From 7ccc09b210469fe598e8c829bccd83f3745b9e38 Mon Sep 17 00:00:00 2001
From: Simon Sapin <simon.sapin@exyr.org>
Date: Mon, 14 Feb 2022 20:05:45 +0100
Subject: [PATCH] Extend ptr::null and null_mut to all thin (including extern)
types
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Fixes https://github.com/rust-lang/rust/issues/93959
This change was accepted in https://rust-lang.github.io/rfcs/2580-ptr-meta.html
Note that this changes the signature of **stable** functions.
The change should be backward-compatible, but it is **insta-stable**
since it cannot (easily, at all?) be made available only
through a `#![feature(…)]` opt-in.
The RFC also proposed the same change for `NonNull::dangling`,
which makes sense it terms of its signature but not in terms of its implementation.
`dangling` uses `align_of()` as an address. But what `align_of()` should be for
extern types or whether it should be allowed at all remains an open question.
This commit depends on https://github.com/rust-lang/rust/pull/93977, which is not yet
part of the bootstrap compiler. So `#[cfg]` is used to only apply the change in
stage 1+. As far a I know bounds cannot be made conditional with `#[cfg]`, so the
entire functions are duplicated. This is unfortunate but temporary.
Since this duplication makes it less obvious in the diff,
the new definitions differ in:
* More permissive bounds (`Thin` instead of implied `Sized`)
* Different implementation
* Having `rustc_allow_const_fn_unstable(ptr_metadata)`
---
library/core/src/ptr/mod.rs | 46 +++++++++++++++++++++++++++
library/core/tests/ptr.rs | 12 +++++++
src/test/ui/cast/casts-issue-46365.rs | 2 +-
3 files changed, 59 insertions(+), 1 deletion(-)
diff --git a/library/core/src/ptr/mod.rs b/library/core/src/ptr/mod.rs
index ba8b0670147..0658ed812d1 100644
--- a/library/core/src/ptr/mod.rs
+++ b/library/core/src/ptr/mod.rs
@@ -507,10 +507,33 @@ pub unsafe fn drop_in_place<T: ?Sized>(to_drop: *mut T) {
#[rustc_promotable]
#[rustc_const_stable(feature = "const_ptr_null", since = "1.24.0")]
#[rustc_diagnostic_item = "ptr_null"]
+#[cfg(bootstrap)]
pub const fn null<T>() -> *const T {
invalid(0)
}
+/// Creates a null raw pointer.
+///
+/// # Examples
+///
+/// ```
+/// use std::ptr;
+///
+/// let p: *const i32 = ptr::null();
+/// assert!(p.is_null());
+/// ```
+#[inline(always)]
+#[must_use]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_promotable]
+#[rustc_const_stable(feature = "const_ptr_null", since = "1.24.0")]
+#[rustc_allow_const_fn_unstable(ptr_metadata)]
+#[rustc_diagnostic_item = "ptr_null"]
+#[cfg(not(bootstrap))]
+pub const fn null<T: ?Sized + Thin>() -> *const T {
+ from_raw_parts(0 as *const (), ())
+}
+
/// Creates a null mutable raw pointer.
///
/// # Examples
@@ -527,6 +550,7 @@ pub const fn null<T>() -> *const T {
#[rustc_promotable]
#[rustc_const_stable(feature = "const_ptr_null", since = "1.24.0")]
#[rustc_diagnostic_item = "ptr_null_mut"]
+#[cfg(bootstrap)]
pub const fn null_mut<T>() -> *mut T {
invalid_mut(0)
}
@@ -657,6 +681,28 @@ where
addr as *mut T
}
+/// Creates a null mutable raw pointer.
+///
+/// # Examples
+///
+/// ```
+/// use std::ptr;
+///
+/// let p: *mut i32 = ptr::null_mut();
+/// assert!(p.is_null());
+/// ```
+#[inline(always)]
+#[must_use]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_promotable]
+#[rustc_const_stable(feature = "const_ptr_null", since = "1.24.0")]
+#[rustc_allow_const_fn_unstable(ptr_metadata)]
+#[rustc_diagnostic_item = "ptr_null_mut"]
+#[cfg(not(bootstrap))]
+pub const fn null_mut<T: ?Sized + Thin>() -> *mut T {
+ from_raw_parts_mut(0 as *mut (), ())
+}
+
/// Forms a raw slice from a pointer and a length.
///
/// The `len` argument is the number of **elements**, not the number of bytes.
diff --git a/library/core/tests/ptr.rs b/library/core/tests/ptr.rs
index 03fe56022b0..c5242ad04de 100644
--- a/library/core/tests/ptr.rs
+++ b/library/core/tests/ptr.rs
@@ -93,6 +93,18 @@ fn test_is_null() {
let nmi: *mut dyn ToString = null_mut::<isize>();
assert!(nmi.is_null());
+
+ #[cfg(not(bootstrap))]
+ {
+ extern "C" {
+ type Extern;
+ }
+ let ec: *const Extern = null::<Extern>();
+ assert!(ec.is_null());
+
+ let em: *mut Extern = null_mut::<Extern>();
+ assert!(em.is_null());
+ }
}
#[test]
diff --git a/src/test/ui/cast/casts-issue-46365.rs b/src/test/ui/cast/casts-issue-46365.rs
index 3d0fea245c0..a2205b718c1 100644
--- a/src/test/ui/cast/casts-issue-46365.rs
+++ b/src/test/ui/cast/casts-issue-46365.rs
@@ -3,5 +3,5 @@ struct Lorem {
}
fn main() {
- let _foo: *mut Lorem = core::ptr::null_mut(); // no error here
+ let _foo: *mut Lorem = core::ptr::NonNull::dangling().as_ptr(); // no error here
}