Add file explorer and tree helper

ref: https://github.com/helix-editor/helix/issues/200
ref: https://github.com/helix-editor/helix/pull/2377
ref: https://github.com/helix-editor/helix/pull/5566
ref: https://github.com/helix-editor/helix/pull/5768

Co-authored-by: cossonleo <cossonleo@foxmail.com>
Co-authored-by: JJ <git@toki.la>
Co-authored-by: Quan Tong <quantonganh@gmail.com>

6 files changed, 4215 insertions, 28 deletions

diff --git a/helix-term/src/ui/editor.rs b/helix-term/src/ui/editor.rs
index ad7aa5c5..7d28b62c 100644
--- a/helix-term/src/ui/editor.rs
+++ b/helix-term/src/ui/editor.rs
@@ -6,7 +6,7 @@ use crate::{
     keymap::{KeymapResult, Keymaps},
     ui::{
         document::{render_document, LinePos, TextRenderer, TranslatedPosition},
-        Completion, ProgressSpinners,
+        Completion, Explorer, ProgressSpinners,
     },
 };
 
@@ -23,7 +23,7 @@ use helix_core::{
 };
 use helix_view::{
     document::{Mode, SavePoint, SCRATCH_BUFFER_NAME},
-    editor::{CompleteAction, CursorShapeConfig},
+    editor::{CompleteAction, CursorShapeConfig, ExplorerPosition},
     graphics::{Color, CursorKind, Modifier, Rect, Style},
     input::{KeyEvent, MouseButton, MouseEvent, MouseEventKind},
     keyboard::{KeyCode, KeyModifiers},
@@ -42,6 +42,7 @@ pub struct EditorView {
     pseudo_pending: Vec<KeyEvent>,
     pub(crate) last_insert: (commands::MappableCommand, Vec<InsertEvent>),
     pub(crate) completion: Option<Completion>,
+    pub(crate) explorer: Option<Explorer>,
     spinners: ProgressSpinners,
     /// Tracks if the terminal window is focused by reaction to terminal focus events
     terminal_focused: bool,
@@ -72,6 +73,7 @@ impl EditorView {
             pseudo_pending: Vec::new(),
             last_insert: (commands::MappableCommand::normal_mode, Vec::new()),
             completion: None,
+            explorer: None,
             spinners: ProgressSpinners::default(),
             terminal_focused: true,
         }
@@ -1288,6 +1290,11 @@ impl Component for EditorView {
         event: &Event,
         context: &mut crate::compositor::Context,
     ) -> EventResult {
+        if let Some(explore) = self.explorer.as_mut() {
+            if let EventResult::Consumed(callback) = explore.handle_event(event, context) {
+                return EventResult::Consumed(callback);
+            }
+        }
         let mut cx = commands::Context {
             editor: context.editor,
             count: None,
@@ -1445,6 +1452,8 @@ impl Component for EditorView {
         surface.set_style(area, cx.editor.theme.get("ui.background"));
         let config = cx.editor.config();
 
+        let editor_area = area.clip_bottom(1);
+
         // check if bufferline should be rendered
         use helix_view::editor::BufferLine;
         let use_bufferline = match config.bufferline {
@@ -1453,17 +1462,47 @@ impl Component for EditorView {
             _ => false,
         };
 
-        // -1 for commandline and -1 for bufferline
-        let mut editor_area = area.clip_bottom(1);
-        if use_bufferline {
-            editor_area = editor_area.clip_top(1);
-        }
+        let editor_area = if use_bufferline {
+            editor_area.clip_top(1)
+        } else {
+            editor_area
+        };
+
+        let bufferline_area = area.with_height(1);
+        let (editor_area, bufferline_area) = if let Some(explorer) = &self.explorer {
+            let explorer_column_width = if explorer.is_opened() {
+                explorer.column_width().saturating_add(2)
+            } else {
+                0
+            };
+            // For future developer:
+            // We should have a Dock trait that allows a component to dock to the top/left/bottom/right
+            // of another component.
+            match config.explorer.position {
+                ExplorerPosition::Left => (
+                    editor_area.clip_left(explorer_column_width),
+                    bufferline_area.clip_left(explorer_column_width),
+                ),
+                ExplorerPosition::Right => (
+                    editor_area.clip_right(explorer_column_width),
+                    bufferline_area.clip_left(explorer_column_width),
+                ),
+            }
+        } else {
+            (editor_area, bufferline_area)
+        };
 
         // if the terminal size suddenly changed, we need to trigger a resize
         cx.editor.resize(editor_area);
 
+        if let Some(explorer) = self.explorer.as_mut() {
+            if !explorer.is_focus() {
+                explorer.render(area, surface, cx);
+            }
+        }
+
         if use_bufferline {
-            Self::render_bufferline(cx.editor, area.with_height(1), surface);
+            Self::render_bufferline(cx.editor, bufferline_area, surface);
         }
 
         for (view, is_focused) in cx.editor.tree.views() {
@@ -1540,9 +1579,23 @@ impl Component for EditorView {
         if let Some(completion) = self.completion.as_mut() {
             completion.render(area, surface, cx);
         }
+
+        if let Some(explore) = self.explorer.as_mut() {
+            if explore.is_focus() {
+                explore.render(area, surface, cx);
+            }
+        }
     }
 
