geomfn: prevent crash with st_snap on empty geometries

After we've upgraded to GEOS 3.12+, apparently we picked up a regression
with the library where it could result in a crash when evaluating `Snap`
on an empty geometry. In such a scenario, the input parameter should be
returned unchanged, so we simply add a short-circuiting logic.

Release note: None

Author: yuzefovich

pkg/geo/geomfn/snap.go

@@ -14,6 +14,11 @@ import (
 // geometry. Tolerance is used to control where snapping is performed.
 // If no snapping occurs then the input geometry is returned unchanged.
 func Snap(input, target geo.Geometry, tolerance float64) (geo.Geometry, error) {
+	if input.Empty() {
+		// If input is empty, return it unchanged (snap has no effect on empty
+		// geoms).
+		return input, nil
+	}
 	snappedEWKB, err := geos.Snap(input.EWKB(), target.EWKB(), tolerance)
 	if err != nil {
 		return geo.Geometry{}, err

pkg/sql/logictest/testdata/logic_test/geospatial

@@ -6378,3 +6378,10 @@ SELECT '{0101000020e6100000cdcccccccc4c1b40cdcccccccc8c4740:0101000020e610000033
 {0101000020E6100000CDCCCCCCCC4C1B40CDCCCCCCCC8C4740:0101000020E6100000333333333333FD3FCDCCCCCCCC0C4640}
 
 subtest end
+
+# Regression test for crashing when evaluating st_snap on an empty geometry
+# (#151103).
+query T
+SELECT st_snap('01010000C0000000000000F87F000000000000F87F000000000000F87F000000000000F87F'::GEOMETRY, '01010000C0000000000000F87F000000000000F87F000000000000F87F000000000000F87F'::GEOMETRY, 0.5::FLOAT8);
+----
+01010000C0000000000000F87F000000000000F87F000000000000F87F000000000000F87F

pkg/sql/tests/rsg_test.go

@@ -435,9 +435,6 @@ func TestRandomSyntaxFunctions(t *testing.T) {
 					"crdb_internal.fingerprint":
 					// Skipped due to long execution time.
 					continue
-				case "st_snap":
-					// TODO(#151103): unskip st_snap.
-					continue
 				}
 				_, variations := builtinsregistry.GetBuiltinProperties(name)
 				for _, builtin := range variations {
@@ -758,10 +755,6 @@ func TestRandomSyntaxSQLSmith(t *testing.T) {
 		return err
 	}, func(ctx context.Context, db *verifyFormatDB, r *rsg.RSG) error {
 		s := smither.Generate()
-		if strings.Contains(s, "st_snap(") {
-			// TODO(#151103): unskip st_snap.
-			return nil
-		}
 		err := db.exec(t, ctx, s)
 		if c := (*crasher)(nil); errors.As(err, &c) {
 			if err := db.exec(t, ctx, "USE defaultdb"); err != nil {