Fix time() behavior.

time() should return the timestamp for which the query is executed, not
the actual current time.

Change-Id: I430a45cabad7785cd58f95b1028a71dff4c87710

rules/ast/functions.go

@@ -75,7 +75,7 @@ func (function *Function) CheckArgTypes(args []Node) error {
 
 // === time() clientmodel.SampleValue ===
 func timeImpl(timestamp clientmodel.Timestamp, view *viewAdapter, args []Node) interface{} {
-	return clientmodel.SampleValue(time.Now().Unix())
+	return clientmodel.SampleValue(timestamp.Unix())
 }
 
 // === delta(matrix MatrixNode, isCounter ScalarNode) Vector ===

rules/rules_test.go

@@ -496,6 +496,12 @@ func TestExpressions(t *testing.T) {
 			fullRanges:     2,
 			intervalRanges: 0,
 		},
+		{
+			expr:           `time()`,
+			output:         []string{`scalar: 3000 @[%v]`},
+			fullRanges:     0,
+			intervalRanges: 0,
+		},
 	}
 
 	tieredStorage, closer := newTestStorage(t)