Exception with edge labels when using fixed positioned ports.

[philip-alldredge]

When using FIXED_POS port constraints and a self loop involving two ports on the same side, an exception is thrown if the edge has a label.

UnsupportedConfigurationException: Node 'n1.n2.p2' has its layer constraint set to FIRST_SEPARATE, but has at least one incoming edge. FIRST_SEPARATE nodes must not have incoming edges.

Example graph:

elk.direction: RIGHT
hierarchyHandling: SEPARATE_CHILDREN
algorithm: org.eclipse.elk.layered
node n1 {
	portConstraints: FREE
	node n2 {
		nodeSize.constraints: "[PORTS]"
        insideSelfLoops.activate: true
		nodeSize.options: "[DEFAULT_MINIMUM_SIZE]"
		portConstraints: FIXED_POS
		port p1 {
			layout [
				size: 23.11979103088379, 40
				position: 0, 31
			]
			org.eclipse.elk.^port.side: WEST
		}
		port p2 {
			layout [
				size: 23.11979103088379, 40
				position: 0, 81
			]
			org.eclipse.elk.^port.side: WEST
		}
	}
	edge e1: n2.p1 -> n2.p2 {
		insideSelfLoops.yo: true
		label "fs"
	}
}

Removing the label produces desired results. Deactivating the self loops produces an undesirable layout.

[uruuru]

Deactivating the self loops produces an undesirable layout.

I presume you mean deactivating inside selfloops.

I could imagine that this is a case nobody checked beforehand. You'd have, internally, two external port dummies for the ports and a label dummy for the edge label. Both port dummies get assigned FIRST_SEPARATE and are connected via dummy edges to the label dummy. And likely the edges are introduced in a generic fashion resulting in one of them pointing into the "wrong" direction.

[Kh4n]

Reversing one of the edge directions seems to work, though you'd have to manually check this case and then flip one (this is only as a workaround, not a fix)

[soerendomroes]

An inside self-loop between nodes of the same side essentially creates an in-layer edge, which is currently not supported by ELK.

I suggest adding a node to route the edge trough to solve this problem:

elk.direction: RIGHT
hierarchyHandling: SEPARATE_CHILDREN
algorithm: org.eclipse.elk.layered
node n1 {
    portConstraints: FREE
    node n2 {
        elk.direction: RIGHT
        nodeSize.constraints: "[PORTS, PORT_LABELS]"
        insideSelfLoops.activate: true
        nodeSize.options: "[DEFAULT_MINIMUM_SIZE]"
        portConstraints: FIXED_POS
        port p1 {
            layout [
                size: 23.11979103088379, 40
                position: 0, 31
            ]
            org.eclipse.elk.^port.side: WEST
        }
        port p2 {
            layout [
                size: 23.11979103088379, 40
                position: 0, 81
            ]
            org.eclipse.elk.^port.side: WEST
        }
        node dummy {
            
            layout [size: 1, 1]
            portConstraints: FIXED_SIDE
            
            port north {
                ^port.side: NORTH
            }
            port south {
                ^port.side: SOUTH
            }
        }
        
        edge p1 -> dummy.north {
            insideSelfLoops.yo: true
            label "fs"
        }
        edge dummy.south -> p2 {
            insideSelfLoops.yo: true
            label "fs"
        }
    }
//    edge e1: n2.p1 -> n2.p2 {
//        insideSelfLoops.yo: true
//        label "fs"
//    }
}
``