rules: Allow for setting labels on LHS on scalars

rules/recording.go

@@ -67,6 +67,7 @@ func (rule RecordingRule) eval(timestamp model.Time, engine *promql.Engine) (mod
 		vector = model.Vector{&model.Sample{
 			Value:     scalar.Value,
 			Timestamp: scalar.Timestamp,
+			Metric:    model.Metric{},
 		}}
 	default:
 		return nil, fmt.Errorf("rule result is not a vector or scalar")

rules/recording_test.go

@@ -0,0 +1,70 @@
+// Copyright 2013 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package rules
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/prometheus/common/model"
+
+	"github.com/prometheus/prometheus/promql"
+	"github.com/prometheus/prometheus/storage/local"
+)
+
+func TestRuleEval(t *testing.T) {
+	storage, closer := local.NewTestStorage(t, 1)
+	defer closer.Close()
+	engine := promql.NewEngine(storage, nil)
+	now := model.Now()
+
+	suite := []struct {
+		name   string
+		expr   promql.Expr
+		labels model.LabelSet
+		result model.Vector
+	}{
+		{
+			name:   "nolabels",
+			expr:   &promql.NumberLiteral{1},
+			labels: model.LabelSet{},
+			result: model.Vector{&model.Sample{
+				Value:     1,
+				Timestamp: now,
+				Metric:    model.Metric{"__name__": "nolabels"},
+			}},
+		},
+		{
+			name:   "labels",
+			expr:   &promql.NumberLiteral{1},
+			labels: model.LabelSet{"foo": "bar"},
+			result: model.Vector{&model.Sample{
+				Value:     1,
+				Timestamp: now,
+				Metric:    model.Metric{"__name__": "labels", "foo": "bar"},
+			}},
+		},
+	}
+
+	for _, test := range suite {
+		rule := NewRecordingRule(test.name, test.expr, test.labels)
+		result, err := rule.eval(now, engine)
+		if err != nil {
+			t.Fatalf("Error evaluating %s", test.name)
+		}
+		if !reflect.DeepEqual(result, test.result) {
+			t.Fatalf("Error: expected %q, got %q", test.result, result)
+		}
+	}
+}