rules: setxkbmap deals with empty component differently

[wismill]

Consider the following dummy rules file ~/.config/xkb/rules/dummy:

! model		=	keycodes
  *		=	evdev

! model		=	geometry
  *		=       pc(pc104)

! layout	variant	=	symbols
  *		*	=	pc+%l%(v)

! layout[1]	variant[1]	=	symbols
  *		*		=	pc+%l[1]%(v[1])

! layout[2]	variant[2]	=	symbols
  *		*		=	+%l[2]%(v[2]):2

! layout[3]	variant[3]	=	symbols
  *		*		=	+%l[3]%(v[3]):3

! layout[4]	variant[3]	=	symbols
  *		*		=	+%l[4]%(v[4]):4

! model		layout		=	compat
  *		*		=	complete

! model		layout[1]	=	compat
  *		*		=	complete

! model		=	types
  *		=	complete

setxkbmap and xkbcli compile-keymap give different result with layout = a,b:

# Note: for setxkbmap you need a corresponding .lst file.
# e.g. `ln -s /usr/share/X11/xkb/rules/evdev.lst ~/.config/xkb/rules/dummy.lst`

###################
# Without variant #
###################

# No symbol match!
> setxkbmap -print -rules ~/.config/xkb/rules/dummy -layout a,b
xkb_keymap {
        xkb_keycodes  { include "evdev" };
        xkb_types     { include "complete"      };
        xkb_compat    { include "complete"      };
        xkb_geometry  { include "pc(pc104)"     };
};

# Not working, “same” as setxkbmap
> ./build/compile-keymap --kccgst --rules dummy --layout a,b

######################
# With empty variant #
######################

# No symbol match!
> setxkbmap -print -rules ~/.config/xkb/rules/dummy -layout a,b -variant ,
xkb_keymap {
        xkb_keycodes  { include "evdev" };
        xkb_types     { include "complete"      };
        xkb_compat    { include "complete"      };
        xkb_geometry  { include "pc(pc104)"     };
};

# Working, contrary to setxkbmap!
> ./build/compile-keymap --kccgst --rules dummy --layout a,b --variant ,
xkb_keymap {
  xkb_keycodes { include "evdev" };
  xkb_types { include "complete" };
  xkb_compat { include "complete" };
  xkb_symbols { include "pc+a+b:2" };
};

#################
# With variants #
#################

# Symbol match!
> setxkbmap -print -rules ~/.config/xkb/rules/dummy -layout a,b -variant x,y
xkb_keymap {
        xkb_keycodes  { include "evdev" };
        xkb_types     { include "complete"      };
        xkb_compat    { include "complete"      };
        xkb_symbols   { include "pc+a(x)+b(y):2"        };
        xkb_geometry  { include "pc(pc104)"     };
};

# Working, same as setxkbmap
> ./build/compile-keymap --kccgst --rules dummy --layout a,b --variant x,y
xkb_keymap {
  xkb_keycodes { include "evdev" };
  xkb_types { include "complete" };
  xkb_compat { include "complete" };
  xkb_symbols { include "pc+a(x)+b(y):2" };
};

So we somehow match on empty variant --layout x,y --variant ,, but not when variant is missing --layout x,y (or --layout x,y --variant "").

This neither consistent nor behaves as setxkbmap, so this is a bug. Agreed, this does not trigger yet because the current rules of xkeyboard-config have cover missing variant, but I did encounter this bug while working on xkeyboard-config#478.

Actions to take:

1. Add a test
2. Fix the bug
3. Update the rules doc page about the wildcard behavior. I initially thought it matched everything, even missing component, but it does require a component value (here a variant) in order to match.