Clear stale geometry fields when decoding into reused objects

geojson/geometry.go

@@ -182,11 +182,16 @@ func (g *Geometry) UnmarshalJSON(data []byte) error {
 		}
 		g.Coordinates = mp
 	case "GeometryCollection":
+		g.Coordinates = nil
 		g.Geometries = jg.Geometries
 	default:
 		return ErrInvalidGeometry
 	}
 
+	if jg.Type != "GeometryCollection" {
+		g.Geometries = nil
+	}
+
 	g.Type = g.Geometry().GeoJSONType()
 
 	return nil
@@ -245,11 +250,16 @@ func (g *Geometry) UnmarshalBSON(data []byte) error {
 		}
 		g.Coordinates = mp
 	case "GeometryCollection":
+		g.Coordinates = nil
 		g.Geometries = bg.Geometries
 	default:
 		return ErrInvalidGeometry
 	}
 
+	if bg.Type != "GeometryCollection" {
+		g.Geometries = nil
+	}
+
 	g.Type = g.Geometry().GeoJSONType()
 
 	return nil

geojson/geometry_reuse_test.go

@@ -0,0 +1,47 @@
+package geojson
+
+import (
+	"encoding/json"
+	"reflect"
+	"testing"
+
+	"github.com/paulmach/orb"
+	"go.mongodb.org/mongo-driver/v2/bson"
+)
+
+func TestGeometryUnmarshalReuse(t *testing.T) {
+	codecs := []struct {
+		name      string
+		marshal   func(interface{}) ([]byte, error)
+		unmarshal func([]byte, interface{}) error
+	}{
+		{"JSON", json.Marshal, json.Unmarshal},
+		{"BSON", bson.Marshal, bson.Unmarshal},
+	}
+	point := orb.Point{1, 2}
+	collection := orb.Collection{orb.Point{3, 4}}
+	for _, codec := range codecs {
+		for _, initial := range []orb.Geometry{point, collection} {
+			t.Run(codec.name+"/"+initial.GeoJSONType(), func(t *testing.T) {
+				var expected orb.Geometry = point
+				if _, ok := initial.(orb.Point); ok {
+					expected = collection
+				}
+				data, err := codec.marshal(NewGeometry(expected))
+				if err != nil {
+					t.Fatal(err)
+				}
+				reused := NewGeometry(initial)
+				if err := codec.unmarshal(data, reused); err != nil {
+					t.Fatal(err)
+				}
+				if !reflect.DeepEqual(reused, NewGeometry(expected)) {
+					t.Fatalf("reused geometry = %#v, want %#v", reused, NewGeometry(expected))
+				}
+				if !reflect.DeepEqual(reused.Geometry(), expected) {
+					t.Errorf("Geometry() = %#v, want %#v", reused.Geometry(), expected)
+				}
+			})
+		}
+	}
+}