fix str mutating through a ptr derived from &self

src/libcore/str/mod.rs

@@ -1757,7 +1757,7 @@ 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))
  }
@@ -1821,7 +1821,7 @@ mod traits {
  }
  #[inline]
  unsafe fn get_unchecked_mut(self, slice: &mut str) -> &mut Self::Output {
- let ptr = slice.as_ptr();
+ let ptr = slice.as_mut_ptr();
  super::from_utf8_unchecked_mut(slice::from_raw_parts_mut(ptr as *mut u8, self.end))
  }
  #[inline]
@@ -1883,7 +1883,7 @@ 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))
  }
@@ -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")]
+ #[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