diff --git a/Cargo.toml b/Cargo.toml
index f8dd465890e0c2..5e44eda500b1d5 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -5,7 +5,7 @@ resolver = "2"
 [workspace.package]
 # Please update rustfmt.toml when bumping the Rust edition
 edition = "2024"
-rust-version = "1.90"
+rust-version = "1.91"
 homepage = "https://docs.astral.sh/ruff"
 documentation = "https://docs.astral.sh/ruff"
 repository = "https://github.com/astral-sh/ruff"
diff --git a/crates/ruff_annotate_snippets/src/lib.rs b/crates/ruff_annotate_snippets/src/lib.rs
index e623489f97ea8c..f8d0e1e5c6028b 100644
--- a/crates/ruff_annotate_snippets/src/lib.rs
+++ b/crates/ruff_annotate_snippets/src/lib.rs
@@ -1,5 +1,3 @@
-#![expect(clippy::needless_doctest_main)]
-
 //! A library for formatting of text or programming code snippets.
 //!
 //! It's primary purpose is to build an ASCII-graphical representation of the snippet
diff --git a/crates/ruff_db/src/diagnostic/mod.rs b/crates/ruff_db/src/diagnostic/mod.rs
index c9013040554c99..f9bb731170faba 100644
--- a/crates/ruff_db/src/diagnostic/mod.rs
+++ b/crates/ruff_db/src/diagnostic/mod.rs
@@ -8,7 +8,6 @@ use ruff_text_size::{Ranged, TextRange, TextSize};
 
 pub use self::render::{
     DisplayDiagnostic, DisplayDiagnostics, DummyFileResolver, FileResolver, Input,
-    ceil_char_boundary,
     github::{DisplayGithubDiagnostics, GithubRenderer},
 };
 use crate::cancellation::CancellationToken;
diff --git a/crates/ruff_db/src/diagnostic/render.rs b/crates/ruff_db/src/diagnostic/render.rs
index 5cd82206943542..9ae7aa623e0774 100644
--- a/crates/ruff_db/src/diagnostic/render.rs
+++ b/crates/ruff_db/src/diagnostic/render.rs
@@ -1087,7 +1087,8 @@ impl<'r> EscapedSourceCode<'r> {
                 continue;
             }
             let start = range.start();
-            let end = ceil_char_boundary(&self.text, start + TextSize::from(1));
+            let end =
+                TextSize::try_from(self.text.ceil_char_boundary(start.to_usize() + 1)).unwrap();
             ann.range = TextRange::new(start, end);
         }
 
@@ -1095,86 +1096,6 @@ impl<'r> EscapedSourceCode<'r> {
     }
 }
 
-/// Finds the closest [`TextSize`] not less than the offset given for which
-/// `is_char_boundary` is `true`. Unless the offset given is greater than
-/// the length of the underlying contents, in which case, the length of the
-/// contents is returned.
-///
-/// Can be replaced with `str::ceil_char_boundary` once it's stable.
-///
-/// # Examples
-///
-/// From `std`:
-///
-/// ```
-/// use ruff_db::diagnostic::ceil_char_boundary;
-/// use ruff_text_size::{Ranged, TextLen, TextSize};
-///
-/// let source = "❤️🧡💛💚💙💜";
-/// assert_eq!(source.text_len(), TextSize::from(26));
-/// assert!(!source.is_char_boundary(13));
-///
-/// let closest = ceil_char_boundary(source, TextSize::from(13));
-/// assert_eq!(closest, TextSize::from(14));
-/// assert_eq!(&source[..closest.to_usize()], "❤️🧡💛");
-/// ```
-///
-/// Additional examples:
-///
-/// ```
-/// use ruff_db::diagnostic::ceil_char_boundary;
-/// use ruff_text_size::{Ranged, TextRange, TextSize};
-///
-/// let source = "Hello";
-///
-/// assert_eq!(
-///     ceil_char_boundary(source, TextSize::from(0)),
-///     TextSize::from(0)
-/// );
-///
-/// assert_eq!(
-///     ceil_char_boundary(source, TextSize::from(5)),
-///     TextSize::from(5)
-/// );
-///
-/// assert_eq!(
-///     ceil_char_boundary(source, TextSize::from(6)),
-///     TextSize::from(5)
-/// );
-///
-/// let source = "α";
-///
-/// assert_eq!(
-///     ceil_char_boundary(source, TextSize::from(0)),
-///     TextSize::from(0)
-/// );
-///
-/// assert_eq!(
-///     ceil_char_boundary(source, TextSize::from(1)),
-///     TextSize::from(2)
-/// );
-///
-/// assert_eq!(
-///     ceil_char_boundary(source, TextSize::from(2)),
-///     TextSize::from(2)
-/// );
-///
-/// assert_eq!(
-///     ceil_char_boundary(source, TextSize::from(3)),
-///     TextSize::from(2)
-/// );
-/// ```
-pub fn ceil_char_boundary(text: &str, offset: TextSize) -> TextSize {
-    let upper_bound = offset
-        .to_u32()
-        .saturating_add(4)
-        .min(text.text_len().to_u32());
-    (offset.to_u32()..upper_bound)
-        .map(TextSize::from)
-        .find(|offset| text.is_char_boundary(offset.to_usize()))
-        .unwrap_or_else(|| TextSize::from(upper_bound))
-}
-
 /// A stub implementation of [`FileResolver`] intended for testing.
 pub struct DummyFileResolver;
 
diff --git a/rust-toolchain.toml b/rust-toolchain.toml
index 50b3f5d4743ad1..79d20990183b65 100644
--- a/rust-toolchain.toml
+++ b/rust-toolchain.toml
@@ -1,2 +1,2 @@
 [toolchain]
-channel = "1.92"
+channel = "1.93"