dom: IntersectionObserver initialization (#35314)

* Add internal slot definition

Signed-off-by: stevennovaryo <steven.novaryo@gmail.com>

* Add initialization for new IntersectionObserver

Signed-off-by: stevennovaryo <steven.novaryo@gmail.com>

* Move observer initialization

Signed-off-by: stevennovaryo <steven.novaryo@gmail.com>

* Update WPT tests

Signed-off-by: stevennovaryo <steven.novaryo@gmail.com>

* Make a copy of style IntersectionObserverRootMargin

Signed-off-by: stevennovaryo <steven.novaryo@gmail.com>

* Move initialization to account for rooted expression

Signed-off-by: stevennovaryo <steven.novaryo@gmail.com>

* Fix some fields typing

Signed-off-by: stevennovaryo <steven.novaryo@gmail.com>

* Impl rest of IntersectionObserver interface

Signed-off-by: stevennovaryo <steven.novaryo@gmail.com>

* Fix tidy issue

Signed-off-by: stevennovaryo <steven.novaryo@gmail.com>

* Apply types logic and tidy fix from suggestions

Signed-off-by: stevennovaryo <steven.novaryo@gmail.com>

* Add allow unrooted for add registration to element

Signed-off-by: stevennovaryo <steven.novaryo@gmail.com>

---------

Signed-off-by: stevennovaryo <steven.novaryo@gmail.com>

components/script/dom/document.rs

@@ -515,6 +515,8 @@ pub(crate) struct Document {
     /// <https://w3c.github.io/webappsec-upgrade-insecure-requests/#insecure-requests-policy>
     #[no_trace]
     inherited_insecure_requests_policy: Cell<Option<InsecureRequestsPolicy>>,
+    /// <https://w3c.github.io/IntersectionObserver/#document-intersectionobservertaskqueued>
+    intersection_observer_task_queued: Cell<bool>,
 }
 
 #[allow(non_snake_case)]
@@ -3744,6 +3746,7 @@ impl Document {
             status_code,
             is_initial_about_blank: Cell::new(is_initial_about_blank),
             inherited_insecure_requests_policy: Cell::new(inherited_insecure_requests_policy),
+            intersection_observer_task_queued: Cell::new(false),
         }
     }
 

components/script/dom/element.rs

@@ -64,6 +64,7 @@ use xml5ever::serialize::TraversalScope::{
 
 use super::customelementregistry::is_valid_custom_element_name;
 use super::htmltablecolelement::{HTMLTableColElement, HTMLTableColElementLayoutHelpers};
+use super::intersectionobserver::{IntersectionObserver, IntersectionObserverRegistration};
 use crate::dom::activation::Activatable;
 use crate::dom::attr::{Attr, AttrHelpersForLayout};
 use crate::dom::bindings::cell::{ref_filter_map, DomRefCell, Ref, RefMut};
@@ -613,6 +614,50 @@ impl Element {
             Some(node) => node.is::<Document>(),
         }
     }
+
+    /// Return all IntersectionObserverRegistration for this element.
+    /// Lazily initialize the raredata if it does not exist.
+    pub(crate) fn registered_intersection_observers_mut(
+        &self,
+    ) -> RefMut<Vec<IntersectionObserverRegistration>> {
+        RefMut::map(self.ensure_rare_data(), |rare_data| {
+            &mut rare_data.registered_intersection_observers
+        })
+    }
+
+    pub(crate) fn registered_intersection_observers(
+        &self,
+    ) -> Option<Ref<Vec<IntersectionObserverRegistration>>> {
+        let rare_data: Ref<_> = self.rare_data.borrow();
+
+        if rare_data.is_none() {
+            return None;
+        }
+        Some(Ref::map(rare_data, |rare_data| {
+            &rare_data
+                .as_ref()
+                .unwrap()
+                .registered_intersection_observers
+        }))
+    }
+
+    /// Add a new IntersectionObserverRegistration to the element.
+    #[cfg_attr(crown, allow(crown::unrooted_must_root))]
+    pub(crate) fn add_intersection_observer_registration(
+        &self,
+        registration: IntersectionObserverRegistration,
+    ) {
+        self.ensure_rare_data()
+            .registered_intersection_observers
+            .push(registration);
+    }
+
+    /// Removes a certain IntersectionObserver.
+    pub(crate) fn remove_intersection_observer(&self, observer: &IntersectionObserver) {
+        self.ensure_rare_data()
+            .registered_intersection_observers
+            .retain(|reg_obs| *reg_obs.observer != *observer)
+    }
 }
 