     fn cursor(&self, _area: Rect, editor: &Editor) -> (Option<Position>, CursorKind) {
+        if let Some(explore) = &self.explorer {
+            if explore.is_focus() {
+                let cursor = explore.cursor(_area, editor);
+                if cursor.0.is_some() {
+                    return cursor;
+                }
+            }
+        }
         match editor.cursor() {
             // all block cursors are drawn manually
             (pos, CursorKind::Block) => {
diff --git a/helix-term/src/ui/explorer.rs b/helix-term/src/ui/explorer.rs
new file mode 100644
index 00000000..6a7b631d
--- /dev/null
+++ b/helix-term/src/ui/explorer.rs
@@ -0,0 +1,1464 @@
+use super::{Prompt, TreeOp, TreeView, TreeViewItem};
+use crate::{
+    compositor::{Component, Context, EventResult},
+    ctrl, key, shift, ui,
+};
+use anyhow::{bail, ensure, Result};
+use helix_core::Position;
+use helix_view::{
+    editor::{Action, ExplorerPosition},
+    graphics::{CursorKind, Rect},
+    info::Info,
+    input::{Event, KeyEvent},
+    theme::Modifier,
+    Editor,
+};
+use std::cmp::Ordering;
+use std::path::{Path, PathBuf};
+use std::{borrow::Cow, fs::DirEntry};
+use tui::{
+    buffer::Buffer as Surface,
+    widgets::{Block, Borders, Widget},
+};
+
+#[derive(PartialEq, Eq, PartialOrd, Ord, Debug, Clone, Copy)]
+enum FileType {
+    File,
+    Folder,
+    Root,
+}
+
+#[derive(PartialEq, Eq, Debug, Clone)]
+struct FileInfo {
+    file_type: FileType,
+    path: PathBuf,
+}
+
+impl FileInfo {
+    fn root(path: PathBuf) -> Self {
+        Self {
+            file_type: FileType::Root,
+            path,
+        }
+    }
+
+    fn get_text(&self) -> Cow<'static, str> {
+        let text = match self.file_type {
+            FileType::Root => self.path.display().to_string(),
+            FileType::File | FileType::Folder => self
+                .path
+                .file_name()
+                .map_or("/".into(), |p| p.to_string_lossy().into_owned()),
+        };
+
+        #[cfg(test)]
+        let text = text.replace(std::path::MAIN_SEPARATOR, "/");
+
+        text.into()
+    }
+}
+
+impl PartialOrd for FileInfo {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for FileInfo {
+    fn cmp(&self, other: &Self) -> Ordering {
+        use FileType::*;
+        match (self.file_type, other.file_type) {
+            (Root, _) => return Ordering::Less,
+            (_, Root) => return Ordering::Greater,
+            _ => {}
+        };
+
+        if let (Some(p1), Some(p2)) = (self.path.parent(), other.path.parent()) {
+            if p1 == p2 {
+                match (self.file_type, other.file_type) {
+                    (Folder, File) => return Ordering::Less,
+                    (File, Folder) => return Ordering::Greater,
+                    _ => {}
+                };
+            }
+        }
+        self.path.cmp(&other.path)
+    }
+}
+
+impl TreeViewItem for FileInfo {
+    type Params = State;
+
+    fn get_children(&self) -> Result<Vec<Self>> {
+        match self.file_type {
+            FileType::Root | FileType::Folder => {}
+            _ => return Ok(vec![]),
+        };
+        let ret: Vec<_> = std::fs::read_dir(&self.path)?
+            .filter_map(|entry| entry.ok())
+            .filter_map(|entry| dir_entry_to_file_info(entry, &self.path))
+            .collect();
+        Ok(ret)
+    }
+
+    fn name(&self) -> String {
+        self.get_text().to_string()
+    }
+
+    fn is_parent(&self) -> bool {
+        matches!(self.file_type, FileType::Folder | FileType::Root)
+    }
+}
+
+fn dir_entry_to_file_info(entry: DirEntry, path: &Path) -> Option<FileInfo> {
+    entry.metadata().ok().map(|meta| {
+        let file_type = match meta.is_dir() {
+            true => FileType::Folder,
+            false => FileType::File,
+        };
+        FileInfo {
+            file_type,
+            path: path.join(entry.file_name()),
+        }
+    })
+}
+
+#[derive(Clone, Debug)]
+enum PromptAction {
+    CreateFileOrFolder,
+    RemoveFolder,
+    RemoveFile,
+    RenameFile,
+}
+
+#[derive(Clone, Debug, Default)]
+struct State {
+    focus: bool,
+    open: bool,
+    current_root: PathBuf,
+    area_width: u16,
+}
+
+impl State {
+    fn new(focus: bool, current_root: PathBuf) -> Self {
+        Self {
+            focus,
+            current_root,
+            open: true,
+            area_width: 0,
+        }
+    }
+}
+
+struct ExplorerHistory {
+    tree: TreeView<FileInfo>,
+    current_root: PathBuf,
+}
+
+pub struct Explorer {
+    tree: TreeView<FileInfo>,
+    history: Vec<ExplorerHistory>,
+    show_help: bool,
+    state: State,
+    prompt: Option<(PromptAction, Prompt)>,
+    #[allow(clippy::type_complexity)]
+    on_next_key: Option<Box<dyn FnMut(&mut Context, &mut Self, &KeyEvent) -> EventResult>>,
+    column_width: u16,
+}
+
+impl Explorer {
+    pub fn new(cx: &mut Context) -> Result<Self> {
+        let current_root = std::env::current_dir()
+            .unwrap_or_else(|_| "./".into())
+            .canonicalize()?;
+        Ok(Self {
+            tree: Self::new_tree_view(current_root.clone())?,
+            history: vec![],
+            show_help: false,
+            state: State::new(true, current_root),
+            prompt: None,
+            on_next_key: None,
+            column_width: cx.editor.config().explorer.column_width as u16,
+        })
+    }
+
+    #[cfg(test)]
+    fn from_path(root: PathBuf, column_width: u16) -> Result<Self> {
+        Ok(Self {
+            tree: Self::new_tree_view(root.clone())?,
+            history: vec![],
+            show_help: false,
+            state: State::new(true, root),
+            prompt: None,
+            on_next_key: None,
+            column_width,
+        })
+    }
+
+    fn new_tree_view(root: PathBuf) -> Result<TreeView<FileInfo>> {
+        let root = FileInfo::root(root);
+        Ok(TreeView::build_tree(root)?.with_enter_fn(Self::toggle_current))
+    }
+
+    fn push_history(&mut self, tree_view: TreeView<FileInfo>, current_root: PathBuf) {
+        self.history.push(ExplorerHistory {
+            tree: tree_view,
+            current_root,
+        });
+        const MAX_HISTORY_SIZE: usize = 20;
+        Vec::truncate(&mut self.history, MAX_HISTORY_SIZE)
+    }
+
+    fn change_root(&mut self, root: PathBuf) -> Result<()> {
+        if self.state.current_root.eq(&root) {
+            return Ok(());
+        }
+        let tree = Self::new_tree_view(root.clone())?;
+        let old_tree = std::mem::replace(&mut self.tree, tree);
+        self.push_history(old_tree, self.state.current_root.clone());
+        self.state.current_root = root;
+        Ok(())
+    }
+
+    pub fn reveal_file(&mut self, path: PathBuf) -> Result<()> {
+        let current_root = &self.state.current_root.canonicalize()?;
+        let current_path = &path.canonicalize()?;
+        let segments = {
+            let stripped = match current_path.strip_prefix(current_root) {
+                Ok(stripped) => Ok(stripped),
+                Err(_) => {
+                    let parent = path.parent().ok_or_else(|| {
+                        anyhow::anyhow!("Failed get parent of '{}'", current_path.to_string_lossy())
+                    })?;
+                    self.change_root(parent.into())?;
+                    current_path
+                        .strip_prefix(parent.canonicalize()?)
+                        .map_err(|_| {
+                            anyhow::anyhow!(
+                                "Failed to strip prefix (parent) '{}' from '{}'",
+                                parent.to_string_lossy(),
+                                current_path.to_string_lossy()
+                            )
+                        })
+                }
+            }?;
+
+            stripped
+                .components()
+                .map(|c| c.as_os_str().to_string_lossy().to_string())
+                .collect::<Vec<_>>()
+        };
+        self.tree.reveal_item(segments)?;
+        Ok(())
+    }
+
+    pub fn reveal_current_file(&mut self, cx: &mut Context) -> Result<()> {
+        self.focus();
+        let current_document_path = doc!(cx.editor).path().cloned();
+        match current_document_path {
+            None => Ok(()),
+            Some(current_path) => self.reveal_file(current_path),
+        }
+    }
+
+    pub fn focus(&mut self) {
+        self.state.focus = true;
+        self.state.open = true;
+    }
+
+    fn unfocus(&mut self) {
+        self.state.focus = false;
+    }
+
+    fn close(&mut self) {
+        self.state.focus = false;
+        self.state.open = false;
+    }
+
+    pub fn is_focus(&self) -> bool {
+        self.state.focus
+    }
+
+    fn new_create_file_or_folder_prompt(&mut self, cx: &mut Context) -> Result<()> {
+        let folder_path = self.nearest_folder()?;
+        self.prompt = Some((
+            PromptAction::CreateFileOrFolder,
+            Prompt::new(
+                format!(
+                    " New file or folder (ends with '{}'): ",
+                    std::path::MAIN_SEPARATOR
+                )
+                .into(),
+                None,
+                ui::completers::none,
+                |_, _, _| {},
+            )
+            .with_line(format!("{}/", folder_path.to_string_lossy()), cx.editor),
+        ));
+        Ok(())
+    }
+
+    fn nearest_folder(&self) -> Result<PathBuf> {
+        let current = self.tree.current()?.item();
+        if current.is_parent() {
+            Ok(current.path.to_path_buf())
+        } else {
+            let parent_path = current.path.parent().ok_or_else(|| {
+                anyhow::anyhow!(format!(
+                    "Unable to get parent path of '{}'",
+                    current.path.to_string_lossy()
+                ))
+            })?;
+            Ok(parent_path.to_path_buf())
+        }
+    }
+
+    fn new_remove_prompt(&mut self) -> Result<()> {
+        let item = self.tree.current()?.item();
+        match item.file_type {
+            FileType::Folder => self.new_remove_folder_prompt(),
+            FileType::File => self.new_remove_file_prompt(),
+            FileType::Root => bail!("Root is not removable"),
+        }
+    }
+
+    fn new_rename_prompt(&mut self, cx: &mut Context) -> Result<()> {
+        let path = self.tree.current_item()?.path.clone();
+        self.prompt = Some((
+            PromptAction::RenameFile,
+            Prompt::new(
+                " Rename to ".into(),
+                None,
+                ui::completers::none,
+                |_, _, _| {},
+            )
+            .with_line(path.to_string_lossy().to_string(), cx.editor),
+        ));
+        Ok(())
+    }
+
+    fn new_remove_file_prompt(&mut self) -> Result<()> {
+        let item = self.tree.current_item()?;
+        ensure!(
+            item.path.is_file(),
+            "The path '{}' is not a file",
+            item.path.to_string_lossy()
+        );
+        self.prompt = Some((
+            PromptAction::RemoveFile,
+            Prompt::new(
+                format!(" Delete file: '{}'? y/N: ", item.path.display()).into(),
+                None,
+                ui::completers::none,
+                |_, _, _| {},
+            ),
+        ));
+        Ok(())
+    }
+
+    fn new_remove_folder_prompt(&mut self) -> Result<()> {
+        let item = self.tree.current_item()?;
+        ensure!(
+            item.path.is_dir(),
+            "The path '{}' is not a folder",
+            item.path.to_string_lossy()
+        );
+
+        self.prompt = Some((
+            PromptAction::RemoveFolder,
+            Prompt::new(
+                format!(" Delete folder: '{}'? y/N: ", item.path.display()).into(),
+                None,
+                ui::completers::none,
+                |_, _, _| {},
+            ),
+        ));
+        Ok(())
+    }
+
+    fn toggle_current(item: &mut FileInfo, cx: &mut Context, state: &mut State) -> TreeOp {
+        (|| -> Result<TreeOp> {
+            if item.path == Path::new("") {
+                return Ok(TreeOp::Noop);
+            }
+            let meta = std::fs::metadata(&item.path)?;
+            if meta.is_file() {
+                cx.editor.open(&item.path, Action::Replace)?;
+                state.focus = false;
+                return Ok(TreeOp::Noop);
+            }
+
+            if item.path.is_dir() {
+                return Ok(TreeOp::GetChildsAndInsert);
+            }
+
+            Err(anyhow::anyhow!("Unknown file type: {:?}", meta.file_type()))
+        })()
+        .unwrap_or_else(|err| {
+            cx.editor.set_error(format!("{err}"));
+            TreeOp::Noop
+        })
+    }
+
+    fn render_tree(
+        &mut self,
+        area: Rect,
+        prompt_area: Rect,
+        surface: &mut Surface,
+        cx: &mut Context,
+    ) {
+        self.tree.render(area, prompt_area, surface, cx);
+    }
+
+    fn render_embed(
+        &mut self,
+        area: Rect,
+        surface: &mut Surface,
+        cx: &mut Context,
+        position: &ExplorerPosition,
+    ) {
+        if !self.state.open {
+            return;
+        }
+        let width = area.width.min(self.column_width + 2);
+
+        self.state.area_width = area.width;
+
+        let side_area = match position {
+            ExplorerPosition::Left => Rect { width, ..area },
+            ExplorerPosition::Right => Rect {
+                x: area.width - width,
+                width,
+                ..area
+            },
+        }
+        .clip_bottom(1);
+        let background = cx.editor.theme.get("ui.background");
+        surface.clear_with(side_area, background);
+
+        let prompt_area = area.clip_top(side_area.height);
+
+        let list_area = match position {
+            ExplorerPosition::Left => {
+                render_block(side_area.clip_left(1), surface, Borders::RIGHT).clip_bottom(1)
+            }
+            ExplorerPosition::Right => {
+                render_block(side_area.clip_right(1), surface, Borders::LEFT).clip_bottom(1)
+            }
+        };
+        self.render_tree(list_area, prompt_area, surface, cx);
+
+        {
+            let statusline = if self.is_focus() {
+                cx.editor.theme.get("ui.statusline")
+            } else {
+                cx.editor.theme.get("ui.statusline.inactive")
+            };
+            let area = side_area.clip_top(list_area.height);
+            let area = match position {
+                ExplorerPosition::Left => area.clip_right(1),
+                ExplorerPosition::Right => area.clip_left(1),
+            };
+            surface.clear_with(area, statusline);
+
+            let title_style = cx.editor.theme.get("ui.text");
+            let title_style = if self.is_focus() {
+                title_style.add_modifier(Modifier::BOLD)
+            } else {
+                title_style
+            };
+            surface.set_stringn(
+                area.x,
+                area.y,
+                if self.is_focus() {
+                    " EXPLORER: press ? for help"
+                } else {
+                    " EXPLORER"
+                },
+                area.width.into(),
+                title_style,
+            );
+        }
+
+        if self.is_focus() && self.show_help {
+            let help_area = match position {
+                ExplorerPosition::Left => area,
+                ExplorerPosition::Right => area.clip_right(list_area.width.saturating_add(2)),
+            };
+            self.render_help(help_area, surface, cx);
+        }
+
+        if let Some((_, prompt)) = self.prompt.as_mut() {
+            prompt.render_prompt(prompt_area, surface, cx)
+        }
+    }
+
+    fn render_help(&mut self, area: Rect, surface: &mut Surface, cx: &mut Context) {
+        Info::new(
+            "Explorer",
+            &[
+                ("?", "Toggle help"),
+                ("a", "Add file/folder"),
+                ("r", "Rename file/folder"),
+                ("d", "Delete file"),
+                ("B", "Change root to parent folder"),
+                ("]", "Change root to current folder"),
+                ("[", "Go to previous root"),
+                ("+, =", "Increase size"),
+                ("-, _", "Decrease size"),
+                ("q", "Close"),
+            ]
+            .into_iter()
+            .chain(ui::tree::tree_view_help().into_iter())
+            .collect::<Vec<_>>(),
+        )
+        .render(area, surface, cx)
+    }
+
+    fn handle_prompt_event(&mut self, event: &KeyEvent, cx: &mut Context) -> EventResult {
+        let result = (|| -> Result<EventResult> {
+            let (action, mut prompt) = match self.prompt.take() {
+                Some((action, p)) => (action, p),
+                _ => return Ok(EventResult::Ignored(None)),
+            };
+            let line = prompt.line();
+
+            let current_item_path = self.tree.current_item()?.path.clone();
+            match (&action, event) {
+                (PromptAction::CreateFileOrFolder, key!(Enter)) => {
+                    if line.ends_with(std::path::MAIN_SEPARATOR) {
+                        self.new_folder(line)?
+                    } else {
+                        self.new_file(line)?
+                    }
+                }
+                (PromptAction::RemoveFolder, key) => {
+                    if let key!('y') = key {
+                        close_documents(current_item_path, cx)?;
+                        self.remove_folder()?;
+                    }
+                }
+                (PromptAction::RemoveFile, key) => {
+                    if let key!('y') = key {
+                        close_documents(current_item_path, cx)?;
+                        self.remove_file()?;
+                    }
+                }
+                (PromptAction::RenameFile, key!(Enter)) => {
+                    close_documents(current_item_path, cx)?;
+                    self.rename_current(line)?;
+                }
+                (_, key!(Esc) | ctrl!('c')) => {}
+                _ => {
+                    prompt.handle_event(&Event::Key(*event), cx);
+                    self.prompt = Some((action, prompt));
+                }
+            }
+            Ok(EventResult::Consumed(None))
+        })();
+        match result {
+            Ok(event_result) => event_result,
+            Err(err) => {
+                cx.editor.set_error(err.to_string());
+                EventResult::Consumed(None)
+            }
+        }
+    }
+
+    fn new_file(&mut self, path: &str) -> Result<()> {
+        let path = helix_stdx::path::normalize(PathBuf::from(path));
+        if let Some(parent) = path.parent() {
+            std::fs::create_dir_all(parent)?;
+        }
+        let mut fd = std::fs::OpenOptions::new();
+        fd.create_new(true).write(true).open(&path)?;
+        self.tree.refresh()?;
+        self.reveal_file(path)
+    }
+
+    fn new_folder(&mut self, path: &str) -> Result<()> {
+        let path = helix_stdx::path::normalize(PathBuf::from(path));
+        std::fs::create_dir_all(&path)?;
+        self.tree.refresh()?;
+        self.reveal_file(path)
+    }
+
+    fn toggle_help(&mut self) {
+        self.show_help = !self.show_help
+    }
+
+    fn go_to_previous_root(&mut self) {
+        if let Some(history) = self.history.pop() {
+            self.tree = history.tree;
+            self.state.current_root = history.current_root
+        }
+    }
+
+    fn change_root_to_current_folder(&mut self) -> Result<()> {
+        self.change_root(self.tree.current_item()?.path.clone())
+    }
+
+    fn change_root_parent_folder(&mut self) -> Result<()> {
+        if let Some(parent) = self.state.current_root.parent() {
+            let path = parent.to_path_buf();
+            self.change_root(path)
+        } else {
+            Ok(())
+        }
+    }
+
+    pub fn is_opened(&self) -> bool {
+        self.state.open
+    }
+
+    pub fn column_width(&self) -> u16 {
+        self.column_width
+    }
+
+    fn increase_size(&mut self) {
+        const EDITOR_MIN_WIDTH: u16 = 10;
+        self.column_width = std::cmp::min(
+            self.state.area_width.saturating_sub(EDITOR_MIN_WIDTH),
+            self.column_width.saturating_add(1),
+        )
+    }
+
+    fn decrease_size(&mut self) {
+        self.column_width = self.column_width.saturating_sub(1)
+    }
+
+    fn rename_current(&mut self, line: &String) -> Result<()> {
+        let item = self.tree.current_item()?;
+        let path = PathBuf::from(line);
+        if let Some(parent) = path.parent() {
