moli/moli-webapi-declare/src/lib.rs

//! Declarative Web API object and interface helpers.
//!
//! This crate is the Rust declaration layer that future WebIDL codegen can
//! target. It intentionally keeps conversion/parsing concerns in
//! `moli-webidl` and focuses on constructing V8 interface objects,
//! prototypes, and branded object instances.
//!
//! # Object declaration model
//!
//! A `#[derive(WebApiObject)]` struct describes the JavaScript surface that must
//! be installed on a V8 object. Field annotations decide whether a Rust field is
//! installed:
//!
//! - `#[webapi(data_property)]` defines a JavaScript own data property. It is
//!   non-enumerable by default and can opt into `enumerable`, `readonly`, or
//!   `dont_delete`. Rust slices, arrays, and vectors whose items implement
//!   `WebApiValue` are converted into V8 arrays, so fixed-shape object records
//!   can declare array-valued fields without hand-building `v8::Array`.
//! - `#[webapi(constant)]` defines a WebIDL constant own property. Constants
//!   are enumerable, read-only, and non-configurable, and must provide
//!   `value = ...`. The declaration installs the same descriptor shape used by
//!   WebIDL constants on constructors and prototypes.
//! - `#[webapi(method)]` defines a JavaScript own function property. Its
//!   `callback = ...` is the V8 callback, and optional `data = ...` is evaluated
//!   while binding the object so callbacks can receive precomputed state.
//!   Methods are non-enumerable, writable, and configurable by default; use
//!   `enumerable`, `readonly`, or `dont_delete` when the target Web API requires
//!   a different value descriptor.
//!   `symbol = "iterator"`, `symbol = "asyncIterator"`, and
//!   `symbol = "toStringTag"` use the matching well-known symbols as the
//!   property key instead of deriving a string key from the Rust field name. A
//!   method field typed as `Option<()>` is installed
//!   only when it is `Some(())`; this is intended for runtime-selected fixed own
//!   methods whose descriptors still belong to the declaration when present.
//! - `#[webapi(alias = "sourceName")]` defines an own data property whose value
//!   is copied from another already-declared own property on the same object.
//!   This is useful when Web APIs expose the same function through multiple
//!   keys, such as a string-named method and a well-known symbol, and JavaScript
//!   must observe the two properties as the exact same function object.
//! - `#[webapi(accessor_property)]` defines a JavaScript accessor property. Its
//!   `getter = ...` and optional `setter = ...` are V8 function callbacks, and
//!   optional `data = ...` follows the same callback-data model as declared
//!   methods. Accessors with different setter callback data can use
//!   `setter_data = ...`; otherwise the setter receives the same data as the
//!   getter. Use `getter_value = ...` instead of `getter = ...` only when the
//!   getter function object is already built or cached by surrounding runtime
//!   code. Accessors also support the same `symbol = ...` keys when the
//!   getter/setter pair represents a symbol-keyed Web API member.
//! - `#[webapi(native_data_property)]` defines a callback-backed V8 native data
//!   property through `Object::set_native_data_property_with_configuration`.
//!   Its `getter = ...` and optional `setter = ...` are V8 property callbacks,
//!   not JavaScript function callbacks. Reserve this for surfaces whose
//!   semantics intentionally operate on `PropertyCallbackArguments::holder()`.
//! - `#[webapi(hidden)]` defines a non-enumerable, string-named own property.
//!   This is useful for legacy bookkeeping, but it is still an own property and
//!   can be found by reflection that asks for all own property names.
//! - `#[webapi(slot)]` stores data in a V8 private slot through
//!   `moli-v8-util`. Use this for internal state that must not appear as a
//!   JavaScript own property.
//! - `#[webapi(prototype)]` and `#[webapi(to_string_tag)]` install runtime
//!   prototype and `Symbol.toStringTag` metadata from field values.
//!   `to_string_tag` fields are non-enumerable by default and can opt into
//!   `readonly` or `dont_delete` descriptor bits.
//! - `#[webapi(init = ...)]` can initialize fixed default values without a
//!   Rust value field: `null`, `undefined`, `object`, `null_object`, `array`,
//!   `true`, `false`, `0`, `""`, or `string("...")`. Object-valued defaults
//!   use named string forms such as `init = "array"`; primitive defaults use
//!   literal or typed initializer syntax.
//!
//! Field names are converted to WebIDL-style camelCase by default. Use
//! struct-level `rename_all = "none"` only for declarations that intentionally
//! expose Rust field spelling. Struct-level `#[webapi(enumerable)]` makes
//! explicitly declared string-keyed data properties, methods, accessor
//! properties, native data properties, and aliases enumerable by default. It
//! can be used with `#[webapi(data_properties)]` for plain objects,
//! or by itself for WebIDL prototype declarations where every operation and
//! attribute should inherit WebIDL's enumerable prototype-member default.
