keep (cursor) position when exactly replacing text

helix-core/src/selection.rs

@@ -177,16 +177,16 @@ impl Range {
 
  let positions_to_map = match self.anchor.cmp(&self.head) {
  Ordering::Equal => [
- (&mut self.anchor, Assoc::After),
- (&mut self.head, Assoc::After),
+ (&mut self.anchor, Assoc::AfterSticky),
+ (&mut self.head, Assoc::AfterSticky),
  ],
  Ordering::Less => [
- (&mut self.anchor, Assoc::After),
- (&mut self.head, Assoc::Before),
+ (&mut self.anchor, Assoc::AfterSticky),
+ (&mut self.head, Assoc::BeforeSticky),
  ],
  Ordering::Greater => [
- (&mut self.head, Assoc::After),
- (&mut self.anchor, Assoc::Before),
+ (&mut self.head, Assoc::AfterSticky),
+ (&mut self.anchor, Assoc::BeforeSticky),
  ],
  };
  changes.update_positions(positions_to_map.into_iter());
@@ -469,16 +469,16 @@ impl Selection {
  range.old_visual_position = None;
  match range.anchor.cmp(&range.head) {
  Ordering::Equal => [
- (&mut range.anchor, Assoc::After),
- (&mut range.head, Assoc::After),
+ (&mut range.anchor, Assoc::AfterSticky),
+ (&mut range.head, Assoc::AfterSticky),
  ],
  Ordering::Less => [
- (&mut range.anchor, Assoc::After),
- (&mut range.head, Assoc::Before),
+ (&mut range.anchor, Assoc::AfterSticky),
+ (&mut range.head, Assoc::BeforeSticky),
  ],
  Ordering::Greater => [
- (&mut range.head, Assoc::After),
- (&mut range.anchor, Assoc::Before),
+ (&mut range.head, Assoc::AfterSticky),
+ (&mut range.anchor, Assoc::BeforeSticky),
  ],
  }
  });

helix-core/src/transaction.rs

@@ -29,6 +29,12 @@ pub enum Assoc {
  /// Acts like `Before` if a word character is inserted
  /// before the position, otherwise acts like `After`
  BeforeWord,
+ /// Acts like `Before` but if the position is within an exact replacement
+ /// (exact size) the offset to the start of the replacement is kept
+ BeforeSticky,
+ /// Acts like `After` but if the position is within an exact replacement
+ /// (exact size) the offset to the start of the replacement is kept
+ AfterSticky,
 }
 
 impl Assoc {
@@ -40,13 +46,17 @@ impl Assoc {
  fn insert_offset(self, s: &str) -> usize {
  let chars = s.chars().count();
  match self {
- Assoc::After => chars,
+ Assoc::After | Assoc::AfterSticky => chars,
  Assoc::AfterWord => s.chars().take_while(|&c| char_is_word(c)).count(),
  // return position before inserted text
- Assoc::Before => 0,
+ Assoc::Before | Assoc::BeforeSticky => 0,
  Assoc::BeforeWord => chars - s.chars().rev().take_while(|&c| char_is_word(c)).count(),
  }
  }
+
+ pub fn sticky(self) -> bool {
+ matches!(self, Assoc::BeforeSticky | Assoc::AfterSticky)
+ }
 }
 
 #[derive(Debug, Default, Clone, PartialEq, Eq)]
@@ -451,8 +461,14 @@ impl ChangeSet {
  if pos == old_pos && assoc.stay_at_gaps() {
  new_pos
  } else {
- // place to end of insert
- new_pos + assoc.insert_offset(s)
+ let ins = assoc.insert_offset(s);
+ // if the deleted and inserted text have the exact same size
+ // keep the relative offset into the new text
+ if *len == ins && assoc.sticky() {
+ new_pos + (pos - old_pos)
+ } else {
+ new_pos + assoc.insert_offset(s)
+ }
  }
  }),
  i