+            std::fs::create_dir_all(parent)?;
+        }
+        std::fs::rename(&item.path, &path)?;
+        self.tree.refresh()?;
+        self.reveal_file(path)
+    }
+
+    fn remove_folder(&mut self) -> Result<()> {
+        let item = self.tree.current_item()?;
+        std::fs::remove_dir_all(&item.path)?;
+        self.tree.refresh()
+    }
+
+    fn remove_file(&mut self) -> Result<()> {
+        let item = self.tree.current_item()?;
+        std::fs::remove_file(&item.path)?;
+        self.tree.refresh()
+    }
+}
+
+fn close_documents(current_item_path: PathBuf, cx: &mut Context) -> Result<()> {
+    let ids = cx
+        .editor
+        .documents
+        .iter()
+        .filter_map(|(id, doc)| {
+            if doc.path()?.starts_with(&current_item_path) {
+                Some(*id)
+            } else {
+                None
+            }
+        })
+        .collect::<Vec<_>>();
+
+    for id in ids {
+        cx.editor.close_document(id, true)?;
+    }
+    Ok(())
+}
+
+impl Component for Explorer {
+    /// Process input events, return true if handled.
+    fn handle_event(&mut self, event: &Event, cx: &mut Context) -> EventResult {
+        if self.tree.prompting() {
+            return self.tree.handle_event(event, cx, &mut self.state);
+        }
+        let key_event = match event {
+            Event::Key(event) => event,
+            Event::Resize(..) => return EventResult::Consumed(None),
+            _ => return EventResult::Ignored(None),
+        };
+        if !self.is_focus() {
+            return EventResult::Ignored(None);
+        }
+        if let Some(mut on_next_key) = self.on_next_key.take() {
+            return on_next_key(cx, self, key_event);
+        }
+
+        if let EventResult::Consumed(c) = self.handle_prompt_event(key_event, cx) {
+            return EventResult::Consumed(c);
+        }
+
+        (|| -> Result<()> {
+            match key_event {
+                key!(Esc) => self.unfocus(),
+                key!('q') => self.close(),
+                key!('?') => self.toggle_help(),
+                key!('a') => self.new_create_file_or_folder_prompt(cx)?,
+                shift!('B') => self.change_root_parent_folder()?,
+                key!(']') => self.change_root_to_current_folder()?,
+                key!('[') => self.go_to_previous_root(),
+                key!('d') => self.new_remove_prompt()?,
+                key!('r') => self.new_rename_prompt(cx)?,
+                key!('-') | key!('_') => self.decrease_size(),
+                key!('+') | key!('=') => self.increase_size(),
+                _ => {
+                    self.tree
+                        .handle_event(&Event::Key(*key_event), cx, &mut self.state);
+                }
+            };
+            Ok(())
+        })()
+        .unwrap_or_else(|err| cx.editor.set_error(format!("{err}")));
+
+        EventResult::Consumed(None)
+    }
+
+    fn render(&mut self, area: Rect, surface: &mut Surface, cx: &mut Context) {
+        if area.width < 10 || area.height < 5 {
+            cx.editor.set_error("explorer render area is too small");
+            return;
+        }
+        let config = &cx.editor.config().explorer;
+        let position = config.position;
+        self.render_embed(area, surface, cx, &position);
+    }
+
+    fn cursor(&self, area: Rect, editor: &Editor) -> (Option<Position>, CursorKind) {
+        if let Some(prompt) = self
+            .prompt
+            .as_ref()
+            .map(|(_, prompt)| prompt)
+            .or_else(|| self.tree.prompt())
+        {
+            let (x, y) = (area.x, area.y + area.height.saturating_sub(1));
+            prompt.cursor(Rect::new(x, y, area.width, 1), editor)
+        } else {
+            (None, CursorKind::Hidden)
+        }
+    }
+}
+
+fn render_block(area: Rect, surface: &mut Surface, borders: Borders) -> Rect {
+    let block = Block::default().borders(borders);
+    let inner = block.inner(area);
+    block.render(area, surface);
+    inner
+}
+
+#[cfg(test)]
+mod test_explorer {
+    use crate::compositor::Component;
+
+    use super::Explorer;
+    use helix_view::graphics::Rect;
+    use std::{fs, path::PathBuf};
+
+    /// This code should create the following file tree:
+    ///
+    ///   <temp_path>
+    ///   ├── index.html
+    ///   ├── .gitignore
+    ///   ├── scripts
+    ///   │   └── main.js
+    ///   └── styles
+    ///      ├── style.css
+    ///      └── public
+    ///          └── file
+    ///
+    fn dummy_file_tree() -> PathBuf {
+        let path = tempfile::tempdir().unwrap().path().to_path_buf();
+        if path.exists() {
+            fs::remove_dir_all(path.clone()).unwrap();
+        }
+        fs::create_dir_all(path.clone()).unwrap();
+        fs::write(path.join("index.html"), "").unwrap();
+        fs::write(path.join(".gitignore"), "").unwrap();
+
+        fs::create_dir_all(path.join("scripts")).unwrap();
+        fs::write(path.join("scripts").join("main.js"), "").unwrap();
+
+        fs::create_dir_all(path.join("styles")).unwrap();
+        fs::write(path.join("styles").join("style.css"), "").unwrap();
+
+        fs::create_dir_all(path.join("styles").join("public")).unwrap();
+        fs::write(path.join("styles").join("public").join("file"), "").unwrap();
+
+        path
+    }
+
+    fn render(explorer: &mut Explorer) -> String {
+        explorer.tree.render_to_string(Rect::new(0, 0, 100, 10))
+    }
+
+    fn new_explorer() -> (PathBuf, Explorer) {
+        let path = dummy_file_tree();
+        (path.clone(), Explorer::from_path(path, 100).unwrap())
+    }
+
+    #[test]
+    fn test_reveal_file() {
+        let (path, mut explorer) = new_explorer();
+
+        let path_str = path.display().to_string();
+
+        // 0a. Expect the "scripts" folder is not opened
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+({path_str})
+⏵ scripts
+⏵ styles
+  .gitignore
+  index.html
+"
+            )
+            .trim()
+        );
+
+        // 1. Reveal "scripts/main.js"
+        explorer.reveal_file(path.join("scripts/main.js")).unwrap();
+
+        // 1a. Expect the "scripts" folder is opened, and "main.js" is focused
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}]
+⏷ [scripts]
+    (main.js)
+⏵ styles
+  .gitignore
+  index.html
+"
+            )
+            .trim()
+        );
+
+        // 2. Change root to "scripts"
+        explorer.tree.move_up(1);
+        explorer.change_root_to_current_folder().unwrap();
+
+        // 2a. Expect the current root is "scripts"
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+({path_str}/scripts)
+  main.js
+"
+            )
+            .trim()
+        );
+
+        // 3. Reveal "styles/public/file", which is outside of the current root
+        explorer
+            .reveal_file(path.join("styles/public/file"))
+            .unwrap();
+
+        // 3a. Expect the current root is "public", and "file" is focused
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}/styles/public]
+  (file)
+"
+            )
+            .trim()
+        );
+    }
+
+    #[tokio::test(flavor = "multi_thread")]
+    async fn test_rename() {
+        let (path, mut explorer) = new_explorer();
+        let path_str = path.display().to_string();
+
+        explorer.handle_events("jjj").unwrap();
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}]
+⏵ scripts
+⏵ styles
+  (.gitignore)
+  index.html
+"
+            )
+            .trim()
+        );
+
+        // 0. Open the rename file prompt
+        explorer.handle_events("r").unwrap();
+
+        // 0.1 Expect the current prompt to be related to file renaming
+        let prompt = &explorer.prompt.as_ref().unwrap().1;
+        assert_eq!(prompt.prompt(), " Rename to ");
+        assert_eq!(
+            prompt.line().replace(std::path::MAIN_SEPARATOR, "/"),
+            format!("{path_str}/.gitignore")
+        );
+
+        // 1. Rename the current file to a name that is lexicographically greater than "index.html"
+        explorer.handle_events("<C-w>who.is<ret>").unwrap();
+
+        // 1a. Expect the file is renamed, and is focused
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}]
+⏵ scripts
+⏵ styles
+  index.html
+  (who.is)
+"
+            )
+            .trim()
+        );
+
+        assert!(path.join("who.is").exists());
+
+        // 2. Rename the current file into an existing folder
+        explorer
+            .handle_events(&format!(
+                "r<C-w>styles{}lol<ret>",
+                std::path::MAIN_SEPARATOR
+            ))
+            .unwrap();
+
+        // 2a. Expect the file is moved to the folder, and is focused
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}]
+⏵ scripts
+⏷ [styles]
+  ⏵ public
+    (lol)
+    style.css
+  index.html
+"
+            )
+            .trim()
+        );
+
+        assert!(path.join("styles/lol").exists());
+
+        // 3. Rename the current file into a non-existent folder
+        explorer
+            .handle_events(&format!(
+                "r<C-u>{}<ret>",
+                path.join("new_folder/sponge/bob").display()
+            ))
+            .unwrap();
+
+        // 3a. Expect the non-existent folder to be created,
+        //     and the file is moved into it,
+        //     and the renamed file is focused
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}]
+⏷ [new_folder]
+  ⏷ [sponge]
+      (bob)
+⏵ scripts
+⏷ styles
+  ⏵ public
+    style.css
+  index.html
+"
+            )
+            .trim()
+        );
+
+        assert!(path.join("new_folder/sponge/bob").exists());
+
+        // 4. Change current root to "new_folder/sponge"
+        explorer.handle_events("k]").unwrap();
+
+        // 4a. Expect the current root to be "sponge"
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+({path_str}/new_folder/sponge)
+  bob
+"
+            )
+            .trim()
+        );
+
+        // 5. Move cursor to "bob", and rename it outside of the current root
+        explorer.handle_events("j").unwrap();
+        explorer
+            .handle_events(&format!(
+                "r<C-u>{}<ret>",
+                path.join("scripts/bob").display()
+            ))
+            .unwrap();
+
+        // 5a. Expect the current root to be "scripts"
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}/scripts]
+  (bob)
+  main.js
+"
+            )
+            .trim()
+        );
+    }
+
+    #[tokio::test(flavor = "multi_thread")]
+    async fn test_new_folder() {
+        let (path, mut explorer) = new_explorer();
+        let path_str = path.display().to_string();
+
+        // 0. Open the add file/folder prompt
+        explorer.handle_events("a").unwrap();
+        let prompt = &explorer.prompt.as_ref().unwrap().1;
+        fn to_forward_slash(s: &str) -> String {
+            s.replace(std::path::MAIN_SEPARATOR, "/")
+        }
+        fn to_os_main_separator(s: &str) -> String {
+            s.replace('/', format!("{}", std::path::MAIN_SEPARATOR).as_str())
+        }
+        assert_eq!(
+            to_forward_slash(prompt.prompt()),
+            " New file or folder (ends with '/'): "
+        );
+        assert_eq!(to_forward_slash(prompt.line()), format!("{path_str}/"));
+
+        // 1. Add a new folder at the root
+        explorer
+            .handle_events(&to_os_main_separator("yoyo/<ret>"))
+            .unwrap();
+
+        // 1a. Expect the new folder is added, and is focused
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}]
+⏵ scripts
+⏵ styles
+⏷ (yoyo)
+  .gitignore
+  index.html
+"
+            )
+            .trim()
+        );
+
+        assert!(fs::read_dir(path.join("yoyo")).is_ok());
+
+        // 2. Move up to "styles"
+        explorer.handle_events("k").unwrap();
+
+        // 3. Add a new folder
+        explorer
+            .handle_events(&to_os_main_separator("asus.sass/<ret>"))
+            .unwrap();
+
+        // 3a. Expect the new folder is added under "styles", although "styles" is not opened
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}]
+⏵ scripts
+⏷ [styles]
+  ⏵ public
+  ⏷ (sus.sass)
+    style.css
+⏷ yoyo
+  .gitignore
+  index.html
+"
+            )
+            .trim()
+        );
+
+        assert!(fs::read_dir(path.join("styles/sus.sass")).is_ok());
+
+        // 4. Add a new folder with non-existent parents
+        explorer
+            .handle_events(&to_os_main_separator("aa/b/c/<ret>"))
+            .unwrap();
+
+        // 4a. Expect the non-existent parents are created,
+        //     and the new folder is created,
+        //     and is focused
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}]
+⏷ [styles]
+  ⏷ [sus.sass]
+    ⏷ [a]
+      ⏷ [b]
+        ⏷ (c)
+    style.css
+⏷ yoyo
+  .gitignore
+  index.html
+"
+            )
+            .trim()
+        );
+
+        assert!(fs::read_dir(path.join("styles/sus.sass/a/b/c")).is_ok());
+
+        // 5. Move to "style.css"
+        explorer.handle_events("j").unwrap();
+
+        // 6. Add a new folder here
+        explorer
+            .handle_events(&to_os_main_separator("afoobar/<ret>"))
+            .unwrap();
+
+        // 6a. Expect the folder is added under "styles",
+        //     because the folder of the current item, "style.css" is "styles/"
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}]
+⏵ scripts
+⏷ [styles]
+  ⏷ (foobar)
+  ⏵ public
+  ⏷ sus.sass
+    ⏷ a
+      ⏷ b
+        ⏷ c
+    style.css
+"
+            )
+            .trim()
+        );
+
+        assert!(fs::read_dir(path.join("styles/foobar")).is_ok());
+    }
+
+    #[tokio::test(flavor = "multi_thread")]
+    async fn test_new_file() {
+        let (path, mut explorer) = new_explorer();
+        let path_str = path.display().to_string();
+
+        // 1. Add a new file at the root
+        explorer.handle_events("ayoyo<ret>").unwrap();
+
+        // 1a. Expect the new file is added, and is focused
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}]
+⏵ scripts
+⏵ styles
+  .gitignore
+  index.html
+  (yoyo)
+"
+            )
+            .trim()
+        );
+
+        assert!(fs::read_to_string(path.join("yoyo")).is_ok());
+
+        // 2. Move up to "styles"
+        explorer.tree.move_up(3);
+
+        // 3. Add a new file
+        explorer.handle_events("asus.sass<ret>").unwrap();
+
+        // 3a. Expect the new file is added under "styles", although "styles" is not opened
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}]
+⏵ scripts
+⏷ [styles]
+  ⏵ public
+    style.css
+    (sus.sass)
+  .gitignore
+  index.html
+  yoyo
+"
+            )
+            .trim()
+        );
+
+        assert!(fs::read_to_string(path.join("styles/sus.sass")).is_ok());
+
+        // 4. Add a new file with non-existent parents
+        explorer.handle_events("aa/b/c<ret>").unwrap();
+
+        // 4a. Expect the non-existent parents are created,
+        //     and the new file is created,
+        //     and is focused
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}]
+⏵ scripts
+⏷ [styles]
+  ⏷ [a]
+    ⏷ [b]
+        (c)
+  ⏵ public
+    style.css
+    sus.sass
+  .gitignore
+"
+            )
+            .trim()
+        );
+
+        assert!(fs::read_to_string(path.join("styles/a/b/c")).is_ok());
+
+        // 5. Move to "style.css"
+        explorer.handle_events("jj").unwrap();
+
+        // 6. Add a new file here
+        explorer.handle_events("afoobar<ret>").unwrap();
+
+        // 6a. Expect the file is added under "styles",
+        //     because the folder of the current item, "style.css" is "styles/"
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}]
+⏷ [styles]
+    ⏷ b
+        c
+  ⏵ public
+    (foobar)
+    style.css
+    sus.sass
+  .gitignore
+  index.html
+"
+            )
+            .trim()
+        );
+
+        assert!(fs::read_to_string(path.join("styles/foobar")).is_ok());
+    }
+
+    #[tokio::test(flavor = "multi_thread")]
+    async fn test_remove_file() {
+        let (path, mut explorer) = new_explorer();
+        let path_str = path.display().to_string();
+
+        // 1. Move to ".gitignore"
+        explorer.handle_events("/.gitignore<ret>").unwrap();
+
+        // 1a. Expect the cursor is at ".gitignore"
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}]
+⏵ scripts
+⏵ styles
+  (.gitignore)
+  index.html
+"
+            )
+            .trim()
+        );
+
+        assert!(fs::read_to_string(path.join(".gitignore")).is_ok());
+
+        // 2. Remove the current file
+        explorer.handle_events("dy").unwrap();
+
+        // 3. Expect ".gitignore" is deleted, and the cursor moved down
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}]
+⏵ scripts
+⏵ styles
+  (index.html)
+"
+            )
+            .trim()
+        );
+
+        assert!(fs::read_to_string(path.join(".gitignore")).is_err());
+
+        // 3a. Expect "index.html" exists
+        assert!(fs::read_to_string(path.join("index.html")).is_ok());
+
+        // 4. Remove the current file
+        explorer.handle_events("dy").unwrap();
+
+        // 4a. Expect "index.html" is deleted, at the cursor moved up
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}]
+⏵ scripts
+⏵ (styles)
+"
+            )
+            .trim()
+        );
+
+        assert!(fs::read_to_string(path.join("index.html")).is_err());
+    }
+
+    #[tokio::test(flavor = "multi_thread")]
+    async fn test_remove_folder() {
+        let (path, mut explorer) = new_explorer();
+        let path_str = path.display().to_string();
+
+        // 1. Move to "styles/"
+        explorer.handle_events("/styles<ret>o").unwrap();
+
+        // 1a. Expect the cursor is at "styles"
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}]
+⏵ scripts
+⏷ (styles)
+  ⏵ public
+    style.css
+  .gitignore
+  index.html
+"
+            )
+            .trim()
+        );
+
+        assert!(fs::read_dir(path.join("styles")).is_ok());
+
+        // 2. Remove the current folder
+        explorer.handle_events("dy").unwrap();
+
+        // 3. Expect "styles" is deleted, and the cursor moved down
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}]
+⏵ scripts
+  (.gitignore)
+  index.html
+"
+            )
+            .trim()
+        );
+
+        assert!(fs::read_dir(path.join("styles")).is_err());
+    }
+
+    #[test]
+    fn test_change_root() {
+        let (path, mut explorer) = new_explorer();
+        let path_str = path.display().to_string();
+
+        // 1. Move cursor to "styles"
+        explorer.reveal_file(path.join("styles")).unwrap();
+
+        // 2. Change root to current folder, and move cursor down
+        explorer.change_root_to_current_folder().unwrap();
+        explorer.tree.move_down(1);
+
+        // 2a. Expect the current root to be "styles", and the cursor is at "public"
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}/styles]
+⏵ (public)
+  style.css
+"
+            )
+            .trim()
+        );
+
+        let current_root = explorer.state.current_root.clone();
+
+        // 3. Change root to the parent of current folder
+        explorer.change_root_parent_folder().unwrap();
+
+        // 3a. Expect the current root to be "change_root"
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+({path_str})
+⏵ scripts
+⏵ styles
+  .gitignore
+  index.html
+"
+            )
+            .trim()
+        );
+
+        // 4. Go back to previous root
+        explorer.go_to_previous_root();
+
+        // 4a. Expect the root te become "styles", and the cursor position is not forgotten
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}/styles]
+⏵ (public)
+  style.css
+"
+            )
+            .trim()
+        );
+        assert_eq!(explorer.state.current_root, current_root);
+
+        // 5. Go back to previous root again
+        explorer.go_to_previous_root();
+
+        // 5a. Expect the current root to be "change_root" again,
+        //     but this time the "styles" folder is opened,
+        //     because it was opened before any change of root
+        assert_eq!(
+            render(&mut explorer),
+            format!(
+                "
+[{path_str}]
+⏵ scripts
+⏷ (styles)
+  ⏵ public
+    style.css
+  .gitignore
+  index.html
+"
+            )
+            .trim()
+        );
+    }
+}
diff --git a/helix-term/src/ui/mod.rs b/helix-term/src/ui/mod.rs
index b5969818..7e210a70 100644
--- a/helix-term/src/ui/mod.rs
+++ b/helix-term/src/ui/mod.rs
@@ -1,6 +1,7 @@
 mod completion;
 mod document;
 pub(crate) mod editor;
+mod explorer;
 mod info;
 pub mod lsp;
 mod markdown;
@@ -12,12 +13,14 @@ mod prompt;
 mod spinner;
 mod statusline;
 mod text;
+mod tree;
 