//! Well-known symbol keys remain non-enumerable unless the field itself
//! declares `enumerable`.
//!
//! Fields without one of those installation annotations are declaration-only
//! inputs. The derive skips them completely, so they do not become properties or
//! private slots. They can still be referenced by method attributes such as
//! `data = self.some_field`, which lets a declaration carry callback data
//! without expanding the object reflection surface.
//!
//! Object declarations choose one role:
//!
//! - `#[webapi(interface = interfaces::Event)]` creates a native instance. It
//!   receives private identity after its fields initialize successfully, whether
//!   called through `bind`, `bind_into`, or `initialize`. Its default prototype
//!   comes from the descriptor; an explicit `prototype` can preserve another
//!   public shape without changing native identity.
//! - `#[webapi(plain)]` describes an ordinary unbranded object, defaulting to
//!   `Object.prototype`. Field annotations and `data_properties` still control
//!   which Rust fields become JavaScript properties.
//! - `#[webapi(fragment)]` installs shared state or members on an existing
//!   target. It assigns no identity and has no implicit prototype. Explicit
//!   prototype or tag declarations are applied by `bind_into`; `initialize`
//!   installs only the declared fields. Fragments never erase native identity.
//!
//! Empty declarations need no special opt-in: creating an empty plain object,
//! branding a native instance and installing prototype metadata all have defined roles.
//! A single lifetime parameter is inferred as the V8 scope lifetime; use
//! `scope_lifetime` only when a declaration has multiple lifetimes. Payload slots
//! hold data, ownership and lifecycle state, not additional boolean brands.
//! Explicit prototype and tag expressions can use `Type::DESCRIPTOR.name()`
//! to share names with generated interface metadata.
//!
//! Implementation sharing does not imply interface inheritance. For example,
//! encoding streams share TransformStream internals but have distinct native
//! interfaces. Their factory assigns the concrete type while the shared state
//! declaration uses `fragment`. Do not turn actual native instances into plain
//! objects to make them pass structured clone.
//!
//! Declare each interface once with `declare_web_api_interfaces!` and reference
//! it using `#[webapi(interface = interfaces::ProgressEvent)]`. The generated
//! descriptor supplies the name and parent to constructor specs, factories and
//! receiver predicates. Initialization registers the full ancestry, including
//! when public constructors are absent. Do not repeat `parent` on object state
//! declarations. A template's optional `name` is only its display name and must
//! not be used to infer the identity of a shared implementation fragment.
//!
//! Identity is independent of realm exposure and mutable JavaScript prototypes.
//! Use `web_api_object_type` for the primary interface. Native factories can use
//! `Interface::DESCRIPTOR.initialize(scope, object)`; dynamic factories resolve
//! their selected name through the same native catalog. JavaScript subclasses
//! retain the interface implemented by their native constructor, and base
//! initialization never downgrades a derived object. Inconsistent parents,
//! cycles and unrelated rebranding fail.
//!
//! `WebApiFunctionTemplate` adapts native constructor
//! callbacks automatically. Hand-written templates can use
//! `web_api_constructor!(interfaces::Interface, callback)` when construction does not
//! already go through a named object declaration. Only successful construction
//! brands the resulting native object; constructors and prototypes are not
//! instances. A factory implemented with a native Proxy must brand its target
//! and call `register_web_api_proxy` with its private handler before publication.
//! The handler belongs to that exact Proxy; author wrappers and revoked Proxies
//! fail identity checks without invoking traps. Registration grants no clone
//! capability. Native factories select names from their own descriptors, never
//! from JavaScript properties such as `new.target.name`. Include detached nodes,
//! workers, iterators, fallback events, and deserialization paths when adding a
//! factory. Receiver identity does not replace resource or realm authorization.
//!
//! Identity alone grants neither serialization nor transfer capability.
//! Structured-clone serializers route every identified object through their
//! explicit codecs and reject unsupported types, including nested instances.
//! Both message serialization and IndexedDB dispatch on the primary interface,
//! as required by the [HTML serialization and transfer rules]. A native derived
//! interface does not implicitly inherit a base interface's codec. The numeric
//! type IDs are isolate-local and must never be persisted or used as wire tags;
//! deserializers use their existing wire tags and native construction paths to
//! assign identity in the receiving isolate.
//!
//! [HTML serialization and transfer rules]: https://html.spec.whatwg.org/multipage/structured-data.html#serializable-objects
