Merge branch 'main' into multibuffer-following

crates/workspace/src/item.rs

@@ -0,0 +1,918 @@
+use std::{
+    any::{Any, TypeId},
+    borrow::Cow,
+    cell::RefCell,
+    fmt,
+    path::PathBuf,
+    rc::Rc,
+    sync::atomic::{AtomicBool, Ordering},
+    time::Duration,
+};
+
+use anyhow::Result;
+use client::proto;
+use gpui::{
+    AnyViewHandle, AppContext, ElementBox, ModelHandle, MutableAppContext, Task, View, ViewContext,
+    ViewHandle, WeakViewHandle,
+};
+use project::{Project, ProjectEntryId, ProjectPath};
+use settings::{Autosave, Settings};
+use smallvec::SmallVec;
+use theme::Theme;
+use util::ResultExt;
+
+use crate::{
+    pane, persistence::model::ItemId, searchable::SearchableItemHandle, DelayedDebouncedEditAction,
+    FollowableItemBuilders, ItemNavHistory, Pane, ToolbarItemLocation, Workspace, WorkspaceId,
+};
+
+#[derive(Eq, PartialEq, Hash)]
+pub enum ItemEvent {
+    CloseItem,
+    UpdateTab,
+    UpdateBreadcrumbs,
+    Edit,
+}
+
+pub trait Item: View {
+    fn deactivated(&mut self, _: &mut ViewContext<Self>) {}
+    fn workspace_deactivated(&mut self, _: &mut ViewContext<Self>) {}
+    fn navigate(&mut self, _: Box<dyn Any>, _: &mut ViewContext<Self>) -> bool {
+        false
+    }
+    fn tab_description<'a>(&'a self, _: usize, _: &'a AppContext) -> Option<Cow<'a, str>> {
+        None
+    }
+    fn tab_content(&self, detail: Option<usize>, style: &theme::Tab, cx: &AppContext)
+        -> ElementBox;
+    fn project_path(&self, cx: &AppContext) -> Option<ProjectPath>;
+    fn project_entry_ids(&self, cx: &AppContext) -> SmallVec<[ProjectEntryId; 3]>;
+    fn is_singleton(&self, cx: &AppContext) -> bool;
+    fn set_nav_history(&mut self, _: ItemNavHistory, _: &mut ViewContext<Self>);
+    fn clone_on_split(&self, _workspace_id: WorkspaceId, _: &mut ViewContext<Self>) -> Option<Self>
+    where
+        Self: Sized,
+    {
+        None
+    }
+    fn is_dirty(&self, _: &AppContext) -> bool {
+        false
+    }
+    fn has_conflict(&self, _: &AppContext) -> bool {
+        false
+    }
+    fn can_save(&self, cx: &AppContext) -> bool;
+    fn save(
+        &mut self,
+        project: ModelHandle<Project>,
+        cx: &mut ViewContext<Self>,
+    ) -> Task<Result<()>>;
+    fn save_as(
+        &mut self,
+        project: ModelHandle<Project>,
+        abs_path: PathBuf,
+        cx: &mut ViewContext<Self>,
+    ) -> Task<Result<()>>;
+    fn reload(
+        &mut self,
+        project: ModelHandle<Project>,
+        cx: &mut ViewContext<Self>,
+    ) -> Task<Result<()>>;
+    fn git_diff_recalc(
+        &mut self,
+        _project: ModelHandle<Project>,
+        _cx: &mut ViewContext<Self>,
+    ) -> Task<Result<()>> {
+        Task::ready(Ok(()))
+    }
+    fn to_item_events(event: &Self::Event) -> Vec<ItemEvent>;
+    fn should_close_item_on_event(_: &Self::Event) -> bool {
+        false
+    }
+    fn should_update_tab_on_event(_: &Self::Event) -> bool {
+        false
+    }
+    fn is_edit_event(_: &Self::Event) -> bool {
+        false
+    }
+    fn act_as_type(
+        &self,
+        type_id: TypeId,
+        self_handle: &ViewHandle<Self>,
+        _: &AppContext,
+    ) -> Option<AnyViewHandle> {
+        if TypeId::of::<Self>() == type_id {
+            Some(self_handle.into())
+        } else {
+            None
+        }
+    }
+    fn as_searchable(&self, _: &ViewHandle<Self>) -> Option<Box<dyn SearchableItemHandle>> {
+        None
+    }
+
+    fn breadcrumb_location(&self) -> ToolbarItemLocation {
+        ToolbarItemLocation::Hidden
+    }
+
+    fn breadcrumbs(&self, _theme: &Theme, _cx: &AppContext) -> Option<Vec<ElementBox>> {
+        None
+    }
+
+    fn added_to_workspace(&mut self, _workspace: &mut Workspace, _cx: &mut ViewContext<Self>) {}
+
+    fn serialized_item_kind() -> Option<&'static str>;
+
+    fn deserialize(
+        project: ModelHandle<Project>,
+        workspace: WeakViewHandle<Workspace>,
