Add initial element inspector for Zed development (#31315)

Open inspector with `dev: toggle inspector` from command palette or
`cmd-alt-i` on mac or `ctrl-alt-i` on linux.

https://github.com/user-attachments/assets/54c43034-d40b-414e-ba9b-190bed2e6d2f

* Picking of elements via the mouse, with scroll wheel to inspect
occluded elements.

* Temporary manipulation of the selected element.

* Layout info and JSON-based style manipulation for `Div`.

* Navigation to code that constructed the element.

Big thanks to @as-cii and @maxdeviant for sorting out how to implement
the core of an inspector.

Release Notes:

- N/A

---------

Co-authored-by: Antonio Scandurra <me@as-cii.com>
Co-authored-by: Marshall Bowers <git@maxdeviant.com>
Co-authored-by: Federico Dionisi <code@fdionisi.me>

crates/editor/src/editor.rs

@@ -138,7 +138,6 @@ pub use git::blame::BlameRenderer;
 pub use proposed_changes_editor::{
     ProposedChangeLocation, ProposedChangesEditor, ProposedChangesEditorToolbar,
 };
-use smallvec::smallvec;
 use std::{cell::OnceCell, iter::Peekable, ops::Not};
 use task::{ResolvedTask, RunnableTag, TaskTemplate, TaskVariables};
 
@@ -176,7 +175,7 @@ use selections_collection::{
 };
 use serde::{Deserialize, Serialize};
 use settings::{Settings, SettingsLocation, SettingsStore, update_settings_file};
-use smallvec::SmallVec;
+use smallvec::{SmallVec, smallvec};
 use snippet::Snippet;
 use std::sync::Arc;
 use std::{
@@ -7993,7 +7992,7 @@ impl Editor {
                     .gap_1()
                     // Workaround: For some reason, there's a gap if we don't do this
                     .ml(-BORDER_WIDTH)
-                    .shadow(smallvec![gpui::BoxShadow {
+                    .shadow(vec![gpui::BoxShadow {
                         color: gpui::black().opacity(0.05),
                         offset: point(px(1.), px(1.)),
                         blur_radius: px(2.),
@@ -16708,7 +16707,7 @@ impl Editor {
     }
 
     pub fn wrap_guides(&self, cx: &App) -> SmallVec<[(usize, bool); 2]> {
-        let mut wrap_guides = smallvec::smallvec![];
+        let mut wrap_guides = smallvec![];
 
         if self.show_wrap_guides == Some(false) {
             return wrap_guides;

crates/editor/src/element.rs

@@ -7181,9 +7181,14 @@ impl Element for EditorElement {
         None
     }
 
+    fn source_location(&self) -> Option<&'static core::panic::Location<'static>> {
+        None
+    }
+
     fn request_layout(
         &mut self,
         _: Option<&GlobalElementId>,
+        __inspector_id: Option<&gpui::InspectorElementId>,
         window: &mut Window,
         cx: &mut App,
     ) -> (gpui::LayoutId, ()) {
@@ -7290,6 +7295,7 @@ impl Element for EditorElement {
     fn prepaint(
         &mut self,
         _: Option<&GlobalElementId>,
+        _inspector_id: Option<&gpui::InspectorElementId>,
         bounds: Bounds<Pixels>,
         _: &mut Self::RequestLayoutState,
         window: &mut Window,
@@ -7761,7 +7767,7 @@ impl Element for EditorElement {
                         // If the fold widths have changed, we need to prepaint
                         // the element again to account for any changes in
                         // wrapping.
-                        return self.prepaint(None, bounds, &mut (), window, cx);
+                        return self.prepaint(None, _inspector_id, bounds, &mut (), window, cx);
                     }
 
                     let longest_line_blame_width = self
@@ -7846,7 +7852,7 @@ impl Element for EditorElement {
                             self.editor.update(cx, |editor, cx| {
                                 editor.resize_blocks(resized_blocks, autoscroll_request, cx)
                             });
-                            return self.prepaint(None, bounds, &mut (), window, cx);
+                            return self.prepaint(None, _inspector_id, bounds, &mut (), window, cx);
                         }
                     };
 
@@ -8345,6 +8351,7 @@ impl Element for EditorElement {
     fn paint(
         &mut self,
         _: Option<&GlobalElementId>,
+        __inspector_id: Option<&gpui::InspectorElementId>,
         bounds: Bounds<gpui::Pixels>,
         _: &mut Self::RequestLayoutState,
         layout: &mut Self::PrepaintState,

crates/editor/src/items.rs

@@ -1135,7 +1135,7 @@ impl SerializableItem for Editor {
                 mtime,
                 ..
             } => {
-                let project_item = project.update(cx, |project, cx| {
+                let opened_buffer = project.update(cx, |project, cx| {
                     let (worktree, path) = project.find_worktree(&abs_path, cx)?;
                     let project_path = ProjectPath {
                         worktree_id: worktree.read(cx).id(),
@@ -1144,13 +1144,10 @@ impl SerializableItem for Editor {
                     Some(project.open_path(project_path, cx))
                 });
 
-                match project_item {
-                    Some(project_item) => {
+                match opened_buffer {
+                    Some(opened_buffer) => {
                         window.spawn(cx, async move |cx| {
-                            let (_, project_item) = project_item.await?;
-                            let buffer = project_item.downcast::<Buffer>().map_err(|_| {
-                                anyhow!("Project item at stored path was not a buffer")
-                            })?;
+                            let (_, buffer) = opened_buffer.await?;
 
                             // This is a bit wasteful: we're loading the whole buffer from
                             // disk and then overwrite the content.