 use crate::compositor::{Component, Compositor};
 use crate::filter_picker_entry;
 use crate::job::{self, Callback};
 pub use completion::{Completion, CompletionItem};
 pub use editor::EditorView;
+pub use explorer::Explorer;
 use helix_stdx::rope;
 pub use markdown::Markdown;
 pub use menu::Menu;
@@ -26,6 +29,7 @@ pub use popup::Popup;
 pub use prompt::{Prompt, PromptEvent};
 pub use spinner::{ProgressSpinners, Spinner};
 pub use text::Text;
+pub use tree::{TreeOp, TreeView, TreeViewItem};
 
 use helix_view::Editor;
 
diff --git a/helix-term/src/ui/overlay.rs b/helix-term/src/ui/overlay.rs
index ff184d40..7b9c0391 100644
--- a/helix-term/src/ui/overlay.rs
+++ b/helix-term/src/ui/overlay.rs
@@ -19,26 +19,7 @@ pub struct Overlay<T> {
 pub fn overlaid<T>(content: T) -> Overlay<T> {
     Overlay {
         content,
-        calc_child_size: Box::new(|rect: Rect| clip_rect_relative(rect.clip_bottom(2), 90, 90)),
-    }
-}
-
-fn clip_rect_relative(rect: Rect, percent_horizontal: u8, percent_vertical: u8) -> Rect {
-    fn mul_and_cast(size: u16, factor: u8) -> u16 {
-        ((size as u32) * (factor as u32) / 100).try_into().unwrap()
-    }
-
-    let inner_w = mul_and_cast(rect.width, percent_horizontal);
-    let inner_h = mul_and_cast(rect.height, percent_vertical);
-
-    let offset_x = rect.width.saturating_sub(inner_w) / 2;
-    let offset_y = rect.height.saturating_sub(inner_h) / 2;
-
-    Rect {
-        x: rect.x + offset_x,
-        y: rect.y + offset_y,
-        width: inner_w,
-        height: inner_h,
+        calc_child_size: Box::new(|rect: Rect| rect.overlaid()),
     }
 }
 
diff --git a/helix-term/src/ui/prompt.rs b/helix-term/src/ui/prompt.rs
index a6ee7f05..78e97c8c 100644
--- a/helix-term/src/ui/prompt.rs
+++ b/helix-term/src/ui/prompt.rs
@@ -108,6 +108,10 @@ impl Prompt {
         self
     }
 
