cranpose_ui/widgets/nodes/

layout_node.rs

use std::{
    any::TypeId,
    cell::{Cell, RefCell},
    rc::Rc,
};

use cranpose_core::{Node, NodeId, NodeIdCell};
use cranpose_foundation::{
    InvalidationKind, ModifierInvalidation, ModifierInvalidations, NodeCapabilities,
    SemanticsConfiguration,
};
use cranpose_ui_layout::MeasurePolicy;

use super::layout_invalidation_diag::log_layout_invalidation_dispatch;
#[cfg(test)]
use crate::layout::LayoutRuntimeDebugStats;
use crate::{
    layout::LayoutRuntimeState,
    modifier::{
        InPlaceUpdate, Modifier, ModifierChainHandle, ModifierLocalToken, ModifierLocalsHandle,
        ModifierNodeSlices, Point, ResolvedModifiers, Size,
    },
    render_state::AppContext,
    widgets::nodes::{
        ChildPlacement, LayoutDirt, LayoutParts, LayoutState, NodeCache,
        layout_node_registry::{
            register_layout_node, resolve_modifier_local_from_parent_chain, unregister_layout_node,
        },
    },
};

/// A node of the layout tree.
///
/// Its fields keep the order they are declared in: what a layout pass reads
/// for every child it binds comes first and fits one cache line, then what
/// measuring the node reads, then what composition reads. Layout reads
/// thousands of nodes a frame, and on a phone its cost is the lines it loads.
#[repr(C)]
pub struct LayoutNode {
    parts: Rc<LayoutParts>,
    // The actual children of this node (folded view - includes virtual nodes as-is)
    pub(crate) children: Vec<NodeId>,

    // Policy that measures and places the children of this node. Change it through
    // `set_measure_policy` so that a measure is scheduled.
    pub(crate) measure_policy: Rc<dyn MeasurePolicy>,
    /// Where the chain's layout modifiers put their content, written by
    /// layout and read by the draws and text the slices collect.
    density: crate::density::Density,
    is_virtual: bool,
    needs_semantics: Cell<bool>,
    /// The semantics tree has to read this node again, though its own
    /// semantics are unchanged: a node below it changed, or its placement
    /// or children did.
    descendant_needs_semantics: Cell<bool>,
    needs_redraw: Cell<bool>,
    needs_pointer_pass: Cell<bool>,
    needs_focus_sync: Cell<bool>,
    modifier_slices_dirty: Cell<bool>,
    debug_modifiers: Cell<bool>,

    id: NodeIdCell,
    parent: NodeIdCell,
    folded_parent: NodeIdCell,
    modifier_slices_snapshot: crate::modifier::SlicesSnapshot,

    /// The chain's modal and hidden flags, read by the modal count and the
    /// modal walk: dropped whenever the chain syncs or semantics are
    /// invalidated, the two ways its semantics change.
    semantics_reach: Cell<Option<cranpose_foundation::SemanticsReach>>,
    owner_context_id: Cell<Option<crate::render_state::AppContextId>>,
    modifier_chain: ModifierChainHandle,
    // The modifier of this node. Change it through `set_modifier` so that the modifier chain
    // updates.
    pub(crate) modifier: Modifier,
    /// Composable definitions responsible for this node, captured only for inspection builds.
    #[cfg(feature = "inspection")]
    pub source_trace: Rc<[cranpose_core::source_trace::SourceLocation]>,
}

pub(crate) fn empty_measure_policy() -> Rc<dyn MeasurePolicy> {
    crate::thread_state::with(|state| {
        Rc::clone(
            state
                .empty_measure_policy
                .get_or_init(|| Rc::new(crate::layout::policies::EmptyMeasurePolicy)),
        )
    })
}

impl LayoutNode {
    /// Creates a node with `modifier` whose children `measure_policy` measures and places.
    pub fn new(modifier: Modifier, measure_policy: Rc<dyn MeasurePolicy>) -> Self {
        Self::new_with_virtual(modifier, measure_policy, false)
    }

