Revert 2e0e86d (Update stack_value helper)

Author: khvzak

src/state/raw.rs

@@ -694,14 +694,16 @@ impl RawLua {
 
     /// Pops a value from the Lua stack.
     ///
-    /// Uses 2 stack spaces, does not call `checkstack`.
+    /// Uses up to 1 stack spaces, does not call `checkstack`.
     pub(crate) unsafe fn pop_value(&self) -> Value {
         let value = self.stack_value(-1, None);
         ffi::lua_pop(self.state(), 1);
         value
     }
 
     /// Returns value at given stack index without popping it.
+    ///
+    /// Uses up to 1 stack spaces, does not call `checkstack`.
     pub(crate) unsafe fn stack_value(&self, idx: c_int, type_hint: Option<c_int>) -> Value {
         let state = self.state();
         match type_hint.unwrap_or_else(|| ffi::lua_type(state, idx)) {
@@ -757,25 +759,21 @@ impl RawLua {
             }
 
             ffi::LUA_TUSERDATA => {
-                let ref_thread = self.ref_thread();
-                ffi::lua_xpush(state, ref_thread, idx);
-
                 // If the userdata is `WrappedFailure`, process it as an error or panic.
                 let failure_mt_ptr = (*self.extra.get()).wrapped_failure_mt_ptr;
-                match get_internal_userdata::<WrappedFailure>(ref_thread, -1, failure_mt_ptr).as_mut() {
-                    Some(WrappedFailure::Error(err)) => {
-                        ffi::lua_pop(ref_thread, 1);
-                        Value::Error(Box::new(err.clone()))
-                    }
+                match get_internal_userdata::<WrappedFailure>(state, idx, failure_mt_ptr).as_mut() {
+                    Some(WrappedFailure::Error(err)) => Value::Error(Box::new(err.clone())),
                     Some(WrappedFailure::Panic(panic)) => {
-                        ffi::lua_pop(ref_thread, 1);
                         if let Some(panic) = panic.take() {
                             resume_unwind(panic);
                         }
                         // Previously resumed panic?
                         Value::Nil
                     }
-                    _ => Value::UserData(AnyUserData(self.pop_ref_thread())),
+                    _ => {
+                        ffi::lua_xpush(state, self.ref_thread(), idx);
+                        Value::UserData(AnyUserData(self.pop_ref_thread()))
+                    }
                 }
             }
 

src/util/userdata.rs

@@ -73,7 +73,7 @@ pub(crate) unsafe fn init_internal_metatable<T: TypeKey>(
     Ok(())
 }
 
-// Uses 2 stack spaces, does not call checkstack
+// Uses up to 1 stack space, does not call `checkstack`
 pub(crate) unsafe fn get_internal_userdata<T: TypeKey>(
     state: *mut ffi::lua_State,
     index: c_int,