[PATCH] xkb: don't setMods locking modifiers (#27903)

[Peter Hutterer]

Locking modifiers (e.g. CapsLock) currently lock the modifier on the first
press and release on the second press. The modifier locking in more details
however works like this:
press   -> modifier locked,     event state has modifier up
release -> modifier locked,     event state has modifier down
press   -> modifier released,   event state has modifier down
release -> modifier released,   event state has modifier down

The second press changes the locked_modifiers, but it also sets the modifier
bit for the current press, effectively still setting the modifier from the
client's perspective. The modifier is not effectively unlocked until the
second _release_ event.

Change this behaviour so that the second key _press_ event releases the
modifier, changing to a sequence of:

press   -> modifier locked,     event state has modifier up
release -> modifier locked,     event state has modifier down
press   -> modifier released,   event state has modifier down
release -> modifier released,   event state has modifier up

As a result, if the modifier is pressed for the second time and held down,
following events have the modifier bits unset.

X.Org Bug 27903 <http://bugs.freedesktop.org/show_bug.cgi?id=27903>

Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
---
I'm not sure there are any other side effects visible from this but the most
obvious one is that if you press, release, then press CapsLock, you'll now
end up with lowercase where it used to be uppercase. 

Thus, if you're a fast typer, the sequence "CapsLock F CapsLock oobar" goes
from "FOobar" to "Foobar" (see bug 27903). I'm not sure there's a use-case
for the current behaviour, so changing this doesn't seem to impact badly.

 xkb/xkbActions.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/xkb/xkbActions.c b/xkb/xkbActions.c
index 4b5405a..9e1d39b 100644
--- a/xkb/xkbActions.c
+++ b/xkb/xkbActions.c
@@ -348,7 +348,11 @@ _XkbFilterLockState(	XkbSrvInfoPtr	xkbi,
 	filter->filter = _XkbFilterLockState;
 	filter->upAction = *pAction;
 	xkbi->state.locked_mods^= pAction->mods.mask;
-	xkbi->setMods = pAction->mods.mask;
+	/* Don't actually change setMods here. We're locking modifiers, so
+	 * the combined results of base + locked is the same regardless. By
+	 * not setting them, we get to release locked modifiers on the
+	 * second key _press_, not release (Bug 27903)
+	 */
     }
     else if (filter->keycode==keycode) {
 	filter->active = 0;
-- 
1.7.6