CellId.AllNeighbors has documented but unchecked precondition

[ymofen]

ll1 := s2.LatLngFromDegrees(30.755702, 114.127656)
c1 := s2.CellIDFromLatLng(ll1)
neighbors := c1.AllNeighbors(8)

[jmr]

Can you put this in the form of a test case we can add to latlng_test.go?

[jmr]

c1 is level 30. You can't get level 8 neighbors from that.

geo/s2/cellid.go

Line 271 in dc45a10

// This requires level >= ci.Level().

You can try c1 := s2.CellIDFromLatLng(ll1).Parent(8).

@rsned Apparently go has no assert / DCHECK. Should this also return an ok bool? There must be many more examples of unchecked preconditions waiting to bite someone and waste time.

[rsned]

It is possible to set up a dcheck equivalent using go build tags. e.g. #141. There are a couple places where I noted the c++ checks something here, but not too many of the DCHECKs are directly referenced in the code.