servo/components/layout_2020/flow/construct.rs

/* 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 crate::cell::ArcRefCell;
use crate::context::LayoutContext;
use crate::dom_traversal::{
    BoxSlot, Contents, NodeAndStyleInfo, NodeExt, NonReplacedContents, TraversalHandler,
};
use crate::element_data::LayoutBox;
use crate::flow::float::FloatBox;
use crate::flow::inline::{InlineBox, InlineFormattingContext, InlineLevelBox, TextRun};
use crate::flow::{BlockContainer, BlockFormattingContext, BlockLevelBox};
use crate::formatting_contexts::IndependentFormattingContext;
use crate::fragments::Tag;
use crate::positioned::AbsolutelyPositionedBox;
use crate::style_ext::{DisplayGeneratingBox, DisplayInside, DisplayOutside};
use rayon::iter::{IntoParallelIterator, ParallelIterator};
use rayon_croissant::ParallelIteratorExt;
use servo_arc::Arc;
use std::borrow::Cow;
use std::convert::{TryFrom, TryInto};
use style::computed_values::white_space::T as WhiteSpace;
use style::properties::longhands::list_style_position::computed_value::T as ListStylePosition;
use style::properties::ComputedValues;
use style::selector_parser::PseudoElement;
use style::values::specified::text::TextDecorationLine;

impl BlockFormattingContext {
    pub fn construct<'dom, Node>(
        context: &LayoutContext,
        info: &NodeAndStyleInfo<Node>,
        contents: NonReplacedContents,
        propagated_text_decoration_line: TextDecorationLine,
        is_list_item: bool,
    ) -> Self
    where
        Node: NodeExt<'dom>,
    {
        let (contents, contains_floats) = BlockContainer::construct(
            context,
            info,
            contents,
            propagated_text_decoration_line,
            is_list_item,
        );
        let bfc = Self {
            contents,
            contains_floats: contains_floats == ContainsFloats::Yes,
        };
        bfc
    }

    pub fn construct_for_text_runs<'dom>(
        runs: impl Iterator<Item = TextRun>,
        text_decoration_line: TextDecorationLine,
    ) -> Self {
        // FIXME: do white space collapsing
        let inline_level_boxes = runs
            .map(|run| ArcRefCell::new(InlineLevelBox::TextRun(run)))
            .collect();

        let ifc = InlineFormattingContext {
            inline_level_boxes,
            text_decoration_line,
            has_first_formatted_line: true,
        };
        let contents = BlockContainer::InlineFormattingContext(ifc);
        let bfc = Self {
            contents,
            contains_floats: false,
        };
        bfc
    }
}

struct BlockLevelJob<'dom, Node> {
    info: NodeAndStyleInfo<Node>,
    box_slot: BoxSlot<'dom>,
    kind: BlockLevelCreator,
}

enum BlockLevelCreator {
    SameFormattingContextBlock(IntermediateBlockContainer),
    Independent {
        display_inside: DisplayInside,
        contents: Contents,
        propagated_text_decoration_line: TextDecorationLine,
    },
    OutOfFlowAbsolutelyPositionedBox {
        display_inside: DisplayInside,
        contents: Contents,
    },
    OutOfFlowFloatBox {
        display_inside: DisplayInside,
        contents: Contents,
    },
}

/// A block container that may still have to be constructed.
///
/// Represents either the inline formatting context of an anonymous block
/// box or the yet-to-be-computed block container generated from the children
/// of a given element.
///
/// Deferring allows using rayon’s `into_par_iter`.
enum IntermediateBlockContainer {
    InlineFormattingContext(InlineFormattingContext),
    Deferred {
        contents: NonReplacedContents,
        propagated_text_decoration_line: TextDecorationLine,
        is_list_item: bool,
    },
}

/// A builder for a block container.
///
/// This builder starts from the first child of a given DOM node
/// and does a preorder traversal of all of its inclusive siblings.
struct BlockContainerBuilder<'dom, 'style, Node> {
    context: &'style LayoutContext<'style>,

