Add `has_metamethod` to `AnyUserData`

src/userdata.rs

@@ -10,7 +10,7 @@ use crate::lua::Lua;
 use crate::table::Table;
 use crate::types::{LuaRef, MaybeSend};
 use crate::util::{assert_stack, get_userdata, StackGuard};
-use crate::value::{FromLua, FromLuaMulti, ToLua, ToLuaMulti};
+use crate::value::{FromLua, FromLuaMulti, ToLua, ToLuaMulti, Value};
 
 /// Kinds of metamethods that can be overridden.
 ///
@@ -460,6 +460,22 @@ impl<'lua> AnyUserData<'lua> {
         V::from_lua(res, lua)
     }
 
+    /// Checks for a metamethod in this `AnyUserData`
+    pub fn has_metamethod(&self, method: MetaMethod) -> Result<bool> {
+        match self.get_metatable() {
+            Ok(mt) => {
+                let name = self.0.lua.create_string(method.name())?;
+                if let Value::Nil = mt.raw_get(name)? {
+                    Ok(false)
+                } else {
+                    Ok(true)
+                }
+            }
+            Err(Error::UserDataTypeMismatch) => Ok(false),
+            Err(e) => Err(e),
+        }
+    }
+
     fn get_metatable(&self) -> Result<Table<'lua>> {
         unsafe {
             let lua = self.0.lua;

tests/userdata.rs

@@ -166,6 +166,12 @@ fn test_metamethods() -> Result<()> {
     assert!(userdata2 != userdata3); // because references are differ
     assert!(userdata2.equals(userdata3)?);
 
+    let userdata1: AnyUserData = globals.get("userdata1")?;
+    assert!(userdata1.has_metamethod(MetaMethod::Add)?);
+    assert!(userdata1.has_metamethod(MetaMethod::Sub)?);
+    assert!(userdata1.has_metamethod(MetaMethod::Index)?);
+    assert!(!userdata1.has_metamethod(MetaMethod::Pow)?);
+
     Ok(())
 }