Add `Range` methods for various kinds of validation.

1 files changed, 12 insertions, 2 deletions

diff --git a/helix-core/src/graphemes.rs b/helix-core/src/graphemes.rs
index f71b6d5f..f7bf66c0 100644
--- a/helix-core/src/graphemes.rs
+++ b/helix-core/src/graphemes.rs
@@ -123,14 +123,24 @@ pub fn next_grapheme_boundary(slice: RopeSlice, char_idx: usize) -> usize {
 
 /// Returns the passed char index if it's already a grapheme boundary,
 /// or the next grapheme boundary char index if not.
-pub fn ensure_grapheme_boundary(slice: RopeSlice, char_idx: usize) -> usize {
+pub fn ensure_grapheme_boundary_next(slice: RopeSlice, char_idx: usize) -> usize {
     if char_idx == 0 {
-        0
+        char_idx
     } else {
         next_grapheme_boundary(slice, char_idx - 1)
     }
 }
 
+/// Returns the passed char index if it's already a grapheme boundary,
+/// or the prev grapheme boundary char index if not.
+pub fn ensure_grapheme_boundary_prev(slice: RopeSlice, char_idx: usize) -> usize {
+    if char_idx == slice.len_chars() {
+        char_idx
+    } else {
+        prev_grapheme_boundary(slice, char_idx + 1)
+    }
+}
+
 /// Returns whether the given char position is a grapheme boundary.
 pub fn is_grapheme_boundary(slice: RopeSlice, char_idx: usize) -> bool {
     // Bounds check