Improve dedent behavior, make kill_to_line_end behave like emacs (#1173)

* restore indent when press esc right after open a new line

* add comment for restore_indent

* fix, and make kill to line end behaves like emacs

* update comment

* fix comment

* adjust cancel restore_indent situation

* check esc logic in mode transaction

* improve comment

* add more check for dedent

* update comment

* use matches to check for last_cmd

* no need to introduct CommandFun type

helix-term/src/commands.rs

@@ -173,6 +173,10 @@ pub fn doc(&self) -> &'static str {
         self.doc
     }
 
+    pub fn fun(&self) -> fn(&mut Context) {
+        self.fun
+    }
+
     #[rustfmt::skip]
     commands!(
         no_op, "Do nothing",
@@ -603,8 +607,15 @@ fn kill_to_line_end(cx: &mut Context) {
 
     let selection = doc.selection(view.id).clone().transform(|range| {
         let line = range.cursor_line(text);
-        let pos = line_end_char_index(&text, line);
-        range.put_cursor(text, pos, true)
+        let line_end_pos = line_end_char_index(&text, line);
+        let pos = range.cursor(text);
+
+        let mut new_range = range.put_cursor(text, line_end_pos, true);
+        // don't want to remove the line separator itself if the cursor doesn't reach the end of line.
+        if pos != line_end_pos {
+            new_range.head = line_end_pos;
+        }
+        new_range
     });
     delete_selection_insert_mode(doc, view, &selection);
 }
@@ -3503,12 +3514,12 @@ fn open(cx: &mut Context, open: Open) {
 }
 
 // o inserts a new line after each line with a selection
-fn open_below(cx: &mut Context) {
+pub(crate) fn open_below(cx: &mut Context) {
     open(cx, Open::Below)
 }
 
 // O inserts a new line before each line with a selection
-fn open_above(cx: &mut Context) {
+pub(crate) fn open_above(cx: &mut Context) {
     open(cx, Open::Above)
 }
 

helix-term/src/ui/editor.rs

@@ -1023,6 +1023,19 @@ fn handle_event(&mut self, event: Event, cx: &mut Context) -> EventResult {
                     (Mode::Insert, Mode::Normal) => {
                         // if exiting insert mode, remove completion
                         self.completion = None;
+
+                        let last_cmd = self.last_insert.0.fun();
+                        const OPEN_BELOW_FUN: fn(&mut commands::Context) = commands::open_below;
+                        const OPEN_ABOVE_FUN: fn(&mut commands::Context) = commands::open_above;
+                        // For user friendly,
+                        // Remove whitespaces if we go from insert mode(through open below/above) to normal mode without any keys in between.
+                        // Example: `o<esc>`.
+                        if matches!(last_cmd, OPEN_BELOW_FUN | OPEN_ABOVE_FUN)
+                            && self.last_insert.1.len() == 1
+                        {
+                            commands::Command::goto_line_start.execute(&mut cxt);
+                            commands::Command::kill_to_line_end.execute(&mut cxt);
+                        }
                     }
                     _ => (),
                 }