geo/geomfn: fix st_shortestline and st_longestline for ZM coords

Previously, we were appending the coords slice for the two endpoints,
which would result in incorrect behaviour when the geometry had
more than two dimensions.

Release note: None

pkg/geo/geomfn/distance.go

@@ -155,7 +155,8 @@ func distanceLineStringInternal(
 	default:
 		return geo.Geometry{}, errors.Newf("programmer error: unknown behavior")
 	}
-	lineString := geom.NewLineStringFlat(geom.XY, append(coordA, coordB...)).SetSRID(int(a.SRID()))
+	lineCoords := []float64{coordA.X(), coordA.Y(), coordB.X(), coordB.Y()}
+	lineString := geom.NewLineStringFlat(geom.XY, lineCoords).SetSRID(int(a.SRID()))
 	return geo.MakeGeometryFromGeomT(lineString)
 }
 

pkg/geo/geomfn/distance_test.go

@@ -38,6 +38,15 @@ var distanceTestCases = []struct {
 		"LINESTRING (1 1, 1 1)",
 		"LINESTRING (1 1, 1 1)",
 	},
+	{
+		"Same 3D POINTs",
+		"POINT(1.0 2.0 3.0)",
+		"POINT(1.0 2.0 3.0)",
+		0,
+		0,
+		"LINESTRING (1 2, 1 2)",
+		"LINESTRING (1 2, 1 2)",
+	},
 	{
 		"Different POINTs",
 		"POINT(1.0 1.0)",
@@ -47,6 +56,15 @@ var distanceTestCases = []struct {
 		"LINESTRING(1.0 1.0, 2.0 1.0)",
 		"LINESTRING (1 1, 2 1)",
 	},
+	{
+		"Different 3D POINTs",
+		"POINT(0.0 1.0 2.0)",
+		"POINT(0.0 3.0 5.0)",
+		2,
+		2,
+		"LINESTRING (0 1, 0 3)",
+		"LINESTRING (0 1, 0 3)",
+	},
 	{
 		"POINT on LINESTRING",
 		"POINT(0.5 0.5)",