properly handle LSP position encoding (#5711)

* properly handle LSP position encoding

* add debug assertion to Transaction::change

* Apply suggestions from code review

Co-authored-by: Michael Davis <mcarsondavis@gmail.com>

---------

Co-authored-by: Michael Davis <mcarsondavis@gmail.com>

helix-core/src/line_ending.rs

@@ -203,6 +203,13 @@ pub fn line_end_char_index(slice: &RopeSlice, line: usize) -> usize {
             .unwrap_or(0)
 }
 
+pub fn line_end_byte_index(slice: &RopeSlice, line: usize) -> usize {
+    slice.line_to_byte(line + 1)
+        - get_line_ending(&slice.line(line))
+            .map(|le| le.as_str().len())
+            .unwrap_or(0)
+}
+
 /// Fetches line `line_idx` from the passed rope slice, sans any line ending.
 pub fn line_without_line_ending<'a>(slice: &'a RopeSlice, line_idx: usize) -> RopeSlice<'a> {
     let start = slice.line_to_char(line_idx);

helix-core/src/transaction.rs

@@ -481,6 +481,11 @@ impl Transaction {
         for (from, to, tendril) in changes {
             // Verify ranges are ordered and not overlapping
             debug_assert!(last <= from);
+            // Verify ranges are correct
+            debug_assert!(
+                from <= to,
+                "Edit end must end before it starts (should {from} <= {to})"
+            );
 
             // Retain from last "to" to current "from"
             changeset.retain(from - last);