Can.. can I do this? Is this a thing that actually works?

Drastic times and all that.

Cargo.toml

@@ -22,12 +22,6 @@ default = ["builtin-lua"]
 #   * LUA_NUMBER as double
 #   * LUA_EXTRASPACE is sizeof(void*)
 builtin-lua = ["gcc"]
-# Error handling is completely broken on windows with
-# https://github.com/rust-lang/rust/pull/46833 merged, and this includes stable
-# rustc 1.24.0+.  This feature fixes error handling on windows, but requires
-# nightly!  See https://github.com/rust-lang/rust/issues/48251 and
-# https://github.com/chucklefish/rlua/issues/71 for details.
-unwind = []
 
 [dependencies]
 libc = { version = "0.2" }

build.rs

@@ -1,16 +1,29 @@
 #[cfg(feature = "builtin-lua")]
 extern crate gcc;
 
-fn main() {
-    #[cfg(feature = "builtin-lua")]
-    {
 use std::env;
 
-        let mut config = gcc::Build::new();
+fn main() {
-
     let target_os = env::var("CARGO_CFG_TARGET_OS");
     let target_family = env::var("CARGO_CFG_TARGET_FAMILY");
 
+    if target_family == Ok("windows".to_string()) {
+        // Error handling is completely broken on windows with
+        // https://github.com/rust-lang/rust/pull/46833 merged, and this includes stable rustc
+        // 1.24.0+.  `#[unwind]` fixes error handling on windows, but requires nightly!  This
+        // HORRIBLE HACK enables `#[unwind]` on stable rust by setting RUSTC_BOOTSTRAP=1 during
+        // build.  This is very evil, don't do this kids.
+        //
+        // See https://github.com/rust-lang/rust/issues/48251 and
+        // https://github.com/chucklefish/rlua/issues/71 for more details.
+        println!("cargo:rustc-env=RUSTC_BOOTSTRAP=1");
+        println!("cargo:rustc-cfg=unwind");
+    }
+
+    #[cfg(feature = "builtin-lua")]
+    {
+        let mut config = gcc::Build::new();
+
         if target_os == Ok("linux".to_string()) {
             config.define("LUA_USE_LINUX", None);
         } else if target_os == Ok("macos".to_string()) {

src/function.rs

@@ -122,7 +122,7 @@ impl<'lua> Function<'lua> {
     /// # }
     /// ```
     pub fn bind<A: ToLuaMulti<'lua>>(&self, args: A) -> Result<Function<'lua>> {
-        #[cfg_attr(feature = "unwind", unwind)]
+        #[cfg_attr(unwind, unwind)]
         unsafe extern "C" fn bind_call_impl(state: *mut ffi::lua_State) -> c_int {
             let nargs = ffi::lua_gettop(state);
             let nbinds = ffi::lua_tointeger(state, ffi::lua_upvalueindex(2)) as c_int;

src/lib.rs

@@ -1,4 +1,4 @@
-#![cfg_attr(feature = "unwind", feature(unwind_attributes))]
+#![cfg_attr(unwind, feature(unwind_attributes))]
 
 //! # High-level bindings to Lua
 //!

src/lua.rs

@@ -759,7 +759,7 @@ impl Lua {
     pub(crate) unsafe fn userdata_metatable<T: UserData>(&self) -> Result<c_int> {
         // Used if both an __index metamethod is set and regular methods, checks methods table
         // first, then __index metamethod.
-        #[cfg_attr(feature = "unwind", unwind)]
+        #[cfg_attr(unwind, unwind)]
         unsafe extern "C" fn meta_index_impl(state: *mut ffi::lua_State) -> c_int {
             ffi::luaL_checkstack(state, 2, ptr::null());
 