 /// <https://dom.spec.whatwg.org/#valid-shadow-host-name>

components/script/dom/intersectionobserver.rs

@@ -2,23 +2,44 @@
  * 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::cell::{Cell, RefCell};
 use std::rc::Rc;
 
+use base::cross_process_instant::CrossProcessInstant;
+use cssparser::{Parser, ParserInput};
 use dom_struct::dom_struct;
 use js::rust::{HandleObject, MutableHandleValue};
+use style::context::QuirksMode;
+use style::parser::{Parse, ParserContext};
+use style::stylesheets::{CssRuleType, Origin};
+use style_traits::{ParsingMode, ToCss};
+use url::Url;
 
 use super::bindings::codegen::Bindings::IntersectionObserverBinding::{
     IntersectionObserverCallback, IntersectionObserverMethods,
 };
-use super::bindings::codegen::UnionTypes::ElementOrDocument;
-use super::types::{Element, IntersectionObserverEntry};
+use super::intersectionobserverentry::IntersectionObserverEntry;
+use super::intersectionobserverrootmargin::IntersectionObserverRootMargin;
+use crate::dom::bindings::cell::DomRefCell;
 use crate::dom::bindings::codegen::Bindings::IntersectionObserverBinding::IntersectionObserverInit;
+use crate::dom::bindings::codegen::UnionTypes::{DoubleOrDoubleSequence, ElementOrDocument};
+use crate::dom::bindings::error::Error;
+use crate::dom::bindings::import::module::Fallible;
+use crate::dom::bindings::num::Finite;
 use crate::dom::bindings::reflector::{reflect_dom_object_with_proto, Reflector};
-use crate::dom::bindings::root::DomRoot;
+use crate::dom::bindings::root::{Dom, DomRoot};
 use crate::dom::bindings::str::DOMString;
+use crate::dom::bindings::utils::to_frozen_array;
+use crate::dom::element::Element;
 use crate::dom::window::Window;
 use crate::script_runtime::{CanGc, JSContext};
 
+/// > The intersection root for an IntersectionObserver is the value of its root attribute if the attribute is non-null;
+/// > otherwise, it is the top-level browsing context’s document node, referred to as the implicit root.
+///
+/// <https://w3c.github.io/IntersectionObserver/#intersectionobserver-intersection-root>
+pub type IntersectionRoot = Option<ElementOrDocument>;
+
 /// The Intersection Observer interface
 ///
 /// > The IntersectionObserver interface can be used to observe changes in the intersection
@@ -29,33 +50,226 @@ use crate::script_runtime::{CanGc, JSContext};
 pub(crate) struct IntersectionObserver {
     reflector_: Reflector,
 
+    /// > The root provided to the IntersectionObserver constructor, or null if none was provided.
+    /// <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-root>
+    root: IntersectionRoot,
+
     /// > This callback will be invoked when there are changes to a target’s intersection
     /// > with the intersection root, as per the processing model.
     /// <https://w3c.github.io/IntersectionObserver/#intersection-observer-callback>
     #[ignore_malloc_size_of = "Rc are hard"]
     callback: Rc<IntersectionObserverCallback>,
+
+    /// <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-queuedentries-slot>
+    queued_entries: DomRefCell<Vec<Dom<IntersectionObserverEntry>>>,
+
+    /// <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-observationtargets-slot>
+    observation_targets: DomRefCell<Vec<Dom<Element>>>,
+
+    /// <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-rootmargin-slot>
+    #[no_trace]
+    #[ignore_malloc_size_of = "Defined in style"]
+    root_margin: RefCell<IntersectionObserverRootMargin>,
+
+    /// <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-scrollmargin-slot>
+    #[no_trace]
+    #[ignore_malloc_size_of = "Defined in style"]
+    scroll_margin: RefCell<IntersectionObserverRootMargin>,
+
+    /// <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-thresholds-slot>
+    thresholds: RefCell<Vec<Finite<f64>>>,
+
+    /// <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-delay-slot>
+    delay: Cell<i32>,
+
+    /// <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-trackvisibility-slot>
+    track_visibility: Cell<bool>,
 }
 
