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Fix individual library open functions #147

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@giodamelio giodamelio commented May 7, 2017

See #146.

I think I got this mostly working, but since I have never programmed in C or used the Rust FFI before things could be totally broken.

The Lua 5.2 Docs say that you should use requiref to require individual libraries. So I basically implement this. My understanding of Lua internals is practically non-existent, so I hope this is right.

Just one part I'm not sure how to do cleanly. See the line comment below.

@@ -27,6 +27,7 @@ pub const LUA_ERRERR: c_int = 6;
pub struct lua_State;

pub type lua_CFunction = extern "C" fn(L: *mut lua_State) -> c_int;
pub type lua_CFunction2 = unsafe extern "C" fn(*mut lua_State);
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I'm not sure why I needed to create this type, I see other FFI declerations use the lua_CFunction type, and the docs for requiref don't seem any different to me.

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@tomaka tomaka May 7, 2017

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Why not change the definition of luaL_requiref to use lua_CFunction instead?

EDIT: Ah nevermind, I see. I suppose you could also cast the function pointers instead.
I'd prefer if bindings remained identical to the C header.

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This is basically what I cobbled together from reading Rust's error messages and trying a bunch of random things. I really don't have the expertise to go much further.

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You should change open_helper to accept a unsafe extern "C" fn(*mut lua_State) instead of a ffi::lua_CFunction2 (which allows you to remove lua_CFunction2 from the bindings).

Then in open_helper you should be able to do something like func as ffi::lua_CFunction. If it doesn't work, use mem::transmute(func). It's the last resort solution, but at least it would compile.

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That still won't help the luaL_requiref binding that needs the lua_CFunction2 though?

@@ -27,6 +27,7 @@ pub const LUA_ERRERR: c_int = 6;
pub struct lua_State;

pub type lua_CFunction = extern "C" fn(L: *mut lua_State) -> c_int;
pub type lua_CFunction2 = unsafe extern "C" fn(*mut lua_State);
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You should change open_helper to accept a unsafe extern "C" fn(*mut lua_State) instead of a ffi::lua_CFunction2 (which allows you to remove lua_CFunction2 from the bindings).

Then in open_helper you should be able to do something like func as ffi::lua_CFunction. If it doesn't work, use mem::transmute(func). It's the last resort solution, but at least it would compile.

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