Add regression tests for metrics mutations in AST.

It turned out in the end, that only drop_common_metrics() produced any
erroneous output in the old system. The second expression in the test
("sum(testmetric) keeping_extra") already worked in the old code, but
why not keep it in...

The way to test ranged evaluations is a bit clumsy so far, so I want to
build a nicer test framework in the end, where all the test cases can be
specified as text files which specify desired inputs, outputs, query
step widths, etc.

Change-Id: I821859789e69b8232bededf670a1b76e9e8c8ca4

rules/ast/ast.go

@@ -40,6 +40,7 @@ type SampleStream struct {
 	Values metric.Values
 }
 
+// Sample is a single sample belonging to a COWMetric.
 type Sample struct {
 	Metric    clientmodel.COWMetric
 	Value     clientmodel.SampleValue
@@ -413,7 +414,7 @@ func EvalVectorRange(node VectorNode, start clientmodel.Timestamp, end clientmod
 	// TODO implement watchdog timer for long-running queries.
 	evalTimer := queryStats.GetTimer(stats.InnerEvalTime).Start()
 	sampleStreams := map[uint64]*SampleStream{}
-	for t := start; t.Before(end); t = t.Add(interval) {
+	for t := start; !t.After(end); t = t.Add(interval) {
 		vector := node.Eval(t)
 		for _, sample := range vector {
 			samplePair := metric.SamplePair{

rules/ast/printer.go

@@ -91,11 +91,12 @@ func (vector Vector) String() string {
 func (matrix Matrix) String() string {
 	metricStrings := make([]string, 0, len(matrix))
 	for _, sampleStream := range matrix {
-		metricName, ok := sampleStream.Metric.Metric[clientmodel.MetricNameLabel]
+		metricName, hasName := sampleStream.Metric.Metric[clientmodel.MetricNameLabel]
-		if !ok {
+		numLabels := len(sampleStream.Metric.Metric)
-			panic("Tried to print matrix without metric name")
+		if hasName {
+			numLabels--
 		}
-		labelStrings := make([]string, 0, len(sampleStream.Metric.Metric)-1)
+		labelStrings := make([]string, 0, numLabels)
 		for label, value := range sampleStream.Metric.Metric {
 			if label != clientmodel.MetricNameLabel {
 				labelStrings = append(labelStrings, fmt.Sprintf("%s=%q", label, value))

rules/rules_test.go

@@ -25,6 +25,7 @@ import (
 	"github.com/prometheus/prometheus/rules/ast"
 	"github.com/prometheus/prometheus/stats"
 	"github.com/prometheus/prometheus/storage/local"
+	"github.com/prometheus/prometheus/storage/metric"
 	"github.com/prometheus/prometheus/utility/test"
 )
 
@@ -60,7 +61,7 @@ func newTestStorage(t testing.TB) (storage local.Storage, closer test.Closer) {
 
 func TestExpressions(t *testing.T) {
 	// Labels in expected output need to be alphabetically sorted.
-	var expressionTests = []struct {
+	expressionTests := []struct {
 		expr           string
 		output         []string
 		shouldFail     bool
@@ -705,6 +706,188 @@ func TestExpressions(t *testing.T) {
 	}
 }
 
