test(spanner/spansql): add fuzz target for ParseQuery (#2909)

This target will be called from a runner managed by the oss-fuzz
project. This target is an experimental test integration with the
oss-fuzz project.

spanner/spansql/fuzz.go

@@ -0,0 +1,28 @@
+// Copyright 2020 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build gofuzz
+
+package spansql
+
+func FuzzParseQuery(data []byte) int {
+	if _, err := ParseQuery(string(data)); err != nil {
+		// The value 0 signals data is an invalid query that should be
+		// added to the corpus.
+		return 0
+	}
+	// The value 1 signals the input was lexically corrent and the
+	// fuzzer should increase the priority of the given input.
+	return 1
+}