    /// This NodeAndStyleInfo contains the root node, the corresponding pseudo
    /// content designator, and the block container style.
    info: &'style NodeAndStyleInfo<Node>,

    /// The list of block-level boxes to be built for the final block container.
    ///
    /// Contains all the block-level jobs we found traversing the tree
    /// so far, if this is empty at the end of the traversal and the ongoing
    /// inline formatting context is not empty, the block container establishes
    /// an inline formatting context (see end of `build`).
    ///
    /// DOM nodes which represent block-level boxes are immediately pushed
    /// to this list with their style without ever being traversed at this
    /// point, instead we just move to their next sibling. If the DOM node
    /// doesn't have a next sibling, we either reached the end of the container
    /// root or there are ongoing inline-level boxes
    /// (see `handle_block_level_element`).
    block_level_boxes: Vec<BlockLevelJob<'dom, Node>>,

    /// The ongoing inline formatting context of the builder.
    ///
    /// Contains all the complete inline level boxes we found traversing the
    /// tree so far. If a block-level box is found during traversal,
    /// this inline formatting context is pushed as a block level box to
    /// the list of block-level boxes of the builder
    /// (see `end_ongoing_inline_formatting_context`).
    ongoing_inline_formatting_context: InlineFormattingContext,

    /// The ongoing stack of inline boxes stack of the builder.
    ///
    /// Contains all the currently ongoing inline boxes we entered so far.
    /// The traversal is at all times as deep in the tree as this stack is,
    /// which is why the code doesn't need to keep track of the actual
    /// container root (see `handle_inline_level_element`).
    ///
    /// Whenever the end of a DOM element that represents an inline box is
    /// reached, the inline box at the top of this stack is complete and ready
    /// to be pushed to the children of the next last ongoing inline box
    /// the ongoing inline formatting context if the stack is now empty,
    /// which means we reached the end of a child of the actual
    /// container root (see `move_to_next_sibling`).
    ongoing_inline_boxes_stack: Vec<InlineBox>,

    /// The style of the anonymous block boxes pushed to the list of block-level
    /// boxes, if any (see `end_ongoing_inline_formatting_context`).
    anonymous_style: Option<Arc<ComputedValues>>,

    /// Whether the resulting block container contains any float box.
    contains_floats: ContainsFloats,
}

impl BlockContainer {
    pub fn construct<'dom, Node>(
        context: &LayoutContext,
        info: &NodeAndStyleInfo<Node>,
        contents: NonReplacedContents,
        propagated_text_decoration_line: TextDecorationLine,
        is_list_item: bool,
    ) -> (BlockContainer, ContainsFloats)
    where
        Node: NodeExt<'dom>,
    {
        let text_decoration_line =
            propagated_text_decoration_line | info.style.clone_text_decoration_line();
        let mut builder = BlockContainerBuilder {
            context,
            info,
            block_level_boxes: Vec::new(),
            ongoing_inline_formatting_context: InlineFormattingContext::new(
                text_decoration_line,
                /* has_first_formatted_line = */ true,
            ),
            ongoing_inline_boxes_stack: Vec::new(),
            anonymous_style: None,
            contains_floats: ContainsFloats::No,
        };

        if is_list_item {
            if let Some(marker_contents) = crate::lists::make_marker(context, info) {
                let _position = info.style.clone_list_style_position();
                // FIXME: implement support for `outside` and remove this:
                let position = ListStylePosition::Inside;
                match position {
                    ListStylePosition::Inside => {
                        builder.handle_list_item_marker_inside(info, marker_contents)
                    },
                    ListStylePosition::Outside => {
                        // FIXME: implement layout for this case
                        // https://github.com/servo/servo/issues/27383
                        // and enable `list-style-position` and the `list-style` shorthand in Stylo.
                    },
                }
            }
        }

        contents.traverse(context, info, &mut builder);

        debug_assert!(builder.ongoing_inline_boxes_stack.is_empty());

