perf: faster WithIndices

src/helpers.rs

@@ -1260,6 +1260,10 @@ pub trait SourceText<'a>: Default + Clone + ToString {
   /// Returns a slice of the text specified by the byte range.
   fn byte_slice(&self, range: Range<usize>) -> Self;
 
+  /// Returns a slice of the text specified by the byte range without bounds checking.
+  #[allow(unsafe_code)]
+  unsafe fn byte_slice_unchecked(&self, range: Range<usize>) -> Self;
+
   /// Returns true if the text is empty.
   fn is_empty(&self) -> bool;
 
@@ -1293,6 +1297,11 @@ impl<'a> SourceText<'a> for Rope<'a> {
     self.byte_slice(range)
   }
 
+  #[allow(unsafe_code)]
+  unsafe fn byte_slice_unchecked(&self, range: Range<usize>) -> Self {
+    self.byte_slice_unchecked(range)
+  }
+
   #[inline]
   fn is_empty(&self) -> bool {
     self.is_empty()
@@ -1330,6 +1339,11 @@ impl<'a> SourceText<'a> for &'a str {
     self.get(range).unwrap_or_default()
   }
 
+  #[allow(unsafe_code)]
+  unsafe fn byte_slice_unchecked(&self, range: Range<usize>) -> Self {
+    self.get_unchecked(range)
+  }
+
   #[inline]
   fn is_empty(&self) -> bool {
     (*self).is_empty()

src/with_indices.rs

@@ -39,7 +39,14 @@ where
     let str_len = self.line.len();
     let start = *indices_indexes.get(start_index).unwrap_or(&str_len);
     let end = *indices_indexes.get(end_index).unwrap_or(&str_len);
-    self.line.byte_slice(start..end)
+
+    #[allow(unsafe_code)]
+    unsafe {
+      // SAFETY: Since `indices` iterates over the `CharIndices` of `self`, we can guarantee
+      // that the indices obtained from it will always be within the bounds of `self` and they
+      // will always lie on UTF-8 sequence boundaries.
+      self.line.byte_slice_unchecked(start..end)
+    }
   }
 }