//!
//! The derive generates a Rust-side `new(...)` constructor by default. The
//! generated constructor takes every non-`()` declaration field as a named
//! argument and fills `()` declaration fields with `()`. If every field is
//! `()`, the generated constructor is `new()`. This keeps dynamic state
//! explicit while removing boilerplate for fixed initialized slots or
//! accessor/method declaration fields. A field can declare
//! `#[webapi(constructor_default = expr)]`, or bare
//! `#[webapi(constructor_default)]` for `Default::default()`, to keep a
//! Rust-side default out of the generated constructor while still installing
//! the field normally; this is distinct from `init = ...`, which creates a
//! JavaScript/V8-side default for a `()` field. Use
//! `#[webapi(no_dynamic_constructor)]` when the declaration already has a
//! hand-written constructor with narrower semantics.
//!
//! # Receiver checks and Promise-returning members
//!
//! `#[webapi(interface = interfaces::Event, receiver)]` checks instance methods
//! and accessors against the declared interface before argument conversion.
//! A field can use `receiver = interfaces::Other::is_instance` to select another
//! interface. Merely naming a template does not enable receiver checks.
//! Invalid receivers throw `TypeError("Illegal invocation")`. Native subtypes
//! and cross-realm objects are accepted even after their JavaScript prototypes
//! change. Forged prototypes, public properties, and author Proxies cannot pass.
//!
//! Struct-level `receiver` supplies the default for instance methods and
//! accessor properties in both derives; a field can override it. Static
//! methods, data properties, and holder-based native data properties do not
//! inherit this policy. Already-built `getter_value` functions cannot use it.
//!
//! `receiver = path` remains available for a custom native predicate with
//! signature `fn(&mut v8::PinScope, v8::Local<v8::Object>) -> bool`. It must not
//! execute JavaScript or throw. Use it for checks that additionally require
//! native resource state; ordinary interface checks should use their descriptor.
//!
//! `returns_promise` on a method (including a static method) or accessor getter
//! converts synchronous exceptions from both the receiver check and the callback
//! into rejected Promises in the callback's realm. Successful return values are
//! unchanged, so cached Promise identity is preserved. An accessor setter still
//! throws synchronously. Callback data and native function descriptors are
//! unchanged: these adapters are Rust callbacks, not JavaScript wrappers.
//!
//! # Function-template declaration model
//!
//! A `#[derive(WebApiFunctionTemplate)]` struct describes a constructor-backed
//! V8 `FunctionTemplate`, its constructor-template static methods, and its
//! prototype-template methods. This is the declaration path for bootstrap
//! surfaces that install onto `FunctionTemplate` and
//! `FunctionTemplate::prototype_template()` instead of an already-created V8
//! object. Template methods are non-enumerable by default, and can opt into
//! `enumerable`, `readonly`, or `dont_delete`; struct-level
//! `#[webapi(enumerable)]` applies the WebIDL operation default to string-keyed
//! methods while leaving well-known symbols explicit. Template
//! `#[webapi(accessor_property)]` creates getter/setter `FunctionTemplate`
//! values through `ObjectTemplate::set_accessor_property`, so callbacks receive
//! the actual JavaScript receiver through `FunctionCallbackArguments::this()`.
//! `#[webapi(native_data_property)]` is the explicit spelling for the
//! holder-based `ObjectTemplate::set_native_data_property_with_configuration`
//! path and should be reserved for internal properties that intentionally
//! operate on the native holder.
//! `#[webapi(intrinsic_data_property = v8::Intrinsic::...)]` installs a
//! realm-correct V8 intrinsic directly on the prototype template. This
//! template-only path avoids reading mutable public builtins such as
//! `globalThis.Array.prototype` and supports the normal descriptor flags and
//! well-known symbol keys.
//! Struct-level
//! `#[webapi(intrinsic_prototype_parent = v8::Intrinsic::...)]` creates the
//! hidden parent template required by V8 and links the declared prototype to a
//! realm-correct intrinsic prototype. This is intended for WebIDL iterator
//! prototypes and special interfaces such as `DOMException`; it does not read
//! public constructors such as `globalThis.Error`.
//! WebIDL iterator templates can pair this with struct-level
//! `readonly_prototype` and `prototype_to_string_tag = "..."`; the latter
//! installs the read-only, non-enumerable `Symbol.toStringTag` required by the
//! iterator prototype algorithms.
//! `#[webapi(constant)]` installs WebIDL constants on both the constructor
//! template and prototype template.
//!
//! Global interface exposure is deliberately outside either derive. The
//! renderer's aggregate exposed-interface installer uses V8 lazy data
//! properties so one complete interface—not an individual declaration
//! fragment—owns first-read materialization.

