qmodifier_value);
   if (INTEGERP (tem)) mod_alt = XINT (tem);
   tem = Fget (Vx_meta_keysym, Qmodifier_value);
@@ -4748,7 +4754,7 @@ x_emacs_to_x_modifiers (struct x_display_info *dpyinfo, EMACS_INT state)
             | ((state & mod_super)	? dpyinfo->super_mod_mask : 0)
             | ((state & mod_hyper)	? dpyinfo->hyper_mod_mask : 0)
             | ((state & shift_modifier)	? ShiftMask        : 0)
-            | ((state & ctrl_modifier)	? ControlMask      : 0)
+            | ((state & mod_ctrl)	? ControlMask      : 0)
             | ((state & mod_meta)	? dpyinfo->meta_mod_mask  : 0));
 }
 
@@ -12863,6 +12869,8 @@ With MS Windows or Nextstep, the value is t.  */);
 #endif
 
   DEFSYM (Qmodifier_value, "modifier-value");
+  DEFSYM (Qctrl, "ctrl");
+  Fput (Qctrl, Qmodifier_value, make_number (ctrl_modifier));
   DEFSYM (Qalt, "alt");
   Fput (Qalt, Qmodifier_value, make_number (alt_modifier));
   DEFSYM (Qhyper, "hyper");
@@ -12872,32 +12880,39 @@ With MS Windows or Nextstep, the value is t.  */);
   DEFSYM (Qsuper, "super");
   Fput (Qsuper, Qmodifier_value, make_number (super_modifier));
 
+  DEFVAR_LISP ("x-ctrl-keysym", Vx_ctrl_keysym,
+    doc: /* Which keys Emacs uses for the ctrl modifier.
+This should be one of the symbols `ctrl', `alt', `hyper', `meta',
+`super'.  For example, `alt' means use the Alt_L and Alt_R keysyms.
+The default is nil, which is the same as `ctrl'.  */);
+  Vx_ctrl_keysym = Qnil;
+
   DEFVAR_LISP ("x-alt-keysym", Vx_alt_keysym,
     doc: /* Which keys Emacs uses for the alt modifier.
-This should be one of the symbols `alt', `hyper', `meta', `super'.
-For example, `alt' means use the Alt_L and Alt_R keysyms.  The default
-is nil, which is the same as `alt'.  */);
+This should be one of the symbols `ctrl', `alt', `hyper', `meta',
+`super'.  For example, `alt' means use the Alt_L and Alt_R keysyms.
+The default is nil, which is the same as `alt'.  */);
   Vx_alt_keysym = Qnil;
 
   DEFVAR_LISP ("x-hyper-keysym", Vx_hyper_keysym,
     doc: /* Which keys Emacs uses for the hyper modifier.
-This should be one of the symbols `alt', `hyper', `meta', `super'.
-For example, `hyper' means use the Hyper_L and Hyper_R keysyms.  The
-default is nil, which is the same as `hyper'.  */);
+This should be one of the symbols `ctrl', `alt', `hyper', `meta',
+`super'.  For example, `alt' means use the Alt_L and Alt_R keysyms.
+The default is nil, which is the same as `hyper'.  */);
   Vx_hyper_keysym = Qnil;
 
   DEFVAR_LISP ("x-meta-keysym", Vx_meta_keysym,
     doc: /* Which keys Emacs uses for the meta modifier.
-This should be one of the symbols `alt', `hyper', `meta', `super'.
-For example, `meta' means use the Meta_L and Meta_R keysyms.  The
-default is nil, which is the same as `meta'.  */);
+This should be one of the symbols `ctrl', `alt', `hyper', `meta',
+`super'.  For example, `alt' means use the Alt_L and Alt_R keysyms.
+The default is nil, which is the same as `meta'.  */);
   Vx_meta_keysym = Qnil;
 
   DEFVAR_LISP ("x-super-keysym", Vx_super_keysym,
     doc: /* Which keys Emacs uses for the super modifier.
-This should be one of the symbols `alt', `hyper', `meta', `super'.
-For example, `super' means use the Super_L and Super_R keysyms.  The
-default is nil, which is the same as `super'.  */);
+This should be one of the symbols `ctrl', `alt', `hyper', `meta',
+`super'.  For example, `alt' means use the Alt_L and Alt_R keysyms.
+The default is nil, which is the same as `super'.  */);
   Vx_super_keysym = Qnil;
 
   DEFVAR_LISP ("x-keysym-table", Vx_keysym_table,
-- 
2.10.1