src/Utils/TypeComparators.php
public static function doTypesOverlap(Schema $schema, CompositeType $typeA, CompositeType $typeB)
    {
        // Equivalent types overlap
        if ($typeA === $typeB) {
            return true;
        }

        if ($typeA instanceof AbstractType) {
            if ($typeB instanceof AbstractType) {
                // If both types are abstract, then determine if there is any intersection
                // between possible concrete types of each.
                foreach ($schema->getPossibleTypes($typeA) as $type) {
                    if ($schema->isPossibleType($typeB, $type)) {
                        return true;
                    }
                }

                return false;
            }

            // Determine if the latter type is a possible concrete type of the former.
            return $schema->isPossibleType($typeA, $typeB);
        }

        if ($typeB instanceof AbstractType) {
            // Determine if the former type is a possible concrete type of the latter.
            return $schema->isPossibleType($typeB, $typeA);
        }

        // Otherwise the types do not overlap.
        return false;
    }
public static function doTypesOverlap(Schema $schema, CompositeType $typeA, CompositeType $typeB)
    {
        // Equivalent types overlap
        if ($typeA === $typeB) {
            return true;
        }

        if ($typeA instanceof AbstractType) {
            if ($typeB instanceof AbstractType) {
                // If both types are abstract, then determine if there is any intersection
                // between possible concrete types of each.
                foreach ($schema->getPossibleTypes($typeA) as $type) {
                    if ($schema->isPossibleType($typeB, $type)) {
                        return true;
                    }
                }

                return false;
            }

            // Determine if the latter type is a possible concrete type of the former.
            return $schema->isPossibleType($typeA, $typeB);
        }

        if ($typeB instanceof AbstractType) {
            // Determine if the former type is a possible concrete type of the latter.
            return $schema->isPossibleType($typeB, $typeA);
        }

        // Otherwise the types do not overlap.
        return false;
    }
Provided two composite types, determine if they "overlap". Two composite
types overlap when the Sets of possible concrete types for each intersect.

This is often used to determine if a fragment of a given type could possibly
be visited in a context of another type.

This function is commutative.

@return bool