app/vmalert/datasource: use plain string literals instead of constants

This removes the unneeded level of indirection and improves code readability.

The "prometheus" and "graphite" constants aren't going to change in the future, so there is no sense in hiding them behind constants.

app/vmalert/datasource/type.go

@@ -7,9 +7,6 @@ import (
 	"github.com/VictoriaMetrics/metricsql"
 )
 
-const graphiteType = "graphite"
-const prometheusType = "prometheus"
-
 // Type represents data source type
 type Type struct {
 	name string
@@ -17,12 +14,16 @@ type Type struct {
 
 // NewPrometheusType returns prometheus datasource type
 func NewPrometheusType() Type {
-	return Type{name: prometheusType}
+	return Type{
+		name: "prometheus",
+	}
 }
 
 // NewGraphiteType returns graphite datasource type
 func NewGraphiteType() Type {
-	return Type{name: graphiteType}
+	return Type{
+		name: "graphite",
+	}
 }
 
 // NewRawType returns datasource type from raw string
@@ -44,19 +45,19 @@ func (t *Type) Set(d Type) {
 // String implements String interface with default value.
 func (t Type) String() string {
 	if t.name == "" {
-		return prometheusType
+		return "prometheus"
 	}
 	return t.name
 }
 
 // ValidateExpr validates query expression with datasource ql.
 func (t *Type) ValidateExpr(expr string) error {
-	switch t.name {
-	case graphiteType:
+	switch t.String() {
+	case "graphite":
 		if _, err := graphiteql.Parse(expr); err != nil {
 			return fmt.Errorf("bad graphite expr: %q, err: %w", expr, err)
 		}
-	case "", prometheusType:
+	case "prometheus":
 		if _, err := metricsql.Parse(expr); err != nil {
 			return fmt.Errorf("bad prometheus expr: %q, err: %w", expr, err)
 		}
@@ -72,12 +73,13 @@ func (t *Type) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	if err := unmarshal(&s); err != nil {
 		return err
 	}
+	if s == "" {
+		s = "prometheus"
+	}
 	switch s {
-	case "":
-		s = prometheusType
-	case graphiteType, prometheusType:
+	case "graphite", "prometheus":
 	default:
-		return fmt.Errorf("unknown datasource type=%q, want %q or %q", s, prometheusType, graphiteType)
+		return fmt.Errorf("unknown datasource type=%q, want %q or %q", s, "prometheus", "graphite")
 	}
 	t.name = s
 	return nil

app/vmalert/datasource/vm.go

@@ -80,10 +80,10 @@ func (s *VMStorage) Query(ctx context.Context, query string) ([]Metric, error) {
 	}
 
 	ts := time.Now()
-	switch s.dataSourceType.name {
-	case "", prometheusType:
+	switch s.dataSourceType.String() {
+	case "prometheus":
 		s.setPrometheusInstantReqParams(req, query, ts)
-	case graphiteType:
+	case "graphite":
 		s.setGraphiteReqParams(req, query, ts)
 	default:
 		return nil, fmt.Errorf("engine not found: %q", s.dataSourceType.name)
@@ -98,7 +98,7 @@ func (s *VMStorage) Query(ctx context.Context, query string) ([]Metric, error) {
 	}()
 
 	parseFn := parsePrometheusResponse
-	if s.dataSourceType.name != prometheusType {
+	if s.dataSourceType.name != "prometheus" {
 		parseFn = parseGraphiteResponse
 	}
 	return parseFn(req, resp)
@@ -108,7 +108,7 @@ func (s *VMStorage) Query(ctx context.Context, query string) ([]Metric, error) {
 // For Prometheus type see https://prometheus.io/docs/prometheus/latest/querying/api/#range-queries
 // Graphite type isn't supported.
 func (s *VMStorage) QueryRange(ctx context.Context, query string, start, end time.Time) ([]Metric, error) {
-	if s.dataSourceType.name != prometheusType {
+	if s.dataSourceType.name != "prometheus" {
 		return nil, fmt.Errorf("%q is not supported for QueryRange", s.dataSourceType.name)
 	}
 	req, err := s.newRequestPOST()

app/vmalert/datasource/vm_test.go

@@ -501,14 +501,14 @@ func TestRequestParams(t *testing.T) {
 			if err != nil {
 				t.Fatalf("unexpected error: %s", err)
 			}
-			switch tc.vm.dataSourceType.name {
-			case "", prometheusType:
+			switch tc.vm.dataSourceType.String() {
+			case "prometheus":
 				if tc.queryRange {
 					tc.vm.setPrometheusRangeReqParams(req, query, timestamp, timestamp)
 				} else {
 					tc.vm.setPrometheusInstantReqParams(req, query, timestamp)
 				}
-			case graphiteType:
+			case "graphite":
 				tc.vm.setGraphiteReqParams(req, query, timestamp)
 			}
 			tc.checkFn(t, req)