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//! Macros to define CSS properties.
use crate::properties::ComputedValues;
/// Trait which all CSS property types should implement.
pub trait Property {
/// Whether the property's computed value inherits from parent to child elements.
///
/// For each property, the CSS or SVG specs say whether the property inherits
/// automatically. When a property is not specified in an element, the return value
/// of this method determines whether the property's value is copied from the parent
/// element (`true`), or whether it resets to the initial/default value (`false`).
fn inherits_automatically() -> bool;
/// Derive the CSS computed value from the parent element's
/// [`ComputedValues`][crate::properties::ComputedValues] and the
/// `self` value.
///
/// The CSS or SVG specs say how to derive this for each property.
fn compute(&self, _: &ComputedValues) -> Self;
}
/// Generates a type for a CSS property.
///
/// Writing a property by hand takes a bit of boilerplate:
///
/// * Define a type to represent the property's values.
///
/// * A [`Parse`] implementation to parse the property.
///
/// * A [`Default`] implementation to define the property's *initial* value.
///
/// * A [`Property`] implementation to define whether the property
/// inherits from the parent element, and how the property derives its
/// computed value.
///
/// When going from [`SpecifiedValues`] to [`ComputedValues`],
/// properties which inherit automatically from the parent element
/// will just have their values cloned. Properties which do not
/// inherit will be reset back to their initial value (i.e. their
/// [`Default`]).
///
/// The default implementation of [`Property::compute()`] is to just
/// clone the property's value. Properties which need more
/// sophisticated computation can override this.
///
/// This macro allows defining properties of different kinds; see the following
/// sections for examples.
///
/// # Simple identifiers
///
/// Many properties are just sets of identifiers and can be represented
/// by simple enums. In this case, you can use the following:
///
/// ```text
/// make_property!(
/// /// Documentation here.
/// StrokeLinejoin,
/// default: Miter,
/// inherits_automatically: true,
///
/// identifiers:
/// "miter" => Miter,
/// "round" => Round,
/// "bevel" => Bevel,
/// );
/// ```
///
/// This generates a simple enum like the following, with implementations of [`Parse`],
/// [`Default`], and [`Property`].
///
/// ```
/// pub enum StrokeLinejoin { Miter, Round, Bevel }
/// ```
///
/// # Properties from an existing, general-purpose type
///
/// For example, both the `lightingColor` and `floodColor` properties can be represented
/// with a `cssparser::Color`, but their intial values are different. In this case, the macro
/// can generate a newtype around `cssparser::Color` for each case:
///
/// ```text
/// make_property!(
/// /// Documentation here.
/// FloodColor,
/// default: cssparser::Color::RGBA(cssparser::RGBA::new(0, 0, 0, 0)),
/// inherits_automatically: false,
/// newtype_parse: cssparser::Color,
/// );
/// ```
///
/// # Properties from custom specific types
///
/// For example, font-related properties have custom, complex types that require an
/// implentation of `Property::compute` that is more than a simple `clone`. In this case,
/// define the custom type separately, and use the macro to specify the default value and
/// the `Property` implementation.
///
/// [`Parse`]: crate::parsers::Parse
/// [`Property`]: crate::property_macros::Property
/// [`ComputedValues`]: crate::properties::ComputedValues
/// [`SpecifiedValues`]: crate::properties::SpecifiedValues
/// [`Property::compute()`]: crate::property_macros::Property::compute
///
#[doc(hidden)]
#[macro_export]
macro_rules! make_property {
($(#[$attr:meta])*
$name: ident,
default: $default: ident,
inherits_automatically: $inherits_automatically: expr,
identifiers:
$($str_prop: expr => $variant: ident,)+
) => {
$(#[$attr])*
#[derive(Debug, Copy, Clone, PartialEq)]
#[repr(C)]
pub enum $name {
$($variant),+
}
impl_default!($name, $name::$default);
impl_property!($name, $inherits_automatically);
impl $crate::parsers::Parse for $name {
fn parse<'i>(parser: &mut ::cssparser::Parser<'i, '_>) -> Result<$name, $crate::error::ParseError<'i>> {
Ok(parse_identifiers!(
parser,
$($str_prop => $name::$variant,)+
)?)
