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fix str mutating through a ptr derived from &self #58200

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Merged
merged 4 commits into from
Feb 13, 2019
Merged

fix str mutating through a ptr derived from &self #58200

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346dc37
fix str mutating through a ptr derived from &self
RalfJung Feb 5, 2019
13bbba2
remove now-unneeded raw ptr casts
RalfJung Feb 6, 2019
a996f2c
add tracking issue
RalfJung Feb 6, 2019
66c894e
also fix bad use of shared ref in split_at_mut
RalfJung Feb 7, 2019
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28 changes: 22 additions & 6 deletions src/libcore/str/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1757,9 +1757,9 @@ mod traits {
}
#[inline]
unsafe fn get_unchecked_mut(self, slice: &mut str) -> &mut Self::Output {
let ptr = slice.as_ptr().add(self.start);
let ptr = slice.as_mut_ptr().add(self.start);
let len = self.end - self.start;
super::from_utf8_unchecked_mut(slice::from_raw_parts_mut(ptr as *mut u8, len))
super::from_utf8_unchecked_mut(slice::from_raw_parts_mut(ptr, len))
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Notice that this raw ptr cast here is the "canary" that gave away that the old code was wrong -- it was actually casting *const u8 to *mut u8, which should not have been necessary.

}
#[inline]
fn index(self, slice: &str) -> &Self::Output {
Expand Down Expand Up @@ -1821,8 +1821,8 @@ mod traits {
}
#[inline]
unsafe fn get_unchecked_mut(self, slice: &mut str) -> &mut Self::Output {
let ptr = slice.as_ptr();
super::from_utf8_unchecked_mut(slice::from_raw_parts_mut(ptr as *mut u8, self.end))
let ptr = slice.as_mut_ptr();
super::from_utf8_unchecked_mut(slice::from_raw_parts_mut(ptr, self.end))
}
#[inline]
fn index(self, slice: &str) -> &Self::Output {
Expand Down Expand Up @@ -1883,9 +1883,9 @@ mod traits {
}
#[inline]
unsafe fn get_unchecked_mut(self, slice: &mut str) -> &mut Self::Output {
let ptr = slice.as_ptr().add(self.start);
let ptr = slice.as_mut_ptr().add(self.start);
let len = slice.len() - self.start;
super::from_utf8_unchecked_mut(slice::from_raw_parts_mut(ptr as *mut u8, len))
super::from_utf8_unchecked_mut(slice::from_raw_parts_mut(ptr, len))
}
#[inline]
fn index(self, slice: &str) -> &Self::Output {
Expand Down Expand Up @@ -2213,6 +2213,22 @@ impl str {
self as *const str as *const u8
}

/// Converts a mutable string slice to a raw pointer.
///
/// As string slices are a slice of bytes, the raw pointer points to a
/// [`u8`]. This pointer will be pointing to the first byte of the string
/// slice.
///
/// It is your responsibility to make sure that the string slice only gets
/// modified in a way that it remains valid UTF-8.
///
/// [`u8`]: primitive.u8.html
#[unstable(feature = "str_as_mut_ptr", issue = "0")]
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r+ with a tracking issue

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I opened a tracking issue in #58215, please check if that looks all right.

#[inline]
pub fn as_mut_ptr(&mut self) -> *mut u8 {
self as *mut str as *mut u8
}

/// Returns a subslice of `str`.
///
/// This is the non-panicking alternative to indexing the `str`. Returns
Expand Down