removed useless invisible participants

src/diagram.typ

@@ -10,6 +10,10 @@
 }
 
 #let diagram(elements) = {
+  if elements == none {
+    return
+  }
+  
   let participants = ()
   let elmts = elements
   let i = 0
@@ -31,6 +35,7 @@
   }
 
   // List participants
+  let linked = ()
   for elmt in elmts {
     if elmt.type == "par" {
       participants.push(elmt)
@@ -42,24 +47,49 @@
         let par = _par(elmt.p2, from-start: not elmt.create-dst).first()
         participants.push(par)
       }
+
+      if elmt.p1 == "?" {
+        linked.push("?" + elmt.p2)
+      } else {
+        linked.push(elmt.p1)
+      }
+      if elmt.p2 == "?" {
+        linked.push(elmt.p1 + "?")
+      } else {
+        linked.push(elmt.p2)
+      }
     }
   }
+  linked = linked.dedup()
 
   let pars = participants
   participants = ()
-  participants.push(_par("[", invisible: true).first())
+  
+  if "[" in linked {
+    participants.push(_par("[", invisible: true).first())
+  }
+  
   for (i, p) in pars.enumerate() {
     let before = _par("?" + p.name, invisible: true).first()
     let after = _par(p.name + "?", invisible: true).first()
-    if i == 0 {
-      participants.push(before)
-    } else {
-      participants.insert(-1, before)
+    
+    if before.name in linked {
+      if participants.len() == 0 or not participants.last().name.ends-with("?") {
+        participants.push(before)
+      } else {
+        participants.insert(-1, before)
+      }
     }
+
     participants.push(p)
-    participants.push(after)
+
+    if after.name in linked {
+      participants.push(after)
+    }
+  }
+  if "]" in linked {
+    participants.push(_par("]", invisible: true).first())
   }
-  participants.push(_par("]", invisible: true).first())
 
   // Add index to participant
   for (i, p) in participants.enumerate() {