+    pub fn prompt(&self) -> &str {
+        self.prompt.as_ref()
+    }
+
     pub fn line(&self) -> &String {
         &self.line
     }
diff --git a/helix-term/src/ui/tree.rs b/helix-term/src/ui/tree.rs
new file mode 100644
index 00000000..d0a9af5b
--- /dev/null
+++ b/helix-term/src/ui/tree.rs
@@ -0,0 +1,2681 @@
+use std::cmp::Ordering;
+
+use anyhow::Result;
+use helix_view::theme::Modifier;
+
+use crate::{
+    compositor::{Component, Context, EventResult},
+    ctrl, key, shift, ui,
+};
+use helix_core::movement::Direction;
+use helix_view::{
+    graphics::Rect,
+    input::{Event, KeyEvent},
+};
+use tui::buffer::Buffer as Surface;
+
+use super::Prompt;
+
+pub trait TreeViewItem: Sized + Ord {
+    type Params: Default;
+
+    fn name(&self) -> String;
+    fn is_parent(&self) -> bool;
+
+    fn filter(&self, s: &str) -> bool {
+        self.name().to_lowercase().contains(&s.to_lowercase())
+    }
+
+    fn get_children(&self) -> Result<Vec<Self>>;
+}
+
+fn tree_item_cmp<T: TreeViewItem>(item1: &T, item2: &T) -> Ordering {
+    T::cmp(item1, item2)
+}
+
+fn vec_to_tree<T: TreeViewItem>(mut items: Vec<T>) -> Vec<Tree<T>> {
+    items.sort();
+    index_elems(
+        0,
+        items
+            .into_iter()
+            .map(|item| Tree::new(item, vec![]))
+            .collect(),
+    )
+}
+
+pub enum TreeOp {
+    Noop,
+    GetChildsAndInsert,
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct Tree<T> {
+    item: T,
+    parent_index: Option<usize>,
+    index: usize,
+    children: Vec<Self>,
+
+    /// Why do we need this property?
+    /// Can't we just use `!children.is_empty()`?
+    ///
+    /// Because we might have for example an open folder that is empty,
+    /// and user just added a new file under that folder,
+    /// and the user refreshes the whole tree.
+    ///
+    /// Without `open`, we will not refresh any node without children,
+    /// and thus the folder still appears empty after refreshing.
+    is_opened: bool,
+}
+
+impl<T: Clone> Clone for Tree<T> {
+    fn clone(&self) -> Self {
+        Self {
+            item: self.item.clone(),
+            index: self.index,
+            children: self.children.clone(),
+            is_opened: self.is_opened,
+            parent_index: self.parent_index,
+        }
+    }
+}
+
+#[derive(Clone)]
+struct TreeIter<'a, T> {
+    current_index_forward: usize,
+    current_index_reverse: isize,
+    tree: &'a Tree<T>,
+}
+
+impl<'a, T> Iterator for TreeIter<'a, T> {
+    type Item = &'a Tree<T>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let index = self.current_index_forward;
+        if index > self.tree.len().saturating_sub(1) {
+            None
+        } else {
+            self.current_index_forward = self.current_index_forward.saturating_add(1);
+            self.tree.get(index)
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.tree.len(), Some(self.tree.len()))
+    }
+}
+
+impl<'a, T> DoubleEndedIterator for TreeIter<'a, T> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        let index = self.current_index_reverse;
+        if index < 0 {
+            None
+        } else {
+            self.current_index_reverse = self.current_index_reverse.saturating_sub(1);
+            self.tree.get(index as usize)
+        }
+    }
+}
+
+impl<'a, T> ExactSizeIterator for TreeIter<'a, T> {}
+
+impl<T: TreeViewItem> Tree<T> {
+    fn open(&mut self) -> Result<()> {
+        if self.item.is_parent() {
+            self.children = self.get_children()?;
+            self.is_opened = true;
+        }
+        Ok(())
+    }
+
+    fn close(&mut self) {
+        self.is_opened = false;
+        self.children = vec![];
+    }
+
+    fn refresh(&mut self) -> Result<()> {
+        if !self.is_opened {
+            return Ok(());
+        }
+        let latest_children = self.get_children()?;
+        let filtered = std::mem::take(&mut self.children)
+            .into_iter()
+            // Remove children that does not exists in latest_children
+            .filter(|tree| {
+                latest_children
+                    .iter()
+                    .any(|child| tree.item.name().eq(&child.item.name()))
+            })
+            .map(|mut tree| {
+                tree.refresh()?;
+                Ok(tree)
+            })
+            .collect::<Result<Vec<_>>>()?;
+
+        // Add new children
+        let new_nodes = latest_children
+            .into_iter()
+            .filter(|child| {
+                !filtered
+                    .iter()
+                    .any(|child_| child.item.name().eq(&child_.item.name()))
+            })
+            .collect::<Vec<_>>();
+
+        self.children = filtered.into_iter().chain(new_nodes).collect();
+
+        self.sort();
+
+        self.regenerate_index();
+
+        Ok(())
+    }
+
+    fn get_children(&self) -> Result<Vec<Tree<T>>> {
+        Ok(vec_to_tree(self.item.get_children()?))
+    }
+
+    fn sort(&mut self) {
+        self.children
+            .sort_by(|a, b| tree_item_cmp(&a.item, &b.item))
+    }
+}
+
+impl<T> Tree<T> {
+    pub fn new(item: T, children: Vec<Tree<T>>) -> Self {
+        let is_opened = !children.is_empty();
+        Self {
+            item,
+            index: 0,
+            parent_index: None,
+            children: index_elems(0, children),
+            is_opened,
+        }
+    }
+
+    fn iter(&self) -> TreeIter<T> {
+        TreeIter {
+            tree: self,
+            current_index_forward: 0,
+            current_index_reverse: (self.len() - 1) as isize,
+        }
+    }
+
+    /// Find an element in the tree with given `predicate`.
+    /// `start_index` is inclusive if direction is `Forward`.
+    /// `start_index` is exclusive if direction is `Backward`.
+    fn find<F>(&self, start_index: usize, direction: Direction, predicate: F) -> Option<usize>
+    where
+        F: Clone + FnMut(&Tree<T>) -> bool,
+    {
+        match direction {
+            Direction::Forward => match self
+                .iter()
+                .skip(start_index)
+                .position(predicate.clone())
+                .map(|index| index + start_index)
+            {
+                Some(index) => Some(index),
+                None => self.iter().position(predicate),
+            },
+
+            Direction::Backward => match self.iter().take(start_index).rposition(predicate.clone())
+            {
+                Some(index) => Some(index),
+                None => self.iter().rposition(predicate),
+            },
+        }
+    }
+
+    pub fn item(&self) -> &T {
+        &self.item
+    }
+
+    fn get(&self, index: usize) -> Option<&Tree<T>> {
+        if self.index == index {
+            Some(self)
+        } else {
+            self.children.iter().find_map(|elem| elem.get(index))
+        }
+    }
+
+    fn get_mut(&mut self, index: usize) -> Option<&mut Tree<T>> {
+        if self.index == index {
+            Some(self)
+        } else {
+            self.children
+                .iter_mut()
+                .find_map(|elem| elem.get_mut(index))
+        }
+    }
+
+    fn len(&self) -> usize {
+        (1_usize).saturating_add(self.children.iter().map(|elem| elem.len()).sum())
+    }
+
+    fn regenerate_index(&mut self) {
+        let items = std::mem::take(&mut self.children);
+        self.children = index_elems(0, items);
+    }
+}
+
+#[derive(Clone, Debug)]
+struct SavedView {
+    selected: usize,
+    winline: usize,
+}
+
+pub struct TreeView<T: TreeViewItem> {
+    tree: Tree<T>,
+
+    search_prompt: Option<(Direction, Prompt)>,
+
+    search_str: String,
+
+    /// Selected item idex
+    selected: usize,
+
+    backward_jumps: Vec<usize>,
+    forward_jumps: Vec<usize>,
+
+    saved_view: Option<SavedView>,
+
+    /// For implementing vertical scroll
+    winline: usize,
+
+    /// For implementing horizontal scoll
+    column: usize,
+
+    /// For implementing horizontal scoll
+    max_len: usize,
+    count: usize,
+    tree_symbol_style: String,
+
+    #[allow(clippy::type_complexity)]
+    pre_render: Option<Box<dyn Fn(&mut Self, Rect) + 'static>>,
+
+    #[allow(clippy::type_complexity)]
+    on_opened_fn: Option<Box<dyn FnMut(&mut T, &mut Context, &mut T::Params) -> TreeOp + 'static>>,
+
+    #[allow(clippy::type_complexity)]
+    on_folded_fn: Option<Box<dyn FnMut(&mut T, &mut Context, &mut T::Params) + 'static>>,
+
+    #[allow(clippy::type_complexity)]
+    on_next_key: Option<Box<dyn FnMut(&mut Context, &mut Self, &KeyEvent) -> Result<()>>>,
+}
+
+impl<T: TreeViewItem> TreeView<T> {
+    pub fn build_tree(root: T) -> Result<Self> {
+        let children = root.get_children()?;
+        let items = vec_to_tree(children);
+        Ok(Self {
+            tree: Tree::new(root, items),
+            selected: 0,
+            backward_jumps: vec![],
+            forward_jumps: vec![],
+            saved_view: None,
+            winline: 0,
+            column: 0,
+            max_len: 0,
+            count: 0,
+            tree_symbol_style: "ui.text".into(),
+            pre_render: None,
+            on_opened_fn: None,
+            on_folded_fn: None,
+            on_next_key: None,
+            search_prompt: None,
+            search_str: "".into(),
+        })
+    }
+
+    pub fn with_enter_fn<F>(mut self, f: F) -> Self
+    where
+        F: FnMut(&mut T, &mut Context, &mut T::Params) -> TreeOp + 'static,
+    {
+        self.on_opened_fn = Some(Box::new(f));
+        self
+    }
+
+    pub fn with_folded_fn<F>(mut self, f: F) -> Self
+    where
+        F: FnMut(&mut T, &mut Context, &mut T::Params) + 'static,
+    {
+        self.on_folded_fn = Some(Box::new(f));
+        self
+    }
+
+    pub fn tree_symbol_style(mut self, style: String) -> Self {
+        self.tree_symbol_style = style;
+        self
+    }
+
+    /// Reveal item in the tree based on the given `segments`.
+    ///
+    /// The name of the root should be excluded.
+    ///
+    /// Example `segments`:
+    ///
+    ///    vec!["helix-term", "src", "ui", "tree.rs"]
+    ///
+    pub fn reveal_item(&mut self, segments: Vec<String>) -> Result<()> {
+        // Expand the tree
+        let root = self.tree.item.name();
+        segments.iter().fold(
+            Ok(&mut self.tree),
+            |current_tree, segment| match current_tree {
+                Err(err) => Err(err),
+                Ok(current_tree) => {
+                    match current_tree
+                        .children
+                        .iter_mut()
+                        .find(|tree| tree.item.name().eq(segment))
+                    {
+                        Some(tree) => {
+                            if !tree.is_opened {
+                                tree.open()?;
+                            }
+                            Ok(tree)
+                        }
+                        None => Err(anyhow::anyhow!(format!(
+                            "Unable to find path: '{}'. current_segment = '{segment}'. current_root = '{root}'",
+                            segments.join("/"),
+                        ))),
+                    }
+                }
+            },
+        )?;
+
+        // Locate the item
+        self.regenerate_index();
+        self.set_selected(
+            segments
+                .iter()
+                .fold(&self.tree, |tree, segment| {
+                    tree.children
+                        .iter()
+                        .find(|tree| tree.item.name().eq(segment))
+                        .expect("Should be unreachable")
+                })
+                .index,
+        );
+
+        self.align_view_center();
+        Ok(())
+    }
+
+    fn align_view_center(&mut self) {
+        self.pre_render = Some(Box::new(|tree, area| {
+            tree.winline = area.height as usize / 2
+        }))
+    }
+
+    fn align_view_top(&mut self) {
+        self.winline = 0
+    }
+
+    fn align_view_bottom(&mut self) {
+        self.pre_render = Some(Box::new(|tree, area| tree.winline = area.height as usize))
+    }
+
+    fn regenerate_index(&mut self) {
+        self.tree.regenerate_index();
+    }
+
+    fn move_to_parent(&mut self) -> Result<()> {
+        if let Some(parent) = self.current_parent()? {
+            let index = parent.index;
+            self.set_selected(index)
+        }
+        Ok(())
+    }
+
+    fn move_to_children(&mut self) -> Result<()> {
+        let current = self.current_mut()?;
+        if current.is_opened {
+            self.set_selected(self.selected + 1);
+            Ok(())
+        } else {
+            current.open()?;
+            if !current.children.is_empty() {
+                self.set_selected(self.selected + 1);
+                self.regenerate_index();
+            }
+            Ok(())
+        }
+    }
+
+    pub fn refresh(&mut self) -> Result<()> {
+        self.tree.refresh()?;
+        self.set_selected(self.selected);
+        Ok(())
+    }
+
+    fn move_to_first_line(&mut self) {
+        self.move_up(usize::MAX / 2)
+    }
+
+    fn move_to_last_line(&mut self) {
+        self.move_down(usize::MAX / 2)
+    }
+
+    fn move_leftmost(&mut self) {
+        self.move_left(usize::MAX / 2);
+    }
+
+    fn move_rightmost(&mut self) {
+        self.move_right(usize::MAX / 2)
+    }
+
+    fn restore_saved_view(&mut self) -> Result<()> {
+        if let Some(saved_view) = self.saved_view.take() {
+            self.selected = saved_view.selected;
+            self.winline = saved_view.winline;
+            self.refresh()
+        } else {
+            Ok(())
+        }
+    }
+
+    pub fn prompt(&self) -> Option<&Prompt> {
+        if let Some((_, prompt)) = self.search_prompt.as_ref() {
+            Some(prompt)
+        } else {
+            None
+        }
+    }
+}
+
+pub fn tree_view_help() -> Vec<(&'static str, &'static str)> {
+    vec![
+        ("o, Enter", "Open/Close"),
+        ("j, down, C-n", "Down"),
+        ("k, up, C-p", "Up"),
+        ("h, left", "Go to parent"),
+        ("l, right", "Expand"),
+        ("J", "Go to next sibling"),
+        ("K", "Go to previous sibling"),
+        ("H", "Go to first child"),
+        ("L", "Go to last child"),
+        ("R", "Refresh"),
+        ("/", "Search"),
+        ("n", "Go to next search match"),
+        ("N", "Go to previous search match"),
+        ("gh, Home", "Scroll to the leftmost"),
+        ("gl, End", "Scroll to the rightmost"),
+        ("C-o", "Jump backward"),
+        ("C-i, Tab", "Jump forward"),
+        ("C-d", "Half page down"),
+        ("C-u", "Half page up"),
+        ("PageDown", "Full page down"),
+        ("PageUp", "Full page up"),
+        ("zt", "Align view top"),
+        ("zz", "Align view center"),
+        ("zb", "Align view bottom"),
+        ("gg", "Go to first line"),
+        ("ge", "Go to last line"),
+    ]
+}
+
+impl<T: TreeViewItem> TreeView<T> {
+    pub fn on_enter(
+        &mut self,
+        cx: &mut Context,
+        params: &mut T::Params,
+        selected_index: usize,
+    ) -> Result<()> {
+        let selected_item = self.get_mut(selected_index)?;
+        if selected_item.is_opened {
+            selected_item.close();
+            self.regenerate_index();
+            return Ok(());
+        }
+
+        if let Some(mut on_open_fn) = self.on_opened_fn.take() {
+            let mut f = || -> Result<()> {
+                let current = self.current_mut()?;
+                match on_open_fn(&mut current.item, cx, params) {
+                    TreeOp::GetChildsAndInsert => {
+                        if let Err(err) = current.open() {
+                            cx.editor.set_error(format!("{err}"))
+                        }
+                    }
+                    TreeOp::Noop => {}
+                };
+                Ok(())
+            };
+            f()?;
+            self.regenerate_index();
+            self.on_opened_fn = Some(on_open_fn);
+        };
+        Ok(())
+    }
+
+    fn set_search_str(&mut self, s: String) {
+        self.search_str = s;
+        self.saved_view = None;
+    }
+
+    fn saved_view(&self) -> SavedView {
+        self.saved_view.clone().unwrap_or(SavedView {
+            selected: self.selected,
+            winline: self.winline,
+        })
+    }
+
+    fn search_next(&mut self, s: &str) {
+        let saved_view = self.saved_view();
+        let skip = std::cmp::max(2, saved_view.selected + 1);
+        self.set_selected(
+            self.tree
+                .find(skip, Direction::Forward, |e| e.item.filter(s))
+                .unwrap_or(saved_view.selected),
+        );
+    }
+
+    fn search_previous(&mut self, s: &str) {
+        let saved_view = self.saved_view();
+        let take = saved_view.selected;
