TryFrom<core::ffi::CStr> implementation for CStr8

After this was reverted in 5f4e158, we now can
add it again, as our MSRV is now recent enough.

Author: phip1611

CHANGELOG.md

@@ -4,6 +4,7 @@
 - Implementations for the trait `EqStrUntilNul` now allow `?Sized` inputs. This means that
   you can write `some_cstr16.eq_str_until_nul("test")` instead of
   `some_cstr16.eq_str_until_nul(&"test")` now.
+- Added `TryFrom<core::ffi::CStr>` implementation for `CStr8`.
 
 ## uefi-macros - [Unreleased]
 

uefi/src/data_types/strs.rs

@@ -1,5 +1,6 @@
 use super::chars::{Char16, Char8, NUL_16, NUL_8};
 use super::UnalignedSlice;
+use core::ffi::CStr;
 use core::fmt;
 use core::iter::Iterator;
 use core::mem::MaybeUninit;
@@ -58,6 +59,11 @@ pub enum FromStrWithBufError {
 /// This type is largely inspired by [`core::ffi::CStr`] with the exception that all characters are
 /// guaranteed to be 8 bit long.
 ///
+/// A [`CStr8`] can be constructed from a [`core::ffi::CStr`] via a `try_from` call:
+/// ```ignore
+/// let cstr8: &CStr8 = TryFrom::try_from(cstr).unwrap();
+/// ```
+///
 /// For convenience, a [`CStr8`] is comparable with [`core::str`] and
 /// `alloc::string::String` from the standard library through the trait [`EqStrUntilNul`].
 #[repr(transparent)]
@@ -156,6 +162,14 @@ impl<StrType: AsRef<str> + ?Sized> EqStrUntilNul<StrType> for CStr8 {
     }
 }
 
+impl<'a> TryFrom<&'a CStr> for &'a CStr8 {
+    type Error = FromSliceWithNulError;
+
+    fn try_from(cstr: &'a CStr) -> Result<Self, Self::Error> {
+        CStr8::from_bytes_with_nul(cstr.to_bytes_with_nul())
+    }
+}
+
 /// An UCS-2 null-terminated string.
 ///
 /// This type is largely inspired by [`core::ffi::CStr`] with the exception that all characters are
@@ -453,6 +467,16 @@ mod tests {
     use crate::alloc::string::String;
     use uefi_macros::{cstr16, cstr8};
 
+    // Tests if our CStr8 type can be constructed from a valid core::ffi::CStr
+    #[test]
+    fn test_cstr8_from_cstr() {
+        let msg = "hello world\0";
+        let cstr = unsafe { CStr::from_ptr(msg.as_ptr().cast()) };
+        let cstr8: &CStr8 = TryFrom::try_from(cstr).unwrap();
+        assert!(cstr8.eq_str_until_nul(msg));
+        assert!(msg.eq_str_until_nul(cstr8));
+    }
+
     #[test]
     fn test_cstr16_num_bytes() {
         let s = CStr16::from_u16_with_nul(&[65, 66, 67, 0]).unwrap();