bug#24456: 25.1; [PATCH] Caps-lock doesn't affect interpretation of key chords

[Dima Kogan]

Hi.

I noticed that on some platforms the caps-lock state can affect how key
chords are interpreted. It is currently inconsistent across platforms.
The behavior that feels correct to me is that caps-lock should affect
the case of letters as they are typed, and NOTHING else.

On gtk, if caps-lock is ON then Control+s produces C-S-s and
Control+Shift+s produces C-s; this is backwards from what I think it
should do.

On OSX it looks like with caps-lock, both shifted and non-shifted
presses produce C-s, which is 50% wrong regardless of how one thinks
this SHOULD work.

On Windows it does the right thing.

In a console on Debian it looks like Control+Shift+s produces C-s
regardless of caps-lock, but I suspect this has a deeper cause than what
this patch touches.


I have tested this patch on gtk (fixes it) and the console (doesn't
change anything). Hopefully it makes osx work properly while letting
windows builds keep working.


>From 7e34d122ff981c4a9eb671aa2400efbf65144506 Mon Sep 17 00:00:00 2001
From: Dima Kogan <dima@secretsauce.net>
Date: Sat, 17 Sep 2016 23:47:48 -0700
Subject: [PATCH] Caps-lock doesn't affect interpretation of key chords

* src/keyboard.c (make_lispy_event): when a user pressed key-chords the
caps-lock no longer affects the "shift" state of the generated chord.  For
instance Control+s produces C-s regardless of the caps-lock state.  And
Control+Shift+s produces C-S-s regardless of the caps-lock state.
---
 src/keyboard.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/src/keyboard.c b/src/keyboard.c
index b8bc361..a977de5 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -5415,6 +5415,32 @@ make_lispy_event (struct input_event *event)
        EMACS_INT c = event->code;
        if (event->kind == ASCII_KEYSTROKE_EVENT)
          {
+            /* Caps-lock shouldn't affect interpretation of key chords:
+               Control+s should produce C-s whether caps-lock is on or
+               not.  And Control+Shift+s should produce C-S-s whether
+               caps-lock is on or not. */
+            if (event->modifiers & ~shift_modifier)
+              {
+                /* this is a key chord: some non-shift modifier is
+                   depressed */
+
+                if ('A' <= c && c <= 'Z' &&
+                    !(event->modifiers & shift_modifier) )
+                  {
+                    /* Got a capital letter without a shift.  The caps
+                       lock is on.   Un-capitalize the letter */
+                    c |= (unsigned)('a' - 'A');
+                  }
+                else if (('a' <= c && c <= 'z') &&
+                         (event->modifiers & shift_modifier) )
+                  {
+                    /* Got a lower-case letter even though shift is
+                       depressed.  The caps lock is on.  Capitalize the
+                       letter */
+                    c &= ~(unsigned)('a' - 'A');
+                  }
+              }
+
            c &= 0377;
            eassert (c == event->code);
            /* Turn ASCII characters into control characters
-- 
2.9.3