    /// Create a virtual LayoutNode for subcomposition slot containers.
    /// Virtual nodes are transparent - their children are flattened into parent's children list.
    pub fn new_virtual() -> Self {
        Self::new_with_virtual(Modifier::empty(), empty_measure_policy(), true)
    }

    fn new_recycled_shell(is_virtual: bool) -> Self {
        let mut shell =
            Self::new_with_virtual(Modifier::empty(), empty_measure_policy(), is_virtual);
        shell.parts.cache().set_dirt(LayoutDirt::CLEAN);
        shell.needs_semantics.set(false);
        shell.descendant_needs_semantics.set(false);
        shell.needs_redraw.set(false);
        shell.needs_pointer_pass.set(false);
        shell.needs_focus_sync.set(false);
        shell.parent.set(None);
        shell.folded_parent.set(None);
        shell.id.set(None);
        shell.owner_context_id.set(None);
        shell.debug_modifiers.set(false);
        shell.modifier_slices_dirty = Cell::new(true);
        shell
    }

    fn new_with_virtual(
        modifier: Modifier,
        measure_policy: Rc<dyn MeasurePolicy>,
        is_virtual: bool,
    ) -> Self {
        let parts = Rc::new(LayoutParts::new(LayoutRuntimeState::new(Rc::clone(
            &measure_policy,
        ))));
        let mut node = Self {
            #[cfg(feature = "inspection")]
            source_trace: cranpose_core::source_trace::current_source_trace(),
            modifier,
            modifier_chain: ModifierChainHandle::detached(),
            measure_policy,
            density: crate::density::Density::default(),
            children: Vec::new(),
            needs_semantics: Cell::new(true),
            descendant_needs_semantics: Cell::new(false),
            semantics_reach: Cell::new(None),
            needs_redraw: Cell::new(true),
            needs_pointer_pass: Cell::new(false),
            needs_focus_sync: Cell::new(false),
            parent: NodeIdCell::new(None),
            folded_parent: NodeIdCell::new(None),
            id: NodeIdCell::new(None),
            owner_context_id: Cell::new(None),
            debug_modifiers: Cell::new(false),
            is_virtual,
            modifier_slices_snapshot: crate::modifier::SlicesSnapshot::default(),
            modifier_slices_dirty: Cell::new(true),
            parts,
        };
        node.sync_modifier_chain(None);
        node
    }

    /// The node's children, in the order they were inserted, virtual nodes as they are.
    pub fn children(&self) -> &[NodeId] {
        &self.children
    }

    /// Returns the modifier that was last set on this node.
    pub fn modifier(&self) -> Modifier {
        self.modifier.clone()
    }

    /// Replaces the node's modifier and updates its modifier chain, invalidating the work that the
    /// change affects.
    pub fn set_modifier(&mut self, modifier: Modifier) {
        #[cfg(feature = "inspection")]
        {
            let trace = cranpose_core::source_trace::current_source_trace();
            if !trace.is_empty() {
                self.source_trace = trace;
            }
        }
        // An equal modifier leaves every element's node as it was. Only a
        // chain reading modifier locals resyncs, since its parent may now
        // provide others.
        if self.modifier == modifier
            && !self
                .modifier_capabilities()
                .contains(NodeCapabilities::MODIFIER_LOCALS)
        {
            return;
        }
        // A change only in elements nothing else reads, as a ticker's text
        // or an animated size, keeps the slices the chain gave.
        let update = self.modifier.in_place_update(&modifier);
        let modifier_changed = update.is_some() || !self.modifier.structural_eq(&modifier);
        self.modifier = modifier;
        self.sync_modifier_chain(update);
        if modifier_changed {
            self.parts.cache().clear();
            self.request_semantics_update();
        }
    }

    /// Reconciles the chain with the node's modifier. `in_place` says how
    /// far the change reaches when the modifier changed only in elements the
    /// chain can update in place: when it does, the current slices are kept.
    fn sync_modifier_chain(&mut self, in_place: Option<InPlaceUpdate>) {
        let prev_caps = self.modifier_capabilities();
        let start_parent = self.parent();
        let mut resolver = move |token: &ModifierLocalToken| {
            resolve_modifier_local_from_parent_chain(start_parent, token)
        };
        self.modifier_chain
            .set_debug_logging(self.debug_modifiers.get());
        let mut context = self.modifier_chain.context(self.id.get());
        let in_place = in_place.is_some_and(|update| {
            self.modifier_chain
                .update_elements_in_place(&self.modifier, update, &mut context)
        });
        let modifier_local_invalidations = if in_place {
            ModifierInvalidations::new()
        } else {
            self.modifier_chain
                .update_with_resolver(&self.modifier, &mut resolver, &mut context)
        };
        if prev_caps.contains(NodeCapabilities::WINDOW_ROOT)
            != self
                .modifier_capabilities()
                .contains(NodeCapabilities::WINDOW_ROOT)
        {
            self.note_semantics_layout_change();
        }
        // An element updated in place reaches nothing, so the update leaves
        // the chain's reach as it was, and the modal count does not read it
        // again.
        if !in_place {
            self.forget_semantics_reach();
        }
        let keep_slices = in_place && !self.modifier_slices_dirty.get();
        if !keep_slices {
            self.modifier_slices_dirty.set(true);
        }

