Show status bar item for project diagnostic summary

Co-Authored-By: Nathan Sobo <nathan@zed.dev>

crates/diagnostics/src/items.rs

@@ -0,0 +1,71 @@
+use gpui::{
+    elements::*, platform::CursorStyle, Entity, ModelHandle, RenderContext, View, ViewContext,
+};
+use postage::watch;
+use project::Project;
+use workspace::{Settings, StatusItemView};
+
+pub struct DiagnosticSummary {
+    settings: watch::Receiver<Settings>,
+    summary: project::DiagnosticSummary,
+}
+
+impl DiagnosticSummary {
+    pub fn new(
+        project: &ModelHandle<Project>,
+        settings: watch::Receiver<Settings>,
+        cx: &mut ViewContext<Self>,
+    ) -> Self {
+        cx.subscribe(project, |this, project, event, cx| {
+            if let project::Event::DiskBasedDiagnosticsUpdated { .. } = event {
+                this.summary = project.read(cx).diagnostic_summary(cx);
+                cx.notify();
+            }
+        })
+        .detach();
+        Self {
+            settings,
+            summary: project.read(cx).diagnostic_summary(cx),
+        }
+    }
+}
+
+impl Entity for DiagnosticSummary {
+    type Event = ();
+}
+
+impl View for DiagnosticSummary {
+    fn ui_name() -> &'static str {
+        "DiagnosticSummary"
+    }
+
+    fn render(&mut self, cx: &mut RenderContext<Self>) -> ElementBox {
+        enum Tag {}
+
+        let theme = &self.settings.borrow().theme.project_diagnostics;
+        MouseEventHandler::new::<Tag, _, _, _>(0, cx, |_, _| {
+            Label::new(
+                format!(
+                    "Errors: {}, Warnings: {}",
+                    self.summary.error_count, self.summary.warning_count
+                ),
+                theme.status_bar_item.text.clone(),
+            )
+            .contained()
+            .with_style(theme.status_bar_item.container)
+            .boxed()
+        })
+        .with_cursor_style(CursorStyle::PointingHand)
+        .on_click(|cx| cx.dispatch_action(crate::Deploy))
+        .boxed()
+    }
+}
+
+impl StatusItemView for DiagnosticSummary {
+    fn set_active_pane_item(
+        &mut self,
+        _: Option<&dyn workspace::ItemViewHandle>,
+        _: &mut ViewContext<Self>,
+    ) {
+    }
+}