3 files changed, 59 insertions, 17 deletions

diff --git a/helix-term/src/commands.rs b/helix-term/src/commands.rs
index e49c780a..462d2a20 100644
--- a/helix-term/src/commands.rs
+++ b/helix-term/src/commands.rs
@@ -10,7 +10,7 @@ use helix_core::{
 use once_cell::sync::Lazy;
 
 use crate::compositor::Compositor;
-use crate::ui::Prompt;
+use crate::ui::{Prompt, PromptEvent};
 
 use helix_view::{
     document::Mode,
@@ -262,18 +262,37 @@ pub fn split_selection(cx: &mut Context) {
     //  # update state
     // }
 
+    let snapshot = cx.view.doc.state.clone();
+
     let prompt = Prompt::new(
         "split:".to_string(),
         |input: &str| Vec::new(), // this is fine because Vec::new() doesn't allocate
-        |editor: &mut Editor, input: &str| {
-            match Regex::new(input) {
-                Ok(regex) => {
+        move |editor: &mut Editor, input: &str, event: PromptEvent| {
+            match event {
+                PromptEvent::Abort => {
+                    // revert state
                     let view = editor.view_mut().unwrap();
-                    let text = &view.doc.text().slice(..);
-                    let selection = selection::split_on_matches(text, view.doc.selection(), &regex);
-                    view.doc.set_selection(selection);
+                    view.doc.state = snapshot.clone();
+                }
+                PromptEvent::Validate => {
+                    //
+                }
+                PromptEvent::Update => {
+                    match Regex::new(input) {
+                        Ok(regex) => {
+                            let view = editor.view_mut().unwrap();
+
+                            // revert state to what it was before the last update
+                            view.doc.state = snapshot.clone();
+
+                            let text = &view.doc.text().slice(..);
+                            let selection =
+                                selection::split_on_matches(text, view.doc.selection(), &regex);
+                            view.doc.set_selection(selection);
+                        }
+                        Err(_) => (), // TODO: mark command line as error
+                    }
                 }
-                Err(_) => (), // TODO: mark command line as error
             }
         },
     );
@@ -416,9 +435,15 @@ pub fn command_mode(cx: &mut Context) {
                     .filter(|command| command.contains(_input))
                     .collect()
             }, // completion
-            |editor: &mut Editor, input: &str| match input {
-                "q" => editor.should_close = true,
-                _ => (),
+            |editor: &mut Editor, input: &str, event: PromptEvent| {
+                if event != PromptEvent::Validate {
+                    return;
+                }
+
+                match input {
+                    "q" => editor.should_close = true,
+                    _ => (),
+                }
             },
         );
         compositor.push(Box::new(prompt));
diff --git a/helix-term/src/ui/mod.rs b/helix-term/src/ui/mod.rs
index bc79e09c..9a70d1bd 100644
--- a/helix-term/src/ui/mod.rs
+++ b/helix-term/src/ui/mod.rs
@@ -2,7 +2,7 @@ mod editor;
 mod prompt;
 
 pub use editor::EditorView;
-pub use prompt::Prompt;
+pub use prompt::{Prompt, PromptEvent};
 
 pub use tui::layout::Rect;
 pub use tui::style::{Color, Modifier, Style};
diff --git a/helix-term/src/ui/prompt.rs b/helix-term/src/ui/prompt.rs
index f5ef9477..07c0f917 100644
--- a/helix-term/src/ui/prompt.rs
+++ b/helix-term/src/ui/prompt.rs
@@ -12,14 +12,24 @@ pub struct Prompt {
     pub completion: Vec<String>,
     pub completion_selection_index: Option<usize>,
     completion_fn: Box<dyn FnMut(&str) -> Vec<String>>,
-    callback_fn: Box<dyn FnMut(&mut Editor, &str)>,
+    callback_fn: Box<dyn FnMut(&mut Editor, &str, PromptEvent)>,
+}
+
+#[derive(PartialEq)]
+pub enum PromptEvent {
+    /// The prompt input has been updated.
+    Update,
+    /// Validate and finalize the change.
+    Validate,
+    /// Abort the change, reverting to the initial state.
+    Abort,
 }
 
 impl Prompt {
     pub fn new(
         prompt: String,
         mut completion_fn: impl FnMut(&str) -> Vec<String> + 'static,
-        callback_fn: impl FnMut(&mut Editor, &str) + 'static,
+        callback_fn: impl FnMut(&mut Editor, &str, PromptEvent) + 'static,
     ) -> Prompt {
         Prompt {
             prompt,
@@ -160,10 +170,14 @@ impl Component for Prompt {
             KeyEvent {
                 code: KeyCode::Char(c),
                 modifiers: KeyModifiers::NONE,
-            } => self.insert_char(c),
+            } => {
+                self.insert_char(c);
+                (self.callback_fn)(cx.editor, &self.line, PromptEvent::Update);
+            }
             KeyEvent {
                 code: KeyCode::Esc, ..
             } => {
+                (self.callback_fn)(cx.editor, &self.line, PromptEvent::Abort);
                 return close_fn;
             }
             KeyEvent {
@@ -185,12 +199,15 @@ impl Component for Prompt {
             KeyEvent {
                 code: KeyCode::Backspace,
                 modifiers: KeyModifiers::NONE,
-            } => self.delete_char_backwards(),
+            } => {
+                self.delete_char_backwards();
+                (self.callback_fn)(cx.editor, &self.line, PromptEvent::Update);
+            }
             KeyEvent {
                 code: KeyCode::Enter,
                 ..
             } => {
-                (self.callback_fn)(cx.editor, &self.line);
+                (self.callback_fn)(cx.editor, &self.line, PromptEvent::Validate);
                 return close_fn;
             }
             KeyEvent {