        let mut invalidations = context.take_invalidations();
        invalidations.extend(modifier_local_invalidations);
        self.dispatch_modifier_invalidations_with_prev(&invalidations, prev_caps, keep_slices);
        // An update in place leaves the node's parent, capabilities and
        // modifier locals as the registry holds them.
        if !in_place {
            self.refresh_registry_state();
        }
    }

    fn update_modifier_slices_cache(&self) {
        self.modifier_slices_snapshot.collect(
            self.modifier_chain.chain(),
            Some(&self.parts),
            self.density.density(),
        );
        self.modifier_slices_dirty.set(false);
    }

    /// Whether the modifier slices are built and current.
    #[cfg(test)]
    pub(crate) fn modifier_slices_ready(&self) -> bool {
        !self.modifier_slices_dirty.get()
    }

    pub(crate) fn mark_modifier_slices_dirty(&self) {
        self.modifier_slices_dirty.set(true);
    }

    #[cfg(test)]
    fn dispatch_modifier_invalidations(&self, invalidations: &[ModifierInvalidation]) {
        self.dispatch_modifier_invalidations_with_prev(
            invalidations,
            NodeCapabilities::empty(),
            false,
        );
    }

    /// Applies `invalidations` to the node. Each marks the slices for a
    /// rebuild unless `keep_slices`.
    fn dispatch_modifier_invalidations_with_prev(
        &self,
        invalidations: &[ModifierInvalidation],
        prev_caps: NodeCapabilities,
        keep_slices: bool,
    ) {
        let curr_caps = self.modifier_capabilities();
        for invalidation in invalidations {
            if !keep_slices {
                self.modifier_slices_dirty.set(true);
            }
            let has_capability =
                |capability| curr_caps.contains(capability) || prev_caps.contains(capability);
            match invalidation.kind() {
                InvalidationKind::Layout => {
                    if has_capability(NodeCapabilities::LAYOUT) {
                        self.mark_needs_measure();
                        if let Some(id) = self.id.get() {
                            log_layout_invalidation_dispatch(
                                id,
                                invalidation,
                                curr_caps,
                                prev_caps,
                                &self.modifier,
                            );
                            let inside_composition =
                                cranpose_core::composer_context::try_with_composer(|_| ())
                                    .is_some();
                            if inside_composition {
                                cranpose_core::bubble_measure_dirty_in_composer(id);
                            } else {
                                crate::schedule_layout_repass(id);
                            }
                        }
                    }
                }
                InvalidationKind::Draw => {
                    if has_capability(NodeCapabilities::DRAW)
                        || invalidation.capabilities().contains(NodeCapabilities::DRAW)
                    {
                        self.mark_needs_redraw();
                    }
                }
                InvalidationKind::PointerInput => {
                    if has_capability(NodeCapabilities::POINTER_INPUT) {
                        self.mark_needs_pointer_pass();
                        crate::request_pointer_invalidation();
                        if let Some(id) = self.id.get() {
                            crate::schedule_pointer_repass(id);
                        }
                    }
                }
                InvalidationKind::Semantics => {
                    self.request_semantics_update();
                }
                InvalidationKind::Focus => {
                    if has_capability(NodeCapabilities::FOCUS) {
                        self.mark_needs_focus_sync();
                        crate::request_focus_invalidation();
                        if let Some(id) = self.id.get() {
                            crate::schedule_focus_invalidation(id);
                        }
                    }
                }
            }
        }
    }