        if !builder
            .ongoing_inline_formatting_context
            .inline_level_boxes
            .is_empty()
        {
            if builder.block_level_boxes.is_empty() {
                let container = BlockContainer::InlineFormattingContext(
                    builder.ongoing_inline_formatting_context,
                );
                return (container, builder.contains_floats);
            }
            builder.end_ongoing_inline_formatting_context();
        }

        let mut contains_floats = builder.contains_floats;
        let mapfold = |contains_floats: &mut ContainsFloats, creator: BlockLevelJob<'dom, _>| {
            let (block_level_box, box_contains_floats) = creator.finish(context);
            *contains_floats |= box_contains_floats;
            block_level_box
        };
        let block_level_boxes = if context.use_rayon {
            builder
                .block_level_boxes
                .into_par_iter()
                .mapfold_reduce_into(
                    &mut contains_floats,
                    mapfold,
                    || ContainsFloats::No,
                    |left, right| {
                        *left |= right;
                    },
                )
                .collect()
        } else {
            builder
                .block_level_boxes
                .into_iter()
                .map(|x| mapfold(&mut contains_floats, x))
                .collect()
        };
        let container = BlockContainer::BlockLevelBoxes(block_level_boxes);

        (container, contains_floats)
    }
}

impl<'dom, Node> TraversalHandler<'dom, Node> for BlockContainerBuilder<'dom, '_, Node>
where
    Node: NodeExt<'dom>,
{
    fn handle_element(
        &mut self,
        info: &NodeAndStyleInfo<Node>,
        display: DisplayGeneratingBox,
        contents: Contents,
        box_slot: BoxSlot<'dom>,
    ) {
        match display {
            DisplayGeneratingBox::OutsideInside { outside, inside } => match outside {
                DisplayOutside::Inline => box_slot.set(LayoutBox::InlineLevel(
                    self.handle_inline_level_element(info, inside, contents),
                )),
                DisplayOutside::Block => {
                    let box_style = info.style.get_box();
                    // Floats and abspos cause blockification, so they only happen in this case.
                    // https://drafts.csswg.org/css2/visuren.html#dis-pos-flo
                    if box_style.position.is_absolutely_positioned() {
                        self.handle_absolutely_positioned_element(info, inside, contents, box_slot)
                    } else if box_style.float.is_floating() {
                        self.handle_float_element(info, inside, contents, box_slot)
                    } else {
                        self.handle_block_level_element(info, inside, contents, box_slot)
                    }
                },
            },
        }
    }

    fn handle_text(&mut self, info: &NodeAndStyleInfo<Node>, input: Cow<'dom, str>) {
        // Skip any leading whitespace as dictated by the node's style.
        let white_space = info.style.get_inherited_text().white_space;
        let (preserved_leading_whitespace, mut input) =
            self.handle_leading_whitespace(&input, white_space);

        if !preserved_leading_whitespace && input.is_empty() {
            return;
        }

        // This text node should be pushed either to the next ongoing
        // inline level box with the parent style of that inline level box
        // that will be ended, or directly to the ongoing inline formatting
        // context with the parent style of that builder.
        let inlines = self.current_inline_level_boxes();

        let mut new_text_run_contents;
        let output;

        {
            let mut last_box = inlines.last_mut().map(|last| last.borrow_mut());
            let last_text = last_box.as_mut().and_then(|last| match &mut **last {
                InlineLevelBox::TextRun(last) => Some(&mut last.text),
                _ => None,
            });

            if let Some(text) = last_text {
                // Append to the existing text run
                new_text_run_contents = None;
                output = text;
            } else {
                new_text_run_contents = Some(String::new());
                output = new_text_run_contents.as_mut().unwrap();
            }

            if preserved_leading_whitespace {
                output.push(' ')
            }

            match (
                white_space.preserve_spaces(),
                white_space.preserve_newlines(),
            ) {
                // All whitespace is significant, so we don't need to transform
                // the input at all.
                (true, true) => {
                    output.push_str(input);
                },

