Fix split and split-range command bugs.

Signed-off-by: Bin Shi <binshi.bing@gmail.com>

pkg/keyspace/tso_keyspace_group.go

@@ -622,7 +622,17 @@ func buildSplitKeyspaces(
 				oldSplit = append(oldSplit, keyspace)
 			}
 		}
-		return oldSplit, new, nil
+		// If newNum != len(newKeyspaceMap), it means the provided new keyspace list contains
+		// duplicate keyspaces, and we need to dedup them (https://github.com/tikv/pd/issues/6687);
+		// otherwise, we can just return the old split and new keyspace list.
+		if newNum == len(newKeyspaceMap) {
+			return oldSplit, new, nil
+		}
+		newSplit := make([]uint32, 0, len(newKeyspaceMap))
+		for keyspace := range newKeyspaceMap {
+			newSplit = append(newSplit, keyspace)
+		}
+		return oldSplit, newSplit, nil
 	}
 	// Split according to the start and end keyspace ID.
 	if startKeyspaceID == 0 && endKeyspaceID == 0 {
@@ -634,7 +644,9 @@ func buildSplitKeyspaces(
 	)
 	for _, keyspace := range old {
 		if keyspace == utils.DefaultKeyspaceID {
-			return nil, nil, ErrModifyDefaultKeyspace
+			// The source keyspace group must be the default keyspace group and we always keep the default
+			// keyspace in the default keyspace group.
+			continue
 		}
 		if startKeyspaceID <= keyspace && keyspace <= endKeyspaceID {
 			newSplit = append(newSplit, keyspace)

pkg/keyspace/tso_keyspace_group_test.go

@@ -483,6 +483,26 @@ func TestBuildSplitKeyspaces(t *testing.T) {
 			new: []uint32{6},
 			err: ErrKeyspaceNotInKeyspaceGroup,
 		},
+		{
+			old: []uint32{1, 2},
+			new: []uint32{2, 2},
+			expectedOld: []uint32{1},
+			expectedNew: []uint32{2},
+		},
+		{
+			old:             []uint32{0, 1, 2, 3, 4, 5},
+			startKeyspaceID: 2,
+			endKeyspaceID:   4,
+			expectedOld:     []uint32{0, 1, 5},
+			expectedNew:     []uint32{2, 3, 4},
+		},
+		{
+			old:             []uint32{0, 1, 2, 3, 4, 5},
+			startKeyspaceID: 0,
+			endKeyspaceID:   4,
+			expectedOld:     []uint32{0, 5},
+			expectedNew:     []uint32{1, 2, 3, 4},
+		},
 		{
 			old:             []uint32{1, 2, 3, 4, 5},
 			startKeyspaceID: 2,