    /// The grid this node was composed against.
    pub fn density(&self) -> crate::density::Density {
        self.density
    }

    /// Records the grid the composition provided, re-measuring if it moved.
    pub fn set_density(&mut self, density: crate::density::Density) {
        if self.density != density {
            self.density = density;
            self.parts.cache().clear();
            self.modifier_slices_dirty.set(true);
            self.mark_needs_measure();
        }
    }

    /// Updates relative modifier placement for this node's composition scope.
    pub fn set_layout_direction(&mut self, direction: crate::LayoutDirection) {
        if self.modifier_chain.set_layout_direction(direction) {
            self.parts.cache().clear();
            self.modifier_slices_dirty.set(true);
            self.mark_needs_measure();
        }
    }

    /// Replaces the measure policy and schedules a measure. Does nothing if `policy` is the same
    /// `Rc` as the current one.
    pub fn set_measure_policy(&mut self, policy: Rc<dyn MeasurePolicy>) {
        if !Rc::ptr_eq(&self.measure_policy, &policy) {
            self.measure_policy = policy;
            self.parts.cache().clear();
            self.mark_needs_measure();
            if let Some(id) = self.id.get() {
                cranpose_core::bubble_measure_dirty_in_composer(id);
            }
        }
    }

    /// Mark this node as needing measure. Also marks it as needing layout.
    pub fn mark_needs_measure(&self) {
        self.parts.cache().mark_needs_measure();
    }

    /// Mark this node as needing layout (but not necessarily measure).
    pub fn mark_needs_layout(&self) {
        self.parts.cache().mark_needs_layout();
    }

    /// Mark this node as needing redraw without forcing measure/layout.
    pub fn mark_needs_redraw(&self) {
        self.needs_redraw.set(true);
        if let Some(id) = self.id.get() {
            crate::schedule_draw_repass(id);
        }
        crate::request_render_invalidation();
    }

    /// Check if this node needs measure.
    pub fn needs_measure(&self) -> bool {
        self.parts.cache().dirt().measure
    }

    /// Check if this node needs layout.
    pub fn needs_layout(&self) -> bool {
        self.parts.cache().dirt().layout
    }

    /// Mark this node as needing semantics recomputation.
    pub fn mark_needs_semantics(&self) {
        self.needs_semantics.set(true);
        self.forget_semantics_reach();
    }

    pub(crate) fn clear_needs_semantics(&self) {
        self.needs_semantics.set(false);
        self.descendant_needs_semantics.set(false);
    }

    /// Returns true when this node's semantics or a descendant's need to be
    /// recomputed.
    pub fn needs_semantics(&self) -> bool {
        self.needs_semantics.get() || self.descendant_needs_semantics.get()
    }

    /// Whether this node's own semantics changed since the tree last read
    /// them, as opposed to only a descendant's.
    pub(crate) fn semantics_changed(&self) -> bool {
        self.needs_semantics.get()
    }

    /// Returns true when this node requested a redraw since the last render pass.
    pub fn needs_redraw(&self) -> bool {
        self.needs_redraw.get()
    }

    /// Clears the pending redraw flag once the node has been drawn.
    pub fn clear_needs_redraw(&self) {
        self.needs_redraw.set(false);
    }

    fn request_semantics_update(&self) {
        let already_dirty = self.needs_semantics.replace(true);
        if already_dirty {
            return;
        }

        if let Some(id) = self.id.get() {
            cranpose_core::queue_semantics_invalidation(id);
        }
    }

    pub(crate) fn clear_needs_measure(&self) {
        self.parts.cache().clear_needs_measure();
    }

    /// Clears the node's layout flag and its descendants': a layout pass
    /// visited them.
    pub(crate) fn clear_needs_layout(&self) {
        self.parts.cache().clear_layout_dirt();
    }

    /// Marks this node as needing a fresh pointer-input pass.
    pub fn mark_needs_pointer_pass(&self) {
        self.needs_pointer_pass.set(true);
    }

    /// Returns true when pointer-input state needs to be recomputed.
    pub fn needs_pointer_pass(&self) -> bool {
        self.needs_pointer_pass.get()
    }

    /// Clears the pointer-input dirty flag after hosts service it.
    pub fn clear_needs_pointer_pass(&self) {
        self.needs_pointer_pass.set(false);
    }

