/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at
https://mozilla.org/MPL/2.0/. */
//! Query features.
use crate::parser::ParserContext;
use crate::values::computed::{self, CSSPixelLength, Ratio, Resolution};
use crate::values::AtomString;
use crate::Atom;
use cssparser::Parser;
use selectors::kleene_value::KleeneValue;
use std::fmt;
use style_traits::ParseError;
/// A generic discriminant for an enum value.
pub type KeywordDiscriminant = u8;
type QueryFeatureGetter<T> = fn(device: &computed::Context) -> T;
/// Serializes a given discriminant.
///
/// FIXME(emilio): we could prevent this allocation if the ToCss code would
/// generate a method for keywords to get the static string or something.
pub type KeywordSerializer = fn(KeywordDiscriminant) -> String;
/// Parses a given identifier.
pub type KeywordParser = for<'a, 'i, 't> fn(
context: &'a ParserContext,
input: &'a mut Parser<'i, 't>,
) -> Result<KeywordDiscriminant, ParseError<'i>>;
/// An evaluator for a given feature.
///
/// This determines the kind of values that get parsed, too.
#[allow(missing_docs)]
pub enum Evaluator {
Length(QueryFeatureGetter<CSSPixelLength>),
OptionalLength(QueryFeatureGetter<Option<CSSPixelLength>>),
Integer(QueryFeatureGetter<i32>),
Float(QueryFeatureGetter<f32>),
BoolInteger(QueryFeatureGetter<bool>),
/// A non-negative number ratio, such as the one from device-pixel-ratio.
NumberRatio(QueryFeatureGetter<Ratio>),
OptionalNumberRatio(QueryFeatureGetter<Option<Ratio>>),
/// A resolution.
Resolution(QueryFeatureGetter<Resolution>),
String(fn(&computed::Context, Option<&AtomString>) -> KleeneValue),
/// A keyword value.
Enumerated {
/// The parser to get a discriminant given a string.
parser: KeywordParser,
/// The serializer to get a string from a discriminant.
///
/// This is guaranteed to be called with a keyword that `parser` has
/// produced.
serializer: KeywordSerializer,
/// The evaluator itself. This is guaranteed to be called with a
/// keyword that `parser` has produced.
evaluator: fn(&computed::Context, Option<KeywordDiscriminant>) -> KleeneValue,
},
}
/// A simple helper macro to create a keyword evaluator.
///
/// This assumes that keyword feature expressions don't accept ranges, and
/// asserts if that's not true. As of today there's nothing like that (does that
/// even make sense?).
macro_rules! keyword_evaluator {
($actual_evaluator:ident, $keyword_type:ty) => {{
fn __parse<'i, 't>(
context: &$crate::parser::ParserContext,
input: &mut $crate::cssparser::Parser<'i, 't>,
) -> Result<$crate::queries::feature::KeywordDiscriminant, ::style_traits::ParseError<
'i>>
{
let kw = <$keyword_type as $crate::parser::Parse>::parse(context, input)?;
Ok(kw as $crate::queries::feature::KeywordDiscriminant)
}
fn __serialize(kw: $crate::queries::feature::KeywordDiscriminant) -> String {
// This unwrap is ok because the only discriminants that get
// back to us is the ones that `parse` produces.
let value: $keyword_type = ::num_traits::cast::FromPrimitive::from_u8(kw).unwrap();
<$keyword_type as ::style_traits::ToCss>::to_css_string(&value)
}
fn __evaluate(
context: &$crate::values::computed::Context,
value: Option<$crate::queries::feature::KeywordDiscriminant>,
) -> selectors::kleene_value::KleeneValue {
// This unwrap is ok because the only discriminants that get
// back to us is the ones that `parse` produces.
let value: Option<$keyword_type> =
value.map(|kw| ::num_traits::cast::FromPrimitive::from_u8(kw).unwrap());
selectors::kleene_value::KleeneValue::from($actual_evaluator(context, value))
}
$crate::queries::feature::Evaluator::Enumerated {
parser: __parse,
serializer: __serialize,
evaluator: __evaluate,
}
}};
}
/// Different flags or toggles that change how a expression is parsed or
/// evaluated.
#[derive(Clone, Copy, Debug, ToShmem)]
pub struct FeatureFlags(u8);
bitflags! {
impl FeatureFlags : u8 {
/// The feature should only be parsed in chrome and ua sheets.
const CHROME_AND_UA_ONLY = 1 << 0;
/// The feature requires a -webkit- prefix.
const WEBKIT_PREFIX = 1 << 1;
/// The feature requires the inline-axis containment.
const CONTAINER_REQUIRES_INLINE_AXIS = 1 << 2;
/// The feature requires the block-axis containment.
const CONTAINER_REQUIRES_BLOCK_AXIS = 1 << 3;
/// The feature requires containment in the physical width axis.
const CONTAINER_REQUIRES_WIDTH_AXIS = 1 << 4;
/// The feature requires containment in the physical height axis.
const CONTAINER_REQUIRES_HEIGHT_AXIS = 1 << 5;
/// The feature evaluation depends on the viewport size.
const VIEWPORT_DEPENDENT = 1 << 6;
}
}
impl FeatureFlags {
/// Returns parsing requirement flags.
pub fn parsing_requirements(self) -> Self {
self.intersection(Self::CHROME_AND_UA_ONLY | Self::WEBKIT_PREFIX)
}
/// Returns all the container axis flags.
pub fn all_container_axes() -> Self {
Self::CONTAINER_REQUIRES_INLINE_AXIS |
Self::CONTAINER_REQUIRES_BLOCK_AXIS |
Self::CONTAINER_REQUIRES_WIDTH_AXIS |
Self::CONTAINER_REQUIRES_HEIGHT_AXIS
}
/// Returns our subset of container axis flags.
pub fn container_axes(self) -> Self {
self.intersection(Self::all_container_axes())
}
}
/// Whether a feature allows ranges or not.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
#[allow(missing_docs)]
pub enum AllowsRanges {
Yes,
No,
}
/// A description of a feature.
pub struct QueryFeatureDescription {
/// The feature name, in ascii lowercase.
pub name: Atom,
/// Whether min- / max- prefixes are allowed or not.
pub allows_ranges: AllowsRanges,
/// The evaluator, which we also use to determine which kind of value to
/// parse.
pub evaluator: Evaluator,
/// Different feature-specific flags.
pub flags: FeatureFlags,
}
impl QueryFeatureDescription {
/// Whether this feature allows ranges.
#[inline]
pub fn allows_ranges(&self) -> bool {
self.allows_ranges == AllowsRanges::Yes
}
}
/// A simple helper to construct a `QueryFeatureDescription`.
macro_rules! feature {
($name:expr, $allows_ranges:expr, $evaluator:expr, $flags:expr,) => {
$crate::queries::feature::QueryFeatureDescription {
name: $name,
allows_ranges: $allows_ranges,
evaluator: $evaluator,
flags: $flags,
}
};
}
impl fmt::Debug for QueryFeatureDescription {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.debug_struct("QueryFeatureDescription")
.field("name", &self.name)
.field("allows_ranges", &self.allows_ranges)
.field("flags", &self.flags)
.finish()
}
}
