Implement in-memory prompt history

Implementation is similar to kakoune: we store the entries into
a register.

5 files changed, 70 insertions, 9 deletions

diff --git a/helix-core/src/register.rs b/helix-core/src/register.rs
index cc881a17..c3e6652e 100644
--- a/helix-core/src/register.rs
+++ b/helix-core/src/register.rs
@@ -22,13 +22,17 @@ impl Register {
         self.name
     }
 
-    pub fn read(&self) -> &Vec<String> {
+    pub fn read(&self) -> &[String] {
         &self.values
     }
 
     pub fn write(&mut self, values: Vec<String>) {
         self.values = values;
     }
+
+    pub fn push(&mut self, value: String) {
+        self.values.push(value);
+    }
 }
 
 /// Currently just wraps a `HashMap` of `Register`s
@@ -42,11 +46,7 @@ impl Registers {
         self.inner.get(&name)
     }
 
-    pub fn get_mut(&mut self, name: char) -> Option<&mut Register> {
-        self.inner.get_mut(&name)
-    }
-
-    pub fn get_or_insert(&mut self, name: char) -> &mut Register {
+    pub fn get_mut(&mut self, name: char) -> &mut Register {
         self.inner
             .entry(name)
             .or_insert_with(|| Register::new(name))
@@ -57,7 +57,7 @@ impl Registers {
             .insert(name, Register::new_with_values(name, values));
     }
 
-    pub fn read(&self, name: char) -> Option<&Vec<String>> {
+    pub fn read(&self, name: char) -> Option<&[String]> {
         self.get(name).map(|reg| reg.read())
     }
 }
diff --git a/helix-term/src/commands.rs b/helix-term/src/commands.rs
index 06dca5d5..c51453b0 100644
--- a/helix-term/src/commands.rs
+++ b/helix-term/src/commands.rs
@@ -1126,7 +1126,7 @@ fn delete_selection(cx: &mut Context) {
     let reg_name = cx.selected_register.name();
     let (view, doc) = current!(cx.editor);
     let registers = &mut cx.editor.registers;
-    let reg = registers.get_or_insert(reg_name);
+    let reg = registers.get_mut(reg_name);
     delete_selection_impl(reg, doc, view.id);
 
     doc.append_changes_to_history(view.id);
@@ -1139,7 +1139,7 @@ fn change_selection(cx: &mut Context) {
     let reg_name = cx.selected_register.name();
     let (view, doc) = current!(cx.editor);
     let registers = &mut cx.editor.registers;
-    let reg = registers.get_or_insert(reg_name);
+    let reg = registers.get_mut(reg_name);
     delete_selection_impl(reg, doc, view.id);
     enter_insert_mode(doc);
 }
@@ -1920,6 +1920,7 @@ mod cmd {
 fn command_mode(cx: &mut Context) {
     let mut prompt = Prompt::new(
         ":".to_owned(),
+        Some(':'),
         |input: &str| {
             // we use .this over split_whitespace() because we care about empty segments
             let parts = input.split(' ').collect::<Vec<&str>>();
diff --git a/helix-term/src/ui/mod.rs b/helix-term/src/ui/mod.rs
index 288d3d2e..9e71cfe7 100644
--- a/helix-term/src/ui/mod.rs
+++ b/helix-term/src/ui/mod.rs
@@ -36,6 +36,7 @@ pub fn regex_prompt(
 
