Tariff: fix memory leak when using formula (#18098)

provider/golang/registry.go

@@ -8,13 +8,6 @@ import (
 	"github.com/traefik/yaegi/interp"
 )
 
-const Imports = `import (
-	"fmt"
-	"math"
-	"strings"
-	"time"
-)`
-
 var (
 	mu       sync.Mutex
 	registry = make(map[string]*interp.Interpreter)
@@ -31,14 +24,10 @@ func RegisteredVM(name, init string) (*interp.Interpreter, error) {
 	// create new VM
 	if !ok {
 		vm = interp.New(interp.Options{})
-
 		if err := vm.Use(stdlib.Symbols); err != nil {
 			return nil, err
 		}
-
-		if _, err := vm.Eval(Imports); err != nil {
-			return nil, err
-		}
+		vm.ImportUsed()
 
 		if init != "" {
 			if _, err := vm.Eval(init); err != nil {

tariff/embed.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"time"
 
-	"github.com/evcc-io/evcc/provider/golang"
 	"github.com/evcc-io/evcc/provider/golang/stdlib"
 	"github.com/traefik/yaegi/interp"
 )
@@ -29,35 +28,24 @@ func (t *embed) init() (err error) {
 		return nil
 	}
 
-	vm := interp.New(interp.Options{})
-	if err := vm.Use(stdlib.Symbols); err != nil {
-		return err
-	}
-
-	if _, err := vm.Eval(fmt.Sprintf(`%s
-	var (
-		price float64
-		charges float64 = %f
-		tax float64 = %f
-		ts time.Time
-	)`, golang.Imports, t.Charges, t.Tax)); err != nil {
-		return err
-	}
-
-	prg, err := vm.Compile(t.Formula)
-	if err != nil {
-		return err
-	}
-
 	t.calc = func(price float64, ts time.Time) (float64, error) {
+		vm := interp.New(interp.Options{})
+		if err := vm.Use(stdlib.Symbols); err != nil {
+			return 0, err
+		}
+		vm.ImportUsed()
+
 		if _, err := vm.Eval(fmt.Sprintf(`
-			price = %f
+		var (
+			price float64 = %f
+			charges float64 = %f
+			tax float64 = %f
 			ts = time.Unix(%d, 0).Local()
-		`, price, ts.Unix())); err != nil {
+		)`, price, t.Charges, t.Tax, ts.Unix())); err != nil {
 			return 0, err
 		}
 
-		res, err := vm.Execute(prg)
+		res, err := vm.Eval(t.Formula)
 		if err != nil {
 			return 0, err
 		}