@@ -995,7 +995,7 @@ impl Lua {
         &'lua self,
         func: Callback<'callback, 'static>,
     ) -> Result<Function<'lua>> {
-        #[cfg_attr(feature = "unwind", unwind)]
+        #[cfg_attr(unwind, unwind)]
         unsafe extern "C" fn callback_call_impl(state: *mut ffi::lua_State) -> c_int {
             callback_error(state, || {
                 let lua = Lua {

src/util.rs

@@ -121,7 +121,7 @@ where
         nresults: c_int,
     }
 
-    #[cfg_attr(feature = "unwind", unwind)]
+    #[cfg_attr(unwind, unwind)]
     unsafe extern "C" fn do_call<F, R>(state: *mut ffi::lua_State) -> c_int
     where
         F: FnOnce(*mut ffi::lua_State) -> R,
@@ -272,7 +272,7 @@ pub unsafe fn take_userdata<T>(state: *mut ffi::lua_State) -> T {
     ptr::read(ud)
 }
 
-#[cfg_attr(feature = "unwind", unwind)]
+#[cfg_attr(unwind, unwind)]
 pub unsafe extern "C" fn userdata_destructor<T>(state: *mut ffi::lua_State) -> c_int {
     callback_error(state, || {
         take_userdata::<T>(state);
@@ -306,7 +306,7 @@ where
 // Takes an error at the top of the stack, and if it is a WrappedError, converts it to an
 // Error::CallbackError with a traceback, if it is some lua type, prints the error along with a
 // traceback, and if it is a WrappedPanic, does not modify it.
-#[cfg_attr(feature = "unwind", unwind)]
+#[cfg_attr(unwind, unwind)]
 pub unsafe extern "C" fn error_traceback(state: *mut ffi::lua_State) -> c_int {
     ffi::luaL_checkstack(state, 2, ptr::null());
 
@@ -337,7 +337,7 @@ pub unsafe extern "C" fn error_traceback(state: *mut ffi::lua_State) -> c_int {
 }
 
 // A variant of pcall that does not allow lua to catch panic errors from callback_error
-#[cfg_attr(feature = "unwind", unwind)]
+#[cfg_attr(unwind, unwind)]
 pub unsafe extern "C" fn safe_pcall(state: *mut ffi::lua_State) -> c_int {
     ffi::luaL_checkstack(state, 2, ptr::null());
 
@@ -360,9 +360,9 @@ pub unsafe extern "C" fn safe_pcall(state: *mut ffi::lua_State) -> c_int {
 }
 
 // A variant of xpcall that does not allow lua to catch panic errors from callback_error
-#[cfg_attr(feature = "unwind", unwind)]
+#[cfg_attr(unwind, unwind)]
 pub unsafe extern "C" fn safe_xpcall(state: *mut ffi::lua_State) -> c_int {
-    #[cfg_attr(feature = "unwind", unwind)]
+    #[cfg_attr(unwind, unwind)]
     unsafe extern "C" fn xpcall_msgh(state: *mut ffi::lua_State) -> c_int {
         ffi::luaL_checkstack(state, 2, ptr::null());
 
@@ -510,7 +510,7 @@ unsafe fn is_wrapped_panic(state: *mut ffi::lua_State, index: c_int) -> bool {
 unsafe fn get_error_metatable(state: *mut ffi::lua_State) -> c_int {
     static ERROR_METATABLE_REGISTRY_KEY: u8 = 0;
 
-    #[cfg_attr(feature = "unwind", unwind)]
+    #[cfg_attr(unwind, unwind)]
     unsafe extern "C" fn error_tostring(state: *mut ffi::lua_State) -> c_int {
         ffi::luaL_checkstack(state, 2, ptr::null());
 
@@ -612,7 +612,7 @@ unsafe fn get_panic_metatable(state: *mut ffi::lua_State) -> c_int {
 unsafe fn get_destructed_userdata_metatable(state: *mut ffi::lua_State) -> c_int {
     static DESTRUCTED_USERDATA_METATABLE: u8 = 0;
 
-    #[cfg_attr(feature = "unwind", unwind)]
+    #[cfg_attr(unwind, unwind)]
     unsafe extern "C" fn destructed_error(state: *mut ffi::lua_State) -> c_int {
         ffi::luaL_checkstack(state, 2, ptr::null());
         push_wrapped_error(state, Error::CallbackDestructed);