Hide servo internal shadow roots from the inspector by default (#35958)

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

components/config/prefs.rs

@@ -146,6 +146,8 @@ pub struct Preferences {
     /// Whether or not subpixel antialiasing is enabled for text rendering.
     pub gfx_subpixel_text_antialiasing_enabled: bool,
     pub gfx_texture_swizzling_enabled: bool,
+    /// Whether or not the DOM inspector should show shadow roots of user-agent shadow trees
+    pub inspector_show_servo_internal_shadow_roots: bool,
     pub js_asmjs_enabled: bool,
     pub js_asyncstack: bool,
     pub js_baseline_interpreter_enabled: bool,
@@ -312,6 +314,7 @@ impl Preferences {
             gfx_text_antialiasing_enabled: true,
             gfx_subpixel_text_antialiasing_enabled: true,
             gfx_texture_swizzling_enabled: true,
+            inspector_show_servo_internal_shadow_roots: false,
             js_asmjs_enabled: true,
             js_asyncstack: false,
             js_baseline_interpreter_enabled: true,

components/script/devtools.rs

@@ -14,6 +14,7 @@ use devtools_traits::{
 use ipc_channel::ipc::IpcSender;
 use js::jsval::UndefinedValue;
 use js::rust::ToString;
+use servo_config::pref;
 use uuid::Uuid;
 
 use crate::document_collection::DocumentCollection;
@@ -162,8 +163,12 @@ pub(crate) fn handle_get_children(
 
             let mut children = vec![];
             if let Some(shadow_root) = parent.downcast::<Element>().and_then(Element::shadow_root) {
+                if !shadow_root.is_user_agent_widget() ||
+                    pref!(inspector_show_servo_internal_shadow_roots)
+                {
                     children.push(shadow_root.upcast::<Node>().summarize());
                 }
+            }
             let children_iter = parent.children().enumerate().filter_map(|(i, child)| {
                 // Filter whitespace only text nodes that are not inline level
                 // https://firefox-source-docs.mozilla.org/devtools-user/page_inspector/how_to/examine_and_edit_html/index.html#whitespace-only-text-nodes

components/script/dom/element.rs

@@ -542,6 +542,7 @@ impl Element {
             mode,
             slot_assignment_mode,
             clonable,
+            is_ua_widget,
             can_gc,
         );
 

components/script/dom/node.rs

@@ -35,6 +35,7 @@ use selectors::matching::{
 };
 use selectors::parser::SelectorList;
 use servo_arc::Arc;
+use servo_config::pref;
 use servo_url::ServoUrl;
 use smallvec::SmallVec;
 use style::context::QuirksMode;
@@ -1209,9 +1210,12 @@ impl Node {
         let host = maybe_shadow_root
             .map(ShadowRoot::Host)
             .map(|host| host.upcast::<Node>().unique_id());
-        let is_shadow_host = self
+        let is_shadow_host = self.downcast::<Element>().is_some_and(|potential_host| {
-            .downcast::<Element>()
+            let Some(root) = potential_host.shadow_root() else {
-            .is_some_and(Element::is_shadow_host);
+                return false;
+            };
+            !root.is_user_agent_widget() || pref!(inspector_show_servo_internal_shadow_roots)
+        });
 
         let num_children = if is_shadow_host {
             // Shadow roots count as children

components/script/dom/shadowroot.rs

@@ -77,6 +77,8 @@ pub(crate) struct ShadowRoot {
     available_to_element_internals: Cell<bool>,
 
     slots: DomRefCell<HashMap<DOMString, Vec<Dom<HTMLSlotElement>>>>,
+
+    is_user_agent_widget: bool,
 }
 
 impl ShadowRoot {
@@ -87,6 +89,7 @@ impl ShadowRoot {
         mode: ShadowRootMode,
         slot_assignment_mode: SlotAssignmentMode,
         clonable: bool,
+        is_user_agent_widget: IsUserAgentWidget,
     ) -> ShadowRoot {
         let document_fragment = DocumentFragment::new_inherited(document);
         let node = document_fragment.upcast::<Node>();
@@ -109,6 +112,7 @@ impl ShadowRoot {
             clonable,
             available_to_element_internals: Cell::new(false),
             slots: Default::default(),
+            is_user_agent_widget: is_user_agent_widget == IsUserAgentWidget::Yes,
         }
     }
 
@@ -118,6 +122,7 @@ impl ShadowRoot {
         mode: ShadowRootMode,
         slot_assignment_mode: SlotAssignmentMode,
         clonable: bool,
+        is_user_agent_widget: IsUserAgentWidget,
         can_gc: CanGc,
     ) -> DomRoot<ShadowRoot> {
         reflect_dom_object(
@@ -127,6 +132,7 @@ impl ShadowRoot {
                 mode,
                 slot_assignment_mode,
                 clonable,
+                is_user_agent_widget,
             )),
             document.window(),
             can_gc,
@@ -266,6 +272,10 @@ impl ShadowRoot {
     pub(crate) fn is_available_to_element_internals(&self) -> bool {
         self.available_to_element_internals.get()
     }
+
+    pub(crate) fn is_user_agent_widget(&self) -> bool {
+        self.is_user_agent_widget
+    }
 }
 
 impl ShadowRootMethods<crate::DomTypeHolder> for ShadowRoot {