layout/
dom_traversal.rs

1/* This Source Code Form is subject to the terms of the Mozilla Public
2 * License, v. 2.0. If a copy of the MPL was not distributed with this
3 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
4
5use std::borrow::Cow;
6
7use fonts::ByteIndex;
8use html5ever::LocalName;
9use layout_api::wrapper_traits::{
10    PseudoElementChain, ThreadSafeLayoutElement, ThreadSafeLayoutNode,
11};
12use layout_api::{LayoutDamage, LayoutElementType, LayoutNodeType};
13use range::Range;
14use script::layout_dom::ServoThreadSafeLayoutNode;
15use selectors::Element as SelectorsElement;
16use servo_arc::Arc as ServoArc;
17use style::dom::NodeInfo;
18use style::properties::ComputedValues;
19use style::selector_parser::PseudoElement;
20use style::values::generics::counters::{Content, ContentItem};
21use style::values::specified::Quotes;
22
23use crate::context::LayoutContext;
24use crate::dom::{BoxSlot, LayoutBox, NodeExt};
25use crate::flow::inline::SharedInlineStyles;
26use crate::quotes::quotes_for_lang;
27use crate::replaced::ReplacedContents;
28use crate::style_ext::{Display, DisplayGeneratingBox, DisplayInside, DisplayOutside};
29
30/// A data structure used to pass and store related layout information together to
31/// avoid having to repeat the same arguments in argument lists.
32#[derive(Clone)]
33pub(crate) struct NodeAndStyleInfo<'dom> {
34    pub node: ServoThreadSafeLayoutNode<'dom>,
35    pub style: ServoArc<ComputedValues>,
36    pub damage: LayoutDamage,
37}
38
39impl<'dom> NodeAndStyleInfo<'dom> {
40    pub(crate) fn new(
41        node: ServoThreadSafeLayoutNode<'dom>,
42        style: ServoArc<ComputedValues>,
43        damage: LayoutDamage,
44    ) -> Self {
45        Self {
46            node,
47            style,
48            damage,
49        }
50    }
51
52    pub(crate) fn pseudo_element_chain(&self) -> PseudoElementChain {
53        self.node.pseudo_element_chain()
54    }
55
56    pub(crate) fn with_pseudo_element(
57        &self,
58        context: &LayoutContext,
59        pseudo_element_type: PseudoElement,
60    ) -> Option<Self> {
61        let element = self.node.as_element()?.with_pseudo(pseudo_element_type)?;
62        let style = element.style(&context.style_context);
63        Some(NodeAndStyleInfo {
64            node: element.as_node(),
65            style,
66            damage: self.damage,
67        })
68    }
69
70    pub(crate) fn get_selection_range(&self) -> Option<Range<ByteIndex>> {
71        self.node.selection()
72    }
73}
74
75#[derive(Debug)]
76pub(super) enum Contents {
77    /// Any kind of content that is not replaced nor a widget, including the contents of pseudo-elements.
78    NonReplaced(NonReplacedContents),
79    /// A widget with native appearance. This has several behavior in common with replaced elements,
80    /// but isn't fully replaced (see discussion in <https://github.com/w3c/csswg-drafts/issues/12876>).
81    /// Examples: `<input>`, `<textarea>`, `<select>`...
82    /// <https://drafts.csswg.org/css-ui/#widget>
83    Widget(NonReplacedContents),
84    /// Example: an `<img src=…>` element.
85    /// <https://drafts.csswg.org/css2/conform.html#replaced-element>
86    Replaced(ReplacedContents),
87}
88
89#[derive(Debug)]
90#[allow(clippy::enum_variant_names)]
91pub(super) enum NonReplacedContents {
92    /// Refers to a DOM subtree, plus `::before` and `::after` pseudo-elements.
93    OfElement,
94    /// Content of a `::before` or `::after` pseudo-element that is being generated.
