From f22dc78bf558cfee4b3d063bdea39d2689e33d77 Mon Sep 17 00:00:00 2001
From: ti-srebot <66930949+ti-srebot@users.noreply.github.com>
Date: Wed, 26 Aug 2020 13:59:18 +0800
Subject: [PATCH] ddl: exit add index on generated column with `case-when`
 expression parse error (#19330) (#19395)

---
 ddl/db_test.go | 17 +++++++++++++++++
 ddl/index.go   | 10 ++++++++++
 2 files changed, 27 insertions(+)

diff --git a/ddl/db_test.go b/ddl/db_test.go
index 2a252c24edcfb..4c3cea1e73624 100644
--- a/ddl/db_test.go
+++ b/ddl/db_test.go
@@ -4676,6 +4676,23 @@ func (s *testSerialDBSuite) TestDDLJobErrorCount(c *C) {
 	}
 }
 
+// TestAddIndexFailOnCaseWhenCanExit is used to close #19325.
+func (s *testSerialDBSuite) TestAddIndexFailOnCaseWhenCanExit(c *C) {
+	c.Assert(failpoint.Enable("github.com/pingcap/tidb/ddl/MockCaseWhenParseFailure", `return(true)`), IsNil)
+	defer func() {
+		c.Assert(failpoint.Disable("github.com/pingcap/tidb/ddl/MockCaseWhenParseFailure"), IsNil)
+	}()
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t(a int, b int)")
+	tk.MustExec("insert into t values(1, 1)")
+	_, err := tk.Exec("alter table t add index idx(b)")
+	c.Assert(err, NotNil)
+	c.Assert(err.Error(), Equals, "[ddl:8214]Cancelled DDL job")
+	tk.MustExec("drop table if exists t")
+}
+
 func init() {
 	// Make sure it will only be executed once.
 	domain.SchemaOutOfDateRetryInterval = int64(50 * time.Millisecond)
diff --git a/ddl/index.go b/ddl/index.go
index 334aa60284102..1e9daf418e6c5 100644
--- a/ddl/index.go
+++ b/ddl/index.go
@@ -1361,6 +1361,16 @@ func (w *worker) addPhysicalTableIndex(t table.PhysicalTable, indexInfo *model.I
 	logutil.BgLogger().Info("[ddl] start to add table index", zap.String("job", job.String()), zap.String("reorgInfo", reorgInfo.String()))
 	totalAddedCount := job.GetRowCount()
 
+	if err := w.isReorgRunnable(reorgInfo.d); err != nil {
+		return errors.Trace(err)
+	}
+
+	failpoint.Inject("MockCaseWhenParseFailure", func(val failpoint.Value) {
+		if val.(bool) {
+			failpoint.Return(errors.New("job.ErrCount:" + strconv.Itoa(int(job.ErrorCount)) + ", mock unknown type: ast.whenClause."))
+		}
+	})
+
 	startHandle, endHandle := reorgInfo.StartHandle, reorgInfo.EndHandle
 	sessCtx := newContext(reorgInfo.d.store)
 	decodeColMap, err := makeupDecodeColMap(sessCtx, t, indexInfo)