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/history.rs

@@ -176,7 +176,7 @@ impl History {
  let pos = current_revision
  .transaction
  .changes()
- .map_pos(to, Assoc::After);
+ .map_pos(to, Assoc::AfterSticky);
  Some(pos)
  }
 

helix-core/src/selection.rs

@@ -167,16 +167,16 @@ impl Range {
  use std::cmp::Ordering;
  let (anchor, head) = match self.anchor.cmp(&self.head) {
  Ordering::Equal => (
- changes.map_pos(self.anchor, Assoc::After),
- changes.map_pos(self.head, Assoc::After),
+ changes.map_pos(self.anchor, Assoc::AfterSticky),
+ changes.map_pos(self.head, Assoc::AfterSticky),
  ),
  Ordering::Less => (
- changes.map_pos(self.anchor, Assoc::After),
- changes.map_pos(self.head, Assoc::Before),
+ changes.map_pos(self.anchor, Assoc::AfterSticky),
+ changes.map_pos(self.head, Assoc::BeforeSticky),
  ),
  Ordering::Greater => (
- changes.map_pos(self.anchor, Assoc::Before),
- changes.map_pos(self.head, Assoc::After),
+ changes.map_pos(self.anchor, Assoc::BeforeSticky),
+ changes.map_pos(self.head, Assoc::AfterSticky),
  ),
  };
 

helix-core/src/transaction.rs

@@ -19,6 +19,22 @@ 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)]
@@ -329,6 +345,9 @@ impl ChangeSet {
  /// 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 unchaged for exact replacements. This is
+ //// desirable for cursors but undesirable for other things like diagnostics
  pub fn map_pos(&self, pos: usize, assoc: Assoc) -> usize {
  use Operation::*;
  let mut old_pos = 0;
@@ -368,11 +387,11 @@ impl ChangeSet {
  if old_end > pos {
  // 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() {
  return new_pos;
  } else {
  // place to end of insert
@@ -383,7 +402,7 @@ impl ChangeSet {
  // at insert point
  if old_pos == pos {
  // return position before inserted text
- if assoc == Assoc::Before {
+ if assoc.before() {
  return new_pos;
  } else {
  // after text