Unrolled build for #145933

Rollup merge of #145933 - GrigorenkoPV:thing_as_thing, r=Amanieu

Expand `str_as_str` to more types

Tracking issue: #130366
ACP: rust-lang/libs-team#643

This PR expands `str_from_str` feature and adds analogous methods to more types. Namely:
- `&CStr`
- `&[T]`, `&mut [T]`
- `&OsStr`
- `&Path`
- `&ByteStr`, `&mut ByteStr` (tracking issue:  #134915) (technically was not part of ACP)

Author: rust-timer

library/core/src/bstr/mod.rs

@@ -68,6 +68,30 @@ impl ByteStr {
         ByteStr::from_bytes(bytes.as_ref())
     }
 
+    /// Returns the same string as `&ByteStr`.
+    ///
+    /// This method is redundant when used directly on `&ByteStr`, but
+    /// it helps dereferencing other "container" types,
+    /// for example `Box<ByteStr>` or `Arc<ByteStr>`.
+    #[inline]
+    // #[unstable(feature = "str_as_str", issue = "130366")]
+    #[unstable(feature = "bstr", issue = "134915")]
+    pub const fn as_byte_str(&self) -> &ByteStr {
+        self
+    }
+
+    /// Returns the same string as `&mut ByteStr`.
+    ///
+    /// This method is redundant when used directly on `&mut ByteStr`, but
+    /// it helps dereferencing other "container" types,
+    /// for example `Box<ByteStr>` or `MutexGuard<ByteStr>`.
+    #[inline]
+    // #[unstable(feature = "str_as_str", issue = "130366")]
+    #[unstable(feature = "bstr", issue = "134915")]
+    pub const fn as_mut_byte_str(&mut self) -> &mut ByteStr {
+        self
+    }
+
     #[doc(hidden)]
     #[unstable(feature = "bstr_internals", issue = "none")]
     #[inline]

library/core/src/ffi/c_str.rs

@@ -648,6 +648,17 @@ impl CStr {
     pub fn display(&self) -> impl fmt::Display {
         crate::bstr::ByteStr::from_bytes(self.to_bytes())
     }
+
+    /// Returns the same string as a string slice `&CStr`.
+    ///
+    /// This method is redundant when used directly on `&CStr`, but
+    /// it helps dereferencing other string-like types to string slices,
+    /// for example references to `Box<CStr>` or `Arc<CStr>`.
+    #[inline]
+    #[unstable(feature = "str_as_str", issue = "130366")]
+    pub const fn as_c_str(&self) -> &CStr {
+        self
+    }
 }
 
 #[stable(feature = "c_string_eq_c_str", since = "1.90.0")]

library/core/src/slice/mod.rs

@@ -4908,6 +4908,28 @@ impl<T> [T] {
 
         if start <= self.len() && end <= self.len() { Some(start..end) } else { None }
     }
+
+    /// Returns the same slice `&[T]`.
+    ///
+    /// This method is redundant when used directly on `&[T]`, but
+    /// it helps dereferencing other "container" types to slices,
+    /// for example `Box<[T]>` or `Arc<[T]>`.
+    #[inline]
+    #[unstable(feature = "str_as_str", issue = "130366")]
+    pub const fn as_slice(&self) -> &[T] {
+        self
+    }
+
+    /// Returns the same slice `&mut [T]`.
+    ///
+    /// This method is redundant when used directly on `&mut [T]`, but
+    /// it helps dereferencing other "container" types to slices,
+    /// for example `Box<[T]>` or `MutexGuard<[T]>`.
+    #[inline]
+    #[unstable(feature = "str_as_str", issue = "130366")]
+    pub const fn as_mut_slice(&mut self) -> &mut [T] {
+        self
+    }
 }
 
 impl<T> [MaybeUninit<T>] {

library/std/src/ffi/os_str.rs

@@ -1278,6 +1278,17 @@ impl OsStr {
     pub fn display(&self) -> Display<'_> {
         Display { os_str: self }
     }
+
+    /// Returns the same string as a string slice `&OsStr`.
+    ///
+    /// This method is redundant when used directly on `&OsStr`, but
+    /// it helps dereferencing other string-like types to string slices,
+    /// for example references to `Box<OsStr>` or `Arc<OsStr>`.
+    #[inline]
+    #[unstable(feature = "str_as_str", issue = "130366")]
+    pub const fn as_os_str(&self) -> &OsStr {
+        self
+    }
 }
 
 #[stable(feature = "box_from_os_str", since = "1.17.0")]

library/std/src/path.rs

@@ -3206,6 +3206,17 @@ impl Path {
         Display { inner: self.inner.display() }
     }
 
+    /// Returns the same path as `&Path`.
+    ///
+    /// This method is redundant when used directly on `&Path`, but
+    /// it helps dereferencing other `PathBuf`-like types to `Path`s,
+    /// for example references to `Box<Path>` or `Arc<Path>`.
+    #[inline]
+    #[unstable(feature = "str_as_str", issue = "130366")]
+    pub const fn as_path(&self) -> &Path {
+        self
+    }
+
     /// Queries the file system to get information about a file, directory, etc.
     ///
     /// This function will traverse symbolic links to query information about the