Issue 840: Fix get field pointer struct (#843)

* improve issue test

* fix #840: pointer to struct env not returning fields

checker/nature/nature.go

@@ -404,8 +404,15 @@ func (n *Nature) getSlow(c *Cache, name string) (Nature, bool) {
 	if nt, ok := n.MethodByName(c, name); ok {
 		return nt, true
 	}
-	if n.Kind == reflect.Struct {
-		if sf := n.structField(c, nil, name); sf != nil {
+	t, k, changed := deref.TypeKind(n.Type, n.Kind)
+	if k == reflect.Struct {
+		var sd *structData
+		if changed {
+			sd = c.getStruct(t).structData
+		} else {
+			sd = n.structData
+		}
+		if sf := sd.structField(c, nil, name); sf != nil {
 			return sf.Nature, true
 		}
 	}

test/issues/840/issue_test.go

@@ -8,23 +8,28 @@ import (
 )
 
 func TestEnvFieldMethods(t *testing.T) {
-	program, err := expr.Compile(`Func(0)`, expr.Env(&Env{}))
+	program, err := expr.Compile(`Func() + Int`, expr.Env(&Env{}))
 	require.NoError(t, err)
 
 	env := &Env{}
 	env.Func = func() int {
-		return 42
+		return 40
+	}
+	env.EmbeddedEnv = &EmbeddedEnv{
+		Int: 2,
 	}
 
-	out, err := expr.Run(program, Env{})
+	out, err := expr.Run(program, env)
 	require.NoError(t, err)
 
 	require.Equal(t, 42, out)
 }
 
 type Env struct {
-	EmbeddedEnv
+	*EmbeddedEnv
 	Func func() int
 }
 
-type EmbeddedEnv struct{}
+type EmbeddedEnv struct {
+	Int int
+}