[PATCH] rust: bitmap: document `next_bit()`/`next_zero_bit()` panics

[Miguel Cordero Pamphile]

`Bitmap::next_bit()` and `Bitmap::next_zero_bit()` panic when
CONFIG_RUST_BITMAP_HARDENED is enabled and `start` is greater than or
equal to `self.len()`, but their documentation did not mention it and
stated instead that `None` would be returned for that input.

Add the missing `# Panics` sections and clarify when `None` is returned,
matching the existing documentation of `set_bit()` and friends.

Link: https://github.com/Rust-for-Linux/linux/issues/1252
Reported-by: Georgios Androutsopoulos <georgeandrout13@xxxxxxxxx>
Signed-off-by: Miguel Cordero Pamphile <miguelcorderopamphile@xxxxxxxxx>
---
 rust/kernel/bitmap.rs | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/bitmap.rs b/rust/kernel/bitmap.rs
index b27e0ec80..5da8b12fb 100644
--- a/rust/kernel/bitmap.rs
+++ b/rust/kernel/bitmap.rs
@@ -459,7 +459,13 @@ pub fn last_bit(&self) -> Option<usize> {
 
     /// Finds next set bit, starting from `start`.
     ///
-    /// Returns `None` if `start` is greater or equal to `self.nbits`.
+    /// If CONFIG_RUST_BITMAP_HARDENED is not enabled and `start` is greater than
+    /// or equal to `self.len()`, returns `None`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if CONFIG_RUST_BITMAP_HARDENED is enabled and `start` is greater than
+    /// or equal to `self.len()`.
     #[inline]
     pub fn next_bit(&self, start: usize) -> Option<usize> {
         bitmap_assert!(
@@ -479,7 +485,14 @@ pub fn next_bit(&self, start: usize) -> Option<usize> {
     }
 
     /// Finds next zero bit, starting from `start`.
-    /// Returns `None` if `start` is greater than or equal to `self.len()`.
+    ///
+    /// If CONFIG_RUST_BITMAP_HARDENED is not enabled and `start` is greater than
+    /// or equal to `self.len()`, returns `None`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if CONFIG_RUST_BITMAP_HARDENED is enabled and `start` is greater than
+    /// or equal to `self.len()`.
     #[inline]
     pub fn next_zero_bit(&self, start: usize) -> Option<usize> {
         bitmap_assert!(
-- 
2.50.1