Do not attempt to shard quantile_over_time if feature flag is disable…

…d. (#11628)

**What this PR does / why we need it**:
If `quantile_over_time` sharding is disabled the code would still shard
it naively. That was a bug.

**Checklist**
- [ ] Reviewed the
[`CONTRIBUTING.md`](https://github.com/grafana/loki/blob/main/CONTRIBUTING.md)
guide (**required**)
- [ ] Documentation added
- [x] Tests updated
- [ ] `CHANGELOG.md` updated
- [ ] If the change is worth mentioning in the release notes, add
`add-to-release-notes` label
- [ ] Changes that require user attention or interaction to upgrade are
documented in `docs/sources/setup/upgrade/_index.md`
- [ ] For Helm chart changes bump the Helm chart version in
`production/helm/loki/Chart.yaml` and update
`production/helm/loki/CHANGELOG.md` and
`production/helm/loki/README.md`. [Example
PR](d10549e)
- [ ] If the change is deprecating or removing a configuration option,
update the `deprecated-config.yaml` and `deleted-config.yaml` files
respectively in the `tools/deprecated-config-checker` directory.
[Example
PR](0d4416a)

pkg/logql/shardmapper.go

@@ -338,11 +338,7 @@ var rangeMergeMap = map[string]string{
 
 func (m ShardMapper) mapRangeAggregationExpr(expr *syntax.RangeAggregationExpr, r *downstreamRecorder) (syntax.SampleExpr, uint64, error) {
 	if !expr.Shardable() {
-		exprStats, err := m.shards.GetStats(expr)
-		if err != nil {
-			return nil, 0, err
-		}
-		return expr, exprStats.Bytes, nil
+		return m.noOp(expr)
 	}
 
 	switch expr.Operation {
@@ -437,7 +433,7 @@ func (m ShardMapper) mapRangeAggregationExpr(expr *syntax.RangeAggregationExpr,
 			return nil, 0, err
 		}
 		if shards == 0 || !m.quantileOverTimeSharding {
-			return m.mapSampleExpr(expr, r)
+			return m.noOp(expr)
 		}
 
 		// quantile_over_time() by (foo) ->
@@ -465,12 +461,16 @@ func (m ShardMapper) mapRangeAggregationExpr(expr *syntax.RangeAggregationExpr,
 
 	default:
 		// don't shard if there's not an appropriate optimization
-		exprStats, err := m.shards.GetStats(expr)
-		if err != nil {
-			return nil, 0, err
-		}
-		return expr, exprStats.Bytes, nil
+		return m.noOp(expr)
+	}
+}
+
+func (m ShardMapper) noOp(expr *syntax.RangeAggregationExpr) (syntax.SampleExpr, uint64, error) {
+	exprStats, err := m.shards.GetStats(expr)
+	if err != nil {
+		return nil, 0, err
 	}
+	return expr, exprStats.Bytes, nil
 }
 
 func badASTMapping(got syntax.Expr) error {

pkg/logql/shardmapper_test.go

@@ -418,7 +418,7 @@ func TestMappingStrings(t *testing.T) {
 }
 
 func TestMapping(t *testing.T) {
-	m := NewShardMapper(ConstantShards(2), nilShardMetrics, []string{ShardQuantileOverTime})
+	m := NewShardMapper(ConstantShards(2), nilShardMetrics, []string{})
 
 	for _, tc := range []struct {
 		in   string
@@ -1340,6 +1340,25 @@ func TestMapping(t *testing.T) {
 				},
 			},
 		},
+		{
+			in: `quantile_over_time(0.8, {foo="bar"} | unwrap bytes [5m]) by (cluster)`,
+			expr: &syntax.RangeAggregationExpr{
+				Operation: syntax.OpRangeTypeQuantile,
+				Params:    float64p(0.8),
+				Left: &syntax.LogRange{
+					Left: &syntax.MatchersExpr{
+						Mts: []*labels.Matcher{mustNewMatcher(labels.MatchEqual, "foo", "bar")},
+					},
+					Unwrap: &syntax.UnwrapExpr{
+						Identifier: "bytes",
+					},
+					Interval: 5 * time.Minute,
+				},
+				Grouping: &syntax.Grouping{
+					Groups: []string{"cluster"},
+				},
+			},
+		},
 	} {
 		t.Run(tc.in, func(t *testing.T) {
 			ast, err := syntax.ParseExpr(tc.in)
@@ -1420,3 +1439,7 @@ func TestStringTrimming(t *testing.T) {
 		})
 	}
 }
+
+func float64p(v float64) *float64 {
+	return &v
+}