                // There are no cases in CSS where where need to preserve spaces
                // but not newlines.
                (true, false) => unreachable!(),

                // Spaces are not significant, but newlines might be. We need
                // to collapse non-significant whitespace as appropriate.
                (false, preserve_newlines) => loop {
                    // If there are any spaces that need preserving, split the string
                    // that precedes them, collapse them into a single whitespace,
                    // then process the remainder of the string independently.
                    if let Some(i) = input
                        .bytes()
                        .position(|b| b.is_ascii_whitespace() && (!preserve_newlines || b != b'\n'))
                    {
                        let (non_whitespace, rest) = input.split_at(i);
                        output.push_str(non_whitespace);
                        output.push(' ');

                        // Find the first byte that is either significant whitespace or
                        // non-whitespace to continue processing it.
                        if let Some(i) = rest.bytes().position(|b| {
                            !b.is_ascii_whitespace() || (preserve_newlines && b == b'\n')
                        }) {
                            input = &rest[i..];
                        } else {
                            break;
                        }
                    } else {
                        // No whitespace found, so no transformation is required.
                        output.push_str(input);
                        break;
                    }
                },
            }
        }

        if let Some(text) = new_text_run_contents {
            inlines.push(ArcRefCell::new(InlineLevelBox::TextRun(TextRun {
                tag: Tag::from_node_and_style_info(info),
                parent_style: Arc::clone(&info.style),
                text,
            })))
        }
    }
}

impl<'dom, Node> BlockContainerBuilder<'dom, '_, Node>
where
    Node: NodeExt<'dom>,
{
    /// Returns:
    ///
    /// * Whether this text run has preserved (non-collapsible) leading whitespace
    /// * The contents starting at the first non-whitespace character (or the empty string)
    fn handle_leading_whitespace<'text>(
        &mut self,
        text: &'text str,
        white_space: WhiteSpace,
    ) -> (bool, &'text str) {
        // FIXME: this is only an approximation of
        // https://drafts.csswg.org/css2/text.html#white-space-model
        if !text.starts_with(|c: char| c.is_ascii_whitespace()) || white_space.preserve_spaces() {
            return (false, text);
        }

        let preserved = match whitespace_is_preserved(self.current_inline_level_boxes()) {
            WhitespacePreservedResult::Unknown => {
                // Paragraph start.
                false
            },
            WhitespacePreservedResult::NotPreserved => false,
            WhitespacePreservedResult::Preserved => true,
        };

        let text = text.trim_start_matches(|c: char| c.is_ascii_whitespace());
        return (preserved, text);

        fn whitespace_is_preserved(
            inline_level_boxes: &[ArcRefCell<InlineLevelBox>],
        ) -> WhitespacePreservedResult {
            for inline_level_box in inline_level_boxes.iter().rev() {
                match *inline_level_box.borrow() {
                    InlineLevelBox::TextRun(ref r) => {
                        if r.text.ends_with(' ') {
                            return WhitespacePreservedResult::NotPreserved;
                        }
                        return WhitespacePreservedResult::Preserved;
                    },
                    InlineLevelBox::Atomic { .. } => {
                        return WhitespacePreservedResult::NotPreserved;
                    },
                    InlineLevelBox::OutOfFlowAbsolutelyPositionedBox(_) |
                    InlineLevelBox::OutOfFlowFloatBox(_) => {},
                    InlineLevelBox::InlineBox(ref b) => {
                        match whitespace_is_preserved(&b.children) {
                            WhitespacePreservedResult::Unknown => {},
                            result => return result,
                        }
                    },
                }
            }

