layout: Combine layout_2020 and layout_thread_2020 into a crate called layout (#36613)

Now that legacy layout has been removed, the name `layout_2020` doesn't
make much sense any longer, also it's 2025 now for better or worse. The
split between the "layout thread" and "layout" also doesn't make as much
sense since layout doesn't run on it's own thread. There's a possibility
that it will in the future, but that should be something that the user
of the crate controls rather than layout iself.

This is part of the larger layout interface cleanup and optimization
that
@Looriool and I are doing.

Testing: Covered by existing tests as this is just code movement.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/layout/dom.rs

@@ -0,0 +1,328 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use std::marker::PhantomData;
+use std::sync::Arc;
+
+use atomic_refcell::{AtomicRef, AtomicRefCell, AtomicRefMut};
+use base::id::{BrowsingContextId, PipelineId};
+use html5ever::{local_name, namespace_url, ns};
+use pixels::Image;
+use script_layout_interface::wrapper_traits::{
+    LayoutDataTrait, LayoutNode, ThreadSafeLayoutElement, ThreadSafeLayoutNode,
+};
+use script_layout_interface::{
+    HTMLCanvasDataSource, LayoutElementType, LayoutNodeType as ScriptLayoutNodeType,
+};
+use servo_arc::Arc as ServoArc;
+use style::properties::ComputedValues;
+use style::selector_parser::PseudoElement;
+
+use crate::cell::ArcRefCell;
+use crate::context::LayoutContext;
+use crate::flexbox::FlexLevelBox;
+use crate::flow::BlockLevelBox;
+use crate::flow::inline::InlineItem;
+use crate::fragment_tree::Fragment;
+use crate::geom::PhysicalSize;
+use crate::replaced::{CanvasInfo, CanvasSource};
+use crate::table::TableLevelBox;
+use crate::taffy::TaffyItemBox;
+
+/// The data that is stored in each DOM node that is used by layout.
+#[derive(Default)]
+pub struct InnerDOMLayoutData {
+    pub(super) self_box: ArcRefCell<Option<LayoutBox>>,
+    pub(super) pseudo_before_box: ArcRefCell<Option<LayoutBox>>,
+    pub(super) pseudo_after_box: ArcRefCell<Option<LayoutBox>>,
+    pub(super) pseudo_marker_box: ArcRefCell<Option<LayoutBox>>,
+}
+
+impl InnerDOMLayoutData {
+    pub(crate) fn for_pseudo(
+        &self,
+        pseudo_element: Option<PseudoElement>,
+    ) -> AtomicRef<Option<LayoutBox>> {
+        match pseudo_element {
+            Some(PseudoElement::Before) => self.pseudo_before_box.borrow(),
+            Some(PseudoElement::After) => self.pseudo_after_box.borrow(),
+            Some(PseudoElement::Marker) => self.pseudo_marker_box.borrow(),
+            _ => self.self_box.borrow(),
+        }
+    }
+}
+
+/// A box that is stored in one of the `DOMLayoutData` slots.
+pub(super) enum LayoutBox {
+    DisplayContents,
+    BlockLevel(ArcRefCell<BlockLevelBox>),
+    InlineLevel(ArcRefCell<InlineItem>),
+    FlexLevel(ArcRefCell<FlexLevelBox>),
+    TableLevelBox(TableLevelBox),
+    TaffyItemBox(ArcRefCell<TaffyItemBox>),
+}
+
+impl LayoutBox {
+    fn invalidate_cached_fragment(&self) {
+        match self {
+            LayoutBox::DisplayContents => {},
+            LayoutBox::BlockLevel(block_level_box) => {
+                block_level_box.borrow().invalidate_cached_fragment()
+            },
+            LayoutBox::InlineLevel(inline_item) => {
+                inline_item.borrow().invalidate_cached_fragment()
+            },
+            LayoutBox::FlexLevel(flex_level_box) => {
+                flex_level_box.borrow().invalidate_cached_fragment()
+            },
+            LayoutBox::TaffyItemBox(taffy_item_box) => {
+                taffy_item_box.borrow_mut().invalidate_cached_fragment()
+            },
+            LayoutBox::TableLevelBox(table_box) => table_box.invalidate_cached_fragment(),
+        }
+    }
+
+    pub(crate) fn fragments(&self) -> Vec<Fragment> {
+        match self {
+            LayoutBox::DisplayContents => vec![],
+            LayoutBox::BlockLevel(block_level_box) => block_level_box.borrow().fragments(),
+            LayoutBox::InlineLevel(inline_item) => inline_item.borrow().fragments(),
+            LayoutBox::FlexLevel(flex_level_box) => flex_level_box.borrow().fragments(),
+            LayoutBox::TaffyItemBox(taffy_item_box) => taffy_item_box.borrow().fragments(),
+            LayoutBox::TableLevelBox(table_box) => table_box.fragments(),
+        }
+    }
+}
+
+/// A wrapper for [`InnerDOMLayoutData`]. This is necessary to give the entire data
+/// structure interior mutability, as we will need to mutate the layout data of
+/// non-mutable DOM nodes.
