Improve undo of EditCommands

Address #190

Formalize the undo role of different edit commands via exhaustive
matching

Open questions:

- [ ] Undo behavior of pure moves
    * Do we want to make them undoable
    * Do we have to register them for accurate undos of true edits
- [ ] Manual backspace and delete
    * Do we want to coalesce them if a whole word is manually deleted?

src/engine.rs

@@ -3,7 +3,7 @@ use {
         completion::{CircularCompletionHandler, CompletionActionHandler},
         core_editor::Editor,
         edit_mode::{EditMode, Emacs},
-        enums::ReedlineEvent,
+        enums::{ReedlineEvent, UndoBehavior},
         hinter::{DefaultHinter, Hinter},
         history::{FileBackedHistory, History, HistoryNavigationQuery},
         painter::Painter,
@@ -820,8 +820,6 @@ impl Reedline {
                         self.wrap(position, prompt)?;
                     }
 
-                    self.editor.remember_undo_state(false);
-
                     self.repaint(prompt)?;
                 }
                 EditCommand::Backspace => self.editor.backspace(),
@@ -843,25 +841,14 @@ impl Reedline {
                 EditCommand::Redo => self.editor.redo(),
             }
 
-            if [
-                EditCommand::MoveToEnd,
-                EditCommand::MoveToStart,
-                EditCommand::MoveLeft,
-                EditCommand::MoveRight,
-                EditCommand::MoveWordLeft,
-                EditCommand::MoveWordRight,
-                EditCommand::Backspace,
-                EditCommand::Delete,
-                EditCommand::BackspaceWord,
-                EditCommand::DeleteWord,
-                EditCommand::CutFromStart,
-                EditCommand::CutToEnd,
-                EditCommand::CutWordLeft,
-                EditCommand::CutWordRight,
-            ]
-            .contains(command)
-            {
-                self.editor.remember_undo_state(true);
+            match command.undo_behavior() {
+                UndoBehavior::Ignore => {}
+                UndoBehavior::Full => {
+                    self.editor.remember_undo_state(true);
+                }
+                UndoBehavior::Coalesce => {
+                    self.editor.remember_undo_state(false);
+                }
             }
         }
 

src/enums.rs

@@ -91,6 +91,58 @@ pub enum EditCommand {
     Redo,
 }
 
+impl EditCommand {
+    /// Determine if a certain operation should be undoable
+    /// or if the operations should be coalesced for undoing
+    pub fn undo_behavior(&self) -> UndoBehavior {
+        match self {
+            // Cursor moves
+            EditCommand::MoveToStart
+            | EditCommand::MoveToEnd
+            | EditCommand::MoveLeft
+            | EditCommand::MoveRight
+            | EditCommand::MoveWordLeft
+            | EditCommand::MoveWordRight => UndoBehavior::Ignore,
+
+            // Coalesceable insert
+            EditCommand::InsertChar(_) => UndoBehavior::Coalesce,
+
+            // Full edits
+            EditCommand::Backspace
+            | EditCommand::Delete
+            | EditCommand::BackspaceWord
+            | EditCommand::DeleteWord
+            | EditCommand::Clear
+            | EditCommand::CutFromStart
+            | EditCommand::CutToEnd
+            | EditCommand::CutWordLeft
+            | EditCommand::CutWordRight
+            | EditCommand::PasteCutBuffer
+            | EditCommand::UppercaseWord
+            | EditCommand::LowercaseWord
+            | EditCommand::CapitalizeChar
+            | EditCommand::SwapWords
+            | EditCommand::SwapGraphemes => UndoBehavior::Full,
+
+            EditCommand::Undo | EditCommand::Redo => UndoBehavior::Ignore,
+        }
+    }
+}
+
+/// Specifies how the (previously executed) operation should be treated in the Undo stack.
+pub enum UndoBehavior {
+    /// Operation is not affecting the LineBuffers content and should be ignored
+    ///
+    /// e.g. the undo commands themselves are not stored in the undo stack
+    Ignore,
+    /// The operation is one logical unit of work that should be stored in the undo stack
+    Full,
+    /// The operation is a single operation that should be best coalesced in logical units such as words
+    ///
+    /// e.g. insertion of characters by typing
+    Coalesce,
+}
+
 /// Reedline supported actions.
 #[derive(Serialize, Deserialize, Clone, PartialEq, Eq, Debug)]
 pub enum ReedlineEvent {

src/lib.rs

@@ -192,7 +192,7 @@ pub use core_editor::LineBuffer;
 mod text_manipulation;
 
 mod enums;
-pub use enums::{EditCommand, ReedlineEvent, Signal};
+pub use enums::{EditCommand, ReedlineEvent, Signal, UndoBehavior};
 
 mod painter;