Okay, so this is the fix for the previously mentioned lifetime problem. I
mimicked the API for `crossbeam::scope` extremely closely for `Lua::scope`, and
for some reason things that would not compile with `crossbeam::scope` WOULD
compile with `Lua::scope`, and I could not figure it out.
So I took the crossbeam source and made tiny edits until I determined the
crossover point where invalid borrows would compile, and it was.. not what I
expected it to be. Simply replacing a RefCell<Option<DtorChain<'a>>> with a
PhantomData<&'a ()> would suddenly cause this to compile with crossbeam:
```
struct Test {
field: i32,
}
crossbeam::scope(|scope| {
let mut t = Test {
field: 0,
};
scope.spawn(|| t.field = 42);
drop(t);
// ...anything
})
```
which is precisely the same problem as `rlua`.
To say I am unsatisfied by this fix is a drastic understatement. SURELY this
must be a compiler bug?
The following code should not compile:
```
struct Test {
field: i32,
}
let lua = Lua::new();
lua.scope(|scope| {
let mut test = Test { field: 0 };
let f = scope
.create_function(|_, ()| {
test.field = 42;
Ok(())
})
.unwrap();
lua.globals().set("bad!", f).unwrap();
});
```
yet it does with this commit. However, I have a fix for this, which I do not in
any way understand.
* Make Lua Send
* Add Send bounds to (nearly) all instances where userdata and functions are
passed to Lua
* Add a "scope" method which takes a callback that accepts a `Scope`, and give
`Scope` the ability to create functions and userdata that are !Send, *and also
functions that are not even 'static!*.
Now, simply remove the userdata table immediately before dropping the userdata.
This does two things, it prevents __gc from double dropping the userdata, and
after the first call to __gc, it prevents the userdata from being identified as
any particular userdata type, so it cannot be misused after being finalized.
This change thus removes the userdata invalidation error, and simplifies a lot
of userdata handling code.
It also fixes a panic bug. Because there is no predictable order for
finalizers, it is possible to run a userdata finalizer that does not resurrect
itself before a lua table finalizer that accesses that userdata, and this means
that there were several asserts that were possible to trigger in normal Lua code
in util.rs related to `WrappedError`.
Now, finalized userdata is simply a userdata with no methods, so any use of
finalized userdata becomes a normal script runtime error (though, with a
potentially confusing error message). As a future improvement, we could set
a metatable on finalized userdata that provides a better error message.
Also, during the implementation of this, I noticed a problem with the 0.10
memory safety, which is that luaL_ref is also memory unsafe. I attempted to
change the API to support luaL_ref potentially returning Result, but this change
will cause an enormous amount of API chaos, (just as an example, it becomes
impossible to implement Clone for LuaRef as is). Instead, luaL_ref now is
guarded by gc_guard.
Also make sure that panic messages clearly state that they are internal errors,
so people report them as a bug. Since the only panics left are all internal
errors, just move the internal error message into the panic / assert macros.
- Update readme, changelog, cargo version number in preparation for release
- Remove panicking behavior on recursive callback calls, add additional error
variant for recursive callback errors.
- auto formatting
- add gc control to ffi
- add gc_guard to util functions
- use gc_guard to make util error handling functions never trigger __gc
metamethod Lua errors even without __gc metatable wrapper
- sort of a technicality, don't call luaL_requiref outside of the Lua
constructor, as it could trigger the garbage collector when user code has had
a chance to set __gc metamethods. Changes the API to load the debug table.
First, make sure that `add_methods` cannot trigger another userdata registry
insert, causing an unintended panic. Second, remove `RefCell` surrounding
userdata hashmap, as this change makes it no longer needed. Third, add a
`RefCell` around `Callback` because FnMut means that callbacks cannot recurse
into themselves, and panic appropriately when this happens. This should
eventually be turned into an error.
The stock Lua interpreter doesn't do this either. AFAIK the "base" library is supposed to be loaded into "_G" only as it contains functions like `assert` and `error`.
setmetatable now wraps a __gc method in a cclosure that aborts on error, also
'debug' library is no longer provided. We could provide just the subset of the
debug library that is sound, though.
kyren