+        workspace_id: WorkspaceId,
+        item_id: ItemId,
+        cx: &mut ViewContext<Pane>,
+    ) -> Task<Result<ViewHandle<Self>>>;
+}
+
+pub trait ItemHandle: 'static + fmt::Debug {
+    fn subscribe_to_item_events(
+        &self,
+        cx: &mut MutableAppContext,
+        handler: Box<dyn Fn(ItemEvent, &mut MutableAppContext)>,
+    ) -> gpui::Subscription;
+    fn tab_description<'a>(&self, detail: usize, cx: &'a AppContext) -> Option<Cow<'a, str>>;
+    fn tab_content(&self, detail: Option<usize>, style: &theme::Tab, cx: &AppContext)
+        -> ElementBox;
+    fn project_path(&self, cx: &AppContext) -> Option<ProjectPath>;
+    fn project_entry_ids(&self, cx: &AppContext) -> SmallVec<[ProjectEntryId; 3]>;
+    fn is_singleton(&self, cx: &AppContext) -> bool;
+    fn boxed_clone(&self) -> Box<dyn ItemHandle>;
+    fn clone_on_split(
+        &self,
+        workspace_id: WorkspaceId,
+        cx: &mut MutableAppContext,
+    ) -> Option<Box<dyn ItemHandle>>;
+    fn added_to_pane(
+        &self,
+        workspace: &mut Workspace,
+        pane: ViewHandle<Pane>,
+        cx: &mut ViewContext<Workspace>,
+    );
+    fn deactivated(&self, cx: &mut MutableAppContext);
+    fn workspace_deactivated(&self, cx: &mut MutableAppContext);
+    fn navigate(&self, data: Box<dyn Any>, cx: &mut MutableAppContext) -> bool;
+    fn id(&self) -> usize;
+    fn window_id(&self) -> usize;
+    fn to_any(&self) -> AnyViewHandle;
+    fn is_dirty(&self, cx: &AppContext) -> bool;
+    fn has_conflict(&self, cx: &AppContext) -> bool;
+    fn can_save(&self, cx: &AppContext) -> bool;
+    fn save(&self, project: ModelHandle<Project>, cx: &mut MutableAppContext) -> Task<Result<()>>;
+    fn save_as(
+        &self,
+        project: ModelHandle<Project>,
+        abs_path: PathBuf,
+        cx: &mut MutableAppContext,
+    ) -> Task<Result<()>>;
+    fn reload(&self, project: ModelHandle<Project>, cx: &mut MutableAppContext)
+        -> Task<Result<()>>;
+    fn git_diff_recalc(
+        &self,
+        project: ModelHandle<Project>,
+        cx: &mut MutableAppContext,
+    ) -> Task<Result<()>>;
+    fn act_as_type(&self, type_id: TypeId, cx: &AppContext) -> Option<AnyViewHandle>;
+    fn to_followable_item_handle(&self, cx: &AppContext) -> Option<Box<dyn FollowableItemHandle>>;
+    fn on_release(
+        &self,
+        cx: &mut MutableAppContext,
+        callback: Box<dyn FnOnce(&mut MutableAppContext)>,
+    ) -> gpui::Subscription;
+    fn to_searchable_item_handle(&self, cx: &AppContext) -> Option<Box<dyn SearchableItemHandle>>;
+    fn breadcrumb_location(&self, cx: &AppContext) -> ToolbarItemLocation;
+    fn breadcrumbs(&self, theme: &Theme, cx: &AppContext) -> Option<Vec<ElementBox>>;
+    fn serialized_item_kind(&self) -> Option<&'static str>;
+}
+
+pub trait WeakItemHandle {
+    fn id(&self) -> usize;
+    fn window_id(&self) -> usize;
+    fn upgrade(&self, cx: &AppContext) -> Option<Box<dyn ItemHandle>>;
+}
+
+impl dyn ItemHandle {
+    pub fn downcast<T: View>(&self) -> Option<ViewHandle<T>> {
+        self.to_any().downcast()
+    }
+
+    pub fn act_as<T: View>(&self, cx: &AppContext) -> Option<ViewHandle<T>> {
+        self.act_as_type(TypeId::of::<T>(), cx)
+            .and_then(|t| t.downcast())
+    }
+}
+
+impl<T: Item> ItemHandle for ViewHandle<T> {
+    fn subscribe_to_item_events(
+        &self,
+        cx: &mut MutableAppContext,
+        handler: Box<dyn Fn(ItemEvent, &mut MutableAppContext)>,
+    ) -> gpui::Subscription {
+        cx.subscribe(self, move |_, event, cx| {
+            for item_event in T::to_item_events(event) {
+                handler(item_event, cx)
+            }
+        })
+    }
+
+    fn tab_description<'a>(&self, detail: usize, cx: &'a AppContext) -> Option<Cow<'a, str>> {
+        self.read(cx).tab_description(detail, cx)
+    }
+
+    fn tab_content(
+        &self,
+        detail: Option<usize>,
+        style: &theme::Tab,
