LibWeb: Emit "selectionchange" event on document

Tests/LibWeb/Text/expected/selectionchange-event.txt

@@ -0,0 +1,6 @@
+
+    Ladybird is an ongoing project to build an independent web browser from scratch.
+  Events:
+selectionchange anchorNode=<#text > anchorOffset=1 type=Caret focusNode=<#text > focusOffset=1 isCollapsed=true
+selectionchange anchorNode=<#text > anchorOffset=1 type=Caret focusNode=<#text > focusOffset=1 isCollapsed=true
+selectionchange anchorNode=<#text > anchorOffset=2 type=Caret focusNode=<#text > focusOffset=2 isCollapsed=true

Tests/LibWeb/Text/input/selectionchange-event.html

@@ -0,0 +1,46 @@
+<script src="include.js"></script>
+<style>
+    #editable {
+        border: 1px solid #ccc;
+        font-size: 30px;
+        width: 400px;
+        height: 100px;
+    }
+</style>
+<div id="editable" contenteditable="true">
+    Ladybird is an ongoing project to build an independent web browser from scratch.
+</div>
+<script>
+    asyncTest(async done => {
+        function elementToString(e) {
+            let element_string = `<${e.nodeName} `;
+            if (e.id) element_string += `id="${e.id}" `;
+            element_string += ">";
+            return element_string;
+        }
+
+        document.addEventListener("selectionchange", function (e) {
+            const selection = window.getSelection();
+            println(
+                `selectionchange anchorNode=${elementToString(selection.anchorNode)} anchorOffset=${
+                    selection.anchorOffset
+                } type=${selection.type} focusNode=${elementToString(
+                    selection.focusNode
+                )} focusOffset=${selection.focusOffset} isCollapsed=${selection.isCollapsed}`
+            );
+        });
+
+        const editable = document.getElementById("editable");
+
+        println("Events:");
+
+        internals.click(20, 10);
+        await new Promise(resolve => setTimeout(resolve, 0));
+        internals.click(30, 10);
+        await new Promise(resolve => setTimeout(resolve, 0));
+        internals.click(40, 10);
+        await new Promise(resolve => setTimeout(resolve, 0));
+
+        done();
+    });
+</script>

Userland/Libraries/LibWeb/DOM/EventHandler.idl

@@ -70,6 +70,7 @@ interface mixin GlobalEventHandlers {
     attribute EventHandler onseeked;
     attribute EventHandler onseeking;
     attribute EventHandler onselect;
+    attribute EventHandler onselectionchange;
     attribute EventHandler onslotchange;
     attribute EventHandler onstalled;
     attribute EventHandler onsubmit;

Userland/Libraries/LibWeb/DOM/Range.cpp

@@ -12,6 +12,7 @@
 #include <LibWeb/DOM/DocumentFragment.h>
 #include <LibWeb/DOM/DocumentType.h>
 #include <LibWeb/DOM/ElementFactory.h>
+#include <LibWeb/DOM/Event.h>
 #include <LibWeb/DOM/Node.h>
 #include <LibWeb/DOM/ProcessingInstruction.h>
 #include <LibWeb/DOM/Range.h>
@@ -100,6 +101,20 @@ void Range::update_associated_selection()
         layout_root->recompute_selection_states();
         layout_root->paintable()->set_needs_display();
     }
+
+    // https://w3c.github.io/selection-api/#selectionchange-event
+    // When the selection is dissociated with its range, associated with a new range or the associated range's boundary
+    // point is mutated either by the user or the content script, the user agent must queue a task on the user interaction
+    // task source to fire an event named selectionchange, which does not bubble and is not cancelable, at the document
+    // associated with the selection.
+    auto document = m_associated_selection->document();
+    queue_global_task(HTML::Task::Source::UserInteraction, relevant_global_object(*document), [document] {
+        EventInit event_init;
+        event_init.bubbles = false;
+        event_init.cancelable = false;
+        auto event = DOM::Event::create(document->realm(), HTML::EventNames::selectionchange, event_init);
+        document->dispatch_event(event);
+    });
 }
 
 // https://dom.spec.whatwg.org/#concept-range-root

Userland/Libraries/LibWeb/HTML/AttributeNames.h

@@ -180,6 +180,7 @@ namespace AttributeNames {
     __ENUMERATE_HTML_ATTRIBUTE(onseeked)                   \
     __ENUMERATE_HTML_ATTRIBUTE(onseeking)                  \
     __ENUMERATE_HTML_ATTRIBUTE(onselect)                   \
+    __ENUMERATE_HTML_ATTRIBUTE(onselectionchange)          \
     __ENUMERATE_HTML_ATTRIBUTE(onslotchange)               \
     __ENUMERATE_HTML_ATTRIBUTE(onstalled)                  \
     __ENUMERATE_HTML_ATTRIBUTE(onstorage)                  \

Userland/Libraries/LibWeb/HTML/EventNames.h

@@ -88,6 +88,7 @@ namespace Web::HTML::EventNames {
     __ENUMERATE_HTML_EVENT(scroll)                   \
     __ENUMERATE_HTML_EVENT(scrollend)                \
     __ENUMERATE_HTML_EVENT(securitypolicyviolation)  \
+    __ENUMERATE_HTML_EVENT(selectionchange)          \
     __ENUMERATE_HTML_EVENT(seeked)                   \
     __ENUMERATE_HTML_EVENT(seeking)                  \
     __ENUMERATE_HTML_EVENT(select)                   \

Userland/Libraries/LibWeb/HTML/GlobalEventHandlers.h

@@ -63,6 +63,7 @@
     E(onseeked, HTML::EventNames::seeked)                                     \
     E(onseeking, HTML::EventNames::seeking)                                   \
     E(onselect, HTML::EventNames::select)                                     \
+    E(onselectionchange, HTML::EventNames::selectionchange)                   \
     E(onslotchange, HTML::EventNames::slotchange)                             \
     E(onstalled, HTML::EventNames::stalled)                                   \
     E(onsubmit, HTML::EventNames::submit)                                     \