LibWeb: Implement the "selectAll" editing command

Author: https://github.com/gmta
Commit: 70af48c18b
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3216

Libraries/LibWeb/Editing/Commands.cpp

@@ -2228,6 +2228,33 @@ bool command_remove_format_action(DOM::Document& document, String const&)
     return true;
 }
 
+// https://w3c.github.io/editing/docs/execCommand/#the-selectall-command
+bool command_select_all_action(DOM::Document& document, String const&)
+{
+    // NOTE: The spec mentions "This is totally broken". So fair warning :^)
+
+    // 1. Let target be the body element of the context object.
+    GC::Ptr<DOM::Node> target = document.body();
+
+    // 2. If target is null, let target be the context object's documentElement.
+    if (!target)
+        target = document.document_element();
+
+    // 3. If target is null, call getSelection() on the context object, and call removeAllRanges() on the result.
+    auto& selection = *document.get_selection();
+    if (!target) {
+        selection.remove_all_ranges();
+    }
+
+    // 4. Otherwise, call getSelection() on the context object, and call selectAllChildren(target) on the result.
+    else {
+        MUST(selection.select_all_children(*target));
+    }
+
+    // 5. Return true.
+    return true;
+}
+
 // https://w3c.github.io/editing/docs/execCommand/#the-strikethrough-command
 bool command_strikethrough_action(DOM::Document& document, String const&)
 {
@@ -2602,6 +2629,11 @@ static Array const commands {
         .command = CommandNames::removeFormat,
         .action = command_remove_format_action,
     },
+    // https://w3c.github.io/editing/docs/execCommand/#the-selectall-command
+    CommandDefinition {
+        .command = CommandNames::selectAll,
+        .action = command_select_all_action,
+    },
     // https://w3c.github.io/editing/docs/execCommand/#the-strikethrough-command
     CommandDefinition {
         .command = CommandNames::strikethrough,