    /// Marks this node as needing a focus synchronization.
    pub fn mark_needs_focus_sync(&self) {
        self.needs_focus_sync.set(true);
    }

    /// Returns true when focus state needs to be synchronized.
    pub fn needs_focus_sync(&self) -> bool {
        self.needs_focus_sync.get()
    }

    /// Clears the focus dirty flag after the focus manager processes it.
    pub fn clear_needs_focus_sync(&self) {
        self.needs_focus_sync.set(false);
    }

    /// Set this node's ID (called by applier after creation).
    pub fn set_node_id(&mut self, id: NodeId) {
        // A redraw asked for before the node had an id went to no draw
        // repass.
        if self.needs_redraw.get() {
            crate::render_state::note_retained_redraw(id);
        }
        let previous = self.id.replace(Some(id));
        if let Some(existing) = previous
            && let Some(owner_context_id) = self.owner_context_id.take()
        {
            unregister_layout_node(owner_context_id, existing);
        }
        self.parts.layout_state().borrow_mut().set_node_id(id);
        // The new entry holds the node's parent, capabilities and modifier
        // locals as they are now.
        let owner_context_id = register_layout_node(id, self);
        self.owner_context_id.set(Some(owner_context_id));

        let mut context = self.modifier_chain.context(Some(id));
        self.modifier_chain.move_to_node(previous, &mut context);
        let invalidations = context.take_invalidations();
        self.dispatch_modifier_invalidations_with_prev(
            &invalidations,
            NodeCapabilities::empty(),
            false,
        );
        // The slices carry the node's id; they are collected again when next read.
        self.modifier_slices_dirty.set(true);
    }

    /// Get this node's ID.
    pub fn node_id(&self) -> Option<NodeId> {
        self.id.get()
    }

    /// Set this node's parent (called when node is added as child).
    /// Sets both folded_parent (direct) and parent (first non-virtual ancestor for bubbling).
    pub fn set_parent(&self, parent: NodeId) {
        // The registry holds the parent the node has; the same one again
        // changes nothing.
        if self.parent.get() == Some(parent) && self.folded_parent.get() == Some(parent) {
            return;
        }
        self.folded_parent.set(Some(parent));
        self.parent.set(Some(parent));
        self.refresh_registry_state();
    }

    /// Clear this node's parent (called when node is removed from parent).
    pub fn clear_parent(&self) {
        self.folded_parent.set(None);
        self.parent.set(None);
        self.refresh_registry_state();
    }

    /// Get this node's parent for dirty flag bubbling (may skip virtual nodes).
    pub fn parent(&self) -> Option<NodeId> {
        self.parent.get()
    }

    /// Get this node's direct parent (may be a virtual node).
    pub fn folded_parent(&self) -> Option<NodeId> {
        self.folded_parent.get()
    }

    pub(crate) fn cache(&self) -> &NodeCache {
        self.parts.cache()
    }

    /// Returns the padding, layout properties and offset that the modifier chain resolved to.
    pub fn resolved_modifiers(&self) -> ResolvedModifiers {
        self.modifier_chain.resolved_modifiers()
    }

    /// What the chain tells the parent's measure policy about this node.
    pub(crate) fn parent_data(&self) -> cranpose_ui_layout::ParentData {
        self.modifier_chain.parent_data()
    }

    /// Returns the union of the capabilities of all nodes in the modifier chain.
    pub fn modifier_capabilities(&self) -> NodeCapabilities {
        self.modifier_chain.capabilities()
    }

    /// Whether this node's modifier chain makes it the root of a separate
    /// window. Its parent lays out as if it had no size and its parent's
    /// scene skips it; its own scene starts here.
    pub fn is_window_root(&self) -> bool {
        self.modifier_capabilities()
            .contains(NodeCapabilities::WINDOW_ROOT)
    }

    /// Returns the capabilities of the chain's nodes counted from the head of the chain. Compose's
    /// `aggregateChildKindSet`.
    pub fn modifier_child_capabilities(&self) -> NodeCapabilities {
        self.modifier_chain.aggregate_child_capabilities()
    }

    /// Turns debug logging of the modifier chain on or off.
    pub fn set_debug_modifiers(&mut self, enabled: bool) {
        self.debug_modifiers.set(enabled);
        self.modifier_chain.set_debug_logging(enabled);
    }