+        cx: &AppContext,
+    ) -> ElementBox {
+        self.read(cx).tab_content(detail, style, cx)
+    }
+
+    fn project_path(&self, cx: &AppContext) -> Option<ProjectPath> {
+        self.read(cx).project_path(cx)
+    }
+
+    fn project_entry_ids(&self, cx: &AppContext) -> SmallVec<[ProjectEntryId; 3]> {
+        self.read(cx).project_entry_ids(cx)
+    }
+
+    fn is_singleton(&self, cx: &AppContext) -> bool {
+        self.read(cx).is_singleton(cx)
+    }
+
+    fn boxed_clone(&self) -> Box<dyn ItemHandle> {
+        Box::new(self.clone())
+    }
+
+    fn clone_on_split(
+        &self,
+        workspace_id: WorkspaceId,
+        cx: &mut MutableAppContext,
+    ) -> Option<Box<dyn ItemHandle>> {
+        self.update(cx, |item, cx| {
+            cx.add_option_view(|cx| item.clone_on_split(workspace_id, cx))
+        })
+        .map(|handle| Box::new(handle) as Box<dyn ItemHandle>)
+    }
+
+    fn added_to_pane(
+        &self,
+        workspace: &mut Workspace,
+        pane: ViewHandle<Pane>,
+        cx: &mut ViewContext<Workspace>,
+    ) {
+        let history = pane.read(cx).nav_history_for_item(self);
+        self.update(cx, |this, cx| {
+            this.set_nav_history(history, cx);
+            this.added_to_workspace(workspace, cx);
+        });
+
+        if let Some(followed_item) = self.to_followable_item_handle(cx) {
+            if let Some(message) = followed_item.to_state_proto(cx) {
+                workspace.update_followers(
+                    proto::update_followers::Variant::CreateView(proto::View {
+                        id: followed_item.id() as u64,
+                        variant: Some(message),
+                        leader_id: workspace.leader_for_pane(&pane).map(|id| id.0),
+                    }),
+                    cx,
+                );
+            }
+        }
+
+        if workspace
+            .panes_by_item
+            .insert(self.id(), pane.downgrade())
+            .is_none()
+        {
+            let mut pending_autosave = DelayedDebouncedEditAction::new();
+            let mut pending_git_update = DelayedDebouncedEditAction::new();
+            let pending_update = Rc::new(RefCell::new(None));
+            let pending_update_scheduled = Rc::new(AtomicBool::new(false));
+
+            let mut event_subscription =
+                Some(cx.subscribe(self, move |workspace, item, event, cx| {
+                    let pane = if let Some(pane) = workspace
+                        .panes_by_item
+                        .get(&item.id())
+                        .and_then(|pane| pane.upgrade(cx))
+                    {
+                        pane
+                    } else {
+                        log::error!("unexpected item event after pane was dropped");
+                        return;
+                    };
+
+                    if let Some(item) = item.to_followable_item_handle(cx) {
+                        let leader_id = workspace.leader_for_pane(&pane);
+
+                        if leader_id.is_some() && item.should_unfollow_on_event(event, cx) {
+                            workspace.unfollow(&pane, cx);
+                        }
+
+                        if item.add_event_to_update_proto(
+                            event,
+                            &mut *pending_update.borrow_mut(),
+                            cx,
+                        ) && !pending_update_scheduled.load(Ordering::SeqCst)
+                        {
+                            pending_update_scheduled.store(true, Ordering::SeqCst);
+                            cx.after_window_update({
+                                let pending_update = pending_update.clone();
+                                let pending_update_scheduled = pending_update_scheduled.clone();
+                                move |this, cx| {
+                                    pending_update_scheduled.store(false, Ordering::SeqCst);
+                                    this.update_followers(
