Merge cea759fca5 into e76020ddb9

helix-core/src/selection.rs

@@ -184,16 +184,16 @@ 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());
@@ -482,16 +482,16 @@ 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)]
@@ -456,8 +466,14 @@ 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