    /// Returns whether debug logging of the modifier chain is on.
    pub fn debug_modifiers_enabled(&self) -> bool {
        self.debug_modifiers.get()
    }

    /// The node's modifier locals, or `None` while its modifiers have never
    /// provided or read one.
    pub fn modifier_locals_handle(&self) -> Option<ModifierLocalsHandle> {
        self.modifier_chain.modifier_locals_handle()
    }

    /// Returns whether the modifier chain contains layout modifier nodes.
    pub fn has_layout_modifier_nodes(&self) -> bool {
        self.modifier_capabilities()
            .contains(NodeCapabilities::LAYOUT)
    }

    /// Returns whether the modifier chain contains draw modifier nodes.
    pub fn has_draw_modifier_nodes(&self) -> bool {
        self.modifier_capabilities()
            .contains(NodeCapabilities::DRAW)
    }

    /// Returns whether the modifier chain contains pointer input modifier nodes.
    pub fn has_pointer_input_modifier_nodes(&self) -> bool {
        self.modifier_capabilities()
            .contains(NodeCapabilities::POINTER_INPUT)
    }

    /// Returns whether the modifier chain contains semantics modifier nodes.
    pub fn has_semantics_modifier_nodes(&self) -> bool {
        self.modifier_capabilities()
            .contains(NodeCapabilities::SEMANTICS)
    }

    /// Returns whether the modifier chain contains focus modifier nodes.
    pub fn has_focus_modifier_nodes(&self) -> bool {
        self.modifier_capabilities()
            .contains(NodeCapabilities::FOCUS)
    }

    fn refresh_registry_state(&self) {
        if let (Some(id), Some(owner_context_id)) = (self.id.get(), self.owner_context_id.get()) {
            let parent = self.parent();
            let capabilities = self.modifier_child_capabilities();
            let modifier_locals = self.modifier_locals_handle();
            let _ = crate::render_state::with_layout_node_registry_by_app_context(
                owner_context_id,
                |registry| {
                    registry.update_entry(id, parent, capabilities, modifier_locals);
                },
            );
        }
    }

    /// Returns the draw commands, pointer input handlers, text and graphics layer data collected
    /// from the modifier nodes. The snapshot is rebuilt after the chain changed.
    pub fn modifier_slices_snapshot(&self) -> Rc<ModifierNodeSlices> {
        if self.modifier_slices_dirty.get() {
            self.update_modifier_slices_cache();
        }
        self.modifier_slices_snapshot.get()
    }

    /// Returns a clone of the current layout state.
    pub fn layout_state(&self) -> LayoutState {
        *self.parts.layout_state().borrow()
    }

    /// Returns the measured size of this node.
    pub fn measured_size(&self) -> Size {
        self.parts.layout_state().borrow().size()
    }

    /// Returns the position of this node relative to its parent.
    pub fn position(&self) -> Point {
        self.parts.layout_state().borrow().position()
    }

    /// Returns true if this node has been placed in the current layout pass.
    pub fn is_placed(&self) -> bool {
        self.parts.layout_state().borrow().is_placed()
    }

    /// Updates the measured size of this node. Called during measurement.
    /// [`LayoutState::set_size`] self-reports actual changes to the scene
    /// phase.
    pub fn set_measured_size(&self, size: Size, context: &AppContext) {
        self.parts
            .layout_state()
            .borrow_mut()
            .set_size(size, context);
    }

    // Updates the position of this node, which `placer` placed. Called
    // during placement. `LayoutState::place` self-reports actual moves to
    // the scene phase.
    pub(crate) fn place(&self, at: ChildPlacement, placer: Option<NodeId>, context: &AppContext) {
        self.parts
            .layout_state()
            .borrow_mut()
            .place_child(at, placer, context);
    }

    /// Records the content offset (e.g. from padding).
    pub fn set_content_offset(&self, offset: Point) {
        self.parts
            .layout_state()
            .borrow_mut()
            .set_content_offset(offset);
    }

    /// Clears the is_placed flag. Called at the start of a layout pass.
    pub fn clear_placed(&self, context: &AppContext) {
        self.parts.layout_state().borrow_mut().clear_placed(context);
    }

    fn note_semantics_layout_change(&self) {
        if let Ok(mut state) = self.parts.layout_state().try_borrow_mut() {
            state.note_semantics_change();
        }
    }

