Use #[rustc_box] in alloc instead of box syntax

Author: est31

library/alloc/src/boxed.rs

@@ -192,7 +192,25 @@ impl<T> Box<T> {
     /// ```
     /// let five = Box::new(5);
     /// ```
-    #[cfg(not(no_global_oom_handling))]
+    #[cfg(all(not(no_global_oom_handling), not(bootstrap)))]
+    #[inline(always)]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
+    pub fn new(x: T) -> Self {
+        #[rustc_box]
+        Box::new(x)
+    }
+
+    /// Allocates memory on the heap and then places `x` into it.
+    ///
+    /// This doesn't actually allocate if `T` is zero-sized.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let five = Box::new(5);
+    /// ```
+    #[cfg(all(not(no_global_oom_handling), bootstrap))]
     #[inline(always)]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[must_use]
@@ -259,7 +277,9 @@ impl<T> Box<T> {
     #[must_use]
     #[inline(always)]
     pub fn pin(x: T) -> Pin<Box<T>> {
-        (box x).into()
+        (#[cfg_attr(not(bootstrap), rustc_box)]
+        Box::new(x))
+        .into()
     }
 
     /// Allocates memory on the heap then places `x` into it,
@@ -1186,7 +1206,8 @@ unsafe impl<#[may_dangle] T: ?Sized, A: Allocator> Drop for Box<T, A> {
 impl<T: Default> Default for Box<T> {
     /// Creates a `Box<T>`, with the `Default` value for T.
     fn default() -> Self {
-        box T::default()
+        #[cfg_attr(not(bootstrap), rustc_box)]
+        Box::new(T::default())
     }
 }
 
@@ -1550,7 +1571,8 @@ impl<T, const N: usize> From<[T; N]> for Box<[T]> {
     /// println!("{boxed:?}");
     /// ```
     fn from(array: [T; N]) -> Box<[T]> {
-        box array
+        #[cfg_attr(not(bootstrap), rustc_box)]
+        Box::new(array)
     }
 }
 

library/alloc/src/lib.rs

@@ -147,7 +147,7 @@
 #![feature(allocator_internals)]
 #![feature(allow_internal_unstable)]
 #![feature(associated_type_bounds)]
-#![feature(box_syntax)]
+#![cfg_attr(bootstrap, feature(box_syntax))]
 #![feature(cfg_sanitize)]
 #![feature(const_deref)]
 #![feature(const_mut_refs)]
@@ -170,6 +170,7 @@
 #![feature(rustc_attrs)]
 #![feature(slice_internals)]
 #![feature(staged_api)]
+#![feature(stmt_expr_attributes)]
 #![cfg_attr(test, feature(test))]
 #![feature(unboxed_closures)]
 #![feature(unsized_fn_params)]

library/alloc/src/macros.rs

@@ -34,7 +34,28 @@
 /// be mindful of side effects.
 ///
 /// [`Vec`]: crate::vec::Vec
-#[cfg(all(not(no_global_oom_handling), not(test)))]
+#[cfg(all(not(no_global_oom_handling), not(test), not(bootstrap)))]
+#[macro_export]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_diagnostic_item = "vec_macro"]
+#[allow_internal_unstable(rustc_attrs, liballoc_internals)]
+macro_rules! vec {
+    () => (
+        $crate::__rust_force_expr!($crate::vec::Vec::new())
+    );
+    ($elem:expr; $n:expr) => (
+        $crate::__rust_force_expr!($crate::vec::from_elem($elem, $n))
+    );
+    ($($x:expr),+ $(,)?) => (
+        $crate::__rust_force_expr!(<[_]>::into_vec(
+            #[rustc_box]
+            $crate::boxed::Box::new([$($x),+])
+        ))
+    );
+}
+
+/// Creates a `Vec` containing the arguments (bootstrap version).
+#[cfg(all(not(no_global_oom_handling), not(test), bootstrap))]
 #[macro_export]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_diagnostic_item = "vec_macro"]
@@ -65,7 +86,7 @@ macro_rules! vec {
         $crate::vec::from_elem($elem, $n)
     );
     ($($x:expr),*) => (
-        $crate::slice::into_vec(box [$($x),*])
+        $crate::slice::into_vec($crate::boxed::Box::new([$($x),*]))
     );
     ($($x:expr,)*) => (vec![$($x),*])
 }

library/alloc/src/vec/mod.rs

@@ -2983,12 +2983,15 @@ impl<T, const N: usize> From<[T; N]> for Vec<T> {
     /// ```
     #[cfg(not(test))]
     fn from(s: [T; N]) -> Vec<T> {
-        <[T]>::into_vec(box s)
+        <[T]>::into_vec(
+            #[cfg_attr(not(bootstrap), rustc_box)]
+            Box::new(s),
+        )
     }
 
     #[cfg(test)]
     fn from(s: [T; N]) -> Vec<T> {
-        crate::slice::into_vec(box s)
+        crate::slice::into_vec(Box::new(s))
     }
 }