Allow on, ignoring, by and without wit empty laberls.

This offers new semantics in allowing on() for matching
two single-element vectors with no known common labels.
Previosuly this was often done using on(dummy).

This also allows making it explict that you meant
to do an aggregation without labels via by().

Fixes #1597.

promql/engine.go

@@ -882,9 +882,9 @@ func (ev *evaluator) vectorBinop(op itemType, lhs, rhs vector, matching *VectorM
 }
 
 // signatureFunc returns a function that calculates the signature for a metric
-// based on the provided labels. If ignoring, then the given labels are ignored instead.
+// ignoring the provided labels. If on, then the given labels are only used instead.
 func signatureFunc(on bool, labels ...model.LabelName) func(m metric.Metric) uint64 {
-	if len(labels) == 0 || !on {
+	if !on {
 		return func(m metric.Metric) uint64 {
 			tmp := m.Metric.Clone()
 			for _, l := range labels {
@@ -905,9 +905,6 @@ func resultMetric(lhs, rhs metric.Metric, op itemType, matching *VectorMatching)
 	if shouldDropMetricName(op) {
 		lhs.Del(model.MetricNameLabel)
 	}
-	if len(matching.MatchingLabels)+len(matching.Include) == 0 {
-		return lhs
-	}
 	if !matching.On {
 		if matching.Card == CardOneToOne {
 			for _, l := range matching.MatchingLabels {

promql/parse.go

@@ -671,14 +671,16 @@ func (p *parser) labels() model.LabelNames {
 	p.expect(itemLeftParen, ctx)
 
 	labels := model.LabelNames{}
-	for {
-		id := p.expect(itemIdentifier, ctx)
-		labels = append(labels, model.LabelName(id.val))
+	if p.peek().typ != itemRightParen {
+		for {
+			id := p.expect(itemIdentifier, ctx)
+			labels = append(labels, model.LabelName(id.val))
 
-		if p.peek().typ != itemComma {
-			break
+			if p.peek().typ != itemComma {
+				break
+			}
+			p.next()
 		}
-		p.next()
 	}
 	p.expect(itemRightParen, ctx)
 

promql/parse_test.go

@@ -547,6 +547,28 @@ var testExpr = []struct {
 				On:             true,
 			},
 		},
+	}, {
+		input: "foo and on() bar",
+		expected: &BinaryExpr{
+			Op: itemLAND,
+			LHS: &VectorSelector{
+				Name: "foo",
+				LabelMatchers: metric.LabelMatchers{
+					{Type: metric.Equal, Name: model.MetricNameLabel, Value: "foo"},
+				},
+			},
+			RHS: &VectorSelector{
+				Name: "bar",
+				LabelMatchers: metric.LabelMatchers{
+					{Type: metric.Equal, Name: model.MetricNameLabel, Value: "bar"},
+				},
+			},
+			VectorMatching: &VectorMatching{
+				Card:           CardManyToMany,
+				MatchingLabels: model.LabelNames{},
+				On:             true,
+			},
+		},
 	}, {
 		input: "foo and ignoring(test,blub) bar",
 		expected: &BinaryExpr{
@@ -568,6 +590,27 @@ var testExpr = []struct {
 				MatchingLabels: model.LabelNames{"test", "blub"},
 			},
 		},
+	}, {
+		input: "foo and ignoring() bar",
+		expected: &BinaryExpr{
+			Op: itemLAND,
+			LHS: &VectorSelector{
+				Name: "foo",
+				LabelMatchers: metric.LabelMatchers{
+					{Type: metric.Equal, Name: model.MetricNameLabel, Value: "foo"},
+				},
+			},
+			RHS: &VectorSelector{
+				Name: "bar",
+				LabelMatchers: metric.LabelMatchers{
+					{Type: metric.Equal, Name: model.MetricNameLabel, Value: "bar"},
+				},
+			},
+			VectorMatching: &VectorMatching{
+				Card:           CardManyToMany,
+				MatchingLabels: model.LabelNames{},
+			},
+		},
 	}, {
 		input: "foo unless on(bar) baz",
 		expected: &BinaryExpr{
@@ -1146,6 +1189,18 @@ var testExpr = []struct {
 			},
 			Grouping: model.LabelNames{"foo"},
 		},
+	}, {
+		input: "sum by ()(some_metric)",
+		expected: &AggregateExpr{
+			Op: itemSum,
+			Expr: &VectorSelector{
+				Name: "some_metric",
+				LabelMatchers: metric.LabelMatchers{
+					{Type: metric.Equal, Name: model.MetricNameLabel, Value: "some_metric"},
+				},
+			},
+			Grouping: model.LabelNames{},
+		},
 	}, {
 		input:  `sum some_metric by (test)`,
 		fail:   true,
@@ -1154,10 +1209,6 @@ var testExpr = []struct {
 		input:  `sum (some_metric) by test`,
 		fail:   true,
 		errMsg: "unexpected identifier \"test\" in grouping opts, expected \"(\"",
-	}, {
-		input:  `sum (some_metric) by ()`,
-		fail:   true,
-		errMsg: "unexpected \")\" in grouping opts, expected identifier",
 	}, {
 		input:  `sum (some_metric) by test`,
 		fail:   true,

promql/testdata/aggregators.test

@@ -37,6 +37,19 @@ eval instant at 50m sum without (instance) (http_requests{job="api-server"})
   {group="canary",job="api-server"} 700
   {group="production",job="api-server"} 300
 
+# Empty by.
+eval instant at 50m sum by () (http_requests{job="api-server"})
+  {} 1000
+
+# No by/without.
+eval instant at 50m sum (http_requests{job="api-server"})
+  {} 1000
+
+# Empty without.
+eval instant at 50m sum without () (http_requests{job="api-server",group="production"})
+  {group="production",job="api-server",instance="0"} 100
+  {group="production",job="api-server",instance="1"} 200
+
 # Without with mismatched and missing labels. Do not do this.
 eval instant at 50m sum without (instance) (http_requests{job="api-server"} or foo)
   {group="canary",job="api-server"} 700

promql/testdata/operators.test

@@ -329,3 +329,21 @@ eval instant at 5m node_cpu > on(job, instance) group_left(target) (threshold or
   node_cpu{instance="abc",job="node",mode="user",target="a@b.com"} 1
   node_cpu{instance="def",job="node",mode="idle"} 8
   node_cpu{instance="def",job="node",mode="user"} 2
+
+clear
+
+load 5m
+  random{foo="bar"} 2
+  metricA{baz="meh"} 3
+  metricB{baz="meh"} 4
+
+# On with no labels, for metrics with no common labels.
+eval instant at 5m random + on() metricA
+  {} 5
+
+# Ignoring with no labels is the same as no ignoring.
+eval instant at 5m metricA + ignoring() metricB
+  {baz="meh"} 7
+
+eval instant at 5m metricA + metricB
+  {baz="meh"} 7