executor: fix the issue that tiflash cop throw exception `Income key …

…ranges is empty for region: 211` (#52763) (#54782)

close #52762

pkg/store/copr/coprocessor_test.go

@@ -439,6 +439,12 @@ func TestSplitKeyRangesByLocationsWithoutBuckets(t *testing.T) {
 	rangeEqual(t, locRanges[1].Ranges.ToRanges(), "g", "h", "h", "m", "n")
 	rangeEqual(t, locRanges[2].Ranges.ToRanges(), "n", "t")
 	rangeEqual(t, locRanges[3].Ranges.ToRanges(), "v", "w")
+
+	locRanges, err = cache.SplitKeyRangesByLocationsWithoutBuckets(bo, NewKeyRanges(BuildKeyRanges("a", "b", "v", "w")), UnspecifiedLimit)
+	require.NoError(t, err)
+	require.Len(t, locRanges, 2)
+	rangeEqual(t, locRanges[0].Ranges.ToRanges(), "a", "b")
+	rangeEqual(t, locRanges[1].Ranges.ToRanges(), "v", "w")
 }
 
 func TestSplitKeyRanges(t *testing.T) {

pkg/store/copr/region_cache.go

@@ -154,9 +154,11 @@ func (c *RegionCache) splitKeyRangesByLocation(loc *tikv.KeyLocation, ranges *Ke
 		}
 	} else {
 		// rs[i] is not in the region.
-		taskRanges := ranges.Slice(0, i)
-		res = append(res, &LocationKeyRanges{Location: loc, Ranges: taskRanges})
-		ranges = ranges.Slice(i, ranges.Len())
+		if i > 0 {
+			taskRanges := ranges.Slice(0, i)
+			res = append(res, &LocationKeyRanges{Location: loc, Ranges: taskRanges})
+			ranges = ranges.Slice(i, ranges.Len())
+		}
 	}
 	return res, ranges, false
 }
@@ -206,12 +208,12 @@ func (c *RegionCache) SplitKeyRangesByLocationsWithoutBuckets(bo *Backoffer, ran
 	}
 	res := make([]*LocationKeyRanges, 0, resCap)
 
+	nextLocIndex := 0
 	for ranges.Len() > 0 {
 		if limit != UnspecifiedLimit && len(res) >= limit {
 			break
 		}
 
-		nextLocIndex := len(res)
 		if nextLocIndex >= len(locs) {
 			err = errors.Errorf("Unexpected loc index %d, which should less than %d", nextLocIndex, len(locs))
 			return nil, err
@@ -223,6 +225,7 @@ func (c *RegionCache) SplitKeyRangesByLocationsWithoutBuckets(bo *Backoffer, ran
 			res = append(res, &LocationKeyRanges{Location: loc, Ranges: ranges})
 			break
 		}
+		nextLocIndex++
 
 		isBreak := false
 		res, ranges, isBreak = c.splitKeyRangesByLocation(loc, ranges, res)