 impl IntersectionObserver {
     pub(crate) fn new_inherited(
         callback: Rc<IntersectionObserverCallback>,
-        _init: &IntersectionObserverInit,
+        root: IntersectionRoot,
+        root_margin: IntersectionObserverRootMargin,
+        scroll_margin: IntersectionObserverRootMargin,
     ) -> Self {
         Self {
             reflector_: Reflector::new(),
+            root,
             callback,
+            queued_entries: Default::default(),
+            observation_targets: Default::default(),
+            root_margin: RefCell::new(root_margin),
+            scroll_margin: RefCell::new(scroll_margin),
+            thresholds: Default::default(),
+            delay: Default::default(),
+            track_visibility: Default::default(),
         }
     }
 
+    /// <https://w3c.github.io/IntersectionObserver/#initialize-new-intersection-observer>
     fn new(
         window: &Window,
         proto: Option<HandleObject>,
         callback: Rc<IntersectionObserverCallback>,
         init: &IntersectionObserverInit,
         can_gc: CanGc,
-    ) -> DomRoot<Self> {
-        let observer = Box::new(Self::new_inherited(callback, init));
-        reflect_dom_object_with_proto(observer, window, proto, can_gc)
+    ) -> Fallible<DomRoot<Self>> {
+        // Step 3.
+        // > Attempt to parse a margin from options.rootMargin. If a list is returned,
+        // > set this’s internal [[rootMargin]] slot to that. Otherwise, throw a SyntaxError exception.
+        let root_margin = if let Ok(margin) = parse_a_margin(init.rootMargin.as_ref()) {
+            margin
+        } else {
+            return Err(Error::Syntax);
+        };
+
+        // Step 4.
+        // > Attempt to parse a margin from options.scrollMargin. If a list is returned,
+        // > set this’s internal [[scrollMargin]] slot to that. Otherwise, throw a SyntaxError exception.
+        let scroll_margin = if let Ok(margin) = parse_a_margin(init.scrollMargin.as_ref()) {
+            margin
+        } else {
+            return Err(Error::Syntax);
+        };
+
+        // Step 1 and step 2, 3, 4 setter
+        // > 1. Let this be a new IntersectionObserver object
+        // > 2. Set this’s internal [[callback]] slot to callback.
+        // > 3. ... set this’s internal [[rootMargin]] slot to that.
+        // > 4. ,.. set this’s internal [[scrollMargin]] slot to that.
+        //
+        // Owned root is also passed to the constructor.
+        let observer = reflect_dom_object_with_proto(
+            Box::new(Self::new_inherited(
+                callback,
+                init.root.clone(),
+                root_margin,
+                scroll_margin,
+            )),
+            window,
+            proto,
+            can_gc,
+        );
+
+        // Step 5-13
+        observer.init_observer(init)?;
+
+        Ok(observer)
+    }
+
+    /// Step 5-13 of <https://w3c.github.io/IntersectionObserver/#initialize-new-intersection-observer>
+    fn init_observer(&self, init: &IntersectionObserverInit) -> Fallible<()> {
+        // Step 5
+        // > Let thresholds be a list equal to options.threshold.
+        //
+        // Non-sequence value should be converted into Vec.
+        // Default value of thresholds is [0].
+        let mut thresholds = match &init.threshold {
+            Some(DoubleOrDoubleSequence::Double(num)) => vec![*num],
+            Some(DoubleOrDoubleSequence::DoubleSequence(sequence)) => sequence.clone(),
+            None => vec![Finite::wrap(0.)],
+        };
+
+        // Step 6
+        // > If any value in thresholds is less than 0.0 or greater than 1.0, throw a RangeError exception.
+        for num in &thresholds {
+            if **num < 0.0 || **num > 1.0 {
+                return Err(Error::Range(
+                    "Value in thresholds should not be less than 0.0 or greater than 1.0"
+                        .to_owned(),
+                ));
+            }
+        }
+
+        // Step 7
+        // > Sort thresholds in ascending order.
+        thresholds.sort_by(|lhs, rhs| lhs.partial_cmp(&**rhs).unwrap());
+
+        // Step 8
