multi_buffer: Fix up some anchor checks (#43454)

Release Notes:

- N/A *or* Added/Fixed/Improved ...

crates/text/src/anchor.rs

@@ -6,7 +6,7 @@ use std::{cmp::Ordering, fmt::Debug, ops::Range};
 use sum_tree::{Bias, Dimensions};
 
 /// A timestamped position in a buffer
-#[derive(Copy, Clone, Eq, PartialEq, Debug, Hash)]
+#[derive(Copy, Clone, Eq, PartialEq, Hash)]
 pub struct Anchor {
     pub timestamp: clock::Lamport,
     /// The byte offset in the buffer
@@ -16,6 +16,24 @@ pub struct Anchor {
     pub buffer_id: Option<BufferId>,
 }
 
+impl Debug for Anchor {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        if *self == Self::MIN {
+            return f.write_str("Anchor::MIN");
+        }
+        if *self == Self::MAX {
+            return f.write_str("Anchor::MAX");
+        }
+
+        f.debug_struct("Anchor")
+            .field("timestamp", &self.timestamp)
+            .field("offset", &self.offset)
+            .field("bias", &self.bias)
+            .field("buffer_id", &self.buffer_id)
+            .finish()
+    }
+}
+
 impl Anchor {
     pub const MIN: Self = Self {
         timestamp: clock::Lamport::MIN,

crates/text/src/text.rs

@@ -2444,7 +2444,9 @@ impl BufferSnapshot {
         } else if bias == Bias::Right && offset == self.len() {
             Anchor::MAX
         } else {
-            if offset > self.visible_text.len() {
+            if cfg!(debug_assertions) {
+                self.visible_text.assert_char_boundary(offset);
+            } else if offset > self.visible_text.len() {
                 panic!("offset {} is out of bounds", offset)
             }
             let (start, _, item) = self.fragments.find::<usize, _>(&None, &offset, bias);
@@ -3137,12 +3139,9 @@ impl ToOffset for Point {
 
 impl ToOffset for usize {
     fn to_offset(&self, snapshot: &BufferSnapshot) -> usize {
-        assert!(
-            *self <= snapshot.len(),
-            "offset {} is out of range, snapshot length is {}",
-            self,
-            snapshot.len()
-        );
+        if cfg!(debug_assertions) {
+            snapshot.as_rope().assert_char_boundary(*self);
+        }
         *self
     }
 }