add index: GetNextStep for mergeStep may ignore error

[ywqzzy]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

func TestGlobalSortBasic(t *testing.T) {
	gcsHost, gcsPort, cloudStorageURI := genStorageURI(t)
	opt := fakestorage.Options{
		Scheme:     "http",
		Host:       gcsHost,
		Port:       gcsPort,
		PublicHost: gcsHost,
	}
	server, err := fakestorage.NewServerWithOptions(opt)
	require.NoError(t, err)
	server.CreateBucketWithOpts(fakestorage.CreateBucketOpts{Name: "sorted"})

	store, dom := realtikvtest.CreateMockStoreAndDomainAndSetup(t)
	tk := testkit.NewTestKit(t, store)
	require.NoError(t, failpoint.Enable("github.com/pingcap/tidb/pkg/disttask/framework/dispatcher/WaitCleanUpFinished", "return()"))
	tk.MustExec("drop database if exists addindexlit;")
	tk.MustExec("create database addindexlit;")
	tk.MustExec("use addindexlit;")
	tk.MustExec(`set @@global.tidb_ddl_enable_fast_reorg = 1;`)
	tk.MustExec("set @@global.tidb_enable_dist_task = 1;")
	tk.MustExec(fmt.Sprintf(`set @@global.tidb_cloud_storage_uri = "%s"`, cloudStorageURI))
	defer func() {
		tk.MustExec("set @@global.tidb_enable_dist_task = 0;")
		variable.CloudStorageURI.Store("")
	}()

	tk.MustExec("create table t (a int, b int, c int);")
	var sb strings.Builder
	sb.WriteString("insert into t values ")
	size := 100
	for i := 0; i < size; i++ {
		sb.WriteString(fmt.Sprintf("(%d, %d, %d)", i, i, i))
		if i != size-1 {
			sb.WriteString(",")
		}
	}
	sb.WriteString(";")
	tk.MustExec(sb.String())

	var jobID int64
	origin := dom.DDL().GetHook()
	onJobUpdated := func(job *model.Job) {
		jobID = job.ID
	}
	hook := &callback.TestDDLCallback{}
	hook.OnJobUpdatedExported.Store(&onJobUpdated)
	dom.DDL().SetHook(hook)

	tk.MustExec("alter table t add index idx(a);")
	dom.DDL().SetHook(origin)
	tk.MustExec("admin check table t;")
	<-dispatcher.WaitCleanUpFinished
	checkFileCleaned(t, jobID, cloudStorageURI)

	require.NoError(t, failpoint.Enable("github.com/pingcap/tidb/pkg/ddl/forceMergeSort", "return()"))
	tk.MustExec("alter table t add index idx1(a);")
	dom.DDL().SetHook(origin)
	tk.MustExec("admin check table t;")
	<-dispatcher.WaitCleanUpFinished

	checkFileCleaned(t, jobID, cloudStorageURI)
	require.NoError(t, failpoint.Disable("github.com/pingcap/tidb/pkg/disttask/framework/dispatcher/WaitCleanUpFinished"))
	require.NoError(t, failpoint.Disable("github.com/pingcap/tidb/pkg/ddl/forceMergeSort"))
}

2. What did you expect to see? (Required)

Run merge sort step.

3. What did you see instead (Required)

Don't run merge sort step

4. What is your TiDB version? (Required)

master