+        self.set_selected(
+            self.tree
+                .find(take, Direction::Backward, |e| e.item.filter(s))
+                .unwrap_or(saved_view.selected),
+        );
+    }
+
+    fn move_to_next_search_match(&mut self) {
+        self.search_next(&self.search_str.clone())
+    }
+
+    fn move_to_previous_next_match(&mut self) {
+        self.search_previous(&self.search_str.clone())
+    }
+
+    pub fn move_down(&mut self, rows: usize) {
+        self.set_selected(self.selected.saturating_add(rows))
+    }
+
+    fn set_selected(&mut self, selected: usize) {
+        let previous_selected = self.selected;
+        self.set_selected_without_history(selected);
+        if previous_selected.abs_diff(selected) > 1 {
+            self.backward_jumps.push(previous_selected)
+        }
+    }
+
+    fn set_selected_without_history(&mut self, selected: usize) {
+        let selected = selected.clamp(0, self.tree.len().saturating_sub(1));
+        if selected > self.selected {
+            // Move down
+            self.winline = selected.min(
+                self.winline
+                    .saturating_add(selected.saturating_sub(self.selected)),
+            );
+        } else {
+            // Move up
+            self.winline = selected.min(
+                self.winline
+                    .saturating_sub(self.selected.saturating_sub(selected)),
+            );
+        }
+        self.selected = selected
+    }
+
+    fn jump_backward(&mut self) {
+        if let Some(index) = self.backward_jumps.pop() {
+            self.forward_jumps.push(self.selected);
+            self.set_selected_without_history(index);
+        }
+    }
+
+    fn jump_forward(&mut self) {
+        if let Some(index) = self.forward_jumps.pop() {
+            self.set_selected(index)
+        }
+    }
+
+    pub fn move_up(&mut self, rows: usize) {
+        self.set_selected(self.selected.saturating_sub(rows))
+    }
+
+    fn move_to_next_sibling(&mut self) -> Result<()> {
+        if let Some(parent) = self.current_parent()? {
+            if let Some(local_index) = parent
+                .children
+                .iter()
+                .position(|child| child.index == self.selected)
+            {
+                if let Some(next_sibling) = parent.children.get(local_index.saturating_add(1)) {
+                    self.set_selected(next_sibling.index)
+                }
+            }
+        }
+        Ok(())
+    }
+
+    fn move_to_previous_sibling(&mut self) -> Result<()> {
+        if let Some(parent) = self.current_parent()? {
+            if let Some(local_index) = parent
+                .children
+                .iter()
+                .position(|child| child.index == self.selected)
+            {
+                if let Some(next_sibling) = parent.children.get(local_index.saturating_sub(1)) {
+                    self.set_selected(next_sibling.index)
+                }
+            }
+        }
+        Ok(())
+    }
+
+    fn move_to_last_sibling(&mut self) -> Result<()> {
+        if let Some(parent) = self.current_parent()? {
+            if let Some(last) = parent.children.last() {
+                self.set_selected(last.index)
+            }
+        }
+        Ok(())
+    }
+
+    fn move_to_first_sibling(&mut self) -> Result<()> {
+        if let Some(parent) = self.current_parent()? {
+            if let Some(last) = parent.children.first() {
+                self.set_selected(last.index)
+            }
+        }
+        Ok(())
+    }
+
+    fn move_left(&mut self, cols: usize) {
+        self.column = self.column.saturating_sub(cols);
+    }
+
+    fn move_right(&mut self, cols: usize) {
+        self.pre_render = Some(Box::new(move |tree, area| {
+            let max_scroll = tree
+                .max_len
+                .saturating_sub(area.width as usize)
+                .saturating_add(1);
+            tree.column = max_scroll.min(tree.column + cols);
+        }));
+    }
+
+    fn move_down_half_page(&mut self) {
+        self.pre_render = Some(Box::new(|tree, area| {
+            tree.move_down((area.height / 2) as usize);
+        }));
+    }
+
+    fn move_up_half_page(&mut self) {
+        self.pre_render = Some(Box::new(|tree, area| {
+            tree.move_up((area.height / 2) as usize);
+        }));
+    }
+
+    fn move_down_page(&mut self) {
+        self.pre_render = Some(Box::new(|tree, area| {
+            tree.move_down((area.height) as usize);
+        }));
+    }
+
+    fn move_up_page(&mut self) {
+        self.pre_render = Some(Box::new(|tree, area| {
+            tree.move_up((area.height) as usize);
+        }));
+    }
+
+    fn save_view(&mut self) {
+        self.saved_view = Some(SavedView {
+            selected: self.selected,
+            winline: self.winline,
+        })
+    }
+
+    fn get(&self, index: usize) -> Result<&Tree<T>> {
+        self.tree.get(index).ok_or_else(|| {
+            anyhow::anyhow!("Programming error: TreeView.get: index {index} is out of bound")
+        })
+    }
+
+    fn get_mut(&mut self, index: usize) -> Result<&mut Tree<T>> {
+        self.tree.get_mut(index).ok_or_else(|| {
+            anyhow::anyhow!("Programming error: TreeView.get_mut: index {index} is out of bound")
+        })
+    }
+
+    pub fn current(&self) -> Result<&Tree<T>> {
+        self.get(self.selected)
+    }
+
+    pub fn current_mut(&mut self) -> Result<&mut Tree<T>> {
+        self.get_mut(self.selected)
+    }
+
+    fn current_parent(&self) -> Result<Option<&Tree<T>>> {
+        if let Some(parent_index) = self.current()?.parent_index {
+            Ok(Some(self.get(parent_index)?))
+        } else {
+            Ok(None)
+        }
+    }
+
+    pub fn current_item(&self) -> Result<&T> {
+        Ok(&self.current()?.item)
+    }
+
+    pub fn winline(&self) -> usize {
+        self.winline
+    }
+}
+
+#[derive(Clone)]
+struct RenderedLine {
+    indent: String,
+    content: String,
+    selected: bool,
+    is_ancestor_of_current_item: bool,
+}
+struct RenderTreeParams<'a, T> {
+    tree: &'a Tree<T>,
+    prefix: &'a String,
+    level: usize,
+    selected: usize,
+}
+
+fn render_tree<T: TreeViewItem>(
+    RenderTreeParams {
+        tree,
+        prefix,
+        level,
+        selected,
+    }: RenderTreeParams<T>,
+) -> Vec<RenderedLine> {
+    let indent = if level > 0 {
+        let indicator = if tree.item().is_parent() {
+            if tree.is_opened {
+                "⏷"
+            } else {
+                "⏵"
+            }
+        } else {
+            " "
+        };
+        format!("{}{} ", prefix, indicator)
+    } else {
+        "".to_string()
+    };
+    let name = tree.item.name();
+    let head = RenderedLine {
+        indent,
+        selected: selected == tree.index,
+        is_ancestor_of_current_item: selected != tree.index && tree.get(selected).is_some(),
+        content: name,
+    };
+    let prefix = format!("{}{}", prefix, if level == 0 { "" } else { "  " });
+    vec![head]
+        .into_iter()
+        .chain(tree.children.iter().flat_map(|elem| {
+            render_tree(RenderTreeParams {
+                tree: elem,
+                prefix: &prefix,
+                level: level + 1,
+                selected,
+            })
+        }))
+        .collect()
+}
+
+impl<T: TreeViewItem + Clone> TreeView<T> {
+    pub fn render(
+        &mut self,
+        area: Rect,
+        prompt_area: Rect,
+        surface: &mut Surface,
+        cx: &mut Context,
+    ) {
+        let style = cx.editor.theme.get(&self.tree_symbol_style);
+        if let Some((_, prompt)) = self.search_prompt.as_mut() {
+            prompt.render_prompt(prompt_area, surface, cx)
+        }
+
+        let ancestor_style = {
+            let style = cx.editor.theme.get("ui.selection");
+            let fg = cx.editor.theme.get("ui.text").fg;
+            match (style.fg, fg) {
+                (None, Some(fg)) => style.fg(fg),
+                _ => style,
+            }
+        };
+
+        let iter = self.render_lines(area).into_iter().enumerate();
+
+        for (index, line) in iter {
+            let area = Rect::new(area.x, area.y.saturating_add(index as u16), area.width, 1);
+            let indent_len = line.indent.chars().count() as u16;
+            surface.set_stringn(
+                area.x,
+                area.y,
+                line.indent.clone(),
+                indent_len as usize,
+                style,
+            );
+
+            let style = if line.selected {
+                style.add_modifier(Modifier::REVERSED)
+            } else {
+                style
+            };
+            let x = area.x.saturating_add(indent_len);
+            surface.set_stringn(
+                x,
+                area.y,
+                line.content.clone(),
+                area.width
+                    .saturating_sub(indent_len)
+                    .saturating_sub(1)
+                    .into(),
+                if line.is_ancestor_of_current_item {
+                    ancestor_style
+                } else {
+                    style
+                },
+            );
+        }
+    }
+
+    #[cfg(test)]
+    pub fn render_to_string(&mut self, area: Rect) -> String {
+        let lines = self.render_lines(area);
+        lines
+            .into_iter()
+            .map(|line| {
+                let name = if line.selected {
+                    format!("({})", line.content)
+                } else if line.is_ancestor_of_current_item {
+                    format!("[{}]", line.content)
+                } else {
+                    line.content
+                };
+                format!("{}{}", line.indent, name)
+            })
+            .collect::<Vec<_>>()
+            .join("\n")
+    }
+
+    fn render_lines(&mut self, area: Rect) -> Vec<RenderedLine> {
+        if let Some(pre_render) = self.pre_render.take() {
+            pre_render(self, area);
+        }
+
+        self.winline = self.winline.min(area.height.saturating_sub(1) as usize);
+        let skip = self.selected.saturating_sub(self.winline);
+        let params = RenderTreeParams {
+            tree: &self.tree,
+            prefix: &"".to_string(),
+            level: 0,
+            selected: self.selected,
+        };
+
+        let lines = render_tree(params);
+
+        self.max_len = lines
+            .iter()
+            .map(|line| {
+                line.indent
+                    .chars()
+                    .count()
+                    .saturating_add(line.content.chars().count())
+            })
+            .max()
+            .unwrap_or(0);
+
+        let max_width = area.width as usize;
+
+        let take = area.height as usize;
+
+        struct RetainAncestorResult {
+            skipped_ancestors: Vec<RenderedLine>,
+            remaining_lines: Vec<RenderedLine>,
+        }
+        fn retain_ancestors(lines: Vec<RenderedLine>, skip: usize) -> RetainAncestorResult {
+            if skip == 0 {
+                return RetainAncestorResult {
+                    skipped_ancestors: vec![],
+                    remaining_lines: lines,
+                };
+            }
+            if let Some(line) = lines.get(0) {
+                if line.selected {
+                    return RetainAncestorResult {
+                        skipped_ancestors: vec![],
+                        remaining_lines: lines,
+                    };
+                }
+            }
+
+            let selected_index = lines.iter().position(|line| line.selected);
+            let skip = match selected_index {
+                None => skip,
+                Some(selected_index) => skip.min(selected_index),
+            };
+            let (skipped, remaining) = lines.split_at(skip.min(lines.len().saturating_sub(1)));
+
+            let skipped_ancestors = skipped
+                .iter()
+                .cloned()
+                .filter(|line| line.is_ancestor_of_current_item)
+                .collect::<Vec<_>>();
+
+            let result = retain_ancestors(remaining.to_vec(), skipped_ancestors.len());
+            RetainAncestorResult {
+                skipped_ancestors: skipped_ancestors
+                    .into_iter()
+                    .chain(result.skipped_ancestors.into_iter())
+                    .collect(),
+                remaining_lines: result.remaining_lines,
+            }
+        }
+
+        let RetainAncestorResult {
+            skipped_ancestors,
+            remaining_lines,
+        } = retain_ancestors(lines, skip);
+
+        let max_ancestors_len = take.saturating_sub(1);
+
+        // Skip furthest ancestors
+        let skipped_ancestors = skipped_ancestors
+            .into_iter()
+            .rev()
+            .take(max_ancestors_len)
+            .rev()
+            .collect::<Vec<_>>();
+
+        let skipped_ancestors_len = skipped_ancestors.len();
+
+        skipped_ancestors
+            .into_iter()
+            .chain(
+                remaining_lines
+                    .into_iter()
+                    .take(take.saturating_sub(skipped_ancestors_len)),
+            )
+            // Horizontal scroll
+            .map(|line| {
+                let skip = self.column;
+                let indent_len = line.indent.chars().count();
+                RenderedLine {
+                    indent: if line.indent.is_empty() {
+                        "".to_string()
+                    } else {
+                        line.indent
+                            .chars()
+                            .skip(skip)
+                            .take(max_width)
+                            .collect::<String>()
+                    },
+                    content: line
+                        .content
+                        .chars()
+                        .skip(skip.saturating_sub(indent_len))
+                        .take((max_width.saturating_sub(indent_len)).clamp(0, line.content.len()))
+                        .collect::<String>(),
+                    ..line
+                }
+            })
+            .collect()
+    }
+
+    #[cfg(test)]
+    pub fn handle_events(
+        &mut self,
+        events: &str,
+        cx: &mut Context,
+        params: &mut T::Params,
+    ) -> Result<()> {
+        use helix_view::input::parse_macro;
+
+        for event in parse_macro(events)? {
+            self.handle_event(&Event::Key(event), cx, params);
+        }
+        Ok(())
+    }
+
+    pub fn handle_event(
+        &mut self,
+        event: &Event,
+        cx: &mut Context,
+        params: &mut T::Params,
+    ) -> EventResult {
+        let key_event = match event {
+            Event::Key(event) => event,
+            Event::Resize(..) => return EventResult::Consumed(None),
+            _ => return EventResult::Ignored(None),
+        };
+        (|| -> Result<EventResult> {
+            if let Some(mut on_next_key) = self.on_next_key.take() {
+                on_next_key(cx, self, key_event)?;
+                return Ok(EventResult::Consumed(None));
+            }
+
+            if let EventResult::Consumed(c) = self.handle_search_event(key_event, cx) {
+                return Ok(EventResult::Consumed(c));
+            }
+
+            let count = std::mem::replace(&mut self.count, 0);
+
+            match key_event {
+                key!(i @ '0'..='9') => {
+                    self.count = i.to_digit(10).unwrap_or(0) as usize + count * 10
+                }
+                shift!('J') => self.move_to_next_sibling()?,
+                shift!('K') => self.move_to_previous_sibling()?,
+                shift!('H') => self.move_to_first_sibling()?,
+                shift!('L') => self.move_to_last_sibling()?,
+                key!('j') | key!(Down) | ctrl!('n') => self.move_down(1.max(count)),
+                key!('k') | key!(Up) | ctrl!('p') => self.move_up(1.max(count)),
+                key!('h') | key!(Left) => self.move_to_parent()?,
+                key!('l') | key!(Right) => self.move_to_children()?,
+                key!(Enter) | key!('o') => self.on_enter(cx, params, self.selected)?,
+                ctrl!('d') => self.move_down_half_page(),
+                ctrl!('u') => self.move_up_half_page(),
+                key!('z') => {
+                    self.on_next_key = Some(Box::new(|_, tree, event| {
+                        match event {
+                            key!('z') => tree.align_view_center(),
+                            key!('t') => tree.align_view_top(),
+                            key!('b') => tree.align_view_bottom(),
+                            _ => {}
+                        };
+                        Ok(())
+                    }));
+                }
