Only add NumLock fallback where necessary.

Previously, we always discarded the NumLock bit when looking up key
bindings for key press events, and we always grabbed every keycode with
and without the NumLock modifier.

With this commit, the NumLock bit is no longer discarded: since the
previous commit 3bd5e6e5c8 we can
correctly look up key bindings with/without the NumLock bit, as both
variants are stored in |keycodes_head|.

Further, before adding the NumLock fallback (resulting in grabbing the
keycode with the NumLock modifier), we now check whether the key has the
same meaning when NumLock is enabled. This correctly distinguishes the
KP_End vs. KP_1 case, i.e. one can now use the following key bindings:

    # No longer accidentally triggered when pressing KP_1.
    bindsym KP_End nop KP_End

    # Properly distinguished now:
    bindsym KP_End nop KP_End
    bindsym Mod2+KP_1 nop KP_1

fixes #2346

testcases/t/264-keypress-numlock.t

@@ -0,0 +1,138 @@
+#!perl
+# vim:ts=4:sw=4:expandtab
+#
+# Please read the following documents before working on tests:
+# • http://build.i3wm.org/docs/testsuite.html
+#   (or docs/testsuite)
+#
+# • http://build.i3wm.org/docs/lib-i3test.html
+#   (alternatively: perldoc ./testcases/lib/i3test.pm)
+#
+# • http://build.i3wm.org/docs/ipc.html
+#   (or docs/ipc)
+#
+# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+#   (unless you are already familiar with Perl)
+#
+# Verifies that one can bind on numpad keys in different numlock states.
+# Ticket: #2346
+# Bug still in: 4.12-78-g85bb324
+use i3test i3_autostart => 0;
+use i3test::XTEST;
+use ExtUtils::PkgConfig;
+
+SKIP: {
+    skip "libxcb-xkb too old (need >= 1.11)", 1 unless
+        ExtUtils::PkgConfig->atleast_version('xcb-xkb', '1.11');
+
+my $config = <<EOT;
+# i3 config file (v4)
+font -misc-fixed-medium-r-normal--13-120-75-75-C-70-iso10646-1
+
+# Same key, different numlock states.
+bindsym Mod2+KP_1 nop KP_1
+bindsym KP_End nop KP_End
+
+# Binding which should work with numlock and without.
+bindsym Mod4+a nop a
+EOT
+
+my $pid = launch_with_config($config);
+
+start_binding_capture;
+
+is(listen_for_binding(
+    sub {
+        xtest_key_press(87); # KP_End
+        xtest_key_release(87); # KP_End
+    },
+    ),
+   'KP_End',
+   'triggered the "KP_End" keybinding');
+
+is(listen_for_binding(
+    sub {
+        xtest_key_press(77); # Num_Lock
+        xtest_key_press(87); # KP_1
+        xtest_key_release(87); # KP_1
+        xtest_key_release(77); # Num_Lock
+    },
+    ),
+   'KP_1',
+   'triggered the "KP_1" keybinding');
+
+is(listen_for_binding(
+    sub {
+        xtest_key_press(133); # Super_L
+        xtest_key_press(38); # a
+        xtest_key_release(38); # a
+        xtest_key_release(133); # Super_L
+    },
+    ),
+   'a',
+   'triggered the "a" keybinding');
+
+is(listen_for_binding(
+    sub {
+        xtest_key_press(77); # Num_Lock
+        xtest_key_press(133); # Super_L
+        xtest_key_press(38); # a
+        xtest_key_release(38); # a
+        xtest_key_release(133); # Super_L
+        xtest_key_release(77); # Num_Lock
+    },
+    ),
+   'a',
+   'triggered the "a" keybinding');
+
+
+sync_with_i3;
+is(scalar @i3test::XTEST::binding_events, 4, 'Received exactly 4 binding events');
+
+exit_gracefully($pid);
+
+################################################################################
+# Verify the binding is only triggered for KP_End, not KP_1
+################################################################################
+
+$config = <<EOT;
+# i3 config file (v4)
+font -misc-fixed-medium-r-normal--13-120-75-75-C-70-iso10646-1
+
+bindsym KP_End nop KP_End
+EOT
+
+$pid = launch_with_config($config);
+
+start_binding_capture;
+
+is(listen_for_binding(
+    sub {
+        xtest_key_press(87); # KP_End
+        xtest_key_release(87); # KP_End
+    },
+    ),
+   'KP_End',
+   'triggered the "KP_End" keybinding');
+
+is(listen_for_binding(
+    sub {
+        xtest_key_press(77); # Num_Lock
+        xtest_key_press(87); # KP_1
+        xtest_key_release(87); # KP_1
+        xtest_key_release(77); # Num_Lock
+    },
+    ),
+   'timeout',
+   'Did not trigger the KP_End keybinding with KP_1');
+
+# TODO: This test does not verify that i3 does _NOT_ grab keycode 87 with Mod2.
+
+sync_with_i3;
+is(scalar @i3test::XTEST::binding_events, 5, 'Received exactly 5 binding events');
+
+exit_gracefully($pid);
+
+}
+
+done_testing;