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use std::fmt;
/// A static accessor to type paths and names.
///
/// The engine uses this trait over [`std::any::type_name`] for stability and flexibility.
///
/// This trait is automatically implemented by the `#[derive(Reflect)]` macro
/// and allows type path information to be processed without an instance of that type.
///
/// Implementors may have difficulty in generating references with static
/// lifetimes. Luckily, this crate comes with some [utility] structs, to make generating these
/// statics much simpler.
///
/// # Stability
///
/// Certain parts of the engine, e.g. [(de)serialization], rely on type paths as identifiers
/// for matching dynamic values to concrete types.
///
/// Using [`std::any::type_name`], a scene containing `my_crate::foo::MyComponent` would break,
/// failing to deserialize if the component was moved from the `foo` module to the `bar` module,
/// becoming `my_crate::bar::MyComponent`.
/// This trait, through attributes when deriving itself or [`Reflect`], can ensure breaking changes are avoidable.
///
/// The only external factor we rely on for stability when deriving is the [`module_path!`] macro,
/// only if the derive does not provide a `#[type_path = "..."]` attribute.
///
/// # Anonymity
///
/// Some methods on this trait return `Option<&'static str>` over `&'static str`
/// because not all types define all parts of a type path, for example the array type `[T; N]`.
///
/// Such types are 'anonymous' in that they have only a defined [`type_path`] and [`short_type_path`]
/// and the methods [`crate_name`], [`module_path`] and [`type_ident`] all return `None`.
///
/// Primitives are treated like anonymous types, except they also have a defined [`type_ident`].
///
/// # Example
///
/// ```
/// use bevy_reflect::TypePath;
///
/// // This type path will not change with compiler versions or recompiles,
/// // although it will not be the same if the definition is moved.
/// #[derive(TypePath)]
/// struct NonStableTypePath;
///
/// // This type path will never change, even if the definition is moved.
/// #[derive(TypePath)]
/// #[type_path = "my_crate::foo"]
/// struct StableTypePath;
///
/// // Type paths can have any number of path segments.
/// #[derive(TypePath)]
/// #[type_path = "my_crate::foo::bar::baz"]
/// struct DeeplyNestedStableTypePath;
///
/// // Including just a crate name!
/// #[derive(TypePath)]
/// #[type_path = "my_crate"]
/// struct ShallowStableTypePath;
///
/// // We can also rename the identifier/name of types.
/// #[derive(TypePath)]
/// #[type_path = "my_crate::foo"]
/// #[type_name = "RenamedStableTypePath"]
/// struct NamedStableTypePath;
///
/// // Generics are also supported.
/// #[derive(TypePath)]
/// #[type_path = "my_crate::foo"]
/// struct StableGenericTypePath<T, const N: usize>([T; N]);
/// ```
///
/// [utility]: crate::utility
/// [(de)serialization]: crate::serde::ReflectDeserializer
/// [`Reflect`]: crate::Reflect
/// [`type_path`]: TypePath::type_path
/// [`short_type_path`]: TypePath::short_type_path
/// [`crate_name`]: TypePath::crate_name
/// [`module_path`]: TypePath::module_path
/// [`type_ident`]: TypePath::type_ident
#[diagnostic::on_unimplemented(
message = "`{Self}` does not have a type path",
note = "consider annotating `{Self}` with `#[derive(Reflect)]` or `#[derive(TypePath)]`"
)]
pub trait TypePath: 'static {
/// Returns the fully qualified path of the underlying type.
///
/// Generic parameter types are also fully expanded.
///
/// For `Option<Vec<usize>>`, this is `"core::option::Option<alloc::vec::Vec<usize>>"`.
fn type_path() -> &'static str;
/// Returns a short, pretty-print enabled path to the type.
///
/// Generic parameter types are also shortened.
///
/// For `Option<Vec<usize>>`, this is `"Option<Vec<usize>>"`.
fn short_type_path() -> &'static str;
/// Returns the name of the type, or [`None`] if it is [anonymous].
