LibWeb+LibJS: Add a naive way to check if a wrapper "is" a certain type

Instead of only checking the class_name(), we now generate an is_foo()
virtual in the wrapper generator. (It's currently something we override
on Bindings::Wrapper, which is not really scalable.)

Longer term we'll need to think up something smarter for verifying that
one wrapper "is" another type of wrapper.

Libraries/LibJS/Runtime/Object.h

@@ -111,6 +111,8 @@ public:
     virtual bool is_symbol_object() const { return false; }
     virtual bool is_bigint_object() const { return false; }
 
+    virtual bool is_web_wrapper() const { return false; }
+
     virtual const char* class_name() const override { return "Object"; }
     virtual void visit_children(Cell::Visitor&) override;
 

Libraries/LibWeb/Bindings/Wrapper.h

@@ -37,11 +37,17 @@ namespace Bindings {
 class Wrapper
     : public JS::Object
     , public Weakable<Wrapper> {
+public:
+    virtual bool is_node_wrapper() const { return false; }
+    virtual bool is_document_wrapper() const { return false; }
+
 protected:
     explicit Wrapper(Object& prototype)
         : Object(&prototype)
     {
     }
+
+    virtual bool is_web_wrapper() const final { return true; }
 };
 
 }

Libraries/LibWeb/CodeGenerators/WrapperGenerator.cpp

@@ -30,16 +30,19 @@
 #include <LibCore/File.h>
 #include <ctype.h>
 
-static String snake_name(const StringView& camel_name)
+static String snake_name(const StringView& title_name)
 {
     StringBuilder builder;
-    for (auto ch : camel_name) {
+    bool first = true;
+    for (auto ch : title_name) {
         if (isupper(ch)) {
-            builder.append('_');
+            if (!first)
+                builder.append('_');
             builder.append(tolower(ch));
         } else {
             builder.append(ch);
         }
+        first = false;
     }
     return builder.to_string();
 }
@@ -338,6 +341,9 @@ static void generate_header(const IDL::Interface& interface)
         out() << "    const " << interface.name << "& impl() const { return static_cast<const " << interface.name << "&>(" << wrapper_base_class << "::impl()); }";
     }
 
+    auto is_foo_wrapper_name = snake_name(String::format("Is%s", wrapper_class.characters()));
+    out() << "    virtual bool " << is_foo_wrapper_name << "() const final { return true; }";
+
     out() << "private:";
     out() << "    virtual const char* class_name() const override { return \"" << interface.name << "\"; }";
 
@@ -407,7 +413,8 @@ void generate_implementation(const IDL::Interface& interface)
     out() << "    auto* this_object = interpreter.this_value(global_object).to_object(interpreter, global_object);";
     out() << "    if (!this_object)";
     out() << "        return {};";
-    out() << "    if (StringView(\"" << interface.name << "\") != this_object->class_name()) {";
+    auto is_foo_wrapper_name = snake_name(String::format("Is%s", wrapper_class.characters()));
+    out() << "    if (!this_object->is_web_wrapper() || !static_cast<Wrapper*>(this_object)->" << is_foo_wrapper_name << "()) {";
     out() << "        interpreter.throw_exception<JS::TypeError>(JS::ErrorType::NotA, \"" << interface.name << "\");";
     out() << "        return nullptr;";
     out() << "    }";