+#[derive(Default)]
+pub struct DOMLayoutData(AtomicRefCell<InnerDOMLayoutData>);
+
+// The implementation of this trait allows the data to be stored in the DOM.
+impl LayoutDataTrait for DOMLayoutData {}
+
+pub struct BoxSlot<'dom> {
+    pub(crate) slot: Option<ArcRefCell<Option<LayoutBox>>>,
+    pub(crate) marker: PhantomData<&'dom ()>,
+}
+
+/// A mutable reference to a `LayoutBox` stored in a DOM element.
+impl BoxSlot<'_> {
+    pub(crate) fn new(slot: ArcRefCell<Option<LayoutBox>>) -> Self {
+        *slot.borrow_mut() = None;
+        let slot = Some(slot);
+        Self {
+            slot,
+            marker: PhantomData,
+        }
+    }
+
+    pub(crate) fn dummy() -> Self {
+        let slot = None;
+        Self {
+            slot,
+            marker: PhantomData,
+        }
+    }
+
+    pub(crate) fn set(mut self, box_: LayoutBox) {
+        if let Some(slot) = &mut self.slot {
+            *slot.borrow_mut() = Some(box_);
+        }
+    }
+}
+
+impl Drop for BoxSlot<'_> {
+    fn drop(&mut self) {
+        if !std::thread::panicking() {
+            if let Some(slot) = &mut self.slot {
+                assert!(slot.borrow().is_some(), "failed to set a layout box");
+            }
+        }
+    }
+}
+
+pub(crate) trait NodeExt<'dom>: 'dom + LayoutNode<'dom> {
+    /// Returns the image if it’s loaded, and its size in image pixels
+    /// adjusted for `image_density`.
+    fn as_image(self) -> Option<(Option<Arc<Image>>, PhysicalSize<f64>)>;
+    fn as_canvas(self) -> Option<(CanvasInfo, PhysicalSize<f64>)>;
+    fn as_iframe(self) -> Option<(PipelineId, BrowsingContextId)>;
+    fn as_video(self) -> Option<(Option<webrender_api::ImageKey>, Option<PhysicalSize<f64>>)>;
+    fn as_typeless_object_with_data_attribute(self) -> Option<String>;
+    fn style(self, context: &LayoutContext) -> ServoArc<ComputedValues>;
+
+    fn layout_data_mut(self) -> AtomicRefMut<'dom, InnerDOMLayoutData>;
+    fn layout_data(self) -> Option<AtomicRef<'dom, InnerDOMLayoutData>>;
+    fn element_box_slot(&self) -> BoxSlot<'dom>;
+    fn pseudo_element_box_slot(&self, which: PseudoElement) -> BoxSlot<'dom>;
+    fn unset_pseudo_element_box(self, which: PseudoElement);
+
+    /// Remove boxes for the element itself, and its `:before` and `:after` if any.
+    fn unset_all_boxes(self);
+
+    fn fragments_for_pseudo(&self, pseudo_element: Option<PseudoElement>) -> Vec<Fragment>;
+    fn invalidate_cached_fragment(self);
+}
+
+impl<'dom, LayoutNodeType> NodeExt<'dom> for LayoutNodeType
+where
+    LayoutNodeType: 'dom + LayoutNode<'dom>,
+{
+    fn as_image(self) -> Option<(Option<Arc<Image>>, PhysicalSize<f64>)> {
+        let node = self.to_threadsafe();
+        let (resource, metadata) = node.image_data()?;
+        let (width, height) = resource
+            .as_ref()
+            .map(|image| (image.width, image.height))
+            .or_else(|| metadata.map(|metadata| (metadata.width, metadata.height)))
+            .unwrap_or((0, 0));
+        let (mut width, mut height) = (width as f64, height as f64);
+        if let Some(density) = node.image_density().filter(|density| *density != 1.) {
+            width /= density;
+            height /= density;
+        }
+        Some((resource, PhysicalSize::new(width, height)))
+    }
+
+    fn as_video(self) -> Option<(Option<webrender_api::ImageKey>, Option<PhysicalSize<f64>>)> {
+        let node = self.to_threadsafe();
+        let data = node.media_data()?;
+        let natural_size = if let Some(frame) = data.current_frame {
+            Some(PhysicalSize::new(frame.width.into(), frame.height.into()))
+        } else {
+            data.metadata
+                .map(|meta| PhysicalSize::new(meta.width.into(), meta.height.into()))
+        };
+        Some((
+            data.current_frame.map(|frame| frame.image_key),
+            natural_size,
+        ))
+    }
+
+    fn as_canvas(self) -> Option<(CanvasInfo, PhysicalSize<f64>)> {
+        let node = self.to_threadsafe();
+        let canvas_data = node.canvas_data()?;
+        let source = match canvas_data.source {
+            HTMLCanvasDataSource::WebGL(texture_id) => CanvasSource::WebGL(texture_id),
+            HTMLCanvasDataSource::Image(image_key) => CanvasSource::Image(image_key),
+            HTMLCanvasDataSource::WebGPU(image_key) => CanvasSource::WebGPU(image_key),
+            HTMLCanvasDataSource::Empty => CanvasSource::Empty,
+        };
+        Some((
+            CanvasInfo { source },
+            PhysicalSize::new(canvas_data.width.into(), canvas_data.height.into()),
+        ))
+    }
+
+    fn as_iframe(self) -> Option<(PipelineId, BrowsingContextId)> {
+        let node = self.to_threadsafe();
+        match (node.iframe_pipeline_id(), node.iframe_browsing_context_id()) {
+            (Some(pipeline_id), Some(browsing_context_id)) => {
+                Some((pipeline_id, browsing_context_id))
+            },
+            _ => None,
+        }
+    }
+
+    fn as_typeless_object_with_data_attribute(self) -> Option<String> {
+        if self.type_id() != ScriptLayoutNodeType::Element(LayoutElementType::HTMLObjectElement) {
+            return None;
+        }
+
+        // TODO: This is the what the legacy layout system did, but really if Servo
+        // supports any `<object>` that's an image, it should support those with URLs
+        // and `type` attributes with image mime types.
