PromQL: Add minute() function

Returns the minutes from the current time in UTC. Related to the
`hour()` function.

Fixes #1983.

promql/functions.go

@@ -909,6 +909,13 @@ func funcHour(ev *evaluator, args Expressions) model.Value {
 	})
 }
 
+// === minute(v vector) scalar ===
+func funcMinute(ev *evaluator, args Expressions) model.Value {
+	return dateWrapper(ev, args, func(t time.Time) model.SampleValue {
+		return model.SampleValue(t.Minute())
+	})
+}
+
 // === month(v vector) scalar ===
 func funcMonth(ev *evaluator, args Expressions) model.Value {
 	return dateWrapper(ev, args, func(t time.Time) model.SampleValue {
@@ -1102,6 +1109,13 @@ var functions = map[string]*Function{
 		ReturnType: model.ValVector,
 		Call:       funcMinOverTime,
 	},
+	"minute": {
+		Name:         "minute",
+		ArgTypes:     []model.ValueType{model.ValVector},
+		OptionalArgs: 1,
+		ReturnType:   model.ValVector,
+		Call:         funcMinute,
+	},
 	"month": {
 		Name:         "month",
 		ArgTypes:     []model.ValueType{model.ValVector},

promql/testdata/functions.test

@@ -383,6 +383,9 @@ eval instant at 0m day_of_week()
 eval instant at 0m hour()
   {} 0
 
+eval instant at 0m minute()
+  {} 0
+
 # 2008-12-31 23:59:59 just before leap second.
 eval instant at 0m year(vector(1230767999))
   {} 2008