Moved unsafe from Iban::rand to util::StrExt::copy_from_str

.github/workflows/test.yml

@@ -65,11 +65,7 @@ jobs:
         with:
           submodules: true
       - uses: dtolnay/rust-toolchain@stable
-        with:
-          profile: minimal
       - uses: dtolnay/rust-toolchain@nightly
-        with:
-          profile: minimal
       - uses: taiki-e/install-action@cargo-llvm-cov
       - run: cargo llvm-cov --all-features --workspace --codecov --output-path codecov.json
       - uses: codecov/codecov-action@v3

src/lib.rs

@@ -8,6 +8,8 @@ use core::{fmt, ops::Deref, str::FromStr};
 use arrayvec::ArrayString;
 
 mod util;
+#[cfg(feature = "rand")]
+use util::StrExt as _;
 use util::{digits, ChunksExt as _, IteratorExt as _};
 
 include!(concat!(env!("OUT_DIR"), "/countries.rs"));
@@ -451,15 +453,13 @@ impl Iban {
         debug_assert_eq!(iban.len(), expected_length);
 
         let check_digits = 98 - calculate_checksum(iban.as_bytes());
-        #[allow(clippy::cast_possible_truncation)]
         let check_digits = [
             b'0' + (check_digits / 10) as u8,
             b'0' + (check_digits % 10) as u8,
         ];
-
-        // TODO: Figure out a way to swap out the characters without unsafe.
-        // SAFETY: All of the characters generated are ASCII, so there are no issues with character boundries.
-        unsafe { &mut iban.as_bytes_mut()[2..4] }.copy_from_slice(&check_digits);
+        let check_digits = core::str::from_utf8(&check_digits)
+            .expect("check digits are ASCII, and by definition valid UTF-8");
+        iban[2..4].copy_from_str(check_digits);
 
         Ok(Self(iban))
     }

src/util.rs

@@ -106,3 +106,24 @@ pub fn digits(mut value: u8) -> impl Iterator<Item = u8> {
         // Ensure at least one value (0) is provided by this iterator.
         .ensure_one(0)
 }
+
+#[cfg(feature = "rand")]
+pub trait StrExt {
+    /// Copies the contents of `src` into `self`, using a memcpy.
+    ///
+    /// The length of `src` must be the same as `self`.
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if the two str have different lengths.
+    fn copy_from_str(&mut self, src: &str);
+}
+
+#[cfg(feature = "rand")]
+impl StrExt for str {
+    #[inline]
+    fn copy_from_str(&mut self, src: &str) {
+        // SAFETY: The entire slice is being overwritten by `src`, which is a valid `str` reference, and as such is valid UTF-8.
+        unsafe { self.as_bytes_mut() }.copy_from_slice(src.as_bytes());
+    }
+}