add --allow-other flag for keybindings

This flag allows other keys to be pressed at the same time as the
binding. This acts as follows:
- All key modifiers not explicitly listed in the binding are ignored.
  The binding's modifiers are still required to be pressed.
- If other keys are pressed between press and release, release is still
  triggered.

include/sway/config.h

@@ -50,6 +50,7 @@ enum binding_flags {
 	BINDING_INHIBITED = 1 << 7, // keyboard only: ignore shortcut inhibitor
 	BINDING_NOREPEAT = 1 << 8, // keyboard only; do not trigger when repeating a held key
 	BINDING_EXACT = 1 << 9, // gesture only; only trigger on exact match
+	BINDING_ALLOWOTHER = 1 << 10, // keyboard only; allow other keys to be pressed at the same time
 };
 
 /**

sway/commands/bind.c

@@ -377,6 +377,8 @@ static struct cmd_results *cmd_bindsym_or_bindcode(int argc, char **argv,
 			warn = false;
 		} else if (strcmp("--no-repeat", argv[0]) == 0) {
 			binding->flags |= BINDING_NOREPEAT;
+		} else if (strcmp("--allow-other", argv[0]) == 0) {
+			binding->flags |= BINDING_ALLOWOTHER;
 		} else {
 			break;
 		}

sway/input/keyboard.c

@@ -162,8 +162,9 @@ static void get_active_binding(const struct sway_shortcut_state *state,
 		bool binding_locked = (binding->flags & BINDING_LOCKED) != 0;
 		bool binding_inhibited = (binding->flags & BINDING_INHIBITED) != 0;
 		bool binding_release = binding->flags & BINDING_RELEASE;
+		bool binding_allowother = (binding->flags & BINDING_ALLOWOTHER) != 0;
 
-		if (modifiers ^ binding->modifiers ||
+		if ((binding_allowother ? (binding->modifiers & modifiers) : modifiers) ^ binding->modifiers ||
 				release != binding_release ||
 				locked > binding_locked ||
 				inhibited > binding_inhibited ||
@@ -175,7 +176,44 @@ static void get_active_binding(const struct sway_shortcut_state *state,
 		}
 
 		bool match = false;
-		if (state->npressed == (size_t)binding->keys->length) {
+		if (binding_allowother) {
+			/*
+			 * Make sure all keys match, but also allow other keys to be pressed.
+			 * In case of a press (as opposed to release), make sure at least one
+			 * of the keys is the current key, otherwise the binding would be
+			 * triggered twice. In case of release, the keys are considered released
+			 * all at once so no check is necessary.
+			 */
+			size_t j = 0;
+			bool one_is_current = false;
+
+			match = binding->keys->length != 0;
+
+			for (int k = 0; k < binding->keys->length; k++) {
+				bool this_key_match = false;
+				uint32_t key = *(uint32_t *)binding->keys->items[k];
+
+				for (; j < state->npressed; j++) {
+					if (key == state->pressed_keys[j]) {
+						this_key_match = true;
+						j++;
+						break;
+					}
+				}
+
+				if (!this_key_match) {
+					match = false;
+					break;
+				}
+				if (key == state->current_key) {
+					one_is_current = true;
+				}
+			}
+
+			if (!release && !one_is_current) {
+				match = false;
+			}
+		} else if (state->npressed == (size_t)binding->keys->length) {
 			match = true;
 			for (size_t j = 0; j < state->npressed; j++) {
 				uint32_t key = *(uint32_t *)binding->keys->items[j];

sway/sway.5.scd

@@ -389,8 +389,8 @@ runtime.
 		for_window <criteria> move container to output <output>
 
 *bindsym* [--whole-window] [--border] [--exclude-titlebar] [--release] [--locked] \
-[--to-code] [--input-device=<device>] [--no-warn] [--no-repeat] [Group<1-4>+]<key combo> \
-<command>
+[--to-code] [--input-device=<device>] [--no-warn] [--no-repeat] [--single-key] \
+[Group<1-4>+]<key combo> <command>
 	Binds _key combo_ to execute the sway command _command_ when pressed. You
 	may use XKB key names here (*wev*(1) is a good tool for discovering these).
 	With the flag _--release_, the command is executed when the key combo is
@@ -419,6 +419,11 @@ runtime.
 	repeatedly when the key is held, according to the repeat
 	settings specified in the input configuration.
 
+	If _--allow-other_ is set, any key sequence containing this key sequence
+	may trigger this binding. For example, a single-key binding with
+	_--allow-other_ set may be executed upon the simultaneous press of one
+	or more keys, one of which is the binding's key.
+
 	Bindings to keysyms are layout-dependent. This can be changed with the
 	_--to-code_ flag. In this case, the keysyms will be translated into the
 	corresponding keycodes in the first configured layout.