This can result in allocating the same slot twice and rewriting old value.
Lua uses (registry) table length to find next free slot and having Nil in the middle of the table can impact length calculation.
With this fix we ensure that Nil values uses a special LUA_REFNIL slot.
Try to double size first, if not fulfilled try halving in a loop till 0.
Fix unwinding after panic in ref_stack_pop.
Add test to check the stack exhaustion.
Motivation behind this change is upcoming breaking change in Rust
compiler v1.52.0 to prevent unwinding across FFI boundaries.
https://github.com/rust-lang/rust/pull/76570
The new functionality requires nightly compiler to declare FFI
functions as "C-unwind".
The fundamental solution is to use C shim to wrap "e" and "m"
Lua functions in pcall.
Additionally define Rust calling convention to trigger lua_error
on Rust behalf.
This is a somewhat involved change with two breaking API changes:
1) Lua::coerce_xxx methods now return Option (this is easier and faster than
dealing with Result)
2) rlua numeric conversions now allow more loss of precision
conversions (e.g. 1.5f32 to 1i32)
The logic for the first breaking change is that mostly the coerce methods are
probably used internally, and they make sense as low-level fallible casts and
are now used as such, and there's no reason to confuse things with a Result with
a large error type and force the user to match on the error which will hopefully
only be FromLuaConversionError anyway.
The logic for the second change is that it matches the behavior of
num_traits::cast, and is more consistent in that *some* loss of precision
conversions were previously allowed (e.g. f64 to f32).
The problem is that now, Lua::coerce_integer and Lua::unpack::<i64> have
different behavior when given, for example, the number 1.5. I still think this
is the best option, though, because the Lua::coerce_xxx methods represent how
Lua works internally and the standard C API cast functions that Lua provides,
and the ToLua / FromLua code represents the most common form of fallible Rust
numeric conversion.
I could revert this change and turn `Lua::eval::<i64>("1.5", None)` back into an
error, but it seems inconsistent to allow f64 -> f32 loss of precision but not
f64 -> i64 loss of precision.
