From ba324b4f5497065f80d18ed42e0cf31d2ee1e3da Mon Sep 17 00:00:00 2001
From: Alex Orlenko <zxteam@protonmail.com>
Date: Mon, 10 Apr 2023 01:49:51 +0100
Subject: [PATCH] Allow deserializing Lua null into unit(`()`) or unit struct.
 See #264

---
 src/serde/de.rs | 24 +++++++++++++++++++++++-
 tests/serde.rs  | 23 ++++++++++++++++++-----
 2 files changed, 41 insertions(+), 6 deletions(-)

diff --git a/src/serde/de.rs b/src/serde/de.rs
index 9703005..aab303d 100644
--- a/src/serde/de.rs
+++ b/src/serde/de.rs
@@ -345,9 +345,31 @@ impl<'lua, 'de> serde::Deserializer<'de> for Deserializer<'lua> {
         }
     }
 
+    #[inline]
+    fn deserialize_unit<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.value {
+            Value::LightUserData(ud) if ud.0.is_null() => visitor.visit_unit(),
+            _ => self.deserialize_any(visitor),
+        }
+    }
+
+    #[inline]
+    fn deserialize_unit_struct<V>(self, _name: &'static str, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.value {
+            Value::LightUserData(ud) if ud.0.is_null() => visitor.visit_unit(),
+            _ => self.deserialize_any(visitor),
+        }
+    }
+
     serde::forward_to_deserialize_any! {
         bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string bytes
-        byte_buf unit unit_struct identifier ignored_any
+        byte_buf identifier ignored_any
     }
 }
 
diff --git a/tests/serde.rs b/tests/serde.rs
index 27a9b23..c092c43 100644
--- a/tests/serde.rs
+++ b/tests/serde.rs
@@ -392,31 +392,44 @@ fn test_from_value_newtype_struct() -> Result<(), Box<dyn StdError>> {
 #[test]
 fn test_from_value_enum() -> Result<(), Box<dyn StdError>> {
     let lua = Lua::new();
+    lua.globals().set("null", lua.null())?;
 
     #[derive(Deserialize, PartialEq, Debug)]
-    enum E {
+    struct UnitStruct;
+
+    #[derive(Deserialize, PartialEq, Debug)]
+    enum E<T = ()> {
         Unit,
         Integer(u32),
         Tuple(u32, u32),
         Struct { a: u32 },
+        Wrap(T),
     }
 
     let value = lua.load(r#""Unit""#).eval()?;
-    let got = lua.from_value(value)?;
+    let got: E = lua.from_value(value)?;
     assert_eq!(E::Unit, got);
 
     let value = lua.load(r#"{Integer = 1}"#).eval()?;
-    let got = lua.from_value(value)?;
+    let got: E = lua.from_value(value)?;
     assert_eq!(E::Integer(1), got);
 
     let value = lua.load(r#"{Tuple = {1, 2}}"#).eval()?;
-    let got = lua.from_value(value)?;
+    let got: E = lua.from_value(value)?;
     assert_eq!(E::Tuple(1, 2), got);
 
     let value = lua.load(r#"{Struct = {a = 3}}"#).eval()?;
-    let got = lua.from_value(value)?;
+    let got: E = lua.from_value(value)?;
     assert_eq!(E::Struct { a: 3 }, got);
 
+    let value = lua.load(r#"{Wrap = null}"#).eval()?;
+    let got = lua.from_value(value)?;
+    assert_eq!(E::Wrap(UnitStruct), got);
+
+    let value = lua.load(r#"{Wrap = null}"#).eval()?;
+    let got = lua.from_value(value)?;
+    assert_eq!(E::Wrap(()), got);
+
     Ok(())
 }