Auto merge of #125966 - schvv31n:impl_os_string_pathbuf_leak, r=workingjubilee

Implement `os_string_pathbuf_leak`

implementation of #125965

ACP: https://github.com/rust-lang/libs-team/issues/389 [ Accepted ]

library/std/src/ffi/os_str.rs

@@ -533,6 +533,25 @@ pub fn into_boxed_os_str(self) -> Box<OsStr> {
         unsafe { Box::from_raw(rw) }
     }
 
+    /// Consumes and leaks the `OsString`, returning a mutable reference to the contents,
+    /// `&'a mut OsStr`.
+    ///
+    /// The caller has free choice over the returned lifetime, including 'static.
+    /// Indeed, this function is ideally used for data that lives for the remainder of
+    /// the program’s life, as dropping the returned reference will cause a memory leak.
+    ///
+    /// It does not reallocate or shrink the `OsString`, so the leaked allocation may include
+    /// unused capacity that is not part of the returned slice. If you want to discard excess
+    /// capacity, call [`into_boxed_os_str`], and then [`Box::leak`] instead.
+    /// However, keep in mind that trimming the capacity may result in a reallocation and copy.
+    ///
+    /// [`into_boxed_os_str`]: Self::into_boxed_os_str
+    #[unstable(feature = "os_string_pathbuf_leak", issue = "125965")]
+    #[inline]
+    pub fn leak<'a>(self) -> &'a mut OsStr {
+        OsStr::from_inner_mut(self.inner.leak())
+    }
+
     /// Part of a hack to make PathBuf::push/pop more efficient.
     #[inline]
     pub(crate) fn as_mut_vec_for_path_buf(&mut self) -> &mut Vec<u8> {

library/std/src/ffi/os_str/tests.rs

@@ -23,6 +23,15 @@ fn test_os_string_clear() {
     assert_eq!(0, os_string.inner.as_inner().len());
 }
 
+#[test]
+fn test_os_string_leak() {
+    let os_string = OsString::from("have a cake");
+    let (len, cap) = (os_string.len(), os_string.capacity());
+    let leaked = os_string.leak();
+    assert_eq!(leaked.as_encoded_bytes(), b"have a cake");
+    unsafe { drop(String::from_raw_parts(leaked as *mut OsStr as _, len, cap)) }
+}
+
 #[test]
 fn test_os_string_capacity() {
     let os_string = OsString::with_capacity(0);

library/std/src/path.rs

@@ -1226,6 +1226,25 @@ pub fn as_path(&self) -> &Path {
         self
     }
 
+    /// Consumes and leaks the `PathBuf`, returning a mutable reference to the contents,
+    /// `&'a mut Path`.
+    ///
+    /// The caller has free choice over the returned lifetime, including 'static.
+    /// Indeed, this function is ideally used for data that lives for the remainder of
+    /// the program’s life, as dropping the returned reference will cause a memory leak.
+    ///
+    /// It does not reallocate or shrink the `PathBuf`, so the leaked allocation may include
+    /// unused capacity that is not part of the returned slice. If you want to discard excess
+    /// capacity, call [`into_boxed_path`], and then [`Box::leak`] instead.
+    /// However, keep in mind that trimming the capacity may result in a reallocation and copy.
+    ///
+    /// [`into_boxed_path`]: Self::into_boxed_path
+    #[unstable(feature = "os_string_pathbuf_leak", issue = "125965")]
+    #[inline]
+    pub fn leak<'a>(self) -> &'a mut Path {
+        Path::from_inner_mut(self.inner.leak())
+    }
+
     /// Extends `self` with `path`.
     ///
     /// If `path` is absolute, it replaces the current path.

library/std/src/path/tests.rs

@@ -126,6 +126,16 @@ fn into() {
     assert_eq!(static_cow_path, owned_cow_path);
 }
 
+#[test]
+fn test_pathbuf_leak() {
+    let string = "/have/a/cake".to_owned();
+    let (len, cap) = (string.len(), string.capacity());
+    let buf = PathBuf::from(string);
+    let leaked = buf.leak();
+    assert_eq!(leaked.as_os_str().as_encoded_bytes(), b"/have/a/cake");
+    unsafe { drop(String::from_raw_parts(leaked.as_mut_os_str() as *mut OsStr as _, len, cap)) }
+}
+
 #[test]
 #[cfg(unix)]
 pub fn test_decompositions_unix() {

library/std/src/sys/os_str/bytes.rs

@@ -176,6 +176,11 @@ pub fn push_slice(&mut self, s: &Slice) {
         self.inner.extend_from_slice(&s.inner)
     }
 
+    #[inline]
+    pub fn leak<'a>(self) -> &'a mut Slice {
+        unsafe { mem::transmute(self.inner.leak()) }
+    }
+
     #[inline]
     pub fn into_box(self) -> Box<Slice> {
         unsafe { mem::transmute(self.inner.into_boxed_slice()) }

library/std/src/sys/os_str/wtf8.rs

@@ -138,6 +138,11 @@ pub fn shrink_to(&mut self, min_capacity: usize) {
         self.inner.shrink_to(min_capacity)
     }
 
+    #[inline]
+    pub fn leak<'a>(self) -> &'a mut Slice {
+        unsafe { mem::transmute(self.inner.leak()) }
+    }
+
     #[inline]
     pub fn into_box(self) -> Box<Slice> {
         unsafe { mem::transmute(self.inner.into_box()) }

library/std/src/sys_common/wtf8.rs

@@ -325,6 +325,11 @@ pub fn shrink_to(&mut self, min_capacity: usize) {
         self.bytes.shrink_to(min_capacity)
     }
 
+    #[inline]
+    pub fn leak<'a>(self) -> &'a mut Wtf8 {
+        unsafe { Wtf8::from_mut_bytes_unchecked(self.bytes.leak()) }
+    }
+
     /// Returns the number of bytes that this string buffer can hold without reallocating.
     #[inline]
     pub fn capacity(&self) -> usize {