     Prompt::new(
         prompt,
+        None,
         |_input: &str| Vec::new(), // this is fine because Vec::new() doesn't allocate
         move |cx: &mut crate::compositor::Context, input: &str, event: PromptEvent| {
             match event {
diff --git a/helix-term/src/ui/picker.rs b/helix-term/src/ui/picker.rs
index 733be2fc..0b67cd9c 100644
--- a/helix-term/src/ui/picker.rs
+++ b/helix-term/src/ui/picker.rs
@@ -43,6 +43,7 @@ impl<T> Picker<T> {
     ) -> Self {
         let prompt = Prompt::new(
             "".to_string(),
+            None,
             |_pattern: &str| Vec::new(),
             |_editor: &mut Context, _pattern: &str, _event: PromptEvent| {
                 //
diff --git a/helix-term/src/ui/prompt.rs b/helix-term/src/ui/prompt.rs
index 2df1e281..57daef3a 100644
--- a/helix-term/src/ui/prompt.rs
+++ b/helix-term/src/ui/prompt.rs
@@ -20,6 +20,8 @@ pub struct Prompt {
     cursor: usize,
     completion: Vec<Completion>,
     selection: Option<usize>,
+    history_register: Option<char>,
+    history_pos: Option<usize>,
     completion_fn: Box<dyn FnMut(&str) -> Vec<Completion>>,
     callback_fn: Box<dyn FnMut(&mut Context, &str, PromptEvent)>,
     pub doc_fn: Box<dyn Fn(&str) -> Option<&'static str>>,
@@ -54,6 +56,7 @@ pub enum Movement {
 impl Prompt {
     pub fn new(
         prompt: String,
+        history_register: Option<char>,
         mut completion_fn: impl FnMut(&str) -> Vec<Completion> + 'static,
         callback_fn: impl FnMut(&mut Context, &str, PromptEvent) + 'static,
     ) -> Self {
@@ -63,6 +66,8 @@ impl Prompt {
             cursor: 0,
             completion: completion_fn(""),
             selection: None,
+            history_register,
+            history_pos: None,
             completion_fn: Box::new(completion_fn),
             callback_fn: Box::new(callback_fn),
             doc_fn: Box::new(|_| None),
@@ -226,6 +231,28 @@ impl Prompt {
         self.exit_selection();
     }
 
+    pub fn change_history(&mut self, register: &[String], direction: CompletionDirection) {
+        if register.is_empty() {
+            return;
+        }
+
+        let end = register.len().saturating_sub(1);
+
+        let index = match direction {
+            CompletionDirection::Forward => self.history_pos.map_or(0, |i| i + 1),
+            CompletionDirection::Backward => {
+                self.history_pos.unwrap_or(register.len()).saturating_sub(1)
+            }
+        }
+        .min(end);
+
+        self.line = register[index].clone();
+
+        self.history_pos = Some(index);
+
+        self.move_end();
+    }
+
     pub fn change_completion_selection(&mut self, direction: CompletionDirection) {
         if self.completion.is_empty() {
             return;
@@ -468,10 +495,41 @@ impl Component for Prompt {
                     self.exit_selection();
                 } else {
                     (self.callback_fn)(cx, &self.line, PromptEvent::Validate);
+
+                    if let Some(register) = self.history_register {
+                        // store in history
+                        let register = cx.editor.registers.get_mut(register);
+                        register.push(self.line.clone());
+                    }
                     return close_fn;
                 }
             }
             KeyEvent {
+                code: KeyCode::Char('p'),
+                modifiers: KeyModifiers::CONTROL,
+            }
+            | KeyEvent {
+                code: KeyCode::Up, ..
+            } => {
+                if let Some(register) = self.history_register {
+                    let register = cx.editor.registers.get_mut(register);
+                    self.change_history(register.read(), CompletionDirection::Backward);
+                }
+            }
+            KeyEvent {
+                code: KeyCode::Char('n'),
+                modifiers: KeyModifiers::CONTROL,
+            }
+            | KeyEvent {
+                code: KeyCode::Down,
+                ..
+            } => {
+                if let Some(register) = self.history_register {
+                    let register = cx.editor.registers.get_mut(register);
+                    self.change_history(register.read(), CompletionDirection::Forward);
+                }
+            }
+            KeyEvent {
                 code: KeyCode::Tab, ..
             } => self.change_completion_selection(CompletionDirection::Forward),
             KeyEvent {