Add commit hook to check the visitor is in sync with the ast

Signed-off-by: Andres Taylor <andres@planetscale.com>

Makefile

@@ -17,6 +17,7 @@ MAKEFLAGS = -s
 export GOBIN=$(PWD)/bin
 export GO111MODULE=on
 export GODEBUG=tls13=0
+export REWRITER=go/vt/sqlparser/rewriter.go
 
 # Disabled parallel processing of target prerequisites to avoid that integration tests are racing each other (e.g. for ports) and may fail.
 # Since we are not using this Makefile for compilation, limiting parallelism will not increase build time.
@@ -89,7 +90,7 @@ parser:
 
 visitor:
 	go build -o visitorgen go/visitorgen/main/main.go
-	./visitorgen -input=go/vt/sqlparser/ast.go -output=go/vt/sqlparser/rewriter.go
+	./visitorgen -input=go/vt/sqlparser/ast.go -output=$(REWRITER)
 	rm ./visitorgen
 
 # To pass extra flags, run test.go manually.

misc/git/hooks/visitorgen

@@ -0,0 +1,25 @@
+#!/bin/bash
+# Copyright 2019 The Vitess Authors.
+#
+# 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.
+
+# this script, which should run before committing code, makes sure that the visitor is re-generated when the ast changes
+
+make visitor REWRITER=tmp_rewriter.go
+if ! cmp -s "tmp_rewriter.go" "go/vt/sqlparser/rewriter.go"; then
+	echo "The ast.go has changed, but not rewriter.go"
+	echo "You should 'make visitor' to update the generated rewriter"
+	rm -f tmp_rewriter.go
+	exit 1
+fi
+rm -f tmp_rewriter.go