parser: truncate keywords.go when re-creating it (#49634)

pkg/parser/generate_keyword/BUILD.bazel

@@ -0,0 +1,14 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
+
+go_library(
+    name = "generate_keyword_lib",
+    srcs = ["genkeyword.go"],
+    importpath = "github.com/pingcap/tidb/pkg/parser/generate_keyword",
+    visibility = ["//visibility:private"],
+)
+
+go_binary(
+    name = "generate_keyword",
+    embed = [":generate_keyword_lib"],
+    visibility = ["//visibility:public"],
+)

pkg/parser/generate_keyword/genkeyword.go

@@ -0,0 +1,146 @@
+// Copyright 2023 PingCAP, Inc.
+//
+// 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,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"regexp"
+	"strings"
+)
+
+const (
+	reservedKeywordStart   = "The following tokens belong to ReservedKeyword"
+	unreservedkeywordStart = "The following tokens belong to UnReservedKeyword"
+	notKeywordStart        = "The following tokens belong to NotKeywordToken"
+	tiDBKeywordStart       = "The following tokens belong to TiDBKeyword"
+)
+
+const (
+	sectionNone = iota
+	sectionReservedKeyword
+	sectionUnreservedKeyword
+	sectionTiDBKeyword
+)
+
+const (
+	fileStart = `// Copyright 2023 PingCAP, Inc.
+//
+// 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,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package parser
+
+// WARNING: This file is generated by 'genkeyword'
+
+// KeywordsType defines the attributes of keywords
+type KeywordsType struct {
+	Word     string
+	Reserved bool
+	Section  string
+}
+
+// Keywords is used for all keywords in TiDB
+var Keywords = []KeywordsType{
+`
+	fileEnd = `}
+`
+)
+
+var keywordRe *regexp.Regexp
+
+// parseLine extracts a keyword from a line of parser.y
+// returns an empty string if there is no match.
+//
+// example data:
+//
+//	add               "ADD"
+//
+// Note that all keywords except `TiDB_CURRENT_TSO` are fully uppercase.
+func parseLine(line string) string {
+	if keywordRe == nil {
+		keywordRe = regexp.MustCompile(`^\s+\w+\s+"(\w+)"$`)
+	}
+	m := keywordRe.FindStringSubmatch(line)
+	if len(m) != 2 {
+		return ""
+	}
+	return m[1]
+}
+
+func main() {
+	parserData, err := os.ReadFile("parser.y")
+	if err != nil {
+		log.Fatalf("Failed to open parser.y: %s", err)
+	}
+	keywordsFile, err := os.OpenFile("keywords.go", os.O_CREATE|os.O_WRONLY, 0600)
+	if err != nil {
+		log.Fatalf("Failed to create keywords.go: %s", err)
+	}
+	err = keywordsFile.Truncate(0)
+	if err != nil {
+		log.Fatalf("Failed to create keywords.go: %s", err)
+	}
+	_, err = keywordsFile.WriteString(fileStart)
+	if err != nil {
+		log.Fatalf("Failed to write fileStart to keywords.go: %s", err)
+	}
+
+	section := sectionNone
+	for _, line := range strings.Split(string(parserData), "\n") {
+		if line == "" { // Empty line indicates section end
+			section = sectionNone
+		} else if strings.Contains(line, reservedKeywordStart) {
+			section = sectionReservedKeyword
+		} else if strings.Contains(line, unreservedkeywordStart) {
+			section = sectionUnreservedKeyword
+		} else if strings.Contains(line, tiDBKeywordStart) {
+			section = sectionTiDBKeyword
+		} else if strings.Contains(line, notKeywordStart) {
+			section = sectionNone
+		}
+
+		switch section {
+		case sectionReservedKeyword:
+			word := parseLine(line)
+			if len(word) > 0 {
+				fmt.Fprintf(keywordsFile, "\t{\"%s\", true, \"reserved\"},\n", word)
+			}
+		case sectionTiDBKeyword:
+			word := parseLine(line)
+			if len(word) > 0 {
+				fmt.Fprintf(keywordsFile, "\t{\"%s\", false, \"tidb\"},\n", word)
+			}
+		case sectionUnreservedKeyword:
+			word := parseLine(line)
+			if len(word) > 0 {
+				fmt.Fprintf(keywordsFile, "\t{\"%s\", false, \"unreserved\"},\n", word)
+			}
+		}
+	}
+
+	_, err = keywordsFile.WriteString(fileEnd)
+	if err != nil {
+		log.Fatalf("Failed to write fileEnd to keywords.go: %s", err)
+	}
+}