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LibWeb: Implement more of the "script-blocking style sheet" mechanism

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The basic idea is that style sheets can block script execution under
some circumstances. With this commit, we now handle the simplest cases
where a parser-inserted link element gets to download its style sheet
before script execution continues.

This improves performance on Speedometer 3 where JavaScript APIs that
depend on layout results (like Element.scrollIntoView()) would get
called too early (before the relevant CSS was downloaded), and so we'd
perform premature layout work. This work then had to be redone after
downloading the CSS anyway, wasting time.

Note that our Text/input/link-re-enable-crash.html test had to be
tweaked after these changes, since it relied on the old, incorrect,
behavior where scripts would run before downloading CSS.
This commit is contained in:
Andreas Kling 2025-04-20 11:31:57 +02:00 • committed by Andreas Kling
parent 8e37cd2f71
commit 0c0650e60a
Notes: github-actions[bot] 2025-04-20 12:55:15 +00:00
9 changed files with 101 additions and 18 deletions
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10
Libraries/LibWeb/DOM/Document.h
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@ -499,7 +499,8 @@ public:
String dump_dom_tree_as_json() const;
bool has_a_style_sheet_that_is_blocking_scripts() const;
[[nodiscard]] bool has_a_style_sheet_that_is_blocking_scripts() const;
[[nodiscard]] bool has_no_style_sheet_that_is_blocking_scripts() const;
bool is_fully_active() const;
bool is_active() const;
@ -897,6 +898,9 @@ public:
ElementByIdMap& element_by_id() const;
auto& script_blocking_style_sheet_set() { return m_script_blocking_style_sheet_set; }
auto const& script_blocking_style_sheet_set() const { return m_script_blocking_style_sheet_set; }
protected:
virtual void initialize(JS::Realm&) override;
virtual void visit_edges(Cell::Visitor&) override;
@ -1030,8 +1034,8 @@ private:
// https://html.spec.whatwg.org/multipage/dynamic-markup-insertion.html#throw-on-dynamic-markup-insertion-counter
u32 m_throw_on_dynamic_markup_insertion_counter { 0 };
// https://html.spec.whatwg.org/multipage/semantics.html#script-blocking-style-sheet-counter
u32 m_script_blocking_style_sheet_counter { 0 };
// https://html.spec.whatwg.org/multipage/semantics.html#script-blocking-style-sheet-set
HashTable<GC::Ref<DOM::Element>> m_script_blocking_style_sheet_set;
GC::Ptr<HTML::History> m_history;