[PATCH v8 4/7] rust: str: implement `strip_prefix` for `BStr`

[Andreas Hindborg <a.hindborg@kernel.org>]

Implement `strip_prefix` for `BStr` by deferring to `slice::strip_prefix`
on the underlying `&[u8]`.

Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
Tested-by: Daniel Almeida <daniel.almeida@collabora.com>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---

It is also possible to get this method by implementing
`core::slice::SlicePattern` for `BStr`. `SlicePattern` is unstable, so this
seems more reasonable.
---
 rust/kernel/str.rs | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index c6bd2c69543d..db272d2198fc 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -31,6 +31,22 @@ pub const fn from_bytes(bytes: &[u8]) -> &Self {
         // SAFETY: `BStr` is transparent to `[u8]`.
         unsafe { &*(bytes as *const [u8] as *const BStr) }
     }
+
+    /// Strip a prefix from `self`. Delegates to [`slice::strip_prefix`].
+    ///
+    /// # Example
+    /// ```
+    /// use kernel::b_str;
+    /// assert_eq!(Some(b_str!("bar")), b_str!("foobar").strip_prefix(b_str!("foo")));
+    /// assert_eq!(None, b_str!("foobar").strip_prefix(b_str!("bar")));
+    /// assert_eq!(Some(b_str!("foobar")), b_str!("foobar").strip_prefix(b_str!("")));
+    /// assert_eq!(Some(b_str!("")), b_str!("foobar").strip_prefix(b_str!("foobar")));
+    /// ```
+    pub fn strip_prefix(&self, pattern: impl AsRef<Self>) -> Option<&BStr> {
+        self.deref()
+            .strip_prefix(pattern.as_ref().deref())
+            .map(Self::from_bytes)
+    }
 }
 
 impl fmt::Display for BStr {

-- 
2.47.0