+                                        proto::update_followers::Variant::UpdateView(
+                                            proto::UpdateView {
+                                                id: item.id() as u64,
+                                                variant: pending_update.borrow_mut().take(),
+                                                leader_id: leader_id.map(|id| id.0),
+                                            },
+                                        ),
+                                        cx,
+                                    );
+                                }
+                            });
+                        }
+                    }
+
+                    for item_event in T::to_item_events(event).into_iter() {
+                        match item_event {
+                            ItemEvent::CloseItem => {
+                                Pane::close_item(workspace, pane, item.id(), cx)
+                                    .detach_and_log_err(cx);
+                                return;
+                            }
+
+                            ItemEvent::UpdateTab => {
+                                pane.update(cx, |_, cx| {
+                                    cx.emit(pane::Event::ChangeItemTitle);
+                                    cx.notify();
+                                });
+                            }
+
+                            ItemEvent::Edit => {
+                                if let Autosave::AfterDelay { milliseconds } =
+                                    cx.global::<Settings>().autosave
+                                {
+                                    let delay = Duration::from_millis(milliseconds);
+                                    let item = item.clone();
+                                    pending_autosave.fire_new(
+                                        delay,
+                                        workspace,
+                                        cx,
+                                        |project, mut cx| async move {
+                                            cx.update(|cx| Pane::autosave_item(&item, project, cx))
+                                                .await
+                                                .log_err();
+                                        },
+                                    );
+                                }
+
+                                let settings = cx.global::<Settings>();
+                                let debounce_delay = settings.git_overrides.gutter_debounce;
+
+                                let item = item.clone();
+
+                                if let Some(delay) = debounce_delay {
+                                    const MIN_GIT_DELAY: u64 = 50;
+
+                                    let delay = delay.max(MIN_GIT_DELAY);
+                                    let duration = Duration::from_millis(delay);
+
+                                    pending_git_update.fire_new(
+                                        duration,
+                                        workspace,
+                                        cx,
+                                        |project, mut cx| async move {
+                                            cx.update(|cx| item.git_diff_recalc(project, cx))
+                                                .await
+                                                .log_err();
+                                        },
+                                    );
+                                } else {
+                                    let project = workspace.project().downgrade();
+                                    cx.spawn_weak(|_, mut cx| async move {
+                                        if let Some(project) = project.upgrade(&cx) {
+                                            cx.update(|cx| item.git_diff_recalc(project, cx))
+                                                .await