+                key!('g') => {
+                    self.on_next_key = Some(Box::new(|_, tree, event| {
+                        match event {
+                            key!('g') => tree.move_to_first_line(),
+                            key!('e') => tree.move_to_last_line(),
+                            key!('h') => tree.move_leftmost(),
+                            key!('l') => tree.move_rightmost(),
+                            _ => {}
+                        };
+                        Ok(())
+                    }));
+                }
+                key!('/') => self.new_search_prompt(Direction::Forward),
+                key!('n') => self.move_to_next_search_match(),
+                shift!('N') => self.move_to_previous_next_match(),
+                key!(PageDown) => self.move_down_page(),
+                key!(PageUp) => self.move_up_page(),
+                shift!('R') => {
+                    if let Err(error) = self.refresh() {
+                        cx.editor.set_error(error.to_string())
+                    }
+                }
+                key!(Home) => self.move_leftmost(),
+                key!(End) => self.move_rightmost(),
+                ctrl!('o') => self.jump_backward(),
+                ctrl!('i') | key!(Tab) => self.jump_forward(),
+                _ => return Ok(EventResult::Ignored(None)),
+            };
+            Ok(EventResult::Consumed(None))
+        })()
+        .unwrap_or_else(|err| {
+            cx.editor.set_error(format!("{err}"));
+            EventResult::Consumed(None)
+        })
+    }
+
+    fn handle_search_event(&mut self, event: &KeyEvent, cx: &mut Context) -> EventResult {
+        if let Some((direction, mut prompt)) = self.search_prompt.take() {
+            match event {
+                key!(Enter) => {
+                    self.set_search_str(prompt.line().clone());
+                    EventResult::Consumed(None)
+                }
+                key!(Esc) => {
+                    if let Err(err) = self.restore_saved_view() {
+                        cx.editor.set_error(format!("{err}"))
+                    }
+                    EventResult::Consumed(None)
+                }
+                _ => {
+                    let event = prompt.handle_event(&Event::Key(*event), cx);
+                    let line = prompt.line();
+                    match direction {
+                        Direction::Forward => {
+                            self.search_next(line);
+                        }
+                        Direction::Backward => self.search_previous(line),
+                    }
+                    self.search_prompt = Some((direction, prompt));
+                    event
+                }
+            }
+        } else {
+            EventResult::Ignored(None)
+        }
+    }
+
+    fn new_search_prompt(&mut self, direction: Direction) {
+        self.save_view();
+        self.search_prompt = Some((
+            direction,
+            Prompt::new("search: ".into(), None, ui::completers::none, |_, _, _| {}),
+        ))
+    }
+
+    pub fn prompting(&self) -> bool {
+        self.search_prompt.is_some() || self.on_next_key.is_some()
+    }
+}
+
+/// Recalculate the index of each item of a tree.
+///
+/// For example:
+///
+/// ```txt
+/// foo (0)
+///   bar (1)
+/// spam (2)
+///   jar (3)
+///     yo (4)
+/// ```
+fn index_elems<T>(parent_index: usize, elems: Vec<Tree<T>>) -> Vec<Tree<T>> {
+    fn index_elems<T>(
+        current_index: usize,
+        elems: Vec<Tree<T>>,
+        parent_index: usize,
+    ) -> (usize, Vec<Tree<T>>) {
+        elems
+            .into_iter()
+            .fold((current_index, vec![]), |(current_index, trees), elem| {
+                let index = current_index;
+                let item = elem.item;
+                let (current_index, folded) = index_elems(current_index + 1, elem.children, index);
+                let tree = Tree {
+                    item,
+                    children: folded,
+                    index,
+                    is_opened: elem.is_opened,
+                    parent_index: Some(parent_index),
+                };
+                (
+                    current_index,
+                    trees.into_iter().chain(vec![tree].into_iter()).collect(),
+                )
+            })
+    }
+    index_elems(parent_index + 1, elems, parent_index).1
+}
+
+#[cfg(test)]
+mod test_tree_view {
+
+    use helix_view::graphics::Rect;
+
+    use crate::compositor::Context;
+
+    use super::{TreeView, TreeViewItem};
+
+    #[derive(PartialEq, Eq, PartialOrd, Ord, Clone)]
+    /// The children of DivisibleItem is the division of itself.
+    /// This is used to ease the creation of a dummy tree without having to specify so many things.
+    struct DivisibleItem<'a> {
+        name: &'a str,
+    }
+
+    fn item(name: &str) -> DivisibleItem {
+        DivisibleItem { name }
+    }
+
+    impl<'a> TreeViewItem for DivisibleItem<'a> {
+        type Params = ();
+
+        fn name(&self) -> String {
+            self.name.to_string()
+        }
+
+        fn is_parent(&self) -> bool {
+            self.name.len() > 2
+        }
+
+        fn get_children(&self) -> anyhow::Result<Vec<Self>> {
+            if self.name.eq("who_lives_in_a_pineapple_under_the_sea") {
+                Ok(vec![
+                    item("gary_the_snail"),
+                    item("krabby_patty"),
+                    item("larry_the_lobster"),
+                    item("patrick_star"),
+                    item("sandy_cheeks"),
+                    item("spongebob_squarepants"),
+                    item("mrs_puff"),
+                    item("king_neptune"),
+                    item("karen"),
+                    item("plankton"),
+                ])
+            } else if self.is_parent() {
+                let (left, right) = self.name.split_at(self.name.len() / 2);
+                Ok(vec![item(left), item(right)])
+            } else {
+                Ok(vec![])
+            }
+        }
+    }
+
+    fn dummy_tree_view<'a>() -> TreeView<DivisibleItem<'a>> {
+        TreeView::build_tree(item("who_lives_in_a_pineapple_under_the_sea")).unwrap()
+    }
+
+    fn dummy_area() -> Rect {
+        Rect::new(0, 0, 50, 5)
+    }
+
+    fn render(view: &mut TreeView<DivisibleItem>) -> String {
+        view.render_to_string(dummy_area())
+    }
+
+    #[test]
+    fn test_init() {
+        let mut view = dummy_tree_view();
+
+        // Expect the items to be sorted
+        assert_eq!(
+            render(&mut view),
+            "
+(who_lives_in_a_pineapple_under_the_sea)
+⏵ gary_the_snail
+⏵ karen
+⏵ king_neptune
+⏵ krabby_patty
+"
+            .trim()
+        );
+    }
+
+    #[test]
+    fn test_move_up_down() {
+        let mut view = dummy_tree_view();
+        view.move_down(1);
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ (gary_the_snail)
+⏵ karen
+⏵ king_neptune
+⏵ krabby_patty
+"
+            .trim()
+        );
+
+        view.move_down(3);
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ gary_the_snail
+⏵ karen
+⏵ king_neptune
+⏵ (krabby_patty)
+"
+            .trim()
+        );
+
+        view.move_down(1);
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ karen
+⏵ king_neptune
+⏵ krabby_patty
+⏵ (larry_the_lobster)
+"
+            .trim()
+        );
+
+        view.move_up(1);
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ karen
+⏵ king_neptune
+⏵ (krabby_patty)
+⏵ larry_the_lobster
+"
+            .trim()
+        );
+
+        view.move_up(3);
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ (gary_the_snail)
+⏵ karen
+⏵ king_neptune
+⏵ krabby_patty
+"
+            .trim()
+        );
+
+        view.move_up(1);
+        assert_eq!(
+            render(&mut view),
+            "
+(who_lives_in_a_pineapple_under_the_sea)
+⏵ gary_the_snail
+⏵ karen
+⏵ king_neptune
+⏵ krabby_patty
+"
+            .trim()
+        );
+
+        view.move_to_first_line();
+        view.move_up(1);
+        assert_eq!(
+            render(&mut view),
+            "
+(who_lives_in_a_pineapple_under_the_sea)
+⏵ gary_the_snail
+⏵ karen
+⏵ king_neptune
+⏵ krabby_patty
+"
+            .trim()
+        );
+
+        view.move_to_last_line();
+        view.move_down(1);
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ patrick_star
+⏵ plankton
+⏵ sandy_cheeks
+⏵ (spongebob_squarepants)
+"
+            .trim()
+        );
+    }
+
+    #[test]
+    fn test_move_to_first_last_sibling() {
+        let mut view = dummy_tree_view();
+        view.move_to_children().unwrap();
+        view.move_to_children().unwrap();
+        view.move_to_parent().unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏷ (gary_the_snail)
+  ⏵ e_snail
+  ⏵ gary_th
+⏵ karen
+"
+            .trim()
+        );
+
+        view.move_to_last_sibling().unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ patrick_star
+⏵ plankton
+⏵ sandy_cheeks
+⏵ (spongebob_squarepants)
+"
+            .trim()
+        );
+
+        view.move_to_first_sibling().unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏷ (gary_the_snail)
+  ⏵ e_snail
+  ⏵ gary_th
+⏵ karen
+"
+            .trim()
+        );
+    }
+
+    #[test]
+    fn test_move_to_previous_next_sibling() {
+        let mut view = dummy_tree_view();
+        view.move_to_children().unwrap();
+        view.move_to_children().unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏷ [gary_the_snail]
+  ⏵ (e_snail)
+  ⏵ gary_th
+⏵ karen
+"
+            .trim()
+        );
+
+        view.move_to_next_sibling().unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏷ [gary_the_snail]
+  ⏵ e_snail
+  ⏵ (gary_th)
+⏵ karen
+"
+            .trim()
+        );
+
+        view.move_to_next_sibling().unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏷ [gary_the_snail]
+  ⏵ e_snail
+  ⏵ (gary_th)
+⏵ karen
+"
+            .trim()
+        );
+
+        view.move_to_previous_sibling().unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏷ [gary_the_snail]
+  ⏵ (e_snail)
+  ⏵ gary_th
+⏵ karen
+"
+            .trim()
+        );
+
+        view.move_to_previous_sibling().unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏷ [gary_the_snail]
+  ⏵ (e_snail)
+  ⏵ gary_th
+⏵ karen
+"
+            .trim()
+        );
+
+        view.move_to_parent().unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏷ (gary_the_snail)
+  ⏵ e_snail
+  ⏵ gary_th
+⏵ karen
+"
+            .trim()
+        );
+
+        view.move_to_next_sibling().unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏷ gary_the_snail
+  ⏵ e_snail
+  ⏵ gary_th
+⏵ (karen)
+"
+            .trim()
+        );
+
+        view.move_to_previous_sibling().unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏷ (gary_the_snail)
+  ⏵ e_snail
+  ⏵ gary_th
+⏵ karen
+"
+            .trim()
+        );
+    }
+
+    #[test]
+    fn test_align_view() {
+        let mut view = dummy_tree_view();
+        view.move_down(5);
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ karen
+⏵ king_neptune
+⏵ krabby_patty
+⏵ (larry_the_lobster)
+"
+            .trim()
+        );
+
+        view.align_view_center();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ krabby_patty
+⏵ (larry_the_lobster)
+⏵ mrs_puff
+⏵ patrick_star
+"
+            .trim()
+        );
+
+        view.align_view_bottom();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ karen
+⏵ king_neptune
+⏵ krabby_patty
+⏵ (larry_the_lobster)
+"
+            .trim()
+        );
+    }
+
+    #[test]
+    fn test_move_to_first_last() {
+        let mut view = dummy_tree_view();
+
+        view.move_to_last_line();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ patrick_star
+⏵ plankton
+⏵ sandy_cheeks
+⏵ (spongebob_squarepants)
+"
+            .trim()
+        );
+
+        view.move_to_first_line();
+        assert_eq!(
+            render(&mut view),
+            "
+(who_lives_in_a_pineapple_under_the_sea)
+⏵ gary_the_snail
+⏵ karen
+⏵ king_neptune
+⏵ krabby_patty
+"
+            .trim()
+        );
+    }
+
+    #[test]
+    fn test_move_half() {
+        let mut view = dummy_tree_view();
+        view.move_down_half_page();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ gary_the_snail
+⏵ (karen)
+⏵ king_neptune
+⏵ krabby_patty
+"
+            .trim()
+        );
+
+        view.move_down_half_page();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ gary_the_snail
+⏵ karen
+⏵ king_neptune
+⏵ (krabby_patty)
+"
+            .trim()
+        );
+
+        view.move_down_half_page();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ king_neptune
+⏵ krabby_patty
+⏵ larry_the_lobster
+⏵ (mrs_puff)
+"
+            .trim()
+        );
+
+        view.move_up_half_page();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ king_neptune
+⏵ (krabby_patty)
+⏵ larry_the_lobster
+⏵ mrs_puff
+"
+            .trim()
+        );
+
+        view.move_up_half_page();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ (karen)
+⏵ king_neptune
+⏵ krabby_patty
+⏵ larry_the_lobster
+"
+            .trim()
+        );
+
+        view.move_up_half_page();
+        assert_eq!(
+            render(&mut view),
+            "
+(who_lives_in_a_pineapple_under_the_sea)
+⏵ gary_the_snail
+⏵ karen
+⏵ king_neptune
+⏵ krabby_patty
+"
+            .trim()
+        );
+    }
+
+    #[test]
+    fn move_to_children_parent() {
+        let mut view = dummy_tree_view();
+        view.move_down(1);
+        view.move_to_children().unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏷ [gary_the_snail]
+  ⏵ (e_snail)
+  ⏵ gary_th
+⏵ karen
+ "
+            .trim()
+        );
+
+        view.move_down(1);
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏷ [gary_the_snail]
+  ⏵ e_snail
+  ⏵ (gary_th)
+⏵ karen
+ "
+            .trim()
+        );
+
+        view.move_to_parent().unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏷ (gary_the_snail)
+  ⏵ e_snail
+  ⏵ gary_th
+⏵ karen
+ "
+            .trim()
+        );
+
+        view.move_to_last_line();
+        view.move_to_parent().unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+(who_lives_in_a_pineapple_under_the_sea)
+⏷ gary_the_snail
+  ⏵ e_snail
+  ⏵ gary_th
+⏵ karen
+ "
+            .trim()
+        );
+    }
+
+    #[test]
+    fn test_move_left_right() {
+        let mut view = dummy_tree_view();
+
+        fn render(view: &mut TreeView<DivisibleItem>) -> String {
+            view.render_to_string(dummy_area().with_width(20))
+        }
+
+        assert_eq!(
+            render(&mut view),
+            "
+(who_lives_in_a_pinea)
+⏵ gary_the_snail
+⏵ karen
+⏵ king_neptune
+⏵ krabby_patty
+"
+            .trim()
+        );
+
+        view.move_right(1);
+        assert_eq!(
+            render(&mut view),
+            "
+(ho_lives_in_a_pineap)
+ gary_the_snail
+ karen
+ king_neptune
+ krabby_patty
+"
+            .trim()
+        );
+
+        view.move_right(1);
+        assert_eq!(
+            render(&mut view),
+            "
+(o_lives_in_a_pineapp)
+gary_the_snail
+karen
+king_neptune
+krabby_patty
+"
+            .trim()
+        );
+
+        view.move_right(1);
+        assert_eq!(
+            render(&mut view),
+            "
+(_lives_in_a_pineappl)
+ary_the_snail
+aren
+ing_neptune
+rabby_patty
+"
+            .trim()
+        );
+
+        view.move_left(1);
+        assert_eq!(
+            render(&mut view),
+            "
+(o_lives_in_a_pineapp)
+gary_the_snail
+karen
+king_neptune
+krabby_patty
+"
+            .trim()
+        );
+
+        view.move_leftmost();
+        assert_eq!(
+            render(&mut view),
+            "
+(who_lives_in_a_pinea)
+⏵ gary_the_snail
+⏵ karen
+⏵ king_neptune
+⏵ krabby_patty
+"
+            .trim()
+        );
+
+        view.move_left(1);
+        assert_eq!(
+            render(&mut view),
+            "
+(who_lives_in_a_pinea)
+⏵ gary_the_snail
+⏵ karen
+⏵ king_neptune
+⏵ krabby_patty
+"
+            .trim()
+        );
+
+        view.move_rightmost();
+        assert_eq!(render(&mut view), "(apple_under_the_sea)\n\n\n\n");
+    }
+
+    #[test]
+    fn test_move_to_parent_child() {
+        let mut view = dummy_tree_view();
+
+        view.move_to_children().unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ (gary_the_snail)
+⏵ karen
+⏵ king_neptune
+⏵ krabby_patty
+"
+            .trim()
+        );
+
+        view.move_to_children().unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏷ [gary_the_snail]
+  ⏵ (e_snail)
+  ⏵ gary_th
+⏵ karen
+"
+            .trim()
+        );
+
+        view.move_down(1);
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏷ [gary_the_snail]
+  ⏵ e_snail
+  ⏵ (gary_th)
+⏵ karen
+"
+            .trim()
+        );
+
+        view.move_to_parent().unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏷ (gary_the_snail)
