Try #19:

.buildbot.sh

@@ -6,11 +6,15 @@ export CARGO_HOME="`pwd`/.cargo"
 export RUSTUP_HOME="`pwd`/.rustup"
 
 curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs > rustup.sh
-# Install no toolchain initially to ensure toolchain rollback.
-sh rustup.sh --default-host x86_64-unknown-linux-gnu --default-toolchain none -y --no-modify-path
-
+sh rustup.sh --default-host x86_64-unknown-linux-gnu --default-toolchain nightly -y --no-modify-path
 export PATH=`pwd`/.cargo/bin/:$PATH
-rustup install nightly
 
-cargo +nightly fmt --all -- --check
+rustup toolchain install nightly --allow-downgrade --profile minimal
 cargo check
+
+if [ `which cargo-fmt` -ne 0 ]; then
+    rm -rf ${RUSTUP_HOME} ${CARGO_HOME}
+    sh rustup.sh --default-host x86_64-unknown-linux-gnu --default-toolchain none -y --no-modify-path
+    rustup toolchain install nightly --allow-downgrade --profile minimal
+fi
+cargo +nightly fmt --all -- --check

src/allocator.rs

@@ -1,5 +1,5 @@
 use std::{
-    alloc::{AllocErr, AllocInit, AllocRef, GlobalAlloc, Layout, MemoryBlock},
+    alloc::{AllocErr, AllocRef, GlobalAlloc, Layout},
     ffi::c_void,
     ptr::NonNull,
 };
@@ -24,13 +24,11 @@ unsafe impl GlobalAlloc for BoehmAllocator {
 }
 
 unsafe impl AllocRef for BoehmGcAllocator {
-    fn alloc(&mut self, layout: Layout, _init: AllocInit) -> Result<MemoryBlock, AllocErr> {
+    fn alloc(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
         let ptr = unsafe { boehm::GC_malloc(layout.size()) } as *mut u8;
         assert!(!ptr.is_null());
-        Ok(MemoryBlock {
-            ptr: unsafe { NonNull::new_unchecked(ptr) },
-            size: layout.size(),
-        })
+        let ptr = unsafe { NonNull::new_unchecked(ptr) };
+        Ok(NonNull::slice_from_raw_parts(ptr, layout.size()))
     }
 
     unsafe fn dealloc(&mut self, _: NonNull<u8>, _: Layout) {}

src/gc.rs

@@ -1,5 +1,5 @@
 use std::{
-    alloc::{AllocInit, AllocRef, Layout},
+    alloc::{AllocRef, Layout},
     any::Any,
     ffi::c_void,
     fmt,
@@ -160,13 +160,7 @@ struct GcBox<T: ?Sized>(ManuallyDrop<T>);
 impl<T> GcBox<T> {
     fn new(value: T) -> *mut GcBox<T> {
         let layout = Layout::new::<T>();
-        let ptr = unsafe {
-            GC_ALLOCATOR
-                .alloc(layout, AllocInit::Uninitialized)
-                .unwrap()
-                .ptr
-                .as_ptr()
-        } as *mut GcBox<T>;
+        let ptr = unsafe { GC_ALLOCATOR.alloc(layout).unwrap().as_ptr() } as *mut GcBox<T>;
         let gcbox = GcBox(ManuallyDrop::new(value));
 
         unsafe {
@@ -180,11 +174,7 @@ impl<T> GcBox<T> {
 
     fn new_from_layout(layout: Layout) -> NonNull<GcBox<MaybeUninit<T>>> {
         unsafe {
-            let base_ptr = GC_ALLOCATOR
-                .alloc(layout, AllocInit::Uninitialized)
-                .unwrap()
-                .ptr
-                .as_ptr() as *mut usize;
+            let base_ptr = GC_ALLOCATOR.alloc(layout).unwrap().as_ptr() as *mut usize;
             NonNull::new_unchecked(base_ptr as *mut GcBox<MaybeUninit<T>>)
         }
     }

src/lib.rs

@@ -3,6 +3,7 @@
 #![feature(alloc_layout_extra)]
 #![feature(arbitrary_self_types)]
 #![feature(dispatch_from_dyn)]
+#![feature(nonnull_slice_from_raw_parts)]
 #![feature(raw_vec_internals)]
 #![feature(const_fn)]
 #![feature(coerce_unsized)]