extern crate self as moli_webapi_declare;

mod brand;
mod callback;
mod declaration;
mod error;
mod interface;
mod property;
mod prototype;
mod value;

pub mod __private;

pub use interface::WebApiInterfaceDescriptor;
pub use moli_webapi_declare_derive::{WebApiFunctionTemplate, WebApiObject};
pub use v8;

/// Adapts a manual native constructor to the same identity initialization used
/// by interface derives. The interface must be a generated native identity type,
/// never a name obtained from `new.target` or another JavaScript property.
#[macro_export]
macro_rules! web_api_constructor {
    ($interface:path, $callback:path) => {{
        fn __moli_native_constructor_adapter<'s>(
            scope: &mut $crate::v8::PinScope<'s, '_>,
            args: $crate::v8::FunctionCallbackArguments<'s>,
            rv: $crate::v8::ReturnValue<'s>,
        ) {
            $crate::__private::invoke_web_api_constructor(
                scope,
                args,
                rv,
                <$interface>::DESCRIPTOR,
                $callback,
            );
        }
        __moli_native_constructor_adapter
    }};
}

pub use brand::{
    WebApiType, implements_interface, initialize_web_api_object, register_web_api_interfaces,
    register_web_api_proxy, web_api_object_type,
};

pub use declaration::{
    DataPropertyDescriptorDeclaration, ObjectLiteralDeclaration, WebApiFunctionTemplateDeclaration,
    WebApiObjectDeclaration,
};
pub use error::BindError;
pub use property::{
    define_bool_property, define_declared_accessor_property,
    define_declared_accessor_property_by_key, define_declared_constant_property,
    define_declared_data_property, define_declared_data_property_with_attributes,
    define_declared_enumerable_data_property, define_declared_hidden_property,
    define_declared_hidden_property_with_descriptor, define_declared_private_slot,
    define_enumerable_value_property, define_hidden_property, define_number_property,
    define_private_slot, define_string_property, define_value_property,
    illegal_constructor_callback, webidl_constant_property_attributes,
};
pub use prototype::{
    define_declared_to_string_tag, define_declared_to_string_tag_with_attributes,
    define_to_string_tag, define_to_string_tag_with_attributes, set_declared_prototype,
    set_interface_prototype, set_required_interface_prototype,
};
pub use value::{WebApiTemplateValue, WebApiValue, define_array_data_property};