            WhitespacePreservedResult::Unknown
        }

        #[derive(Clone, Copy, PartialEq)]
        enum WhitespacePreservedResult {
            Preserved,
            NotPreserved,
            Unknown,
        }
    }

    fn handle_list_item_marker_inside(
        &mut self,
        info: &NodeAndStyleInfo<Node>,
        contents: Vec<crate::dom_traversal::PseudoElementContentItem>,
    ) {
        let marker_style = self
            .context
            .shared_context()
            .stylist
            .style_for_anonymous::<Node::ConcreteElement>(
                &self.context.shared_context().guards,
                &PseudoElement::ServoText, // FIMXE: use `PseudoElement::Marker` when we add it
                &info.style,
            );
        self.handle_inline_level_element(
            &info.new_replacing_style(marker_style),
            DisplayInside::Flow {
                is_list_item: false,
            },
            Contents::OfPseudoElement(contents),
        );
    }

    fn handle_inline_level_element(
        &mut self,
        info: &NodeAndStyleInfo<Node>,
        display_inside: DisplayInside,
        contents: Contents,
    ) -> ArcRefCell<InlineLevelBox> {
        let box_ = if let (DisplayInside::Flow { is_list_item }, false) =
            (display_inside, contents.is_replaced())
        {
            // We found un inline box.
            // Whatever happened before, all we need to do before recurring
            // is to remember this ongoing inline level box.
            self.ongoing_inline_boxes_stack.push(InlineBox {
                tag: Tag::from_node_and_style_info(info),
                style: info.style.clone(),
                first_fragment: true,
                last_fragment: false,
                children: vec![],
            });

            if is_list_item {
                if let Some(marker_contents) = crate::lists::make_marker(self.context, info) {
                    // Ignore `list-style-position` here:
                    // “If the list item is an inline box: this value is equivalent to `inside`.”
                    // https://drafts.csswg.org/css-lists/#list-style-position-outside
                    self.handle_list_item_marker_inside(info, marker_contents)
                }
            }

            // `unwrap` doesn’t panic here because `is_replaced` returned `false`.
            NonReplacedContents::try_from(contents)
                .unwrap()
                .traverse(self.context, info, self);

            let mut inline_box = self
                .ongoing_inline_boxes_stack
                .pop()
                .expect("no ongoing inline level box found");
            inline_box.last_fragment = true;
            ArcRefCell::new(InlineLevelBox::InlineBox(inline_box))
        } else {
            ArcRefCell::new(InlineLevelBox::Atomic(
                IndependentFormattingContext::construct(
                    self.context,
                    info,
                    display_inside,
                    contents,
                    // Text decorations are not propagated to atomic inline-level descendants.
                    TextDecorationLine::NONE,
                ),
            ))
        };
        self.current_inline_level_boxes().push(box_.clone());
        box_
    }

    fn handle_block_level_element(
        &mut self,
        info: &NodeAndStyleInfo<Node>,
        display_inside: DisplayInside,
        contents: Contents,
        box_slot: BoxSlot<'dom>,
    ) {
        // We just found a block level element, all ongoing inline level boxes
        // need to be split around it. We iterate on the fragmented inline
        // level box stack to take their contents and set their first_fragment
        // field to false, for the fragmented inline level boxes that will
        // come after the block level element.
        let mut fragmented_inline_boxes =
            self.ongoing_inline_boxes_stack
                .iter_mut()
                .rev()
                .map(|ongoing| {
                    let fragmented = InlineBox {
                        tag: ongoing.tag,
                        style: ongoing.style.clone(),
                        first_fragment: ongoing.first_fragment,
                        // The fragmented boxes before the block level element
                        // are obviously not the last fragment.
                        last_fragment: false,
                        children: std::mem::take(&mut ongoing.children),
                    };
                    ongoing.first_fragment = false;
                    fragmented
                });

        if let Some(last) = fragmented_inline_boxes.next() {
            // There were indeed some ongoing inline level boxes before
            // the block, we accumulate them as a single inline level box
            // to be pushed to the ongoing inline formatting context.
            let mut fragmented_inline = InlineLevelBox::InlineBox(last);
            for mut fragmented_parent_inline_box in fragmented_inline_boxes {
                fragmented_parent_inline_box
                    .children
                    .push(ArcRefCell::new(fragmented_inline));
                fragmented_inline = InlineLevelBox::InlineBox(fragmented_parent_inline_box);
            }

            self.ongoing_inline_formatting_context
                .inline_level_boxes
                .push(ArcRefCell::new(fragmented_inline));
        }

        let propagated_text_decoration_line =
            self.ongoing_inline_formatting_context.text_decoration_line;