+        // > If thresholds is empty, append 0 to thresholds.
+        if thresholds.is_empty() {
+            thresholds.push(Finite::wrap(0.));
+        }
+
+        // Step 9
+        // > The thresholds attribute getter will return this sorted thresholds list.
+        //
+        // Set this’s internal [[thresholds]] slot to the sorted thresholds list
+        // and getter will return the internal [[thresholds]] slot.
+        self.thresholds.replace(thresholds);
+
+        // Step 10
+        // > Let delay be the value of options.delay.
+        //
+        // Default value of delay is 0.
+        let mut delay = init.delay.unwrap_or(0);
+
+        // Step 11
+        // > If options.trackVisibility is true and delay is less than 100, set delay to 100.
+        if init.trackVisibility {
+            delay = delay.max(100);
+        }
+
+        // Step 12
+        // > Set this’s internal [[delay]] slot to options.delay to delay.
+        self.delay.set(delay);
+
+        // Step 13
+        // > Set this’s internal [[trackVisibility]] slot to options.trackVisibility.
+        self.track_visibility.set(init.trackVisibility);
+
+        Ok(())
+    }
+
+    /// <https://w3c.github.io/IntersectionObserver/#observe-target-element>
+    fn observe_target_element(&self, target: &Element) {
+        // Step 1
+        // > If target is in observer’s internal [[ObservationTargets]] slot, return.
+        let is_present = self
+            .observation_targets
+            .borrow()
+            .iter()
+            .any(|element| &**element == target);
+        if is_present {
+            return;
+        }
+
+        // Step 2
+        // > Let intersectionObserverRegistration be an IntersectionObserverRegistration record with
+        // > an observer property set to observer, a previousThresholdIndex property set to -1,
+        // > a previousIsIntersecting property set to false, and a previousIsVisible property set to false.
+        // Step 3
+        // > Append intersectionObserverRegistration to target’s internal [[RegisteredIntersectionObservers]] slot.
+        target.add_intersection_observer_registration(IntersectionObserverRegistration {
+            observer: Dom::from_ref(self),
+            previous_threshold_index: Cell::new(-1),
+            previous_is_intersecting: Cell::new(false),
+            last_update_time: Cell::new(CrossProcessInstant::epoch()),
+            previous_is_visible: Cell::new(false),
+        });
+
+        // Step 4
+        // > Add target to observer’s internal [[ObservationTargets]] slot.
+        self.observation_targets
+            .borrow_mut()
+            .push(Dom::from_ref(target));
+    }
+
+    /// <https://w3c.github.io/IntersectionObserver/#unobserve-target-element>
+    fn unobserve_target_element(&self, target: &Element) {
+        // Step 1
+        // > Remove the IntersectionObserverRegistration record whose observer property is equal to
+        // > this from target’s internal [[RegisteredIntersectionObservers]] slot, if present.
+        target
+            .registered_intersection_observers_mut()
+            .retain(|registration| &*registration.observer != self);
+
+        // Step 2
+        // > Remove target from this’s internal [[ObservationTargets]] slot, if present
+        self.observation_targets
+            .borrow_mut()
+            .retain(|element| &**element != target);
     }
 }
 
@@ -64,7 +278,7 @@ impl IntersectionObserverMethods<crate::DomTypeHolder> for IntersectionObserver
     ///
     /// <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-root>
     fn GetRoot(&self) -> Option<ElementOrDocument> {
-        None
+        self.root.clone()
     }
 
     /// > Offsets applied to the root intersection rectangle, effectively growing or
@@ -74,7 +288,7 @@ impl IntersectionObserverMethods<crate::DomTypeHolder> for IntersectionObserver
     ///
     /// <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-rootmargin>
     fn RootMargin(&self) -> DOMString {
-        DOMString::new()
+        DOMString::from_string(self.root_margin.borrow().to_css_string())
     }
 