95    /// <https://drafts.csswg.org/css2/generate.html#content>
96    OfPseudoElement(Vec<PseudoElementContentItem>),
97}
98
99#[derive(Debug)]
100pub(super) enum PseudoElementContentItem {
101    Text(String),
102    Replaced(ReplacedContents),
103}
104
105pub(super) trait TraversalHandler<'dom> {
106    fn handle_text(&mut self, info: &NodeAndStyleInfo<'dom>, text: Cow<'dom, str>);
107
108    /// Or pseudo-element
109    fn handle_element(
110        &mut self,
111        info: &NodeAndStyleInfo<'dom>,
112        display: DisplayGeneratingBox,
113        contents: Contents,
114        box_slot: BoxSlot<'dom>,
115    );
116
117    /// Notify the handler that we are about to recurse into a `display: contents` element.
118    fn enter_display_contents(&mut self, _: SharedInlineStyles) {}
119
120    /// Notify the handler that we have finished a `display: contents` element.
121    fn leave_display_contents(&mut self) {}
122}
123
124fn traverse_children_of<'dom>(
125    parent_element_info: &NodeAndStyleInfo<'dom>,
126    context: &LayoutContext,
127    handler: &mut impl TraversalHandler<'dom>,
128) {
129    traverse_eager_pseudo_element(PseudoElement::Before, parent_element_info, context, handler);
130
131    // TODO(stevennovaryo): In the past we are rendering text input as a normal element,
132    //                      and the processing of text is happening here. Remove this
133    //                      special case after the implementation of UA Shadow DOM for
134    //                      all affected input elements.
135    if parent_element_info.node.is_text_input() {
136        let node_text_content = parent_element_info.node.node_text_content();
137        if node_text_content.is_empty() {
138            handler.handle_text(parent_element_info, "\u{200B}".into());
139        } else {
140            handler.handle_text(parent_element_info, node_text_content);
141        }
142    } else {
143        for child in parent_element_info.node.children() {
144            if child.is_text_node() {
145                let info = NodeAndStyleInfo::new(
146                    child,
147                    child.style(&context.style_context),
148                    child.take_restyle_damage(),
149                );
150                handler.handle_text(&info, child.node_text_content());
151            } else if child.is_element() {
152                traverse_element(child, context, handler);
153            }
154        }
155    }
156
157    traverse_eager_pseudo_element(PseudoElement::After, parent_element_info, context, handler);
158}
159
160fn traverse_element<'dom>(
161    element: ServoThreadSafeLayoutNode<'dom>,
162    context: &LayoutContext,
163    handler: &mut impl TraversalHandler<'dom>,
164) {
165    let damage = element.take_restyle_damage();
166    if damage.has_box_damage() {
167        element.unset_all_pseudo_boxes();
168    }
169
170    let style = element.style(&context.style_context);
171    let info = NodeAndStyleInfo::new(element, style, damage);
172
173    match Display::from(info.style.get_box().display) {
174        Display::None => element.unset_all_boxes(),
175        Display::Contents => {
176            if ReplacedContents::for_element(element, context).is_some() {
177                // `display: content` on a replaced element computes to `display: none`
178                // <https://drafts.csswg.org/css-display-3/#valdef-display-contents>
179                element.unset_all_boxes()
180            } else {
181                let shared_inline_styles: SharedInlineStyles = (&info).into();
182                element
183                    .box_slot()
184                    .set(LayoutBox::DisplayContents(shared_inline_styles.clone()));
185
186                handler.enter_display_contents(shared_inline_styles);
187                traverse_children_of(&info, context, handler);
188                handler.leave_display_contents();
189            }
190        },
191        Display::GeneratingBox(display) => {
192            let contents = Contents::for_element(element, context);
193            let display = display.used_value_for_contents(&contents);
194            let box_slot = element.box_slot();
195            handler.handle_element(&info, display, contents, box_slot);
196        },
197    }
198}
199
200fn traverse_eager_pseudo_element<'dom>(
201    pseudo_element_type: PseudoElement,
202    node_info: &NodeAndStyleInfo<'dom>,
203    context: &LayoutContext,
204    handler: &mut impl TraversalHandler<'dom>,
205) {
206    assert!(pseudo_element_type.is_eager());
207
208    // If this node doesn't have this eager pseudo-element, exit early. This depends on
209    // the style applied to the element.
