Properly check if interface is any

Fixes #744

test/interface/interface_method_test.go

@@ -1,4 +1,4 @@
-package interface_method_test
+package interface_test
 
 import (
 	"testing"

test/interface/interface_test.go

@@ -0,0 +1,40 @@
+package interface_test
+
+import (
+	"testing"
+
+	"github.com/expr-lang/expr"
+	"github.com/expr-lang/expr/internal/testify/assert"
+)
+
+type StoreInterface interface {
+	Get(string) int
+}
+
+type StoreImpt struct{}
+
+func (f StoreImpt) Get(s string) int {
+	return 42
+}
+
+func (f StoreImpt) Set(s string, i int) bool {
+	return true
+}
+
+type Env struct {
+	Store StoreInterface `expr:"store"`
+}
+
+func TestInterfaceHide(t *testing.T) {
+	var env Env
+	p, err := expr.Compile(`store.Get("foo")`, expr.Env(env))
+	assert.NoError(t, err)
+
+	out, err := expr.Run(p, Env{Store: StoreImpt{}})
+	assert.NoError(t, err)
+	assert.Equal(t, 42, out)
+
+	_, err = expr.Compile(`store.Set("foo", 100)`, expr.Env(env))
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "type interface_test.StoreInterface has no method Set")
+}