MiniZinc::simplify_bool_constraint(): Assertion 'nonfixed >= 0' failed.

[LebedevRI]

Probably not fully reduced:

int: NUM_GRAPH_NODES = 7; % par
int: NUM_GRAPH_EDGES = length(j,i in GRAPH_NODES where i > j)(1); % par

enum GRAPH_NODES = GN(1..NUM_GRAPH_NODES);
enum GRAPH_EDGES = GE(1..NUM_GRAPH_EDGES);
enum DISJOINT_SUBGRAPH_INDICES = DG(1..NUM_GRAPH_NODES);
enum DISJOINT_SUBGRAPH_NODES = DGn(GRAPH_NODES);
enum DISJOINT_SUBGRAPH_EDGE_INDICES = DGe(DISJOINT_SUBGRAPH_INDICES);

array[GRAPH_EDGES] of GRAPH_NODES: GRAPH_LEAVING_NODE  = [ j | j,i in GRAPH_NODES where i > j ];
array[GRAPH_EDGES] of GRAPH_NODES: GRAPH_ENTERING_NODE = [ i | j,i in GRAPH_NODES where i > j ];

array[GRAPH_NODES] of var bool: GraphNodes; % par
array[GRAPH_EDGES] of var bool: GraphEdges; % par
array[GRAPH_EDGES] of DISJOINT_SUBGRAPH_NODES: DISJOINT_SUBGRAPH_LEAVING_NODE = [DGn(GRAPH_LEAVING_NODE[e]) | e in GRAPH_EDGES];
array[GRAPH_EDGES] of DISJOINT_SUBGRAPH_NODES: DISJOINT_SUBGRAPH_ENTERING_NODE = [DGn(GRAPH_ENTERING_NODE[e]) | e in GRAPH_EDGES];
array[GRAPH_NODES] of var DISJOINT_SUBGRAPH_INDICES: NodeDisjointSubgraphIndex;
array[DISJOINT_SUBGRAPH_NODES] of var bool: NodeRootnessMask;
array[GRAPH_NODES] of var GRAPH_NODES: parent; 
array[GRAPH_NODES,GRAPH_NODES] of var bool: HardWires;

constraint forall (j,i in GRAPH_NODES)(
  let {
    GRAPH_NODES: m = min(i,j);
    GRAPH_NODES: M = max(i,j);
  } in
   HardWires[m,M] == ((m,M) == (1,2) \/ (m,M) == (2,3) \/ (m,M) == (2,7) \/ (m,M) == (4,5))
);

constraint forall (n in GRAPH_NODES)(
  GraphNodes[n] == exists(HardWires[n,..])
);
constraint forall (e in GRAPH_EDGES)(
  GraphEdges[e] == HardWires[GRAPH_LEAVING_NODE[e],GRAPH_ENTERING_NODE[e]]
);
constraint forall(n in GRAPH_NODES)(
  parent[n] != n -> exists(e in index_set(GRAPH_LEAVING_NODE) where GRAPH_ENTERING_NODE[e] = n)(GraphEdges[e] /\ GRAPH_LEAVING_NODE[e] = parent[n])
);

$ minizinc --version
MiniZinc to FlatZinc converter, version 2.8.5

[LebedevRI]

(I think this is new in 2.8.5, never seen that with .4)