Fix some clippy warnings & minor changes

src/ffi/compat53.rs

@@ -250,6 +250,7 @@ end
 
 #[cfg(any(feature = "lua51", feature = "luajit"))]
 pub unsafe fn lua_arith(L: *mut lua_State, op: c_int) {
+    #[allow(clippy::manual_range_contains)]
     if op < LUA_OPADD || op > LUA_OPUNM {
         luaL_error(L, cstr!("invalid 'op' argument for lua_arith"));
     }

src/lua.rs

@@ -1557,7 +1557,7 @@ impl Lua {
         let mut extra_tables_count = 0;
 
         let mut field_getters_index = None;
-        let has_field_getters = fields.field_getters.len() > 0;
+        let has_field_getters = !fields.field_getters.is_empty();
         if has_field_getters {
             protect_lua_closure(self.state, 0, 1, |state| {
                 ffi::lua_newtable(state);
@@ -1575,7 +1575,7 @@ impl Lua {
         }
 
         let mut field_setters_index = None;
-        let has_field_setters = fields.field_setters.len() > 0;
+        let has_field_setters = !fields.field_setters.is_empty();
         if has_field_setters {
             protect_lua_closure(self.state, 0, 1, |state| {
                 ffi::lua_newtable(state);
@@ -1594,9 +1594,9 @@ impl Lua {
 
         let mut methods_index = None;
         #[cfg(feature = "async")]
-        let has_methods = methods.methods.len() > 0 || methods.async_methods.len() > 0;
+        let has_methods = !methods.methods.is_empty() || !methods.async_methods.is_empty();
         #[cfg(not(feature = "async"))]
-        let has_methods = methods.methods.len() > 0;
+        let has_methods = !methods.methods.is_empty();
         if has_methods {
             protect_lua_closure(self.state, 0, 1, |state| {
                 ffi::lua_newtable(state);
@@ -2546,6 +2546,7 @@ impl<'lua, T: 'static + UserData> StaticUserDataMethods<'lua, T> {
 struct StaticUserDataFields<'lua, T: 'static + UserData> {
     field_getters: Vec<(Vec<u8>, Callback<'lua, 'static>)>,
     field_setters: Vec<(Vec<u8>, Callback<'lua, 'static>)>,
+    #[allow(clippy::type_complexity)]
     meta_fields: Vec<(
         MetaMethod,
         Box<dyn Fn(&'lua Lua) -> Result<Value<'lua>> + 'static>,

src/scope.rs

@@ -258,7 +258,7 @@ impl<'lua, 'scope> Scope<'lua, 'scope> {
                         if ffi::lua_getmetatable(lua.state, -1) == 0 {
                             return Err(Error::UserDataTypeMismatch);
                         }
-                        ffi::lua_pushstring(lua.state, cstr!("__mlua"));
+                        ffi::lua_pushstring(lua.state, cstr!("__mlua_ptr"));
                         if ffi::lua_rawget(lua.state, -2) == ffi::LUA_TLIGHTUSERDATA {
                             let ud_ptr = ffi::lua_touserdata(lua.state, -1);
                             if ud_ptr == check_data.as_ptr() as *mut c_void {
@@ -330,7 +330,7 @@ impl<'lua, 'scope> Scope<'lua, 'scope> {
                 ffi::lua_newtable(state);
 
                 // Add internal metamethod to store reference to the data
-                ffi::lua_pushstring(state, cstr!("__mlua"));
+                ffi::lua_pushstring(state, cstr!("__mlua_ptr"));
                 ffi::lua_pushlightuserdata(lua.state, data.as_ptr() as *mut c_void);
                 ffi::lua_rawset(state, -3);
             })?;
@@ -353,7 +353,7 @@ impl<'lua, 'scope> Scope<'lua, 'scope> {
             let metatable_index = ffi::lua_absindex(lua.state, -1);
 
             let mut field_getters_index = None;
-            if ud_fields.field_getters.len() > 0 {
+            if !ud_fields.field_getters.is_empty() {
                 protect_lua_closure(lua.state, 0, 1, |state| {
                     ffi::lua_newtable(state);
                 })?;
@@ -369,7 +369,7 @@ impl<'lua, 'scope> Scope<'lua, 'scope> {
             }
 
             let mut field_setters_index = None;
-            if ud_fields.field_setters.len() > 0 {
+            if !ud_fields.field_setters.is_empty() {
                 protect_lua_closure(lua.state, 0, 1, |state| {
                     ffi::lua_newtable(state);
                 })?;
@@ -385,7 +385,7 @@ impl<'lua, 'scope> Scope<'lua, 'scope> {
             }
 
             let mut methods_index = None;
-            if ud_methods.methods.len() > 0 {
+            if !ud_methods.methods.is_empty() {
                 // Create table used for methods lookup
                 protect_lua_closure(lua.state, 0, 1, |state| {
                     ffi::lua_newtable(state);
@@ -738,6 +738,7 @@ impl<'lua, T: UserData> UserDataMethods<'lua, T> for NonStaticUserDataMethods<'l
 struct NonStaticUserDataFields<'lua, T: UserData> {
     field_getters: Vec<(Vec<u8>, NonStaticMethod<'lua, T>)>,
     field_setters: Vec<(Vec<u8>, NonStaticMethod<'lua, T>)>,
+    #[allow(clippy::type_complexity)]
     meta_fields: Vec<(MetaMethod, Box<dyn Fn(&'lua Lua) -> Result<Value<'lua>>>)>,
 }
 

src/userdata.rs

@@ -187,7 +187,9 @@ impl MetaMethod {
             MetaMethod::Custom(name) if name == "__metatable" => {
                 Err(Error::MetaMethodRestricted(name))
             }
-            MetaMethod::Custom(name) if name == "__mlua" => Err(Error::MetaMethodRestricted(name)),
+            MetaMethod::Custom(name) if name.starts_with("__mlua") => {
+                Err(Error::MetaMethodRestricted(name))
+            }
             _ => Ok(self),
         }
     }
@@ -714,7 +716,9 @@ impl<'lua> AnyUserData<'lua> {
     /// Returns a metatable of this `UserData`.
     ///
     /// Returned [`UserDataMetatable`] object wraps the original metatable and
-    /// allows to provide safe access to it methods.
+    /// provides safe access to it methods.
+    ///
+    /// For `T: UserData + 'static` returned metatable is shared among all instances of type `T`.
     ///
     /// [`UserDataMetatable`]: struct.UserDataMetatable.html
     pub fn get_metatable(&self) -> Result<UserDataMetatable<'lua>> {