The change clarifies the conditions for forcing routing steps and
simplifies the codebase to support it.
- Makes explicity the search runtime condition for forcing a routing
step. Namely, the node is a source of the forward and reverse searches,
and it's one of the pre-identified nodes that requires a step to
be forced.
- Consolidate the two lists of force nodes into one. Not only is there
no algorithmic value in separating the nodes by geometric direction,
the improvements to via-routes with u-turns mean atleast one of these
lists will be empty for any search.
- Rename 'force loop' to 'force step'. This moves the code away
from the original CH-specific language for checking for self-loops
in the case where this condition is met. MLD does not have loops.
Additional cucumber tests are added to cover the logic related to
negative search weights and forcing routing steps on via-route
paths.
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