+func TestRangedEvaluationRegressions(t *testing.T) {
+	scenarios := []struct {
+		in   ast.Matrix
+		out  ast.Matrix
+		expr string
+	}{
+		{
+			// Testing COWMetric behavior in drop_common_labels.
+			in: ast.Matrix{
+				{
+					Metric: clientmodel.COWMetric{
+						Metric: clientmodel.Metric{
+							clientmodel.MetricNameLabel: "testmetric",
+							"testlabel":                 "1",
+						},
+					},
+					Values: metric.Values{
+						{
+							Timestamp: testStartTime,
+							Value:     1,
+						},
+						{
+							Timestamp: testStartTime.Add(time.Hour),
+							Value:     1,
+						},
+					},
+				},
+				{
+					Metric: clientmodel.COWMetric{
+						Metric: clientmodel.Metric{
+							clientmodel.MetricNameLabel: "testmetric",
+							"testlabel":                 "2",
+						},
+					},
+					Values: metric.Values{
+						{
+							Timestamp: testStartTime.Add(time.Hour),
+							Value:     2,
+						},
+					},
+				},
+			},
+			out: ast.Matrix{
+				{
+					Metric: clientmodel.COWMetric{
+						Metric: clientmodel.Metric{
+							clientmodel.MetricNameLabel: "testmetric",
+						},
+					},
+					Values: metric.Values{
+						{
+							Timestamp: testStartTime,
+							Value:     1,
+						},
+					},
+				},
+				{
+					Metric: clientmodel.COWMetric{
+						Metric: clientmodel.Metric{
+							clientmodel.MetricNameLabel: "testmetric",
+							"testlabel":                 "1",
+						},
+					},
+					Values: metric.Values{
+						{
+							Timestamp: testStartTime.Add(time.Hour),
+							Value:     1,
+						},
+					},
+				},
+				{
+					Metric: clientmodel.COWMetric{
+						Metric: clientmodel.Metric{
+							clientmodel.MetricNameLabel: "testmetric",
+							"testlabel":                 "2",
+						},
+					},
+					Values: metric.Values{
+						{
+							Timestamp: testStartTime.Add(time.Hour),
+							Value:     2,
+						},
+					},
+				},
+			},
+			expr: "drop_common_labels(testmetric)",
+		},
+		{
+			// Testing COWMetric behavior in vector aggregation.
+			in: ast.Matrix{
+				{
+					Metric: clientmodel.COWMetric{
+						Metric: clientmodel.Metric{
+							clientmodel.MetricNameLabel: "testmetric",
+							"testlabel":                 "1",
+						},
+					},
+					Values: metric.Values{
+						{
+							Timestamp: testStartTime,
+							Value:     1,
+						},
+						{
+							Timestamp: testStartTime.Add(time.Hour),
+							Value:     1,
+						},
+					},
+				},
+				{
+					Metric: clientmodel.COWMetric{
+						Metric: clientmodel.Metric{
+							clientmodel.MetricNameLabel: "testmetric",
+							"testlabel":                 "2",
+						},
+					},
+					Values: metric.Values{
+						{
+							Timestamp: testStartTime,
+							Value:     2,
+						},
+					},
+				},
+			},
+			out: ast.Matrix{
+				{
+					Metric: clientmodel.COWMetric{
+						Metric: clientmodel.Metric{},
+					},
+					Values: metric.Values{
+						{
+							Timestamp: testStartTime,
+							Value:     3,
+						},
+					},
+				},
+				{
+					Metric: clientmodel.COWMetric{
+						Metric: clientmodel.Metric{
+							"testlabel": "1",
+						},
+					},
+					Values: metric.Values{
+						{
+							Timestamp: testStartTime.Add(time.Hour),
+							Value:     1,
+						},
+					},
+				},
+			},
+			expr: "sum(testmetric) keeping_extra",
+		},
+	}
+
+	for i, s := range scenarios {
+		storage, closer := local.NewTestStorage(t)
+		storeMatrix(storage, s.in)
+
+		expr, err := LoadExprFromString(s.expr)
+		if err != nil {
+			t.Fatalf("%d. Error parsing expression: %v", i, err)
+		}
+
+		got, err := ast.EvalVectorRange(
+			expr.(ast.VectorNode),
+			testStartTime,
+			testStartTime.Add(time.Hour),
+			time.Hour,
+			storage,
+			stats.NewTimerGroup(),
+		)
+		if err != nil {
+			t.Fatalf("%d. Error evaluating expression: %v", i, err)
+		}
+
+		if got.String() != s.out.String() {
+			t.Fatalf("%d. Expression: %s\n\ngot:\n=====\n%v\n====\n\nwant:\n=====\n%v\n=====\n", i, s.expr, got.String(), s.out.String())
+		}
+
+		closer.Close()
+	}
+}
+
 var ruleTests = []struct {
 	inputFile         string
 	shouldFail        bool