Implement unary expression for vector types.

Closes #956

promql/engine.go

@@ -691,11 +691,19 @@ func (ev *evaluator) eval(expr Expr) Value {
 		return &String{Value: e.Val, Timestamp: ev.Timestamp}
 
 	case *UnaryExpr:
-		smpl := ev.evalScalar(e.Expr)
+		se := ev.evalOneOf(e.Expr, ExprScalar, ExprVector)
+		// Only + and - are possible operators.
 		if e.Op == itemSUB {
-			smpl.Value = -smpl.Value
+			switch v := se.(type) {
+			case *Scalar:
+				v.Value = -v.Value
+			case Vector:
+				for i, sv := range v {
+					v[i].Value = -sv.Value
 				}
-		return smpl
+			}
+		}
+		return se
 
 	case *VectorSelector:
 		return ev.vectorSelector(e)

promql/parse.go

@@ -1075,7 +1075,9 @@ func (p *parser) checkType(node Node) (typ ExprType) {
 		if n.Op != itemADD && n.Op != itemSUB {
 			p.errorf("only + and - operators allowed for unary expressions")
 		}
-		p.expectType(n.Expr, ExprScalar, "unary expression")
+		if t := p.checkType(n.Expr); t != ExprScalar && t != ExprVector {
+			p.errorf("unary expression only allowed on expressions of type scalar or vector, got %q", t)
+		}
 
 	case *NumberLiteral, *MatrixSelector, *StringLiteral, *VectorSelector:
 		// Nothing to do for terminals.

promql/parse_test.go

@@ -123,6 +123,26 @@ var testExpr = []struct {
 				}},
 			},
 		},
+	}, {
+		input: "-some_metric", expected: &UnaryExpr{
+			Op: itemSUB,
+			Expr: &VectorSelector{
+				Name: "some_metric",
+				LabelMatchers: metric.LabelMatchers{
+					{Type: metric.Equal, Name: clientmodel.MetricNameLabel, Value: "some_metric"},
+				},
+			},
+		},
+	}, {
+		input: "+some_metric", expected: &UnaryExpr{
+			Op: itemADD,
+			Expr: &VectorSelector{
+				Name: "some_metric",
+				LabelMatchers: metric.LabelMatchers{
+					{Type: metric.Equal, Name: clientmodel.MetricNameLabel, Value: "some_metric"},
+				},
+			},
+		},
 	}, {
 		input:  "",
 		fail:   true,
@@ -191,14 +211,18 @@ var testExpr = []struct {
 		input:  "1 =~ 1",
 		fail:   true,
 		errMsg: "could not parse remaining input \"=~ 1\"...",
-	}, {
-		input:  "-some_metric",
-		fail:   true,
-		errMsg: "expected type scalar in unary expression, got vector",
 	}, {
 		input:  `-"string"`,
 		fail:   true,
-		errMsg: "expected type scalar in unary expression, got string",
+		errMsg: `unary expression only allowed on expressions of type scalar or vector, got "string"`,
+	}, {
+		input:  `-test[5m]`,
+		fail:   true,
+		errMsg: `unary expression only allowed on expressions of type scalar or vector, got "matrix"`,
+	}, {
+		input:  `*test`,
+		fail:   true,
+		errMsg: "no valid expression found",
 	},
 	// Vector binary operations.
 	{
@@ -950,18 +974,15 @@ var testExpr = []struct {
 		input:  "-=",
 		fail:   true,
 		errMsg: `no valid expression found`,
-	},
-	{
+	}, {
 		input:  "++-++-+-+-<",
 		fail:   true,
 		errMsg: `no valid expression found`,
-	},
-	{
+	}, {
 		input:  "e-+=/(0)",
 		fail:   true,
 		errMsg: `no valid expression found`,
-	},
-	{
+	}, {
 		input:  "-If",
 		fail:   true,
 		errMsg: `no valid expression found`,