+                                                .log_err();
+                                        }
+                                    })
+                                    .detach();
+                                }
+                            }
+
+                            _ => {}
+                        }
+                    }
+                }));
+
+            cx.observe_focus(self, move |workspace, item, focused, cx| {
+                if !focused && cx.global::<Settings>().autosave == Autosave::OnFocusChange {
+                    Pane::autosave_item(&item, workspace.project.clone(), cx)
+                        .detach_and_log_err(cx);
+                }
+            })
+            .detach();
+
+            let item_id = self.id();
+            cx.observe_release(self, move |workspace, _, _| {
+                workspace.panes_by_item.remove(&item_id);
+                event_subscription.take();
+            })
+            .detach();
+        }
+
+        cx.defer(|workspace, cx| {
+            workspace.serialize_workspace(cx);
+        });
+    }
+
+    fn deactivated(&self, cx: &mut MutableAppContext) {
+        self.update(cx, |this, cx| this.deactivated(cx));
+    }
+
+    fn workspace_deactivated(&self, cx: &mut MutableAppContext) {
+        self.update(cx, |this, cx| this.workspace_deactivated(cx));
+    }
+
+    fn navigate(&self, data: Box<dyn Any>, cx: &mut MutableAppContext) -> bool {
+        self.update(cx, |this, cx| this.navigate(data, cx))
+    }
+
+    fn id(&self) -> usize {
+        self.id()
+    }
+
+    fn window_id(&self) -> usize {
+        self.window_id()
+    }
+
+    fn to_any(&self) -> AnyViewHandle {
+        self.into()
+    }
+
+    fn is_dirty(&self, cx: &AppContext) -> bool {
+        self.read(cx).is_dirty(cx)
+    }
+
+    fn has_conflict(&self, cx: &AppContext) -> bool {
+        self.read(cx).has_conflict(cx)
+    }
+
+    fn can_save(&self, cx: &AppContext) -> bool {
+        self.read(cx).can_save(cx)
+    }
+
+    fn save(&self, project: ModelHandle<Project>, cx: &mut MutableAppContext) -> Task<Result<()>> {
+        self.update(cx, |item, cx| item.save(project, cx))
+    }
+
+    fn save_as(
+        &self,
+        project: ModelHandle<Project>,
+        abs_path: PathBuf,
+        cx: &mut MutableAppContext,
+    ) -> Task<anyhow::Result<()>> {
+        self.update(cx, |item, cx| item.save_as(project, abs_path, cx))
+    }
+
+    fn reload(
+        &self,
+        project: ModelHandle<Project>,
+        cx: &mut MutableAppContext,
+    ) -> Task<Result<()>> {
+        self.update(cx, |item, cx| item.reload(project, cx))
+    }
+
+    fn git_diff_recalc(
+        &self,
+        project: ModelHandle<Project>,
+        cx: &mut MutableAppContext,
+    ) -> Task<Result<()>> {
+        self.update(cx, |item, cx| item.git_diff_recalc(project, cx))
+    }
+
+    fn act_as_type(&self, type_id: TypeId, cx: &AppContext) -> Option<AnyViewHandle> {
+        self.read(cx).act_as_type(type_id, self, cx)
+    }
+
+    fn to_followable_item_handle(&self, cx: &AppContext) -> Option<Box<dyn FollowableItemHandle>> {
+        if cx.has_global::<FollowableItemBuilders>() {
+            let builders = cx.global::<FollowableItemBuilders>();
+            let item = self.to_any();
+            Some(builders.get(&item.view_type())?.1(item))
+        } else {
+            None
+        }
+    }
+
+    fn on_release(
+        &self,
+        cx: &mut MutableAppContext,
+        callback: Box<dyn FnOnce(&mut MutableAppContext)>,
+    ) -> gpui::Subscription {
+        cx.observe_release(self, move |_, cx| callback(cx))
+    }
+
+    fn to_searchable_item_handle(&self, cx: &AppContext) -> Option<Box<dyn SearchableItemHandle>> {
+        self.read(cx).as_searchable(self)
+    }
+
+    fn breadcrumb_location(&self, cx: &AppContext) -> ToolbarItemLocation {
+        self.read(cx).breadcrumb_location()
+    }
+
