lazyquerier: deep copy hints (#10228)

* lazyquerier: deep copy hints

The promQL engine can modify the grouping that it passes to us after calling. First the LazyQuerier is called in [`populateSeries`](https://github.com/grafana/mimir/blob/76ab843e3bb3d6517fcd1ee47e919bd9d107ef0d/vendor/github.com/prometheus/prometheus/promql/engine.go#L953-L976), and then the grouping is changed (via sorting) when evaluating the [aggregate expression](https://github.com/grafana/mimir/blob/76ab843e3bb3d6517fcd1ee47e919bd9d107ef0d/vendor/github.com/prometheus/prometheus/promql/engine.go#L1571-L1573)

Signed-off-by: Dimitar Dimitrov <[email protected]>

* Don't copy nil params

Signed-off-by: Dimitar Dimitrov <[email protected]>

* Fix filename typo

Signed-off-by: Dimitar Dimitrov <[email protected]>

* Clean up code a bit

Signed-off-by: Dimitar Dimitrov <[email protected]>

---------

Signed-off-by: Dimitar Dimitrov <[email protected]>

pkg/storage/lazyquery/lazyquery.go

@@ -7,6 +7,7 @@ package lazyquery
 
 import (
 	"context"
+	"slices"
 
 	"github.com/prometheus/prometheus/model/labels"
 	"github.com/prometheus/prometheus/storage"
@@ -49,15 +50,26 @@ func (l LazyQuerier) Select(ctx context.Context, selectSorted bool, params *stor
 	// make sure there is space in the buffer, to unblock the goroutine and let it die even if nobody is
 	// waiting for the result yet (or anymore).
 	future := make(chan storage.SeriesSet, 1)
+	copiedParams := copyParams(params)
 	go func() {
-		future <- l.next.Select(ctx, selectSorted, params, matchers...)
+		future <- l.next.Select(ctx, selectSorted, copiedParams, matchers...)
 	}()
 
 	return &lazySeriesSet{
 		future: future,
 	}
 }
 
+func copyParams(params *storage.SelectHints) *storage.SelectHints {
+	if params == nil {
+		return nil
+	}
+	copiedParams := *params
+	copiedParams.Grouping = slices.Clone(params.Grouping)
+
+	return &copiedParams
+}
+
 // LabelValues implements Storage.Querier
 func (l LazyQuerier) LabelValues(ctx context.Context, name string, hints *storage.LabelHints, matchers ...*labels.Matcher) ([]string, annotations.Annotations, error) {
 	return l.next.LabelValues(ctx, name, hints, matchers...)

pkg/storage/lazyquery/lazyquery_test.go

@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: AGPL-3.0-only
+
+package lazyquery
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/prometheus/prometheus/storage"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCopyParamsDeepCopy(t *testing.T) {
+	original := &storage.SelectHints{
+		Start:    1000,
+		End:      2000,
+		Step:     10,
+		Range:    3600,
+		Func:     "rate",
+		Grouping: []string{"label1", "label2"},
+	}
+
+	copied := copyParams(original)
+
+	// First verify the structs themselves are different
+	assert.NotSame(t, original, copied)
+
+	// Then check each field is a different pointer
+	originalVal := reflect.ValueOf(original).Elem()
+	copiedVal := reflect.ValueOf(copied).Elem()
+	typ := originalVal.Type()
+	for i := 0; i < typ.NumField(); i++ {
+		originalField := originalVal.Field(i)
+		copiedField := copiedVal.Field(i)
+
+		// Check if values are equal
+		assert.Equal(t, originalField.Interface(), copiedField.Interface(), "Field %s has different values", typ.Field(i).Name)
+
+		switch originalField.Kind() {
+		// For reference types, ensure they point to different memory
+		case reflect.Slice, reflect.Map, reflect.Ptr:
+			if !originalField.IsNil() {
+				assert.NotEqual(t, originalField.UnsafePointer(), copiedField.UnsafePointer(), "Field %s shares memory between original and copy", typ.Field(i).Name)
+			}
+		default:
+			// Any other types are copied by value, so the assert.Equal above is enough.
+		}
+	}
+}