ladybird/Documentation/Browser/AddNewIDLFile.md

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# Adding a new IDL file
Serenity's build system does a lot of work of turning the IDL from a Web spec into code, but there are a few things you'll need to do yourself.
For the sake of example, let's say you're wanting to add the `HTMLDetailsElement`.
1. Create `LibWeb/HTML/HTMLDetailsElement.idl` with the contents of the IDL section of the spec. In this case, that would be:
```webidl
[Exposed=Window]
interface HTMLDetailsElement : HTMLElement {
[HTMLConstructor] constructor();
[CEReactions] attribute boolean open;
};
```
2. If the IDL refers to other IDL types, you need to import those. For example, `CSSRule` has an attribute that returns a `CSSStyleSheet`, so that needs to be imported:
```webidl
#import <CSS/CSSStyleSheet.idl>
interface CSSRule {
readonly attribute CSSStyleSheet? parentStyleSheet;
};
```
3. If the IDL starts with `[Exposed=Window]`, add the following to [`LibWeb/Bindings/WindowObjectHelper.h`](../../Userland/Libraries/LibWeb/Bindings/WindowObjectHelper.h):
- `#include <LibWeb/Bindings/HTMLDetailsElementConstructor.h>` and
- `#include <LibWeb/Bindings/HTMLDetailsElementPrototype.h>` to the includes list.
- `ADD_WINDOW_OBJECT_INTERFACE(HTMLDetailsElement) \` to the macro at the bottom.
4. Add a `libweb_js_wrapper(HTML/HTMLDetailsElement)` call to [`LibWeb/idl_files.cmake`](../../Userland/Libraries/LibWeb/idl_files.cmake)
5. Forward declare the generated classes in [`LibWeb/Forward.h`](../../Userland/Libraries/LibWeb/Forward.h):
- `HTMLDetailsElement` in its namespace.
- `HTMLDetailsElementWrapper` in the `Web::Bindings` namespace.
6. The C++ class equivalent of the IDL interface has a few requirements:
- It must inherit from `public RefCounted<HTMLDetailsElement>` and `public Bindings::Wrappable`
- It must have a public `using WrapperType = Bindings::HTMLDetailsElementWrapper;`
7. Depending on what kind of thing your interface is, you may need to add it to the `WrapperFactory` of that kind:
- CSSRules: [`LibWeb/Bindings/CSSRuleWrapperFactory.cpp`](../../Userland/Libraries/LibWeb/Bindings/CSSRuleWrapperFactory.cpp)
- Events: [`LibWeb/Bindings/EventWrapperFactory.cpp`](../../Userland/Libraries/LibWeb/Bindings/EventWrapperFactory.cpp)
- Elements: [`LibWeb/Bindings/NodeWrapperFactory.cpp`](../../Userland/Libraries/LibWeb/Bindings/NodeWrapperFactory.cpp)
Open the relevant wrapper factory file, and add `#include` directives and an `if` statement for your new type.
8. If your type isn't an Event or Element, you will need to add it to [`is_wrappable_type()`](../../Meta/Lagom/Tools/CodeGenerators/LibWeb/WrapperGenerator/IDLGenerators.cpp)
so that it can be accepted as an IDL parameter, attribute or return type.