Fix touches for multi geoms

Only one of the geoms in g2 MUST touch the geom in g1, all others MUST be disjoint or touching.

This could potentially be accelerated by building an STRtree if the query width is long enough, or we may also need some tree interface / preparation here.  E.g. Canada has a lot of islands that a tree approach could get rid of.

Author: asinghvi17

src/methods/geom_relations/touches.jl

@@ -225,19 +225,49 @@ _touches(
 
 # # Geometries touch multi-geometry/geometry collections
 
-#= Geometry touch a multi-geometry or a collection if the geometry touches at
-least one of the elements of the collection. =#
+#= 
+
+A geometry touches a multi-geometry or a collection if the geometry touches at
+least one of the elements of the collection.
+
+This is a bit tricky to implement - we have to actually check every geometry, 
+and make sure that each geom is either disjoint or touching.
+
+Problem here is that we would end up doing double the work.
+
+Either you check disjointness first, and then check touches - in which case
+you have already done the work for the touches check, but can't take advantage of it.
+
+Or you check touches first, and if that is false, you check disjointness.  But if touches failed,
+and you don't know _why_ it was false (disjoint or contained / intersecting), you have to iterate
+over every point twice -- again!
+
+
+At this point we actually need a fast return function...or some more detail returned from the process functions.
+
+That's a project for later though.  Right now we need to get this correct, so I'm going to do the dumb thing.
+
+=#
 function _touches(
     ::Union{GI.PointTrait, GI.AbstractCurveTrait, GI.PolygonTrait}, g1,
     ::Union{
         GI.MultiPointTrait, GI.AbstractMultiCurveTrait,
         GI.MultiPolygonTrait, GI.GeometryCollectionTrait,
     }, g2,
 )
+    has_touched = false
     for sub_g2 in GI.getgeom(g2)
-        !touches(g1, sub_g2) && return false
+        if touches(g1, sub_g2)
+            has_touched = true
+        else 
+            # if not touching, they are either intersecting or disjoint
+            # if disjoint, then we can continue
+            # else, we can short circuit, since the geoms are not touching and not disjoint
+            # i.e. they are intersecting
+            disjoint(g1, sub_g2) || return false
+        end
     end
-    return true
+    return has_touched
 end
 
 # # Multi-geometry/geometry collections cross geometries
@@ -251,8 +281,16 @@ function _touches(
     }, g1,
     ::GI.AbstractGeometryTrait, g2,
 )
+    has_touched = false
     for sub_g1 in GI.getgeom(g1)
-        !touches(sub_g1, g2) && return false
+        if touches(sub_g1, g2)
+            has_touched = true
+        else 
+            # if not touching, they are either intersecting or disjoint
+            # if disjoint, then we can continue
+            # else, we can short circuit, since the geoms are not touching and not disjoint
+            disjoint(sub_g1, g2) || return false
+        end
     end
-    return true
+    return has_touched
 end