Do operator check after env is set (#309)

Author: krvladislav

conf/config.go

@@ -51,19 +51,6 @@ func (c *Config) WithEnv(env interface{}) {
 
 func (c *Config) Operator(operator string, fns ...string) {
 	c.Operators[operator] = append(c.Operators[operator], fns...)
-	for _, fn := range fns {
-		fnType, ok := c.Types[fn]
-		if !ok || fnType.Type.Kind() != reflect.Func {
-			panic(fmt.Errorf("function %s for %s operator does not exist in the environment", fn, operator))
-		}
-		requiredNumIn := 2
-		if fnType.Method {
-			requiredNumIn = 3 // As first argument of method is receiver.
-		}
-		if fnType.Type.NumIn() != requiredNumIn || fnType.Type.NumOut() != 1 {
-			panic(fmt.Errorf("function %s for %s operator does not have a correct signature", fn, operator))
-		}
-	}
 }
 
 func (c *Config) ConstExpr(name string) {
@@ -76,3 +63,21 @@ func (c *Config) ConstExpr(name string) {
 	}
 	c.ConstFns[name] = fn
 }
+
+func (c *Config) Check() {
+	for operator, fns := range c.Operators {
+		for _, fn := range fns {
+			fnType, ok := c.Types[fn]
+			if !ok || fnType.Type.Kind() != reflect.Func {
+				panic(fmt.Errorf("function %s for %s operator does not exist in the environment", fn, operator))
+			}
+			requiredNumIn := 2
+			if fnType.Method {
+				requiredNumIn = 3 // As first argument of method is receiver.
+			}
+			if fnType.Type.NumIn() != requiredNumIn || fnType.Type.NumOut() != 1 {
+				panic(fmt.Errorf("function %s for %s operator does not have a correct signature", fn, operator))
+			}
+		}
+	}
+}

expr.go

@@ -135,6 +135,7 @@ func Compile(input string, ops ...Option) (*vm.Program, error) {
 	for _, op := range ops {
 		op(config)
 	}
+	config.Check()
 
 	if len(config.Operators) > 0 {
 		config.Visitors = append(config.Visitors, &conf.OperatorPatcher{

expr_test.go

@@ -490,6 +490,19 @@ func TestOperator_struct(t *testing.T) {
 	require.Equal(t, true, output)
 }
 
+func TestOperator_options_another_order(t *testing.T) {
+	code := `BirthDay == "2017-10-23"`
+	_, err := expr.Compile(code, expr.Operator("==", "DateEqual"), expr.Env(&mockEnv{}))
+	require.NoError(t, err)
+}
+
+func TestOperator_no_env(t *testing.T) {
+	code := `BirthDay == "2017-10-23"`
+	require.Panics(t, func() {
+		_, _ = expr.Compile(code, expr.Operator("==", "DateEqual"))
+	})
+}
+
 func TestOperator_interface(t *testing.T) {
 	env := &mockEnv{
 		Ticket: &ticket{Price: 100},