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Fixes the is_null method in PtrExt for fat pointers. #23163

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Fixes the is_null method in PtrExt for fat pointers. #23163

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9 changes: 7 additions & 2 deletions src/libcore/ptr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -320,7 +320,12 @@ impl<T: ?Sized> PtrExt for *const T {

#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
fn is_null(self) -> bool { self == 0 as *const T }
fn is_null(self) -> bool {
unsafe {
let ptr_ptr: *const usize = mem::transmute(&self);
*ptr_ptr == 0
}
}

#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
Expand All @@ -347,7 +352,7 @@ impl<T: ?Sized> PtrExt for *mut T {

#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
fn is_null(self) -> bool { self == 0 as *mut T }
fn is_null(self) -> bool { (self as *const T).is_null() }

#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
Expand Down
27 changes: 27 additions & 0 deletions src/libcoretest/ptr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@
use core::ptr::*;
use core::mem;
use std::iter::repeat;
use core::slice;

#[test]
fn test() {
Expand Down Expand Up @@ -66,6 +67,17 @@ fn test_is_null() {

let mq = unsafe { mp.offset(1) };
assert!(!mq.is_null());

unsafe {
let sn = slice::from_raw_parts(null(), 0) as *const [u32];
assert!(sn.is_null());

let s = &[1, 2, 3] as *const [u32];
assert!(!s.is_null());
}

let s: *const str = "rust" as *const str;
assert!(!s.is_null());
}

#[test]
Expand All @@ -89,6 +101,15 @@ fn test_as_ref() {
let p: *const int = &u as *const _;
assert_eq!(p.as_ref().unwrap(), &2);
}

let sn = slice::from_raw_parts(null(), 0) as *const [u32];
assert_eq!(sn.as_ref(), None);
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This is "6.1.3.2.3 Behavior considered undefined" because we put a null pointer inside a &[T]. It's just a test case, so I guess it can do no harm. I don't know what I want to say more than this is UB and rustc doesn't have to compile it into a sane test case if it doesn't want to.


let sl = &[1, 2, 3] as *const [u32];
assert_eq!(sl.as_ref().unwrap(), &[1, 2, 3]);

let s = "rust" as *const str;
assert_eq!(s.as_ref().unwrap(), "rust");
}
}

Expand All @@ -107,6 +128,12 @@ fn test_as_mut() {
let p: *mut int = &mut u as *mut _;
assert!(p.as_mut().unwrap() == &mut 2);
}

let sn = slice::from_raw_parts_mut(null_mut(), 0) as *mut [u32];
assert_eq!(sn.as_ref(), None);

let s = &mut [1, 2, 3] as *mut [u32];
assert_eq!(s.as_mut().unwrap(), &mut [1, 2, 3]);
}
}

Expand Down