+    fn breadcrumbs(&self, theme: &Theme, cx: &AppContext) -> Option<Vec<ElementBox>> {
+        self.read(cx).breadcrumbs(theme, cx)
+    }
+
+    fn serialized_item_kind(&self) -> Option<&'static str> {
+        T::serialized_item_kind()
+    }
+}
+
+impl From<Box<dyn ItemHandle>> for AnyViewHandle {
+    fn from(val: Box<dyn ItemHandle>) -> Self {
+        val.to_any()
+    }
+}
+
+impl From<&Box<dyn ItemHandle>> for AnyViewHandle {
+    fn from(val: &Box<dyn ItemHandle>) -> Self {
+        val.to_any()
+    }
+}
+
+impl Clone for Box<dyn ItemHandle> {
+    fn clone(&self) -> Box<dyn ItemHandle> {
+        self.boxed_clone()
+    }
+}
+
+impl<T: Item> WeakItemHandle for WeakViewHandle<T> {
+    fn id(&self) -> usize {
+        self.id()
+    }
+
+    fn window_id(&self) -> usize {
+        self.window_id()
+    }
+
+    fn upgrade(&self, cx: &AppContext) -> Option<Box<dyn ItemHandle>> {
+        self.upgrade(cx).map(|v| Box::new(v) as Box<dyn ItemHandle>)
+    }
+}
+
+pub trait ProjectItem: Item {
+    type Item: project::Item;
+
+    fn for_project_item(
+        project: ModelHandle<Project>,
+        item: ModelHandle<Self::Item>,
+        cx: &mut ViewContext<Self>,
+    ) -> Self;
+}
+
+pub trait FollowableItem: Item {
+    fn to_state_proto(&self, cx: &AppContext) -> Option<proto::view::Variant>;
+    fn from_state_proto(
+        pane: ViewHandle<Pane>,
+        project: ModelHandle<Project>,
+        state: &mut Option<proto::view::Variant>,
+        cx: &mut MutableAppContext,
+    ) -> Option<Task<Result<ViewHandle<Self>>>>;
+    fn add_event_to_update_proto(
+        &self,
+        event: &Self::Event,
+        update: &mut Option<proto::update_view::Variant>,
+        cx: &AppContext,
+    ) -> bool;
+    fn apply_update_proto(
+        &mut self,
+        project: &ModelHandle<Project>,
+        message: proto::update_view::Variant,
+        cx: &mut ViewContext<Self>,
+    ) -> Task<Result<()>>;
+
+    fn set_leader_replica_id(&mut self, leader_replica_id: Option<u16>, cx: &mut ViewContext<Self>);
+    fn should_unfollow_on_event(event: &Self::Event, cx: &AppContext) -> bool;
+}
+
+pub trait FollowableItemHandle: ItemHandle {
+    fn set_leader_replica_id(&self, leader_replica_id: Option<u16>, cx: &mut MutableAppContext);
+    fn to_state_proto(&self, cx: &AppContext) -> Option<proto::view::Variant>;
+    fn add_event_to_update_proto(
+        &self,
+        event: &dyn Any,
+        update: &mut Option<proto::update_view::Variant>,
+        cx: &AppContext,
+    ) -> bool;
+    fn apply_update_proto(
+        &self,
+        project: &ModelHandle<Project>,
+        message: proto::update_view::Variant,
+        cx: &mut MutableAppContext,
+    ) -> Task<Result<()>>;
+    fn should_unfollow_on_event(&self, event: &dyn Any, cx: &AppContext) -> bool;
+}
+
+impl<T: FollowableItem> FollowableItemHandle for ViewHandle<T> {
+    fn set_leader_replica_id(&self, leader_replica_id: Option<u16>, cx: &mut MutableAppContext) {
+        self.update(cx, |this, cx| {
+            this.set_leader_replica_id(leader_replica_id, cx)
+        })
+    }
+
+    fn to_state_proto(&self, cx: &AppContext) -> Option<proto::view::Variant> {
+        self.read(cx).to_state_proto(cx)
+    }
+
+    fn add_event_to_update_proto(
+        &self,
+        event: &dyn Any,
+        update: &mut Option<proto::update_view::Variant>,
+        cx: &AppContext,
+    ) -> bool {
+        if let Some(event) = event.downcast_ref() {
+            self.read(cx).add_event_to_update_proto(event, update, cx)
+        } else {
+            false
+        }
+    }
+
+    fn apply_update_proto(
+        &self,
+        project: &ModelHandle<Project>,
+        message: proto::update_view::Variant,
+        cx: &mut MutableAppContext,
+    ) -> Task<Result<()>> {
+        self.update(cx, |this, cx| this.apply_update_proto(project, message, cx))
+    }
+
+    fn should_unfollow_on_event(&self, event: &dyn Any, cx: &AppContext) -> bool {