    /// Returns the semantics that the modifier chain reports, or `None` if it reports none.
    pub fn semantics_configuration(&self) -> Option<SemanticsConfiguration> {
        crate::modifier::collect_semantics_from_chain(self.modifier_chain.chain())
    }

    /// Drops the cached reach and queues the node for the modal count.
    fn forget_semantics_reach(&self) {
        self.semantics_reach.set(None);
        crate::modal_nodes::reach_changed(self.id.get());
    }

    /// Whether this node's modifiers make it modal or hidden.
    pub fn semantics_reach(&self) -> cranpose_foundation::SemanticsReach {
        // A chain without semantics reaches nothing, known without touching it.
        if !self
            .modifier_capabilities()
            .contains(NodeCapabilities::SEMANTICS)
        {
            return cranpose_foundation::SemanticsReach::default();
        }
        if let Some(reach) = self.semantics_reach.get() {
            return reach;
        }
        let reach = crate::modifier::semantics_reach_of_chain(self.modifier_chain.chain());
        self.semantics_reach.set(Some(reach));
        reach
    }

    pub(crate) fn modifier_chain(&self) -> &ModifierChainHandle {
        &self.modifier_chain
    }

    /// Runs `read` on the node's layout state, without a copy of it.
    pub fn with_layout_state<R>(&self, read: impl FnOnce(&LayoutState) -> R) -> R {
        read(&self.parts.layout_state().borrow())
    }

    pub(crate) fn layout_parts(&self) -> &Rc<LayoutParts> {
        &self.parts
    }

    pub(crate) fn layout_runtime_state(&self) -> &RefCell<LayoutRuntimeState> {
        self.parts.runtime_state()
    }

    #[cfg(test)]
    pub(crate) fn layout_runtime_debug_stats(&self) -> LayoutRuntimeDebugStats {
        self.parts.runtime_state().borrow().debug_stats()
    }
}
impl Clone for LayoutNode {
    fn clone(&self) -> Self {
        let mut node = Self {
            #[cfg(feature = "inspection")]
            source_trace: Rc::clone(&self.source_trace),
            modifier: self.modifier.clone(),
            modifier_chain: ModifierChainHandle::for_layout_direction(
                self.modifier_chain.layout_direction(),
            ),
            measure_policy: Rc::clone(&self.measure_policy),
            density: self.density,
            children: self.children.clone(),
            needs_semantics: Cell::new(self.needs_semantics.get()),
            descendant_needs_semantics: Cell::new(self.descendant_needs_semantics.get()),
            semantics_reach: Cell::new(None),
            needs_redraw: Cell::new(self.needs_redraw.get()),
            needs_pointer_pass: Cell::new(self.needs_pointer_pass.get()),
            needs_focus_sync: Cell::new(self.needs_focus_sync.get()),
            parent: NodeIdCell::new(self.parent.get()),
            folded_parent: NodeIdCell::new(self.folded_parent.get()),
            id: NodeIdCell::new(None),
            owner_context_id: Cell::new(None),
            debug_modifiers: Cell::new(self.debug_modifiers.get()),
            is_virtual: self.is_virtual,
            modifier_slices_snapshot: crate::modifier::SlicesSnapshot::default(),
            modifier_slices_dirty: Cell::new(true),
            parts: Rc::clone(&self.parts),
        };
        node.sync_modifier_chain(None);
        node
    }
}

impl Node for LayoutNode {
    fn mount(&mut self) {
        self.modifier_chain.remount(self.id.get());
        crate::modal_nodes::reach_changed(self.id.get());
    }

    fn unmount(&mut self) {
        self.modifier_chain.chain_mut().detach_nodes();
    }

    fn set_node_id(&mut self, id: NodeId) {
        Self::set_node_id(self, id);
    }

    fn insert_child(&mut self, child: NodeId) -> bool {
        if self.children.contains(&child) {
            return false;
        }
        self.children.push(child);
        self.parts.cache().clear();
        self.mark_needs_measure();
        self.note_semantics_layout_change();
        true
    }

