Auto merge of #17501 - jyc:Text-children_changed, r=emilio

Have CharacterData call children_changed on its parent when data is set.

**Can't run WPT on my computer, so pushing here to run tests 😢**

Have CharacterData.SetData call children_changed on its parent when
data is set (if it is a Text node) so that HTMLStyleElement parents can
re-parse. Add variant ChildrenMutation::Text for it to use as the
mutation.

This fixes an issue where an empty <style> element's data is set but the
style is not updated. An HTMLStyleElement parent re-parses in its
children_changed implementation.

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes are part of a series to fix #17182 (github issue number if applicable).

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components/script/dom/characterdata.rs

@@ -6,6 +6,7 @@
 
 use dom::bindings::cell::DOMRefCell;
 use dom::bindings::codegen::Bindings::CharacterDataBinding::CharacterDataMethods;
+use dom::bindings::codegen::Bindings::NodeBinding::NodeBinding::NodeMethods;
 use dom::bindings::codegen::Bindings::ProcessingInstructionBinding::ProcessingInstructionMethods;
 use dom::bindings::codegen::InheritTypes::{CharacterDataTypeId, NodeTypeId};
 use dom::bindings::codegen::UnionTypes::NodeOrString;
@@ -16,9 +17,10 @@ use dom::bindings::str::DOMString;
 use dom::comment::Comment;
 use dom::document::Document;
 use dom::element::Element;
-use dom::node::{Node, NodeDamage};
+use dom::node::{ChildrenMutation, Node, NodeDamage};
 use dom::processinginstruction::ProcessingInstruction;
 use dom::text::Text;
+use dom::virtualmethods::vtable_for;
 use dom_struct::dom_struct;
 use servo_config::opts;
 use std::cell::Ref;
@@ -85,6 +87,16 @@ impl CharacterDataMethods for CharacterData {
         self.content_changed();
         let node = self.upcast::<Node>();
         node.ranges().replace_code_units(node, 0, old_length, new_length);
+
+        // If this is a Text node, we might need to re-parse (say, if our parent
+        // is a <style> element.) We don't need to if this is a Comment or
+        // ProcessingInstruction.
+        if let Some(_) = self.downcast::<Text>() {
+            if let Some(parent_node) = node.GetParentNode() {
+                let mutation = ChildrenMutation::ChangeText;
+                vtable_for(&parent_node).children_changed(&mutation);
+            }
+        }
     }
 
     // https://dom.spec.whatwg.org/#dom-characterdata-length

components/script/dom/node.rs

@@ -2490,6 +2490,11 @@ pub enum ChildrenMutation<'a> {
         next: Option<&'a Node>,
     },
     ReplaceAll { removed: &'a [&'a Node], added: &'a [&'a Node] },
+    /// Mutation for when a Text node's data is modified.
+    /// This doesn't change the structure of the list, which is what the other
+    /// variants' fields are stored for at the moment, so this can just have no
+    /// fields.
+    ChangeText,
 }
 
 impl<'a> ChildrenMutation<'a> {
@@ -2541,6 +2546,9 @@ impl<'a> ChildrenMutation<'a> {
     }
 
     /// Get the child that follows the added or removed children.
+    /// Currently only used when this mutation might force us to
+    /// restyle later children (see HAS_SLOW_SELECTOR_LATER_SIBLINGS and
+    /// Element's implementation of VirtualMethods::children_changed).
     pub fn next_child(&self) -> Option<&Node> {
         match *self {
             ChildrenMutation::Append { .. } => None,
@@ -2548,6 +2556,7 @@ impl<'a> ChildrenMutation<'a> {
             ChildrenMutation::Prepend { next, .. } => Some(next),
             ChildrenMutation::Replace { next, .. } => next,
             ChildrenMutation::ReplaceAll { .. } => None,
+            ChildrenMutation::ChangeText => None,
         }
     }
 
@@ -2585,6 +2594,7 @@ impl<'a> ChildrenMutation<'a> {
 
             ChildrenMutation::Replace { prev: None, next: None, .. } => unreachable!(),
             ChildrenMutation::ReplaceAll { .. } => None,
+            ChildrenMutation::ChangeText => None,
         }
     }
 }

components/script/dom/nodelist.rs

@@ -279,6 +279,7 @@ impl ChildrenList {
                     self.last_index.set(middle as u32);
                 }
             },
+            ChildrenMutation::ChangeText => {},
         }
     }