[WIP] Try to fix proc_macro abi incompatibility

Author: bjorn3

src/libproc_macro/bridge/buffer.rs

@@ -9,6 +9,7 @@ use std::slice;
 struct Slice<'a, T> {
     data: &'a [T; 0],
     len: usize,
+    _a: u8, // Force ByRef passing of this struct
 }
 
 unsafe impl<'a, T: Sync> Sync for Slice<'a, T> {}
@@ -23,7 +24,7 @@ impl<T> Clone for Slice<'a, T> {
 
 impl<T> From<&'a [T]> for Slice<'a, T> {
     fn from(xs: &'a [T]) -> Self {
-        Slice { data: unsafe { &*(xs.as_ptr() as *const [T; 0]) }, len: xs.len() }
+        Slice { data: unsafe { &*(xs.as_ptr() as *const [T; 0]) }, len: xs.len(), _a: 0 }
     }
 }
 

src/libproc_macro/bridge/client.rs

@@ -44,7 +44,7 @@ macro_rules! define_handles {
         }
 
         $(
-            #[repr(C)]
+            #[repr(transparent)]
             pub(crate) struct $oty(handle::Handle);
             impl !Send for $oty {}
             impl !Sync for $oty {}
@@ -119,7 +119,7 @@ macro_rules! define_handles {
         )*
 
         $(
-            #[repr(C)]
+            #[repr(transparent)]
             #[derive(Copy, Clone, PartialEq, Eq, Hash)]
             pub(crate) struct $ity(handle::Handle);
             impl !Send for $ity {}

src/libproc_macro/bridge/closure.rs

@@ -4,6 +4,7 @@
 pub struct Closure<'a, A, R> {
     call: unsafe extern "C" fn(&mut Env, A) -> R,
     env: &'a mut Env,
+    _a: u8, // Force ByRef abi
 }
 
 extern "C" {
@@ -18,7 +19,7 @@ impl<'a, A, R, F: FnMut(A) -> R> From<&'a mut F> for Closure<'a, A, R> {
         unsafe extern "C" fn call<A, R, F: FnMut(A) -> R>(env: &mut Env, arg: A) -> R {
             (*(env as *mut _ as *mut F))(arg)
         }
-        Closure { call: call::<A, R, F>, env: unsafe { &mut *(f as *mut _ as *mut Env) } }
+        Closure { call: call::<A, R, F>, env: unsafe { &mut *(f as *mut _ as *mut Env) }, _a: 0 }
     }
 }
 

src/libproc_macro/lib.rs

@@ -72,6 +72,7 @@ pub fn is_available() -> bool {
 /// and `#[proc_macro_derive]` definitions.
 #[stable(feature = "proc_macro_lib", since = "1.15.0")]
 #[derive(Clone)]
+#[repr(transparent)]
 pub struct TokenStream(bridge::client::TokenStream);
 
 #[stable(feature = "proc_macro_lib", since = "1.15.0")]