///
/// Primitive types will return [`Some`].
///
/// For `Option<Vec<usize>>`, this is `"Option"`.
///
/// [anonymous]: TypePath#anonymity
fn type_ident() -> Option<&'static str> {
None
}
/// Returns the name of the crate the type is in, or [`None`] if it is [anonymous].
///
/// For `Option<Vec<usize>>`, this is `"core"`.
///
/// [anonymous]: TypePath#anonymity
fn crate_name() -> Option<&'static str> {
None
}
/// Returns the path to the module the type is in, or [`None`] if it is [anonymous].
///
/// For `Option<Vec<usize>>`, this is `"core::option"`.
///
/// [anonymous]: TypePath#anonymity
fn module_path() -> Option<&'static str> {
None
}
}
/// Dynamic dispatch for [`TypePath`].
///
/// Since this is a supertrait of [`Reflect`] its methods can be called on a `dyn Reflect`.
///
/// [`Reflect`]: crate::Reflect
#[diagnostic::on_unimplemented(
message = "`{Self}` can not be used as a dynamic type path",
note = "consider annotating `{Self}` with `#[derive(Reflect)]` or `#[derive(TypePath)]`"
)]
pub trait DynamicTypePath {
/// See [`TypePath::type_path`].
fn reflect_type_path(&self) -> &str;
/// See [`TypePath::short_type_path`].
fn reflect_short_type_path(&self) -> &str;
/// See [`TypePath::type_ident`].
fn reflect_type_ident(&self) -> Option<&str>;
/// See [`TypePath::crate_name`].
fn reflect_crate_name(&self) -> Option<&str>;
/// See [`TypePath::module_path`].
fn reflect_module_path(&self) -> Option<&str>;
}
impl<T: TypePath> DynamicTypePath for T {
#[inline]
fn reflect_type_path(&self) -> &str {
Self::type_path()
}
#[inline]
fn reflect_short_type_path(&self) -> &str {
Self::short_type_path()
}
#[inline]
fn reflect_type_ident(&self) -> Option<&str> {
Self::type_ident()
}
#[inline]
fn reflect_crate_name(&self) -> Option<&str> {
Self::crate_name()
}
#[inline]
fn reflect_module_path(&self) -> Option<&str> {
Self::module_path()
}
}
/// Provides dynamic access to all methods on [`TypePath`].
#[derive(Clone, Copy)]
pub struct TypePathTable {
// Cache the type path as it is likely the only one that will be used.
type_path: &'static str,
short_type_path: fn() -> &'static str,
type_ident: fn() -> Option<&'static str>,
crate_name: fn() -> Option<&'static str>,
module_path: fn() -> Option<&'static str>,
}
impl fmt::Debug for TypePathTable {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("TypePathVtable")
.field("type_path", &self.type_path)
.field("short_type_path", &(self.short_type_path)())
.field("type_ident", &(self.type_ident)())
.field("crate_name", &(self.crate_name)())
.field("module_path", &(self.module_path)())
.finish()
}
}
impl TypePathTable {
/// Creates a new table from a type.
pub fn of<T: TypePath + ?Sized>() -> Self {
Self {
type_path: T::type_path(),
short_type_path: T::short_type_path,
type_ident: T::type_ident,
crate_name: T::crate_name,
module_path: T::module_path,
}
}
/// See [`TypePath::type_path`].
pub fn path(&self) -> &'static str {
self.type_path
}
/// See [`TypePath::short_type_path`].
pub fn short_path(&self) -> &'static str {
(self.short_type_path)()
}
/// See [`TypePath::type_ident`].
pub fn ident(&self) -> Option<&'static str> {
(self.type_ident)()
}
/// See [`TypePath::crate_name`].
pub fn crate_name(&self) -> Option<&'static str> {
(self.crate_name)()
}
/// See [`TypePath::module_path`].
pub fn module_path(&self) -> Option<&'static str> {
(self.module_path)()
}
}