only keep selections invariant under replacement

Keeping selections unchanged if they are inside an exact replacement
is intuitive. However, for diagnostics this is not desirable as
helix would otherwise fail to remove diagnostics if replacing parts
of the document.

helix-core/src/selection.rs

@@ -175,16 +175,16 @@ 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());
@@ -467,16 +467,16 @@ 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

@@ -22,6 +22,22 @@ pub enum Operation {
 pub enum Assoc {
  Before,
  After,
+ BeforeSticky,
+ AfterSticky,
+}
+
+impl Assoc {
+ pub fn before(self) -> bool {
+ matches!(self, Assoc::Before | Assoc::BeforeSticky)
+ }
+
+ pub fn after(self) -> bool {
+ matches!(self, Assoc::After | Assoc::AfterSticky)
+ }
+
+ pub fn sticky(self) -> bool {
+ matches!(self, Assoc::BeforeSticky | Assoc::AfterSticky)
+ }
 }
 
 #[derive(Debug, Default, Clone, PartialEq, Eq)]
@@ -420,14 +436,14 @@ impl ChangeSet {
  old_end = old_pos + len;
  // in range of replaced text
  map!(
- |pos, assoc| (old_end > pos).then(|| {
+ |pos, assoc: Assoc| (old_end > pos).then(|| {
  // if the deleted and inserted text have the exact same size
  // keep the relative offset into the new text
- if *len == ins {
+ if *len == ins && assoc.sticky() {
  return new_pos + (pos - old_pos);
  }
  // at point or tracking before
- if pos == old_pos || assoc == Assoc::Before {
+ if pos == old_pos || assoc.before() {
  new_pos
  } else {
  // place to end of insert
@@ -439,9 +455,9 @@ impl ChangeSet {
  } else {
  // at insert point
  map!(
- |pos, assoc| (old_pos == pos).then(|| {
+ |pos, assoc: Assoc| (old_pos == pos).then(|| {
  // return position before inserted text
- if assoc == Assoc::Before {
+ if assoc.before() {
  new_pos
  } else {
  // after text
@@ -464,10 +480,14 @@ impl ChangeSet {
 
  /// Map a position through the changes.
  ///
- /// `assoc` indicates which side to associate the position with. `Before` will keep the
+ /// `assoc` indicates which size to associate the position with. `Before` will keep the
  /// position close to the character before, and will place it before insertions over that
  /// range, or at that point. `After` will move it forward, placing it at the end of such
  /// insertions.
+ ///
+ /// The "stick" variants of these two indicate that `pos` should remain
+ //// unchanged for exact replacements. This is desirable for cursors but
+ //// undesirable for other things like diagnostics
  pub fn map_pos(&self, mut pos: usize, assoc: Assoc) -> usize {
  self.update_positions(once((&mut pos, assoc)));
  pos