    fn remove_child(&mut self, child: NodeId) -> bool {
        let before = self.children.len();
        self.children.retain(|&id| id != child);
        let removed = self.children.len() < before;
        if removed {
            self.parts.cache().clear();
            self.mark_needs_measure();
            self.note_semantics_layout_change();
        }
        removed
    }

    fn move_child(&mut self, from: usize, to: usize) {
        if from == to || from >= self.children.len() {
            return;
        }
        let child = self.children.remove(from);
        let target = to.min(self.children.len());
        self.children.insert(target, child);
        self.parts.cache().clear();
        self.mark_needs_measure();
        self.note_semantics_layout_change();
    }

    fn update_children(&mut self, children: &[NodeId]) {
        self.children.clear();
        self.children.extend_from_slice(children);
        self.parts.cache().clear();
        self.mark_needs_measure();
        self.note_semantics_layout_change();
    }

    fn collect_children_into(&self, out: &mut smallvec::SmallVec<[NodeId; 8]>) {
        out.clear();
        out.extend_from_slice(&self.children);
    }

    fn for_each_child(&self, f: &mut dyn FnMut(NodeId)) {
        for &child in &self.children {
            f(child);
        }
    }

    fn owned_child_index(&self, child: NodeId) -> Option<usize> {
        self.children.iter().position(|&id| id == child)
    }

    fn on_attached_to_parent(&mut self, parent: NodeId) {
        self.set_parent(parent);
    }

    fn on_removed_from_parent(&mut self) {
        self.clear_parent();
    }

    fn parent(&self) -> Option<NodeId> {
        self.parent.get()
    }

    fn mark_needs_layout(&self) {
        Self::mark_needs_layout(self);
    }

    fn needs_layout(&self) -> bool {
        Self::needs_layout(self)
    }

    fn mark_needs_measure(&self) {
        Self::mark_needs_measure(self);
    }

    fn needs_measure(&self) -> bool {
        Self::needs_measure(self)
    }

    fn mark_descendant_needs_layout(&self, measure: bool) {
        self.parts.cache().mark_descendant_needs_layout(measure);
    }

    fn descendant_needs_layout(&self) -> bool {
        self.parts.cache().dirt().descendant.layout
    }

    fn is_virtual(&self) -> bool {
        self.is_virtual
    }

    fn descendant_needs_measure(&self) -> bool {
        self.parts.cache().dirt().descendant.measure
    }

    fn mark_needs_semantics(&self) {
        self.needs_semantics.set(true);
        self.forget_semantics_reach();
    }

    fn mark_descendant_needs_semantics(&self) {
        self.descendant_needs_semantics.set(true);
    }

    fn needs_semantics(&self) -> bool {
        Self::needs_semantics(self)
    }

    fn set_parent_for_bubbling(&mut self, parent: NodeId) {
        if self.parent.get().is_none() {
            self.parent.set(Some(parent));
        }
    }

    fn recycle_key(&self) -> Option<TypeId> {
        Some(TypeId::of::<Self>())
    }

    fn recycle_pool_limit(&self) -> Option<usize> {
        Some(super::node_pool_limit::node_pool_limit())
    }

    fn prepare_for_recycle(&mut self) {
        *self = Self::new_recycled_shell(self.is_virtual);
    }

    fn rehouse_for_recycle(&self) -> Option<Box<dyn Node>> {
        Some(Box::new(Self::new_recycled_shell(self.is_virtual)))
    }

    fn rehouse_for_live_compaction(&mut self) -> Option<Box<dyn Node>> {
        // The whole node moves into the new box. Its modifier nodes keep
        // what the user is doing with it, such as a focus, a held press or an
        // IME composition, and its caches and registry entry stay true for
        // it. Only its child list, which a spike of children may have grown,
        // is cut to size. The shell left behind has no id to unregister.
        let mut node = std::mem::replace(self, Self::new_recycled_shell(self.is_virtual));
        node.children.shrink_to_fit();
        Some(Box::new(node))
    }
}

impl Drop for LayoutNode {
    fn drop(&mut self) {
        self.parts.cache().advance_revision();
        if let (Some(id), Some(owner_context_id)) = (self.id.get(), self.owner_context_id.get()) {
            unregister_layout_node(owner_context_id, id);
        }
    }
}

#[cfg(test)]
#[path = "tests/layout_node_tests.rs"]
mod tests;