+        if let Some(event) = event.downcast_ref() {
+            T::should_unfollow_on_event(event, cx)
+        } else {
+            false
+        }
+    }
+}
+
+#[cfg(test)]
+pub(crate) mod test {
+    use std::{any::Any, borrow::Cow, cell::Cell};
+
+    use gpui::{
+        elements::Empty, AppContext, Element, ElementBox, Entity, ModelHandle, RenderContext, Task,
+        View, ViewContext, ViewHandle, WeakViewHandle,
+    };
+    use project::{Project, ProjectEntryId, ProjectPath};
+    use smallvec::SmallVec;
+
+    use crate::{sidebar::SidebarItem, ItemId, ItemNavHistory, Pane, Workspace, WorkspaceId};
+
+    use super::{Item, ItemEvent};
+
+    pub struct TestItem {
+        pub workspace_id: WorkspaceId,
+        pub state: String,
+        pub label: String,
+        pub save_count: usize,
+        pub save_as_count: usize,
+        pub reload_count: usize,
+        pub is_dirty: bool,
+        pub is_singleton: bool,
+        pub has_conflict: bool,
+        pub project_entry_ids: Vec<ProjectEntryId>,
+        pub project_path: Option<ProjectPath>,
+        pub nav_history: Option<ItemNavHistory>,
+        pub tab_descriptions: Option<Vec<&'static str>>,
+        pub tab_detail: Cell<Option<usize>>,
+    }
+
+    pub enum TestItemEvent {
+        Edit,
+    }
+
+    impl Clone for TestItem {
+        fn clone(&self) -> Self {
+            Self {
+                state: self.state.clone(),
+                label: self.label.clone(),
+                save_count: self.save_count,
+                save_as_count: self.save_as_count,
+                reload_count: self.reload_count,
+                is_dirty: self.is_dirty,
+                is_singleton: self.is_singleton,
+                has_conflict: self.has_conflict,
+                project_entry_ids: self.project_entry_ids.clone(),
+                project_path: self.project_path.clone(),
+                nav_history: None,
+                tab_descriptions: None,
+                tab_detail: Default::default(),
+                workspace_id: self.workspace_id,
+            }
+        }
+    }
+
+    impl TestItem {
+        pub fn new() -> Self {
+            Self {
+                state: String::new(),
+                label: String::new(),
+                save_count: 0,
+                save_as_count: 0,
+                reload_count: 0,
+                is_dirty: false,
+                has_conflict: false,
+                project_entry_ids: Vec::new(),
+                project_path: None,
+                is_singleton: true,
+                nav_history: None,
+                tab_descriptions: None,
+                tab_detail: Default::default(),
+                workspace_id: 0,
+            }
+        }
+
+        pub fn new_deserialized(id: WorkspaceId) -> Self {
+            let mut this = Self::new();
+            this.workspace_id = id;
+            this
+        }
+
+        pub fn with_label(mut self, state: &str) -> Self {
+            self.label = state.to_string();
+            self
+        }
+
+        pub fn with_singleton(mut self, singleton: bool) -> Self {
+            self.is_singleton = singleton;
+            self
+        }
+
+        pub fn with_project_entry_ids(mut self, project_entry_ids: &[u64]) -> Self {
+            self.project_entry_ids.extend(
+                project_entry_ids
+                    .iter()
+                    .copied()
+                    .map(ProjectEntryId::from_proto),
+            );
+            self
+        }
+
+        pub fn set_state(&mut self, state: String, cx: &mut ViewContext<Self>) {
+            self.push_to_nav_history(cx);
+            self.state = state;
+        }
+
+        fn push_to_nav_history(&mut self, cx: &mut ViewContext<Self>) {
+            if let Some(history) = &mut self.nav_history {
+                history.push(Some(Box::new(self.state.clone())), cx);
+            }
+        }
+    }
+
+    impl Entity for TestItem {
+        type Event = TestItemEvent;