+  ⏵ e_snail
+  ⏵ gary_th
+⏵ karen
+"
+            .trim()
+        );
+
+        view.move_to_parent().unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+(who_lives_in_a_pineapple_under_the_sea)
+⏷ gary_the_snail
+  ⏵ e_snail
+  ⏵ gary_th
+⏵ karen
+"
+            .trim()
+        );
+
+        view.move_to_parent().unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+(who_lives_in_a_pineapple_under_the_sea)
+⏷ gary_the_snail
+  ⏵ e_snail
+  ⏵ gary_th
+⏵ karen
+"
+            .trim()
+        )
+    }
+
+    #[test]
+    fn test_search_next() {
+        let mut view = dummy_tree_view();
+
+        view.search_next("pat");
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ gary_the_snail
+⏵ karen
+⏵ king_neptune
+⏵ (krabby_patty)
+"
+            .trim()
+        );
+
+        view.search_next("larr");
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ karen
+⏵ king_neptune
+⏵ krabby_patty
+⏵ (larry_the_lobster)
+"
+            .trim()
+        );
+
+        view.move_to_last_line();
+        view.search_next("who_lives");
+        assert_eq!(
+            render(&mut view),
+            "
+(who_lives_in_a_pineapple_under_the_sea)
+⏵ gary_the_snail
+⏵ karen
+⏵ king_neptune
+⏵ krabby_patty
+"
+            .trim()
+        );
+    }
+
+    #[test]
+    fn test_search_previous() {
+        let mut view = dummy_tree_view();
+
+        view.search_previous("larry");
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ karen
+⏵ king_neptune
+⏵ krabby_patty
+⏵ (larry_the_lobster)
+"
+            .trim()
+        );
+
+        view.move_to_last_line();
+        view.search_previous("krab");
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ karen
+⏵ king_neptune
+⏵ (krabby_patty)
+⏵ larry_the_lobster
+"
+            .trim()
+        );
+    }
+
+    #[test]
+    fn test_move_to_next_search_match() {
+        let mut view = dummy_tree_view();
+        view.set_search_str("pat".to_string());
+        view.move_to_next_search_match();
+
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ gary_the_snail
+⏵ karen
+⏵ king_neptune
+⏵ (krabby_patty)
+ "
+            .trim()
+        );
+
+        view.move_to_next_search_match();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ krabby_patty
+⏵ larry_the_lobster
+⏵ mrs_puff
+⏵ (patrick_star)
+ "
+            .trim()
+        );
+
+        view.move_to_next_search_match();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ (krabby_patty)
+⏵ larry_the_lobster
+⏵ mrs_puff
+⏵ patrick_star
+ "
+            .trim()
+        );
+    }
+
+    #[test]
+    fn test_move_to_previous_search_match() {
+        let mut view = dummy_tree_view();
+        view.set_search_str("pat".to_string());
+        view.move_to_previous_next_match();
+
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ krabby_patty
+⏵ larry_the_lobster
+⏵ mrs_puff
+⏵ (patrick_star)
+ "
+            .trim()
+        );
+
+        view.move_to_previous_next_match();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ (krabby_patty)
+⏵ larry_the_lobster
+⏵ mrs_puff
+⏵ patrick_star
+ "
+            .trim()
+        );
+
+        view.move_to_previous_next_match();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ krabby_patty
+⏵ larry_the_lobster
+⏵ mrs_puff
+⏵ (patrick_star)
+ "
+            .trim()
+        );
+    }
+
+    #[test]
+    fn test_jump_backward_forward() {
+        let mut view = dummy_tree_view();
+        view.move_down_half_page();
+        render(&mut view);
+
+        view.move_down_half_page();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ gary_the_snail
+⏵ karen
+⏵ king_neptune
+⏵ (krabby_patty)
+          "
+            .trim()
+        );
+
+        view.jump_backward();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ gary_the_snail
+⏵ (karen)
+⏵ king_neptune
+⏵ krabby_patty
+          "
+            .trim()
+        );
+
+        view.jump_backward();
+        assert_eq!(
+            render(&mut view),
+            "
+(who_lives_in_a_pineapple_under_the_sea)
+⏵ gary_the_snail
+⏵ karen
+⏵ king_neptune
+⏵ krabby_patty
+          "
+            .trim()
+        );
+
+        view.jump_forward();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ gary_the_snail
+⏵ (karen)
+⏵ king_neptune
+⏵ krabby_patty
+          "
+            .trim()
+        );
+
+        view.jump_forward();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ gary_the_snail
+⏵ karen
+⏵ king_neptune
+⏵ (krabby_patty)
+          "
+            .trim()
+        );
+
+        view.jump_backward();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ gary_the_snail
+⏵ (karen)
+⏵ king_neptune
+⏵ krabby_patty
+          "
+            .trim()
+        );
+    }
+
+    mod static_tree {
+        use crate::ui::{TreeView, TreeViewItem};
+
+        use super::dummy_area;
+
+        #[derive(PartialEq, Eq, PartialOrd, Ord, Clone)]
+        /// This is used for test cases where the structure of the tree has to be known upfront
+        pub struct StaticItem<'a> {
+            pub name: &'a str,
+            pub children: Option<Vec<StaticItem<'a>>>,
+        }
+
+        pub fn parent<'a>(name: &'a str, children: Vec<StaticItem<'a>>) -> StaticItem<'a> {
+            StaticItem {
+                name,
+                children: Some(children),
+            }
+        }
+
+        pub fn child(name: &str) -> StaticItem {
+            StaticItem {
+                name,
+                children: None,
+            }
+        }
+
+        impl<'a> TreeViewItem for StaticItem<'a> {
+            type Params = ();
+
+            fn name(&self) -> String {
+                self.name.to_string()
+            }
+
+            fn is_parent(&self) -> bool {
+                self.children.is_some()
+            }
+
+            fn get_children(&self) -> anyhow::Result<Vec<Self>> {
+                match &self.children {
+                    Some(children) => Ok(children.clone()),
+                    None => Ok(vec![]),
+                }
+            }
+        }
+
+        pub fn render(view: &mut TreeView<StaticItem<'_>>) -> String {
+            view.render_to_string(dummy_area().with_height(3))
+        }
+    }
+
+    #[test]
+    fn test_sticky_ancestors() {
+        // The ancestors of the current item should always be visible
+        // However, if there's not enough space, the current item will take precedence,
+        // and the nearest ancestor has higher precedence than further ancestors
+        use static_tree::*;
+
+        let mut view = TreeView::build_tree(parent(
+            "root",
+            vec![
+                parent("a", vec![child("aa"), child("ab")]),
+                parent(
+                    "b",
+                    vec![parent(
+                        "ba",
+                        vec![parent("baa", vec![child("baaa"), child("baab")])],
+                    )],
+                ),
+            ],
+        ))
+        .unwrap();
+
+        assert_eq!(
+            render(&mut view),
+            "
+(root)
+⏵ a
+⏵ b
+          "
+            .trim()
+        );
+
+        // 1. Move down to "a", and expand it
+        view.move_down(1);
+        view.move_to_children().unwrap();
+
+        assert_eq!(
+            render(&mut view),
+            "
+[root]
+⏷ [a]
+    (aa)
+          "
+            .trim()
+        );
+
+        // 2. Move down by 1
+        view.move_down(1);
+
+        // 2a. Expect all ancestors (i.e. "root" and "a") are visible,
+        //     and the cursor is at "ab"
+        assert_eq!(
+            render(&mut view),
+            "
+[root]
+⏷ [a]
+    (ab)
+          "
+            .trim()
+        );
+
+        // 3. Move down by 1
+        view.move_down(1);
+
+        // 3a. Expect "a" is out of view, because it is no longer the ancestor of the current item
+        assert_eq!(
+            render(&mut view),
+            "
+[root]
+    ab
+⏵ (b)
+          "
+            .trim()
+        );
+
+        // 4. Move to the children of "b", which is "ba"
+        view.move_to_children().unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+[root]
+⏷ [b]
+  ⏵ (ba)
+          "
+            .trim()
+        );
+
+        // 5. Move to the children of "ba", which is "baa"
+        view.move_to_children().unwrap();
+
+        // 5a. Expect the furthest ancestor "root" is out of view,
+        //     because when there's no enough space, the nearest ancestor takes precedence
+        assert_eq!(
+            render(&mut view),
+            "
+⏷ [b]
+  ⏷ [ba]
+    ⏵ (baa)
+          "
+            .trim()
+        );
+
+        // 5.1 Move to child
+        view.move_to_children().unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+  ⏷ [ba]
+    ⏷ [baa]
+        (baaa)
+"
+            .trim_matches('\n')
+        );
+
+        // 5.2 Move down
+        view.move_down(1);
+        assert_eq!(
+            render(&mut view),
+            "
+  ⏷ [ba]
+    ⏷ [baa]
+        (baab)
+"
+            .trim_matches('\n')
+        );
+
+        // 5.3 Move up
+        view.move_up(1);
+        assert_eq!(view.current_item().unwrap().name, "baaa");
+        assert_eq!(
+            render(&mut view),
+            "
+  ⏷ [ba]
+    ⏷ [baa]
+        (baaa)
+"
+            .trim_matches('\n')
+        );
+
+        // 5.4 Move up
+        view.move_up(1);
+        assert_eq!(
+            render(&mut view),
+            "
+⏷ [b]
+  ⏷ [ba]
+    ⏷ (baa)
+          "
+            .trim()
+        );
+
+        // 6. Move up by one
+        view.move_up(1);
+
+        // 6a. Expect "root" is visible again, because now there's enough space to render all
+        //     ancestors
+        assert_eq!(
+            render(&mut view),
+            "
+[root]
+⏷ [b]
+  ⏷ (ba)
+          "
+            .trim()
+        );
+
+        // 7. Move up by one
+        view.move_up(1);
+        assert_eq!(
+            render(&mut view),
+            "
+[root]
+⏷ (b)
+  ⏷ ba
+          "
+            .trim()
+        );
+
+        // 8. Move up by one
+        view.move_up(1);
+        assert_eq!(
+            render(&mut view),
+            "
+[root]
+⏷ [a]
+    (ab)
+          "
+            .trim()
+        );
+
+        // 9. Move up by one
+        view.move_up(1);
+        assert_eq!(
+            render(&mut view),
+            "
+[root]
+⏷ [a]
+    (aa)
+          "
+            .trim()
+        );
+    }
+
+    #[tokio::test(flavor = "multi_thread")]
+    async fn test_search_prompt() {
+        let mut editor = Context::dummy_editor();
+        let mut jobs = Context::dummy_jobs();
+        let mut cx = Context::dummy(&mut jobs, &mut editor);
+        let mut view = dummy_tree_view();
+
+        view.handle_events("/an", &mut cx, &mut ()).unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ larry_the_lobster
+⏵ mrs_puff
+⏵ patrick_star
+⏵ (plankton)
+            "
+            .trim()
+        );
+
+        view.handle_events("t<ret>", &mut cx, &mut ()).unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ patrick_star
+⏵ plankton
+⏵ sandy_cheeks
+⏵ (spongebob_squarepants)
+            "
+            .trim()
+        );
+
+        view.handle_events("/larry", &mut cx, &mut ()).unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ karen
+⏵ king_neptune
+⏵ krabby_patty
+⏵ (larry_the_lobster)
+           "
+            .trim()
+        );
+
+        view.handle_events("<esc>", &mut cx, &mut ()).unwrap();
+        assert_eq!(
+            render(&mut view),
+            "
+[who_lives_in_a_pineapple_under_the_sea]
+⏵ patrick_star
+⏵ plankton
+⏵ sandy_cheeks
+⏵ (spongebob_squarepants)
+           "
+            .trim()
+        );
+    }
+}
+
+#[cfg(test)]
+mod test_tree {
+    use helix_core::movement::Direction;
+
+    use super::Tree;
+
+    #[test]
+    fn test_get() {
+        let result = Tree::new(
+            "root",
+            vec![
+                Tree::new("foo", vec![Tree::new("bar", vec![])]),
+                Tree::new(
+                    "spam",
+                    vec![Tree::new("jar", vec![Tree::new("yo", vec![])])],
+                ),
+            ],
+        );
+        assert_eq!(result.get(0).unwrap().item, "root");
+        assert_eq!(result.get(1).unwrap().item, "foo");
+        assert_eq!(result.get(2).unwrap().item, "bar");
+        assert_eq!(result.get(3).unwrap().item, "spam");
+        assert_eq!(result.get(4).unwrap().item, "jar");
+        assert_eq!(result.get(5).unwrap().item, "yo");
+    }
+
+    #[test]
+    fn test_iter() {
+        let tree = Tree::new(
+            "spam",
+            vec![
+                Tree::new("jar", vec![Tree::new("yo", vec![])]),
+                Tree::new("foo", vec![Tree::new("bar", vec![])]),
+            ],
+        );
+
+        let mut iter = tree.iter();
+        assert_eq!(iter.next().map(|tree| tree.item), Some("spam"));
+        assert_eq!(iter.next().map(|tree| tree.item), Some("jar"));
+        assert_eq!(iter.next().map(|tree| tree.item), Some("yo"));
+        assert_eq!(iter.next().map(|tree| tree.item), Some("foo"));
+        assert_eq!(iter.next().map(|tree| tree.item), Some("bar"));
+
+        assert_eq!(iter.next().map(|tree| tree.item), None)
+    }
+
+    #[test]
+    fn test_iter_double_ended() {
+        let tree = Tree::new(
+            "spam",
+            vec![
+                Tree::new("jar", vec![Tree::new("yo", vec![])]),
+                Tree::new("foo", vec![Tree::new("bar", vec![])]),
+            ],
+        );
+
+        let mut iter = tree.iter();
+        assert_eq!(iter.next_back().map(|tree| tree.item), Some("bar"));
+        assert_eq!(iter.next_back().map(|tree| tree.item), Some("foo"));
+        assert_eq!(iter.next_back().map(|tree| tree.item), Some("yo"));
+        assert_eq!(iter.next_back().map(|tree| tree.item), Some("jar"));
+        assert_eq!(iter.next_back().map(|tree| tree.item), Some("spam"));
+        assert_eq!(iter.next_back().map(|tree| tree.item), None)
+    }
+
+    #[test]
+    fn test_len() {
+        let tree = Tree::new(
+            "spam",
+            vec![
+                Tree::new("jar", vec![Tree::new("yo", vec![])]),
+                Tree::new("foo", vec![Tree::new("bar", vec![])]),
+            ],
+        );
+
+        assert_eq!(tree.len(), 5)
+    }
+
+    #[test]
+    fn test_find_forward() {
+        let tree = Tree::new(
+            ".cargo",
+            vec![
+                Tree::new("jar", vec![Tree::new("Cargo.toml", vec![])]),
+                Tree::new("Cargo.toml", vec![Tree::new("bar", vec![])]),
+            ],
+        );
+        let result = tree.find(0, Direction::Forward, |tree| {
+            tree.item.to_lowercase().contains(&"cargo".to_lowercase())
+        });
+
+        assert_eq!(result, Some(0));
+
+        let result = tree.find(1, Direction::Forward, |tree| {
+            tree.item.to_lowercase().contains(&"cargo".to_lowercase())
+        });
+
+        assert_eq!(result, Some(2));
+
+        let result = tree.find(2, Direction::Forward, |tree| {
+            tree.item.to_lowercase().contains(&"cargo".to_lowercase())
+        });
+
+        assert_eq!(result, Some(2));
+
+        let result = tree.find(3, Direction::Forward, |tree| {
+            tree.item.to_lowercase().contains(&"cargo".to_lowercase())
+        });
+
+        assert_eq!(result, Some(3));
+
+        let result = tree.find(4, Direction::Forward, |tree| {
+            tree.item.to_lowercase().contains(&"cargo".to_lowercase())
+        });
+
+        assert_eq!(result, Some(0));
+    }
+
+    #[test]
+    fn test_find_backward() {
+        let tree = Tree::new(
+            ".cargo",
+            vec![
+                Tree::new("jar", vec![Tree::new("Cargo.toml", vec![])]),
+                Tree::new("Cargo.toml", vec![Tree::new("bar", vec![])]),
+            ],
+        );
+        let result = tree.find(0, Direction::Backward, |tree| {
+            tree.item.to_lowercase().contains(&"cargo".to_lowercase())
+        });
+
+        assert_eq!(result, Some(3));
+
+        let result = tree.find(1, Direction::Backward, |tree| {
+            tree.item.to_lowercase().contains(&"cargo".to_lowercase())
+        });
+
+        assert_eq!(result, Some(0));
+
+        let result = tree.find(2, Direction::Backward, |tree| {
+            tree.item.to_lowercase().contains(&"cargo".to_lowercase())
+        });
+
+        assert_eq!(result, Some(0));
+
+        let result = tree.find(3, Direction::Backward, |tree| {
+            tree.item.to_lowercase().contains(&"cargo".to_lowercase())
+        });
+
+        assert_eq!(result, Some(2));
+
+        let result = tree.find(4, Direction::Backward, |tree| {
+            tree.item.to_lowercase().contains(&"cargo".to_lowercase())
+        });
+
+        assert_eq!(result, Some(3));
+    }
+}