git: Fix out-of-bounds indexing when diff bases contain CRLF (#52605)

Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Release Notes:

- N/A

crates/buffer_diff/src/buffer_diff.rs

@@ -1651,6 +1651,7 @@ impl BufferDiff {
         language: Option<Arc<Language>>,
         cx: &App,
     ) -> Task<BufferDiffUpdate> {
+        let base_text = base_text.map(|t| text::LineEnding::normalize_arc(t));
         let prev_base_text = self.base_text(cx).as_rope().clone();
         let base_text_changed = base_text_change.is_some();
         let compute_base_text_edits = base_text_change == Some(true);
@@ -3947,4 +3948,36 @@ mod tests {
             }
         }
     }
+
+    #[gpui::test]
+    async fn test_set_base_text_with_crlf(cx: &mut gpui::TestAppContext) {
+        let base_text_crlf = "one\r\ntwo\r\nthree\r\nfour\r\nfive\r\n";
+        let base_text_lf = "one\ntwo\nthree\nfour\nfive\n";
+        assert_ne!(base_text_crlf.len(), base_text_lf.len());
+
+        let buffer_text = "one\nTWO\nthree\nfour\nfive\n";
+        let buffer = Buffer::new(
+            ReplicaId::LOCAL,
+            BufferId::new(1).unwrap(),
+            buffer_text.to_string(),
+        );
+        let buffer_snapshot = buffer.snapshot();
+
+        let diff = cx.new(|cx| BufferDiff::new(&buffer_snapshot, cx));
+        diff.update(cx, |diff, cx| {
+            diff.set_base_text(
+                Some(Arc::from(base_text_crlf)),
+                None,
+                buffer_snapshot.clone(),
+                cx,
+            )
+        })
+        .await
+        .ok();
+        cx.run_until_parked();
+
+        let snapshot = diff.update(cx, |diff, cx| diff.snapshot(cx));
+        snapshot.buffer_point_to_base_text_range(Point::new(0, 0), &buffer_snapshot);
+        snapshot.buffer_point_to_base_text_range(Point::new(1, 0), &buffer_snapshot);
+    }
 }