+        let element = self.to_threadsafe().as_element()?;
+        if element.get_attr(&ns!(), &local_name!("type")).is_some() {
+            return None;
+        }
+        element
+            .get_attr(&ns!(), &local_name!("data"))
+            .map(|string| string.to_owned())
+    }
+
+    fn style(self, context: &LayoutContext) -> ServoArc<ComputedValues> {
+        self.to_threadsafe().style(context.shared_context())
+    }
+
+    fn layout_data_mut(self) -> AtomicRefMut<'dom, InnerDOMLayoutData> {
+        if LayoutNode::layout_data(&self).is_none() {
+            self.initialize_layout_data::<DOMLayoutData>();
+        }
+        LayoutNode::layout_data(&self)
+            .unwrap()
+            .downcast_ref::<DOMLayoutData>()
+            .unwrap()
+            .0
+            .borrow_mut()
+    }
+
+    fn layout_data(self) -> Option<AtomicRef<'dom, InnerDOMLayoutData>> {
+        LayoutNode::layout_data(&self)
+            .map(|data| data.downcast_ref::<DOMLayoutData>().unwrap().0.borrow())
+    }
+
+    fn element_box_slot(&self) -> BoxSlot<'dom> {
+        BoxSlot::new(self.layout_data_mut().self_box.clone())
+    }
+
+    fn pseudo_element_box_slot(&self, pseudo_element_type: PseudoElement) -> BoxSlot<'dom> {
+        let data = self.layout_data_mut();
+        let cell = match pseudo_element_type {
+            PseudoElement::Before => &data.pseudo_before_box,
+            PseudoElement::After => &data.pseudo_after_box,
+            PseudoElement::Marker => &data.pseudo_marker_box,
+            _ => unreachable!(
+                "Asked for box slot for unsupported pseudo-element: {:?}",
+                pseudo_element_type
+            ),
+        };
+        BoxSlot::new(cell.clone())
+    }
+
+    fn unset_pseudo_element_box(self, pseudo_element_type: PseudoElement) {
+        let data = self.layout_data_mut();
+        let cell = match pseudo_element_type {
+            PseudoElement::Before => &data.pseudo_before_box,
+            PseudoElement::After => &data.pseudo_after_box,
+            PseudoElement::Marker => &data.pseudo_marker_box,
+            _ => unreachable!(
+                "Asked for box slot for unsupported pseudo-element: {:?}",
+                pseudo_element_type
+            ),
+        };
+        *cell.borrow_mut() = None;
+    }
+
+    fn unset_all_boxes(self) {
+        let data = self.layout_data_mut();
+        *data.self_box.borrow_mut() = None;
+        *data.pseudo_before_box.borrow_mut() = None;
+        *data.pseudo_after_box.borrow_mut() = None;
+        *data.pseudo_marker_box.borrow_mut() = None;
+        // Stylo already takes care of removing all layout data
+        // for DOM descendants of elements with `display: none`.
+    }
+
+    fn invalidate_cached_fragment(self) {
+        let data = self.layout_data_mut();
+        if let Some(data) = data.self_box.borrow_mut().as_mut() {
+            data.invalidate_cached_fragment();
+        }
+    }
+
+    fn fragments_for_pseudo(&self, pseudo_element: Option<PseudoElement>) -> Vec<Fragment> {
+        NodeExt::layout_data(*self)
+            .and_then(|layout_data| {
+                layout_data
+                    .for_pseudo(pseudo_element)
+                    .as_ref()
+                    .map(LayoutBox::fragments)
+            })
+            .unwrap_or_default()
+    }
+}