assistant2: Sketch in directory context picker (#22148)

This PR sketches in the structure for the directory context picker.

Waiting on implementing the actual behavior until we fix the issues with
the file context picker.

Release Notes:

- N/A

crates/assistant2/src/context_picker/directory_context_picker.rs

@@ -0,0 +1,117 @@
+// TODO: Remove this once we've implemented the functionality.
+#![allow(unused)]
+
+use std::sync::Arc;
+
+use fuzzy::PathMatch;
+use gpui::{AppContext, DismissEvent, FocusHandle, FocusableView, Task, View, WeakModel, WeakView};
+use picker::{Picker, PickerDelegate};
+use project::{PathMatchCandidateSet, WorktreeId};
+use ui::{prelude::*, ListItem};
+use util::ResultExt as _;
+use workspace::Workspace;
+
+use crate::context_picker::ContextPicker;
+use crate::context_store::ContextStore;
+
+pub struct DirectoryContextPicker {
+    picker: View<Picker<DirectoryContextPickerDelegate>>,
+}
+
+impl DirectoryContextPicker {
+    pub fn new(
+        context_picker: WeakView<ContextPicker>,
+        workspace: WeakView<Workspace>,
+        context_store: WeakModel<ContextStore>,
+        cx: &mut ViewContext<Self>,
+    ) -> Self {
+        let delegate =
+            DirectoryContextPickerDelegate::new(context_picker, workspace, context_store);
+        let picker = cx.new_view(|cx| Picker::uniform_list(delegate, cx));
+
+        Self { picker }
+    }
+}
+
+impl FocusableView for DirectoryContextPicker {
+    fn focus_handle(&self, cx: &AppContext) -> FocusHandle {
+        self.picker.focus_handle(cx)
+    }
+}
+
+impl Render for DirectoryContextPicker {
+    fn render(&mut self, _cx: &mut ViewContext<Self>) -> impl IntoElement {
+        self.picker.clone()
+    }
+}
+
+pub struct DirectoryContextPickerDelegate {
+    context_picker: WeakView<ContextPicker>,
+    workspace: WeakView<Workspace>,
+    context_store: WeakModel<ContextStore>,
+    matches: Vec<PathMatch>,
+    selected_index: usize,
+}
+
+impl DirectoryContextPickerDelegate {
+    pub fn new(
+        context_picker: WeakView<ContextPicker>,
+        workspace: WeakView<Workspace>,
+        context_store: WeakModel<ContextStore>,
+    ) -> Self {
+        Self {
+            context_picker,
+            workspace,
+            context_store,
+            matches: Vec::new(),
+            selected_index: 0,
+        }
+    }
+}
+
+impl PickerDelegate for DirectoryContextPickerDelegate {
+    type ListItem = ListItem;
+
+    fn match_count(&self) -> usize {
+        self.matches.len()
+    }
+
+    fn selected_index(&self) -> usize {
+        self.selected_index
+    }
+
+    fn set_selected_index(&mut self, ix: usize, cx: &mut ViewContext<Picker<Self>>) {
+        self.selected_index = ix;
+    }
+
+    fn placeholder_text(&self, _cx: &mut WindowContext) -> Arc<str> {
+        "Search folders…".into()
+    }
+
+    fn update_matches(&mut self, _query: String, _cx: &mut ViewContext<Picker<Self>>) -> Task<()> {
+        // TODO: Implement this once we fix the issues with the file context picker.
+        Task::ready(())
+    }
+
+    fn confirm(&mut self, _secondary: bool, _cx: &mut ViewContext<Picker<Self>>) {
+        // TODO: Implement this once we fix the issues with the file context picker.
+    }
+
+    fn dismissed(&mut self, cx: &mut ViewContext<Picker<Self>>) {
+        self.context_picker
+            .update(cx, |this, cx| {
+                this.reset_mode();
+                cx.emit(DismissEvent);
+            })
+            .ok();
+    }
+
+    fn render_match(
+        &self,
+        _ix: usize,
+        _selected: bool,
+        _cx: &mut ViewContext<Picker<Self>>,
+    ) -> Option<Self::ListItem> {
+        None
+    }
+}