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 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.
CallbackError now, instead of displaying the cause description, instead prints
"callback error: <traceback>". Since the cause is already in the cause chain of
the error, this avoids repeatedly printing the cause of callback errors along
the chain, and also actually prints the callback when using Display on each
error in the chain.
Since this is `rlua::Error`, it should be clear that it refers to
Lua-related errors. Downstream crates want to define their own error
enums, which can add a prefix like "lua error:" to disambiguate.
Previously, the traceback would be printed, but not the actual error.
I've removed traceback printing completely, not sure if that's a good
idea. A `Display` impl that outputs multiple lines feels weird.
I didn't yet document *everything* there is to say (in particular, how
exactly custom Rust errors can be passed through Lua), but I've some
changes to this type in mind that I'll do next.
Rename the following:
LuaNil => Nil
LuaExternalError => ExternalError
LuaExternalResult => ExternalResult
LuaCallback => Callback (internal only)
Use qualified re-exports at the top of the module.
Add a new public 'prelude' module which re-exports everything with a
non-conflicting name (Adds back the Lua prefix), and is meant to be imported
unqualified.
It, ahem "should not" be possible to exhaust lua stack space in normal usage,
and causing stack errors to be Err is slightly obnoxious. I have been wanting
to make this change for a while, and removing the callback API from tables makes
this sensible *I think*.
I can think of a couple of ways that this is not technically true, but I think
that they are acceptable, or should be handled differently.
One, you can make arbitrarily sized LuaVariadic values. I think this is maybe a
bug already, because there is an argument limit in Lua which is lower than the
stack limit. I'm not sure what happens there, but if it is a stack based panic,
(or any panic?) it is a bug.
Two, I believe that if you recurse over and over between lua -> rust -> lua ->
rust etc, and call rlua API functions, you might get a stack panic. I think for
trusted lua code, this is morally equivalent to a regular stack overflow in
plain rust, which is already.. well it's not a panic but it's some kind of safe
crash I'm not sure, so I think this is acceptable. For *untrusted* lua code,
this could theoretically be a problem if the API provided a callback that would
call back into lua, then some lua script could force a stack based panic. There
are so many concerns with untrusted lua code, and this library is NOT safe
enough yet for untrusted code (it doesn't even provide an option to limit lua to
the safe API subset yet!), so this is not currently an issue. When the library
provides support for "safe lua", it should come with big warnings anyway, and
being able to force a stack panic is pretty minor in comparison.
I think if there are other ways to cause unbounded stack usage, that it is a
bug, or there can be an error just for that situation, like argument count
limits.
This commit also fixes several stupid bugs with tests, stack checking, and
panics.
Alex Orlenko