     /// > Offsets are applied to scrollports on the path from intersection root to target,
@@ -82,7 +296,7 @@ impl IntersectionObserverMethods<crate::DomTypeHolder> for IntersectionObserver
     ///
     /// <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-scrollmargin>
     fn ScrollMargin(&self) -> DOMString {
-        DOMString::new()
+        DOMString::from_string(self.scroll_margin.borrow().to_css_string())
     }
 
     /// > A list of thresholds, sorted in increasing numeric order, where each threshold
@@ -92,39 +306,59 @@ impl IntersectionObserverMethods<crate::DomTypeHolder> for IntersectionObserver
     /// > constructor, or the sequence is empty, the value of this attribute will be `[0]`.
     ///
     /// <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-thresholds>
-    fn Thresholds(&self, _context: JSContext, _retval: MutableHandleValue) {}
+    fn Thresholds(&self, context: JSContext, retval: MutableHandleValue) {
+        to_frozen_array(&self.thresholds.borrow(), context, retval);
+    }
 
     /// > A number indicating the minimum delay in milliseconds between notifications from
     /// > this observer for a given target.
     ///
     /// <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-delay>
     fn Delay(&self) -> i32 {
-        0
+        self.delay.get()
     }
 
     /// > A boolean indicating whether this IntersectionObserver will track changes in a target’s visibility.
     ///
     /// <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-trackvisibility>
     fn TrackVisibility(&self) -> bool {
-        false
+        self.track_visibility.get()
     }
 
     /// > Run the observe a target Element algorithm, providing this and target.
     ///
     /// <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-observe>
-    fn Observe(&self, _target: &Element) {}
+    fn Observe(&self, target: &Element) {
+        self.observe_target_element(target);
+    }
 
     /// > Run the unobserve a target Element algorithm, providing this and target.
     ///
     /// <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-unobserve>
-    fn Unobserve(&self, _target: &Element) {}
+    fn Unobserve(&self, target: &Element) {
+        self.unobserve_target_element(target);
+    }
 
     /// <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-disconnect>
-    fn Disconnect(&self) {}
+    fn Disconnect(&self) {
+        // > For each target in this’s internal [[ObservationTargets]] slot:
+        self.observation_targets.borrow().iter().for_each(|target| {
+            // > 1. Remove the IntersectionObserverRegistration record whose observer property is equal to
+            // >    this from target’s internal [[RegisteredIntersectionObservers]] slot.
+            target.remove_intersection_observer(self);
+        });
+        // > 2. Remove target from this’s internal [[ObservationTargets]] slot.
+        self.observation_targets.borrow_mut().clear();
+    }
 
     /// <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-takerecords>
     fn TakeRecords(&self) -> Vec<DomRoot<IntersectionObserverEntry>> {
-        vec![]
+        // Step 1-3.
+        self.queued_entries
+            .take()
+            .iter()
+            .map(|entry| entry.as_rooted())
+            .collect()
     }
 
     /// <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-intersectionobserver>
@@ -134,7 +368,50 @@ impl IntersectionObserverMethods<crate::DomTypeHolder> for IntersectionObserver
         can_gc: CanGc,
         callback: Rc<IntersectionObserverCallback>,
         init: &IntersectionObserverInit,
-    ) -> DomRoot<IntersectionObserver> {
+    ) -> Fallible<DomRoot<IntersectionObserver>> {
         Self::new(window, proto, callback, init, can_gc)
     }
 }
+
+/// <https://w3c.github.io/IntersectionObserver/#intersectionobserverregistration>
+#[derive(JSTraceable, MallocSizeOf)]
+#[cfg_attr(crown, crown::unrooted_must_root_lint::must_root)]
+pub(crate) struct IntersectionObserverRegistration {
+    pub(crate) observer: Dom<IntersectionObserver>,
+    previous_threshold_index: Cell<i32>,
+    previous_is_intersecting: Cell<bool>,
+    #[no_trace]
+    last_update_time: Cell<CrossProcessInstant>,
+    previous_is_visible: Cell<bool>,
+}
+
+/// <https://w3c.github.io/IntersectionObserver/#parse-a-margin>
+fn parse_a_margin(value: Option<&DOMString>) -> Result<IntersectionObserverRootMargin, ()> {
+    // <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserverinit-rootmargin> &&
+    // <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserverinit-scrollmargin>
+    // > ... defaulting to "0px".
+    let value = match value {
+        Some(str) => str.str(),
+        _ => "0px",
+    };
+
+    // Create necessary style ParserContext and utilize stylo's IntersectionObserverRootMargin
+    let mut input = ParserInput::new(value);
+    let mut parser = Parser::new(&mut input);
+
+    let url = Url::parse("about:blank").unwrap().into();
+    let context = ParserContext::new(
+        Origin::Author,
+        &url,
+        Some(CssRuleType::Style),
+        ParsingMode::DEFAULT,
+        QuirksMode::NoQuirks,
+        /* namespaces = */ Default::default(),
+        None,
+        None,
+    );
+
+    parser
+        .parse_entirely(|p| IntersectionObserverRootMargin::parse(&context, p))
+        .map_err(|_| ())
+}

