ddl: fix args count for modify column (#58855)

close #58843

Author: D3Hunter

pkg/meta/model/job_args.go

@@ -1688,6 +1688,12 @@ type ModifyColumnArgs struct {
 }
 
 func (a *ModifyColumnArgs) getArgsV1(*Job) []any {
+	// during upgrade, if https://github.com/pingcap/tidb/issues/54689 triggered,
+	// older node might run the job submitted by new version, but it expects 5
+	// args initially, and append the later 3 at runtime.
+	if a.ChangingColumn == nil {
+		return []any{a.Column, a.OldColumnName, a.Position, a.ModifyColumnType, a.NewShardBits}
+	}
 	return []any{
 		a.Column, a.OldColumnName, a.Position, a.ModifyColumnType,
 		a.NewShardBits, a.ChangingColumn, a.ChangingIdxs, a.RedundantIdxs,

pkg/meta/model/job_args_test.go

@@ -1129,6 +1129,12 @@ func TestModifyColumnsArgs(t *testing.T) {
 		require.Equal(t, *inArgs.ChangingColumn, *args.ChangingColumn)
 		require.Equal(t, inArgs.ChangingIdxs, args.ChangingIdxs)
 		require.Equal(t, inArgs.RedundantIdxs, args.RedundantIdxs)
+
+		if v == JobVersion1 {
+			var rawArgs []json.RawMessage
+			require.NoError(t, json.Unmarshal(j2.RawArgs, &rawArgs))
+			require.Len(t, rawArgs, 8)
+		}
 	}
 
 	for _, v := range []JobVersion{JobVersion1, JobVersion2} {
@@ -1140,4 +1146,10 @@ func TestModifyColumnsArgs(t *testing.T) {
 		require.Equal(t, inArgs.IndexIDs, args.IndexIDs)
 		require.Equal(t, inArgs.PartitionIDs, args.PartitionIDs)
 	}
+
+	j2 := &Job{}
+	require.NoError(t, j2.Decode(getJobBytes(t, &ModifyColumnArgs{}, JobVersion1, ActionModifyColumn)))
+	var rawArgs []json.RawMessage
+	require.NoError(t, json.Unmarshal(j2.RawArgs, &rawArgs))
+	require.Len(t, rawArgs, 5)
 }