Fix func calls with nil types value

Fixes #688

Author: antonmedv

test/issues/688/issue_test.go

@@ -0,0 +1,52 @@
+package issue_test
+
+import (
+	"testing"
+
+	"github.com/expr-lang/expr"
+	"github.com/expr-lang/expr/internal/testify/require"
+)
+
+type Foo interface {
+	Add(a int, b *int) int
+}
+
+type FooImpl struct {
+}
+
+func (*FooImpl) Add(a int, b *int) int {
+	return 0
+}
+
+type Env struct {
+	Foo Foo `expr:"foo"`
+}
+
+func (Env) Any(x any) any {
+	return x
+}
+
+func TestNoInterfaceMethodWithNil(t *testing.T) {
+	program, err := expr.Compile(`foo.Add(1, nil)`)
+	require.NoError(t, err)
+
+	_, err = expr.Run(program, Env{Foo: &FooImpl{}})
+	require.NoError(t, err)
+}
+
+func TestNoInterfaceMethodWithNil_with_env(t *testing.T) {
+	program, err := expr.Compile(`foo.Add(1, nil)`, expr.Env(Env{}))
+	require.NoError(t, err)
+
+	_, err = expr.Run(program, Env{Foo: &FooImpl{}})
+	require.NoError(t, err)
+}
+
+func TestNoInterfaceMethodWithNil_with_any(t *testing.T) {
+	program, err := expr.Compile(`Any(nil)`, expr.Env(Env{}))
+	require.NoError(t, err)
+
+	out, err := expr.Run(program, Env{Foo: &FooImpl{}})
+	require.NoError(t, err)
+	require.Equal(t, nil, out)
+}

vm/vm.go

@@ -334,10 +334,8 @@ func (vm *VM) Run(program *Program, env any) (_ any, err error) {
 			in := make([]reflect.Value, size)
 			for i := int(size) - 1; i >= 0; i-- {
 				param := vm.pop()
-				if param == nil && reflect.TypeOf(param) == nil {
-					// In case of nil value and nil type use this hack,
-					// otherwise reflect.Call will panic on zero value.
-					in[i] = reflect.ValueOf(&param).Elem()
+				if param == nil {
+					in[i] = reflect.Zero(fn.Type().In(i))
 				} else {
 					in[i] = reflect.ValueOf(param)
 				}