tor-browser

feature.rs (7376B)

---

/* 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::derives::*;
use crate::parser::ParserContext;
use crate::values::computed::{self, CSSPixelLength, Ratio, Resolution};
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>),
   /// 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;
       /// The feature evaluation depends on style queries.
       const STYLE = 1 << 7;
   }
}

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()
   }
}