components/script/dom/intersectionobserverrootmargin.rs

@@ -0,0 +1,84 @@
+/* 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/. */
+
+//! Copy of Stylo Gecko's [`style::values::specified::gecko::IntersectionObserverRootMargin`] implementation.
+//! TODO: expose the object to servo as well in Stylo
+
+use std::fmt;
+
+use cssparser::{match_ignore_ascii_case, Parser, Token};
+use style::parser::{Parse, ParserContext};
+use style::values::computed::{self, Length, LengthPercentage};
+use style::values::generics::rect::Rect;
+use style_traits::values::SequenceWriter;
+use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};
+
+fn parse_pixel_or_percent<'i>(
+    _context: &ParserContext,
+    input: &mut Parser<'i, '_>,
+) -> Result<LengthPercentage, ParseError<'i>> {
+    let location = input.current_source_location();
+    let token = input.next()?;
+    let value = match *token {
+        Token::Dimension {
+            value, ref unit, ..
+        } => {
+            match_ignore_ascii_case! { unit,
+                "px" => Ok(LengthPercentage::new_length(Length::new(value))),
+                _ => Err(()),
+            }
+        },
+        Token::Percentage { unit_value, .. } => Ok(LengthPercentage::new_percent(
+            computed::Percentage(unit_value),
+        )),
+        _ => Err(()),
+    };
+    value.map_err(|()| location.new_custom_error(StyleParseErrorKind::UnspecifiedError))
+}
+
+/// The value of an IntersectionObserver's rootMargin property.
+///
+/// Only bare px or percentage values are allowed. Other length units and
+/// calc() values are not allowed.
+///
+/// <https://w3c.github.io/IntersectionObserver/#parse-a-root-margin>
+#[repr(transparent)]
+pub struct IntersectionObserverRootMargin(pub Rect<LengthPercentage>);
+
+impl Parse for IntersectionObserverRootMargin {
+    fn parse<'i>(
+        context: &ParserContext,
+        input: &mut Parser<'i, '_>,
+    ) -> Result<Self, ParseError<'i>> {
+        use style::Zero;
+        if input.is_exhausted() {
+            // If there are zero elements in tokens, set tokens to ["0px"].
+            return Ok(IntersectionObserverRootMargin(Rect::all(
+                LengthPercentage::zero(),
+            )));
+        }
+        let rect = Rect::parse_with(context, input, parse_pixel_or_percent)?;
+        Ok(IntersectionObserverRootMargin(rect))
+    }
+}
+
+// Strictly speaking this is not ToCss. It's serializing for DOM. But
+// we can just reuse the infrastructure of this.
+//
+// <https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-rootmargin>
+impl ToCss for IntersectionObserverRootMargin {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: fmt::Write,
+    {
+        // We cannot use the ToCss impl of Rect, because that would
+        // merge items when they are equal. We want to list them all.
+        let mut writer = SequenceWriter::new(dest, " ");
+        let rect = &self.0;
+        writer.item(&rect.0)?;
+        writer.item(&rect.1)?;
+        writer.item(&rect.2)?;
+        writer.item(&rect.3)
+    }
+}

