From f20e4c0ec0d687fb7b679ed276684a7714b2226d Mon Sep 17 00:00:00 2001
From: lance6716 <lance6716@gmail.com>
Date: Fri, 26 Nov 2021 14:52:26 +0800
Subject: [PATCH 1/3] parser: respect TiDB comment when DROP INDEX IF EXISTS

---
 parser/ast/ddl.go      |  9 ++++++++-
 parser/ast/ddl_test.go | 27 ++++++++++++++++++++++++++-
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/parser/ast/ddl.go b/parser/ast/ddl.go
index b537012a9c226..b04ce3252838e 100644
--- a/parser/ast/ddl.go
+++ b/parser/ast/ddl.go
@@ -15,6 +15,7 @@ package ast
 
 import (
 	"github.com/pingcap/errors"
+
 	"github.com/pingcap/tidb/parser/auth"
 	"github.com/pingcap/tidb/parser/format"
 	"github.com/pingcap/tidb/parser/model"
@@ -1689,7 +1690,13 @@ type DropIndexStmt struct {
 func (n *DropIndexStmt) Restore(ctx *format.RestoreCtx) error {
 	ctx.WriteKeyWord("DROP INDEX ")
 	if n.IfExists {
-		ctx.WriteKeyWord("IF EXISTS ")
+		if ctx.Flags.HasTiDBSpecialCommentFlag() {
+			ctx.WriteWithSpecialComments("", func() {
+				ctx.WriteKeyWord("IF EXISTS")
+			})
+		} else {
+			ctx.WriteKeyWord("IF EXISTS ")
+		}
 	}
 	ctx.WriteName(n.IndexName)
 	ctx.WriteKeyWord(" ON ")
diff --git a/parser/ast/ddl_test.go b/parser/ast/ddl_test.go
index a4809d5791cb4..4eb2668f34ae4 100644
--- a/parser/ast/ddl_test.go
+++ b/parser/ast/ddl_test.go
@@ -16,9 +16,10 @@ package ast_test
 import (
 	"testing"
 
+	"github.com/stretchr/testify/require"
+
 	. "github.com/pingcap/tidb/parser/ast"
 	"github.com/pingcap/tidb/parser/format"
-	"github.com/stretchr/testify/require"
 )
 
 func TestDDLVisitorCover(t *testing.T) {
@@ -623,3 +624,27 @@ func TestSequenceRestore(t *testing.T) {
 	}
 	runNodeRestoreTest(t, testCases, "%s", extractNodeFunc)
 }
+
+
+func TestDropIndexRestore(t *testing.T) {
+	t.Parallel()
+	sourceSQL := "drop index if exists idx on t"
+	cases := [] struct {
+		flags format.RestoreFlags
+		expectSQL string
+	}{
+		{format.DefaultRestoreFlags, "DROP INDEX IF EXISTS `idx` ON `t`"},
+		{format.DefaultRestoreFlags|format.RestoreTiDBSpecialComment, "DROP INDEX /*T! IF EXISTS */`idx` ON `t`"},
+	}
+
+	extractNodeFunc := func(node Node) Node {
+		return node
+	}
+
+	for _, ca := range cases {
+		testCases := []NodeRestoreTestCase{
+			{sourceSQL, ca.expectSQL},
+		}
+		runNodeRestoreTestWithFlags(t, testCases, "%s", extractNodeFunc, ca.flags)
+	}
+}

From eb37727dce871522a23f336d330bad3bbe3e77e1 Mon Sep 17 00:00:00 2001
From: lance6716 <lance6716@gmail.com>
Date: Fri, 26 Nov 2021 15:04:59 +0800
Subject: [PATCH 2/3] address comment

---
 parser/ast/ddl.go      | 8 ++------
 parser/ast/ddl_test.go | 2 +-
 2 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/parser/ast/ddl.go b/parser/ast/ddl.go
index b04ce3252838e..28834697b1961 100644
--- a/parser/ast/ddl.go
+++ b/parser/ast/ddl.go
@@ -1690,13 +1690,9 @@ type DropIndexStmt struct {
 func (n *DropIndexStmt) Restore(ctx *format.RestoreCtx) error {
 	ctx.WriteKeyWord("DROP INDEX ")
 	if n.IfExists {
-		if ctx.Flags.HasTiDBSpecialCommentFlag() {
-			ctx.WriteWithSpecialComments("", func() {
-				ctx.WriteKeyWord("IF EXISTS")
-			})
-		} else {
+		ctx.WriteWithSpecialComments("", func() {
 			ctx.WriteKeyWord("IF EXISTS ")
-		}
+		})
 	}
 	ctx.WriteName(n.IndexName)
 	ctx.WriteKeyWord(" ON ")
diff --git a/parser/ast/ddl_test.go b/parser/ast/ddl_test.go
index 4eb2668f34ae4..3e8b1243b5c2f 100644
--- a/parser/ast/ddl_test.go
+++ b/parser/ast/ddl_test.go
@@ -634,7 +634,7 @@ func TestDropIndexRestore(t *testing.T) {
 		expectSQL string
 	}{
 		{format.DefaultRestoreFlags, "DROP INDEX IF EXISTS `idx` ON `t`"},
-		{format.DefaultRestoreFlags|format.RestoreTiDBSpecialComment, "DROP INDEX /*T! IF EXISTS */`idx` ON `t`"},
+		{format.DefaultRestoreFlags|format.RestoreTiDBSpecialComment, "DROP INDEX /*T! IF EXISTS  */`idx` ON `t`"},
 	}
 
 	extractNodeFunc := func(node Node) Node {

From ef0bbf33cfe7f7498a0f677e3a383099642ccfce Mon Sep 17 00:00:00 2001
From: lance6716 <lance6716@gmail.com>
Date: Fri, 26 Nov 2021 15:34:02 +0800
Subject: [PATCH 3/3] fix make fmt

---
 parser/ast/ddl_test.go | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/parser/ast/ddl_test.go b/parser/ast/ddl_test.go
index 3e8b1243b5c2f..cb0e9c9f25dc8 100644
--- a/parser/ast/ddl_test.go
+++ b/parser/ast/ddl_test.go
@@ -625,16 +625,15 @@ func TestSequenceRestore(t *testing.T) {
 	runNodeRestoreTest(t, testCases, "%s", extractNodeFunc)
 }
 
-
 func TestDropIndexRestore(t *testing.T) {
 	t.Parallel()
 	sourceSQL := "drop index if exists idx on t"
-	cases := [] struct {
-		flags format.RestoreFlags
+	cases := []struct {
+		flags     format.RestoreFlags
 		expectSQL string
 	}{
 		{format.DefaultRestoreFlags, "DROP INDEX IF EXISTS `idx` ON `t`"},
-		{format.DefaultRestoreFlags|format.RestoreTiDBSpecialComment, "DROP INDEX /*T! IF EXISTS  */`idx` ON `t`"},
+		{format.DefaultRestoreFlags | format.RestoreTiDBSpecialComment, "DROP INDEX /*T! IF EXISTS  */`idx` ON `t`"},
 	}
 
 	extractNodeFunc := func(node Node) Node {