LibWeb: Make <input type=checkbox> honor the "checked" attribute

Implemented according to spec, although it's very possible that I missed
one or two details. :^)

Userland/Libraries/LibWeb/HTML/HTMLInputElement.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2018-2022, Andreas Kling <kling@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -61,14 +61,37 @@ RefPtr<Layout::Node> HTMLInputElement::create_layout_node(NonnullRefPtr<CSS::Sty
     return layout_node;
 }
 
-void HTMLInputElement::set_checked(bool checked)
+void HTMLInputElement::set_checked(bool checked, ChangeSource change_source, ShouldRunActivationBehavior should_run_activation_behavior)
 {
     if (m_checked == checked)
         return;
+
+    // The dirty checkedness flag must be initially set to false when the element is created,
+    // and must be set to true whenever the user interacts with the control in a way that changes the checkedness.
+    if (change_source == ChangeSource::User)
+        m_dirty_checkedness = true;
+
     m_checked = checked;
     if (layout_node())
         layout_node()->set_needs_display();
 
+    if (should_run_activation_behavior == ShouldRunActivationBehavior::Yes)
+        run_activation_behavior();
+}
+
+void HTMLInputElement::run_activation_behavior()
+{
+    // The activation behavior for input elements are these steps:
+
+    // FIXME: 1. If this element is not mutable and is not in the Checkbox state and is not in the Radio state, then return.
+
+    // 2. Run this element's input activation behavior, if any, and do nothing otherwise.
+    run_input_activation_behavior();
+}
+
+// https://html.spec.whatwg.org/multipage/input.html#input-activation-behavior
+void HTMLInputElement::run_input_activation_behavior()
+{
     dispatch_event(DOM::Event::create(EventNames::change));
 }
 
@@ -139,4 +162,26 @@ void HTMLInputElement::removed_from(DOM::Node* old_parent)
     set_form(nullptr);
 }
 
+void HTMLInputElement::parse_attribute(FlyString const& name, String const& value)
+{
+    FormAssociatedElement::parse_attribute(name, value);
+    if (name == HTML::AttributeNames::checked) {
+        // When the checked content attribute is added, if the control does not have dirty checkedness,
+        // the user agent must set the checkedness of the element to true
+        if (!m_dirty_checkedness)
+            set_checked(true, ChangeSource::Programmatic, ShouldRunActivationBehavior::No);
+    }
+}
+
+void HTMLInputElement::did_remove_attribute(FlyString const& name)
+{
+    FormAssociatedElement::did_remove_attribute(name);
+    if (name == HTML::AttributeNames::checked) {
+        // When the checked content attribute is removed, if the control does not have dirty checkedness,
+        // the user agent must set the checkedness of the element to false.
+        if (!m_dirty_checkedness)
+            set_checked(false, ChangeSource::Programmatic, ShouldRunActivationBehavior::No);
+    }
+}
+
 }

Userland/Libraries/LibWeb/HTML/HTMLInputElement.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2018-2022, Andreas Kling <kling@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -28,7 +28,15 @@ public:
     void set_value(String);
 
     bool checked() const { return m_checked; }
-    void set_checked(bool);
+    enum class ChangeSource {
+        Programmatic,
+        User,
+    };
+    enum class ShouldRunActivationBehavior {
+        No,
+        Yes,
+    };
+    void set_checked(bool, ChangeSource = ChangeSource::Programmatic, ShouldRunActivationBehavior = ShouldRunActivationBehavior::Yes);
 
     bool enabled() const;
 
@@ -36,6 +44,9 @@ public:
 
     virtual bool is_focusable() const override;
 
+    virtual void parse_attribute(FlyString const&, String const&) override;
+    virtual void did_remove_attribute(FlyString const&) override;
+
 private:
     // ^DOM::Node
     virtual void inserted() override;
@@ -43,11 +54,16 @@ private:
 
     // ^DOM::EventTarget
     virtual void did_receive_focus() override;
+    virtual void run_activation_behavior() override;
 
     void create_shadow_tree_if_needed();
+    void run_input_activation_behavior();
 
     RefPtr<DOM::Text> m_text_node;
     bool m_checked { false };
+
+    // https://html.spec.whatwg.org/multipage/input.html#concept-input-checked-dirty-flag
+    bool m_dirty_checkedness { false };
 };
 
 }

Userland/Libraries/LibWeb/Layout/CheckBox.cpp

@@ -9,6 +9,7 @@
 #include <LibGfx/Painter.h>
 #include <LibGfx/StylePainter.h>
 #include <LibWeb/HTML/BrowsingContext.h>
+#include <LibWeb/HTML/HTMLInputElement.h>
 #include <LibWeb/Layout/CheckBox.h>
 #include <LibWeb/Layout/Label.h>
 
@@ -62,7 +63,7 @@ void CheckBox::handle_mouseup(Badge<EventHandler>, const Gfx::IntPoint& position
         is_inside_node_or_label = Label::is_inside_associated_label(*this, position);
 
     if (is_inside_node_or_label)
-        dom_node().set_checked(!dom_node().checked());
+        dom_node().set_checked(!dom_node().checked(), HTML::HTMLInputElement::ChangeSource::User);
 
     m_being_pressed = false;
     m_tracking_mouse = false;
@@ -102,7 +103,7 @@ void CheckBox::handle_associated_label_mouseup(Badge<Label>)
     // NOTE: Changing the checked state of the DOM node may run arbitrary JS, which could disappear this node.
     NonnullRefPtr protect = *this;
 
-    dom_node().set_checked(!dom_node().checked());
+    dom_node().set_checked(!dom_node().checked(), HTML::HTMLInputElement::ChangeSource::User);
     m_being_pressed = false;
 }
 

Userland/Libraries/LibWeb/Layout/RadioButton.cpp

@@ -114,12 +114,12 @@ void RadioButton::set_checked_within_group()
     if (dom_node().checked())
         return;
 
-    dom_node().set_checked(true);
+    dom_node().set_checked(true, HTML::HTMLInputElement::ChangeSource::User);
     String name = dom_node().name();
 
     document().for_each_in_inclusive_subtree_of_type<HTML::HTMLInputElement>([&](auto& element) {
         if (element.checked() && (element.layout_node() != this) && (element.name() == name))
-            element.set_checked(false);
+            element.set_checked(false, HTML::HTMLInputElement::ChangeSource::User);
         return IterationDecision::Continue;
     });
 }