Fix cycle creation in crossover for feed-forward networks

- Add cycle checking in DefaultGenome.configure_crossover when config.feed_forward=True
- Prevent inheritance of connections that would create cycles during crossover
- Remove outdated TODO comment in DefaultReproduction
- Uses existing creates_cycle function from neat.graphs for detection
- Maintains backward compatibility and all existing functionality

Fixes the issue where crossover could produce genomes with cycles even when
feed_forward=True was configured, which would cause errors when creating
FeedForwardNetwork instances.

Author: CodeReclaimers

neat/genome.py

@@ -302,13 +302,22 @@ def configure_crossover(self, genome1, genome2, config):
                     )
                     # Take the gene from the fitter parent
                     new_gene = cg1.copy()
+                    # For feed-forward networks, check if this connection would create a cycle
+                    if config.feed_forward and creates_cycle(list(self.connections), new_gene.key):
+                        continue
                     self.connections[new_gene.key] = new_gene
                 else:
                     new_gene = cg1.crossover(cg2)
+                    # For feed-forward networks, check if this connection would create a cycle
+                    if config.feed_forward and creates_cycle(list(self.connections), new_gene.key):
+                        continue
                     self.connections[new_gene.key] = new_gene
             elif cg1 is not None:
                 # Disjoint or excess gene from fittest parent (parent1)
                 new_gene = cg1.copy()
+                # For feed-forward networks, check if this connection would create a cycle
+                if config.feed_forward and creates_cycle(list(self.connections), new_gene.key):
+                    continue
                 self.connections[new_gene.key] = new_gene
             # Note: genes only in parent2 (less fit) are not inherited
 

neat/reproduction.py

@@ -270,7 +270,6 @@ def reproduce(self, config, species, pop_size, generation):
                 child = config.genome_type(gid)
                 child.configure_crossover(parent1, parent2, config.genome_config)
                 child.mutate(config.genome_config)
-                # TODO: if config.genome_config.feed_forward, no cycles should exist
                 new_population[gid] = child
                 self.ancestors[gid] = (parent1_id, parent2_id)