        // We found a block level element, so the ongoing inline formatting
        // context needs to be ended.
        self.end_ongoing_inline_formatting_context();

        let kind = match contents.try_into() {
            Ok(contents) => match display_inside {
                DisplayInside::Flow { is_list_item } => {
                    BlockLevelCreator::SameFormattingContextBlock(
                        IntermediateBlockContainer::Deferred {
                            contents,
                            propagated_text_decoration_line,
                            is_list_item,
                        },
                    )
                },
                _ => BlockLevelCreator::Independent {
                    display_inside,
                    contents: contents.into(),
                    propagated_text_decoration_line,
                },
            },
            Err(contents) => {
                let contents = Contents::Replaced(contents);
                BlockLevelCreator::Independent {
                    display_inside,
                    contents,
                    propagated_text_decoration_line,
                }
            },
        };
        self.block_level_boxes.push(BlockLevelJob {
            info: info.clone(),
            box_slot,
            kind,
        });
    }

    fn handle_absolutely_positioned_element(
        &mut self,
        info: &NodeAndStyleInfo<Node>,
        display_inside: DisplayInside,
        contents: Contents,
        box_slot: BoxSlot<'dom>,
    ) {
        if !self.has_ongoing_inline_formatting_context() {
            let kind = BlockLevelCreator::OutOfFlowAbsolutelyPositionedBox {
                contents,
                display_inside,
            };
            self.block_level_boxes.push(BlockLevelJob {
                info: info.clone(),
                box_slot,
                kind,
            });
        } else {
            let box_ = ArcRefCell::new(InlineLevelBox::OutOfFlowAbsolutelyPositionedBox(
                ArcRefCell::new(AbsolutelyPositionedBox::construct(
                    self.context,
                    info,
                    display_inside,
                    contents,
                )),
            ));
            self.current_inline_level_boxes().push(box_.clone());
            box_slot.set(LayoutBox::InlineLevel(box_))
        }
    }

    fn handle_float_element(
        &mut self,
        info: &NodeAndStyleInfo<Node>,
        display_inside: DisplayInside,
        contents: Contents,
        box_slot: BoxSlot<'dom>,
    ) {
        self.contains_floats = ContainsFloats::Yes;

        if !self.has_ongoing_inline_formatting_context() {
            let kind = BlockLevelCreator::OutOfFlowFloatBox {
                contents,
                display_inside,
            };
            self.block_level_boxes.push(BlockLevelJob {
                info: info.clone(),
                box_slot,
                kind,
            });
        } else {
            let box_ = ArcRefCell::new(InlineLevelBox::OutOfFlowFloatBox(FloatBox::construct(
                self.context,
                info,
                display_inside,
                contents,
            )));
            self.current_inline_level_boxes().push(box_.clone());
            box_slot.set(LayoutBox::InlineLevel(box_))
        }
    }

    fn end_ongoing_inline_formatting_context(&mut self) {
        if self
            .ongoing_inline_formatting_context
            .inline_level_boxes
            .is_empty()
        {
            // There should never be an empty inline formatting context.
            self.ongoing_inline_formatting_context
                .has_first_formatted_line = false;
            return;
        }

        let context = self.context;
        let block_container_style = &self.info.style;
        let anonymous_style = self.anonymous_style.get_or_insert_with(|| {
            context
                .shared_context()
                .stylist
                .style_for_anonymous::<Node::ConcreteElement>(
                    &context.shared_context().guards,
                    &PseudoElement::ServoText,
                    block_container_style,
                )
        });

        let kind = BlockLevelCreator::SameFormattingContextBlock(
            IntermediateBlockContainer::InlineFormattingContext(std::mem::take(
                &mut self.ongoing_inline_formatting_context,
            )),
        );
        let info = self.info.new_replacing_style(anonymous_style.clone());
        self.block_level_boxes.push(BlockLevelJob {
            info,
            // FIXME(nox): We should be storing this somewhere.
            box_slot: BoxSlot::dummy(),
            kind,
        });
    }

