Nightly constify to_str (and everything on its path)

src/lib.rs

@@ -1,6 +1,8 @@
 #![cfg_attr(not(feature = "std"), no_std)]
 #![warn(rust_2018_idioms)]
 #![cfg_attr(feature = "nightly", feature(const_raw_ptr_deref))]
+#![cfg_attr(feature = "nightly", feature(const_slice_from_raw_parts))]
+#![cfg_attr(feature = "nightly", feature(const_str_from_utf8))]
 
 #[cfg(test)]
 extern crate std;
@@ -1155,11 +1157,40 @@ impl CStr {
     /// assert_eq!(cstr.to_bytes(), b"foo");
     /// ```
     #[inline]
+    #[cfg(not(feature = "nightly"))]
     pub fn to_bytes(&self) -> &[u8] {
         let bytes = self.to_bytes_with_nul();
         &bytes[..bytes.len() - 1]
     }
 
+    /// Converts this C string to a byte slice.
+    ///
+    /// The returned slice will **not** contain the trailing nul terminator that this C
+    /// string has.
+    ///
+    /// > **Note**: This method is currently implemented as a constant-time
+    /// > cast, but it is planned to alter its definition in the future to
+    /// > perform the length calculation whenever this method is called.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use cstr_core::CStr;
+    ///
+    /// let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
+    /// assert_eq!(cstr.to_bytes(), b"foo");
+    /// ```
+    #[inline]
+    #[cfg(feature = "nightly")]
+    pub const fn to_bytes(&self) -> &[u8] {
+        let bytes = self.to_bytes_with_nul();
+        // unsafe: This is just like [:len - 1] (but const usable), and any underflow of the `- 1`
+        // is avoided by the type's guarantee that there is a trailing nul byte.
+        unsafe {
+            slice::from_raw_parts(bytes.as_ptr(), bytes.len() - 1)
+        }
+    }
+
     /// Converts this C string to a byte slice containing the trailing 0 byte.
     ///
     /// This function is the equivalent of [`to_bytes`] except that it will retain
@@ -1180,6 +1211,32 @@ impl CStr {
     /// assert_eq!(cstr.to_bytes_with_nul(), b"foo\0");
     /// ```
     #[inline]
+    #[cfg(feature = "nightly")]
+    pub const fn to_bytes_with_nul(&self) -> &[u8] {
+        unsafe { &*(&self.inner as *const [c_char] as *const [u8]) }
+    }
+
+    /// Converts this C string to a byte slice containing the trailing 0 byte.
+    ///
+    /// This function is the equivalent of [`to_bytes`] except that it will retain
+    /// the trailing nul terminator instead of chopping it off.
+    ///
+    /// > **Note**: This method is currently implemented as a 0-cost cast, but
+    /// > it is planned to alter its definition in the future to perform the
+    /// > length calculation whenever this method is called.
+    ///
+    /// [`to_bytes`]: #method.to_bytes
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use cstr_core::CStr;
+    ///
+    /// let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
+    /// assert_eq!(cstr.to_bytes_with_nul(), b"foo\0");
+    /// ```
+    #[inline]
+    #[cfg(not(feature = "nightly"))]
     pub fn to_bytes_with_nul(&self) -> &[u8] {
         unsafe { &*(&self.inner as *const [c_char] as *const [u8]) }
     }
@@ -1198,7 +1255,31 @@ impl CStr {
     /// let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
     /// assert_eq!(cstr.to_str(), Ok("foo"));
     /// ```
-    pub fn to_str(&self) -> Result<&str, Utf8Error> {
+    #[cfg(not(feature = "nightly"))]
+    pub  fn to_str(&self) -> Result<&str, Utf8Error> {
+        // N.B., when `CStr` is changed to perform the length check in `.to_bytes()`
+        // instead of in `from_ptr()`, it may be worth considering if this should
+        // be rewritten to do the UTF-8 check inline with the length calculation
+        // instead of doing it afterwards.
+        str::from_utf8(self.to_bytes())
+    }
+
+    /// Yields a [`&str`] slice if the `CStr` contains valid UTF-8.
+    ///
+    /// If the contents of the `CStr` are valid UTF-8 data, this
+    /// function will return the corresponding [`&str`] slice. Otherwise,
+    /// it will return an error with details of where UTF-8 validation failed.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use cstr_core::CStr;
+    ///
+    /// let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
+    /// assert_eq!(cstr.to_str(), Ok("foo"));
+    /// ```
+    #[cfg(feature = "nightly")]
+    pub const fn to_str(&self) -> Result<&str, Utf8Error> {
         // N.B., when `CStr` is changed to perform the length check in `.to_bytes()`
         // instead of in `from_ptr()`, it may be worth considering if this should
         // be rewritten to do the UTF-8 check inline with the length calculation