210    let Some(pseudo_element_info) = node_info.with_pseudo_element(context, pseudo_element_type)
211    else {
212        return;
213    };
214    if pseudo_element_info.style.ineffective_content_property() {
215        return;
216    }
217
218    match Display::from(pseudo_element_info.style.get_box().display) {
219        Display::None => {},
220        Display::Contents => {
221            let items = generate_pseudo_element_content(&pseudo_element_info, context);
222            let box_slot = pseudo_element_info.node.box_slot();
223            let shared_inline_styles: SharedInlineStyles = (&pseudo_element_info).into();
224            box_slot.set(LayoutBox::DisplayContents(shared_inline_styles.clone()));
225
226            handler.enter_display_contents(shared_inline_styles);
227            traverse_pseudo_element_contents(&pseudo_element_info, context, handler, items);
228            handler.leave_display_contents();
229        },
230        Display::GeneratingBox(display) => {
231            let items = generate_pseudo_element_content(&pseudo_element_info, context);
232            let box_slot = pseudo_element_info.node.box_slot();
233            let contents = Contents::for_pseudo_element(items);
234            handler.handle_element(&pseudo_element_info, display, contents, box_slot);
235        },
236    }
237}
238
239fn traverse_pseudo_element_contents<'dom>(
240    info: &NodeAndStyleInfo<'dom>,
241    context: &LayoutContext,
242    handler: &mut impl TraversalHandler<'dom>,
243    items: Vec<PseudoElementContentItem>,
244) {
245    let mut anonymous_info = None;
246    for item in items {
247        match item {
248            PseudoElementContentItem::Text(text) => handler.handle_text(info, text.into()),
249            PseudoElementContentItem::Replaced(contents) => {
250                let anonymous_info = anonymous_info.get_or_insert_with(|| {
251                    info.with_pseudo_element(context, PseudoElement::ServoAnonymousBox)
252                        .unwrap_or_else(|| info.clone())
253                });
254                let display_inline = DisplayGeneratingBox::OutsideInside {
255                    outside: DisplayOutside::Inline,
256                    inside: DisplayInside::Flow {
257                        is_list_item: false,
258                    },
259                };
260                // `display` is not inherited, so we get the initial value
261                debug_assert!(
262                    Display::from(anonymous_info.style.get_box().display) ==
263                        Display::GeneratingBox(display_inline)
264                );
265                handler.handle_element(
266                    anonymous_info,
267                    display_inline,
268                    Contents::Replaced(contents),
269                    anonymous_info.node.box_slot(),
270                )
271            },
272        }
273    }
274}
275
276impl Contents {
277    /// Returns true iff the `try_from` impl below would return `Err(_)`
278    pub fn is_replaced(&self) -> bool {
279        matches!(self, Contents::Replaced(_))
280    }
281
282    pub(crate) fn for_element(
283        node: ServoThreadSafeLayoutNode<'_>,
284        context: &LayoutContext,
285    ) -> Self {
286        if let Some(replaced) = ReplacedContents::for_element(node, context) {
287            return Self::Replaced(replaced);
288        }
289        let is_widget = matches!(
290            node.type_id(),
291            Some(LayoutNodeType::Element(
292                LayoutElementType::HTMLInputElement |
293                    LayoutElementType::HTMLSelectElement |
294                    LayoutElementType::HTMLTextAreaElement
295            ))
296        );
297        if is_widget {
298            Self::Widget(NonReplacedContents::OfElement)
299        } else {
300            Self::NonReplaced(NonReplacedContents::OfElement)
301        }
302    }
303
304    pub(crate) fn for_pseudo_element(contents: Vec<PseudoElementContentItem>) -> Self {
305        Self::NonReplaced(NonReplacedContents::OfPseudoElement(contents))
306    }
307
308    pub(crate) fn non_replaced_contents(self) -> Option<NonReplacedContents> {
309        match self {
310            Self::NonReplaced(contents) | Self::Widget(contents) => Some(contents),
311            Self::Replaced(_) => None,
312        }
313    }
314}
315
316impl NonReplacedContents {
317    pub(crate) fn traverse<'dom>(
318        self,
319        context: &LayoutContext,
320        info: &NodeAndStyleInfo<'dom>,
321        handler: &mut impl TraversalHandler<'dom>,
322    ) {
323        match self {
324            NonReplacedContents::OfElement => traverse_children_of(info, context, handler),
325            NonReplacedContents::OfPseudoElement(items) => {
326                traverse_pseudo_element_contents(info, context, handler, items)
327            },
328        }
329    }
330}
331
332fn get_quote_from_pair<I, S>(item: &ContentItem<I>, opening: &S, closing: &S) -> String
333where
334    S: ToString + ?Sized,
335{
336    match item {