+    }
+
+    impl View for TestItem {
+        fn ui_name() -> &'static str {
+            "TestItem"
+        }
+
+        fn render(&mut self, _: &mut RenderContext<Self>) -> ElementBox {
+            Empty::new().boxed()
+        }
+    }
+
+    impl Item for TestItem {
+        fn tab_description<'a>(&'a self, detail: usize, _: &'a AppContext) -> Option<Cow<'a, str>> {
+            self.tab_descriptions.as_ref().and_then(|descriptions| {
+                let description = *descriptions.get(detail).or_else(|| descriptions.last())?;
+                Some(description.into())
+            })
+        }
+
+        fn tab_content(&self, detail: Option<usize>, _: &theme::Tab, _: &AppContext) -> ElementBox {
+            self.tab_detail.set(detail);
+            Empty::new().boxed()
+        }
+
+        fn project_path(&self, _: &AppContext) -> Option<ProjectPath> {
+            self.project_path.clone()
+        }
+
+        fn project_entry_ids(&self, _: &AppContext) -> SmallVec<[ProjectEntryId; 3]> {
+            self.project_entry_ids.iter().copied().collect()
+        }
+
+        fn is_singleton(&self, _: &AppContext) -> bool {
+            self.is_singleton
+        }
+
+        fn set_nav_history(&mut self, history: ItemNavHistory, _: &mut ViewContext<Self>) {
+            self.nav_history = Some(history);
+        }
+
+        fn navigate(&mut self, state: Box<dyn Any>, _: &mut ViewContext<Self>) -> bool {
+            let state = *state.downcast::<String>().unwrap_or_default();
+            if state != self.state {
+                self.state = state;
+                true
+            } else {
+                false
+            }
+        }
+
+        fn deactivated(&mut self, cx: &mut ViewContext<Self>) {
+            self.push_to_nav_history(cx);
+        }
+
+        fn clone_on_split(
+            &self,
+            _workspace_id: WorkspaceId,
+            _: &mut ViewContext<Self>,
+        ) -> Option<Self>
+        where
+            Self: Sized,
+        {
+            Some(self.clone())
+        }
+
+        fn is_dirty(&self, _: &AppContext) -> bool {
+            self.is_dirty
+        }
+
+        fn has_conflict(&self, _: &AppContext) -> bool {
+            self.has_conflict
+        }
+
+        fn can_save(&self, _: &AppContext) -> bool {
+            !self.project_entry_ids.is_empty()
+        }
+
+        fn save(
+            &mut self,
+            _: ModelHandle<Project>,
+            _: &mut ViewContext<Self>,
+        ) -> Task<anyhow::Result<()>> {
+            self.save_count += 1;
+            self.is_dirty = false;
+            Task::ready(Ok(()))
+        }
+
+        fn save_as(
+            &mut self,
+            _: ModelHandle<Project>,
+            _: std::path::PathBuf,
+            _: &mut ViewContext<Self>,
+        ) -> Task<anyhow::Result<()>> {
+            self.save_as_count += 1;
+            self.is_dirty = false;
+            Task::ready(Ok(()))
+        }
+
+        fn reload(
+            &mut self,
+            _: ModelHandle<Project>,
+            _: &mut ViewContext<Self>,
+        ) -> Task<anyhow::Result<()>> {
+            self.reload_count += 1;
+            self.is_dirty = false;
+            Task::ready(Ok(()))
+        }
+
+        fn to_item_events(_: &Self::Event) -> Vec<ItemEvent> {
+            vec![ItemEvent::UpdateTab, ItemEvent::Edit]
+        }
+
+        fn serialized_item_kind() -> Option<&'static str> {
+            None
+        }
+
+        fn deserialize(
+            _project: ModelHandle<Project>,
+            _workspace: WeakViewHandle<Workspace>,
+            workspace_id: WorkspaceId,
+            _item_id: ItemId,
+            cx: &mut ViewContext<Pane>,
+        ) -> Task<anyhow::Result<ViewHandle<Self>>> {
+            let view = cx.add_view(|_cx| Self::new_deserialized(workspace_id));
+            Task::Ready(Some(anyhow::Ok(view)))
+        }
+    }
+
+    impl SidebarItem for TestItem {}
+}