Introduce pid criteria token

This can be used as a workaround to flag terminal windows as urgent when
commands are completed, until urgency is introduced in the Wayland
protocol.

Configure your shell to run `swaymsg "[pid=$PPID] urgent enable"` when
commands are completed, and use a terminal which uses one process per
window.

include/sway/criteria.h

@@ -46,6 +46,7 @@ struct criteria {
 	bool tiling;
 	char urgent; // 'l' for latest or 'o' for oldest
 	struct pattern *workspace;
+	pid_t pid;
 };
 
 bool criteria_is_empty(struct criteria *criteria);

sway/criteria.c

@@ -31,7 +31,8 @@ bool criteria_is_empty(struct criteria *criteria) {
 		&& !criteria->floating
 		&& !criteria->tiling
 		&& !criteria->urgent
-		&& !criteria->workspace;
+		&& !criteria->workspace
+		&& !criteria->pid;
 }
 
 // The error pointer is used for parsing functions, and saves having to pass it
@@ -370,6 +371,12 @@ static bool criteria_matches_view(struct criteria *criteria,
 		}
 	}
 
+	if (criteria->pid) {
+		if (criteria->pid != view->pid) {
+			return false;
+		}
+	}
+
 	return true;
 }
 
@@ -458,6 +465,7 @@ enum criteria_token {
 	T_TITLE,
 	T_URGENT,
 	T_WORKSPACE,
+	T_PID,
 
 	T_INVALID,
 };
@@ -493,6 +501,8 @@ static enum criteria_token token_from_name(char *name) {
 		return T_TILING;
 	} else if (strcmp(name, "floating") == 0) {
 		return T_FLOATING;
+	} else if (strcmp(name, "pid") == 0) {
+		return T_PID;
 	}
 	return T_INVALID;
 }
@@ -587,6 +597,12 @@ static bool parse_token(struct criteria *criteria, char *name, char *value) {
 	case T_WORKSPACE:
 		pattern_create(&criteria->workspace, value);
 		break;
+	case T_PID:
+		criteria->pid = strtoul(value, &endptr, 10);
+		if (*endptr != 0) {
+			error = strdup("The value for 'pid' should be numeric");
+		}
+		break;
 	case T_INVALID:
 		break;
 	}

sway/sway.5.scd

@@ -850,6 +850,9 @@ The following attributes may be matched with:
 	value is \_\_focused\_\_, then the window instance must be the same as that
 	of the currently focused window.
 
+*pid*
+	Compare value against the window's process ID. Must be numeric.
+
 *shell*
 	Compare value against the window shell, such as "xdg_shell" or "xwayland".
 	Can be a regular expression. If value is \_\_focused\_\_, then the shell