337        ContentItem::OpenQuote => opening.to_string(),
338        ContentItem::CloseQuote => closing.to_string(),
339        _ => unreachable!("Got an unexpected ContentItem type when processing quotes."),
340    }
341}
342
343/// <https://www.w3.org/TR/CSS2/generate.html#propdef-content>
344fn generate_pseudo_element_content(
345    pseudo_element_info: &NodeAndStyleInfo,
346    context: &LayoutContext,
347) -> Vec<PseudoElementContentItem> {
348    match &pseudo_element_info.style.get_counters().content {
349        Content::Items(items) => {
350            let mut vec = vec![];
351            for item in items.items.iter() {
352                match item {
353                    ContentItem::String(s) => {
354                        vec.push(PseudoElementContentItem::Text(s.to_string()));
355                    },
356                    ContentItem::Attr(attr) => {
357                        let element = pseudo_element_info
358                            .node
359                            .as_element()
360                            .expect("Expected an element");
361
362                        // From
363                        // <https://html.spec.whatwg.org/multipage/#case-sensitivity-of-the-css-%27attr%28%29%27-function>
364                        //
365                        // > CSS Values and Units leaves the case-sensitivity of attribute names for
366                        // > the purpose of the `attr()` function to be defined by the host language.
367                        // > [[CSSVALUES]].
368                        // >
369                        // > When comparing the attribute name part of a CSS `attr()`function to the
370                        // > names of namespace-less attributes on HTML elements in HTML documents,
371                        // > the name part of the CSS `attr()` function must first be converted to
372                        // > ASCII lowercase. The same function when compared to other attributes must
373                        // > be compared according to its original case. In both cases, to match the
374                        // > values must be identical to each other (and therefore the comparison is
375                        // > case sensitive).
376                        let attr_name = match element.is_html_element_in_html_document() {
377                            true => &*attr.attribute.to_ascii_lowercase(),
378                            false => &*attr.attribute,
379                        };
380
381                        let attr_val =
382                            element.get_attr(&attr.namespace_url, &LocalName::from(attr_name));
383                        vec.push(PseudoElementContentItem::Text(
384                            attr_val.map_or("".to_string(), |s| s.to_string()),
385                        ));
386                    },
387                    ContentItem::Image(image) => {
388                        if let Some(replaced_content) =
389                            ReplacedContents::from_image(pseudo_element_info.node, context, image)
390                        {
391                            vec.push(PseudoElementContentItem::Replaced(replaced_content));
392                        }
393                    },
394                    ContentItem::OpenQuote | ContentItem::CloseQuote => {
395                        // TODO(xiaochengh): calculate quote depth
396                        let maybe_quote = match &pseudo_element_info.style.get_list().quotes {
397                            Quotes::QuoteList(quote_list) => {
398                                quote_list.0.first().map(|quote_pair| {
399                                    get_quote_from_pair(
400                                        item,
401                                        &*quote_pair.opening,
402                                        &*quote_pair.closing,
403                                    )
404                                })
405                            },
406                            Quotes::Auto => {
407                                let lang = &pseudo_element_info.style.get_font()._x_lang;
408                                let quotes = quotes_for_lang(lang.0.as_ref(), 0);
409                                Some(get_quote_from_pair(item, &quotes.opening, &quotes.closing))
410                            },
411                        };
412                        if let Some(quote) = maybe_quote {
413                            vec.push(PseudoElementContentItem::Text(quote));
414                        }
415                    },
416                    ContentItem::Counter(_, _) |
417                    ContentItem::Counters(_, _, _) |
418                    ContentItem::NoOpenQuote |
419                    ContentItem::NoCloseQuote => {
420                        // TODO: Add support for counters and quotes.
421                    },
422                }
423            }
424            vec
425        },
426        Content::Normal | Content::None => unreachable!(),
427    }
428}
layout/dom_traversal.rs

layout/
dom_traversal.rs