components/script/dom/mod.rs

@@ -422,6 +422,7 @@ pub(crate) mod imagedata;
 pub(crate) mod inputevent;
 pub(crate) mod intersectionobserver;
 pub(crate) mod intersectionobserverentry;
+pub(crate) mod intersectionobserverrootmargin;
 pub(crate) mod keyboardevent;
 pub(crate) mod location;
 pub(crate) mod mediadeviceinfo;

components/script/dom/raredata.rs

@@ -13,6 +13,7 @@ use crate::dom::customelementregistry::{
 };
 use crate::dom::elementinternals::ElementInternals;
 use crate::dom::htmlslotelement::SlottableData;
+use crate::dom::intersectionobserver::IntersectionObserverRegistration;
 use crate::dom::mutationobserver::RegisteredObserver;
 use crate::dom::node::UniqueId;
 use crate::dom::shadowroot::ShadowRoot;
@@ -58,4 +59,9 @@ pub(crate) struct ElementRareData {
     pub(crate) client_rect: Option<LayoutValue<Rect<i32>>>,
     /// <https://html.spec.whatwg.org/multipage#elementinternals>
     pub(crate) element_internals: Option<Dom<ElementInternals>>,
+
+    /// <https://w3c.github.io/IntersectionObserver/#element-private-slots>
+    /// > Element objects have an internal [[RegisteredIntersectionObservers]] slot,
+    /// > which is initialized to an empty list. This list holds IntersectionObserverRegistration records, which have:
+    pub(crate) registered_intersection_observers: Vec<IntersectionObserverRegistration>,
 }

components/script_bindings/codegen/Bindings.conf

@@ -608,6 +608,10 @@ Unions = {
     'derives': ['Clone']
 },
 
+'ElementOrDocument': {
+    'derives': ['Clone', 'MallocSizeOf']
+},
+
 'HTMLCanvasElementOrOffscreenCanvas': {
     'derives': ['Clone', 'MallocSizeOf']
 },

components/script_bindings/webidls/IntersectionObserver.webidl

@@ -18,7 +18,7 @@ dictionary IntersectionObserverInit {
 
 [Pref="dom_intersection_observer_enabled", Exposed=(Window)]
 interface IntersectionObserver {
-  constructor(IntersectionObserverCallback callback, optional IntersectionObserverInit options = {});
+  [Throws] constructor(IntersectionObserverCallback callback, optional IntersectionObserverInit options = {});
   readonly attribute (Element or Document)? root;
   readonly attribute DOMString rootMargin;
   readonly attribute DOMString scrollMargin;

tests/wpt/meta/intersection-observer/idlharness.window.js.ini

@@ -1,3 +0,0 @@
-[idlharness.window.html]
-  [IntersectionObserver interface: observer must inherit property "thresholds" with the proper type]
-    expected: FAIL

tests/wpt/meta/intersection-observer/observer-attributes.html.ini

@@ -1,21 +0,0 @@
-[observer-attributes.html]
-  [observer.thresholds]
-    expected: FAIL
-
-  [observer.rootMargin]
-    expected: FAIL
-
-  [empty observer.thresholds]
-    expected: FAIL
-
-  [whitespace observer.rootMargin]
-    expected: FAIL
-
-  [set observer.root]
-    expected: FAIL
-
-  [set observer.thresholds]
-    expected: FAIL
-
-  [set observer.rootMargin]
-    expected: FAIL

tests/wpt/meta/intersection-observer/observer-exceptions.html.ini

@@ -1,21 +0,0 @@
-[observer-exceptions.html]
-  [IntersectionObserver constructor with { threshold: [1.1\] }]
-    expected: FAIL
-
-  [IntersectionObserver constructor with { rootMargin: "1" }]
-    expected: FAIL
-
-  [IntersectionObserver constructor with { rootMargin: "2em" }]
-    expected: FAIL
-
-  [IntersectionObserver constructor with { rootMargin: "auto" }]
-    expected: FAIL
-
-  [IntersectionObserver constructor with { rootMargin: "calc(1px + 2px)" }]
-    expected: FAIL
-
-  [IntersectionObserver constructor with { rootMargin: "1px !important" }]
-    expected: FAIL
-
-  [IntersectionObserver constructor with { rootMargin: "1px 1px 1px 1px 1px" }]
-    expected: FAIL