}
}
};
($(#[$attr:meta])*
$name: ident,
default: $default: ident,
identifiers: { $($str_prop: expr => $variant: ident,)+ },
property_impl: { $prop: item }
) => {
$(#[$attr])*
#[derive(Debug, Copy, Clone, PartialEq)]
#[repr(C)]
pub enum $name {
$($variant),+
}
impl_default!($name, $name::$default);
$prop
impl $crate::parsers::Parse for $name {
fn parse<'i>(parser: &mut ::cssparser::Parser<'i, '_>) -> Result<$name, $crate::error::ParseError<'i>> {
Ok(parse_identifiers!(
parser,
$($str_prop => $name::$variant,)+
)?)
}
}
};
($(#[$attr:meta])*
$name: ident,
default: $default: expr,
inherits_automatically: $inherits_automatically: expr,
newtype_parse: $type: ty,
) => {
$(#[$attr])*
#[derive(Debug, Clone, PartialEq)]
pub struct $name(pub $type);
impl_default!($name, $name($default));
impl_property!($name, $inherits_automatically);
impl $crate::parsers::Parse for $name {
fn parse<'i>(parser: &mut ::cssparser::Parser<'i, '_>) -> Result<$name, $crate::error::ParseError<'i>> {
Ok($name(<$type as $crate::parsers::Parse>::parse(parser)?))
}
}
};
($(#[$attr:meta])*
$name: ident,
default: $default: expr,
property_impl: { $prop: item }
) => {
impl_default!($name, $default);
$prop
};
($name: ident,
default: $default: expr,
inherits_automatically: $inherits_automatically: expr,
) => {
impl_default!($name, $default);
impl_property!($name, $inherits_automatically);
};
($name: ident,
default: $default: expr,
inherits_automatically: $inherits_automatically: expr,
parse_impl: { $parse: item }
) => {
impl_default!($name, $default);
impl_property!($name, $inherits_automatically);
$parse
};
($(#[$attr:meta])*
$name: ident,
default: $default: expr,
newtype: $type: ty,
property_impl: { $prop: item },
parse_impl: { $parse: item }
) => {
$(#[$attr])*
#[derive(Debug, Clone, PartialEq)]
pub struct $name(pub $type);
impl_default!($name, $name($default));
$prop
$parse
};
// pending - only XmlLang
($(#[$attr:meta])*
$name: ident,
default: $default: expr,
inherits_automatically: $inherits_automatically: expr,
newtype: $type: ty,
parse_impl: { $parse: item },
) => {
$(#[$attr])*
#[derive(Debug, Clone, PartialEq)]
pub struct $name(pub $type);
impl_default!($name, $name($default));
impl_property!($name, $inherits_automatically);
$parse
};
($(#[$attr:meta])*
$name: ident,
inherits_automatically: $inherits_automatically: expr,
fields: {
$($field_name: ident : $field_type: ty, default: $field_default : expr,)+
}
parse_impl: { $parse: item }
) => {
$(#[$attr])*
#[derive(Debug, Clone, PartialEq)]
pub struct $name {
$(pub $field_name: $field_type),+
}
impl_default!($name, $name { $($field_name: $field_default),+ });
impl_property!($name, $inherits_automatically);
$parse
};
}
#[doc(hidden)]
#[macro_export]
macro_rules! impl_default {
($name:ident, $default:expr) => {
impl Default for $name {
fn default() -> $name {
$default
}
}
};
}
#[doc(hidden)]
#[macro_export]
macro_rules! impl_property {
($name:ident, $inherits_automatically:expr) => {
impl $crate::property_macros::Property for $name {
fn inherits_automatically() -> bool {
$inherits_automatically
}
fn compute(&self, _v: &$crate::properties::ComputedValues) -> Self {
self.clone()
}
}
};
}