    fn current_inline_level_boxes(&mut self) -> &mut Vec<ArcRefCell<InlineLevelBox>> {
        match self.ongoing_inline_boxes_stack.last_mut() {
            Some(last) => &mut last.children,
            None => &mut self.ongoing_inline_formatting_context.inline_level_boxes,
        }
    }

    fn has_ongoing_inline_formatting_context(&self) -> bool {
        !self
            .ongoing_inline_formatting_context
            .inline_level_boxes
            .is_empty() ||
            !self.ongoing_inline_boxes_stack.is_empty()
    }
}

impl<'dom, Node> BlockLevelJob<'dom, Node>
where
    Node: NodeExt<'dom>,
{
    fn finish(self, context: &LayoutContext) -> (ArcRefCell<BlockLevelBox>, ContainsFloats) {
        let info = &self.info;
        let (block_level_box, contains_floats) = match self.kind {
            BlockLevelCreator::SameFormattingContextBlock(contents) => {
                let (contents, contains_floats) = contents.finish(context, info);
                let block_level_box = ArcRefCell::new(BlockLevelBox::SameFormattingContextBlock {
                    tag: Tag::from_node_and_style_info(info),
                    contents,
                    style: Arc::clone(&info.style),
                });
                (block_level_box, contains_floats)
            },
            BlockLevelCreator::Independent {
                display_inside,
                contents,
                propagated_text_decoration_line,
            } => {
                let context = IndependentFormattingContext::construct(
                    context,
                    info,
                    display_inside,
                    contents,
                    propagated_text_decoration_line,
                );
                (
                    ArcRefCell::new(BlockLevelBox::Independent(context)),
                    ContainsFloats::No,
                )
            },
            BlockLevelCreator::OutOfFlowAbsolutelyPositionedBox {
                display_inside,
                contents,
            } => {
                let block_level_box = ArcRefCell::new(
                    BlockLevelBox::OutOfFlowAbsolutelyPositionedBox(ArcRefCell::new(
                        AbsolutelyPositionedBox::construct(context, info, display_inside, contents),
                    )),
                );
                (block_level_box, ContainsFloats::No)
            },
            BlockLevelCreator::OutOfFlowFloatBox {
                display_inside,
                contents,
            } => {
                let block_level_box = ArcRefCell::new(BlockLevelBox::OutOfFlowFloatBox(
                    FloatBox::construct(context, info, display_inside, contents),
                ));
                (block_level_box, ContainsFloats::Yes)
            },
        };
        self.box_slot
            .set(LayoutBox::BlockLevel(block_level_box.clone()));
        (block_level_box, contains_floats)
    }
}

impl IntermediateBlockContainer {
    fn finish<'dom, Node>(
        self,
        context: &LayoutContext,
        info: &NodeAndStyleInfo<Node>,
    ) -> (BlockContainer, ContainsFloats)
    where
        Node: NodeExt<'dom>,
    {
        match self {
            IntermediateBlockContainer::Deferred {
                contents,
                propagated_text_decoration_line,
                is_list_item,
            } => BlockContainer::construct(
                context,
                info,
                contents,
                propagated_text_decoration_line,
                is_list_item,
            ),
            IntermediateBlockContainer::InlineFormattingContext(ifc) => {
                // If that inline formatting context contained any float, those
                // were already taken into account during the first phase of
                // box construction.
                (
                    BlockContainer::InlineFormattingContext(ifc),
                    ContainsFloats::No,
                )
            },
        }
    }
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub(crate) enum ContainsFloats {
    No,
    Yes,
}

impl std::ops::BitOrAssign for ContainsFloats {
    fn bitor_assign(&mut self, other: Self) {
        if other == ContainsFloats::Yes {
            *self = ContainsFloats::Yes;
        }
    }
}