Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 740 insertions, 0 deletions

diff --git a/servo/components/style/queries/feature_expression.rs b/servo/components/style/queries/feature_expression.rs
new file mode 100644
index 0000000000..394efe1656
--- /dev/null
+++ b/servo/components/style/queries/feature_expression.rs
@@ -0,0 +1,740 @@
+/* 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/. */
+
+//! Parsing for query feature expressions, like `(foo: bar)` or
+//! `(width >= 400px)`.
+
+use super::feature::{Evaluator, QueryFeatureDescription};
+use super::feature::{FeatureFlags, KeywordDiscriminant};
+use crate::parser::{Parse, ParserContext};
+use crate::queries::condition::KleeneValue;
+use crate::str::{starts_with_ignore_ascii_case, string_as_ascii_lowercase};
+use crate::values::computed::{self, Ratio, ToComputedValue};
+use crate::values::specified::{Integer, Length, Number, Resolution};
+use crate::values::CSSFloat;
+use crate::{Atom, Zero};
+use cssparser::{Parser, Token};
+use std::cmp::{Ordering, PartialOrd};
+use std::fmt::{self, Write};
+use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};
+
+/// Whether we're parsing a media or container query feature.
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToShmem)]
+pub enum FeatureType {
+    /// We're parsing a media feature.
+    Media,
+    /// We're parsing a container feature.
+    Container,
+}
+
+impl FeatureType {
+    fn features(&self) -> &'static [QueryFeatureDescription] {
+        #[cfg(feature = "gecko")]
+        use crate::gecko::media_features::MEDIA_FEATURES;
+        #[cfg(feature = "servo")]
+        use crate::servo::media_queries::MEDIA_FEATURES;
+
+        use crate::stylesheets::container_rule::CONTAINER_FEATURES;
+
+        match *self {
+            FeatureType::Media => &MEDIA_FEATURES,
+            FeatureType::Container => &CONTAINER_FEATURES,
+        }
+    }
+
+    fn find_feature(&self, name: &Atom) -> Option<(usize, &'static QueryFeatureDescription)> {
+        self.features()
+            .iter()
+            .enumerate()
+            .find(|(_, f)| f.name == *name)
+    }
+}
+
+/// The kind of matching that should be performed on a feature value.
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToShmem)]
+enum LegacyRange {
+    /// At least the specified value.
+    Min,
+    /// At most the specified value.
+    Max,
+}
+
+/// The operator that was specified in this feature.
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToShmem)]
+enum Operator {
+    /// =
+    Equal,
+    /// >
+    GreaterThan,
+    /// >=
+    GreaterThanEqual,
+    /// <
+    LessThan,
+    /// <=
+    LessThanEqual,
+}
+
+impl ToCss for Operator {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: fmt::Write,
+    {
+        dest.write_str(match *self {
+            Self::Equal => "=",
+            Self::LessThan => "<",
+            Self::LessThanEqual => "<=",
+            Self::GreaterThan => ">",
+            Self::GreaterThanEqual => ">=",
+        })
+    }
+}
+
+impl Operator {
+    fn is_compatible_with(self, right_op: Self) -> bool {
+        // Some operators are not compatible with each other in multi-range
+        // context.
+        match self {
+            Self::Equal => false,
+            Self::GreaterThan | Self::GreaterThanEqual => {
+                matches!(right_op, Self::GreaterThan | Self::GreaterThanEqual)
+            },
+            Self::LessThan | Self::LessThanEqual => {
+                matches!(right_op, Self::LessThan | Self::LessThanEqual)
+            },
+        }
+    }
+
+    fn evaluate(&self, cmp: Ordering) -> bool {
+        match *self {
+            Self::Equal => cmp == Ordering::Equal,
+            Self::GreaterThan => cmp == Ordering::Greater,
+            Self::GreaterThanEqual => cmp == Ordering::Equal || cmp == Ordering::Greater,
+            Self::LessThan => cmp == Ordering::Less,
+            Self::LessThanEqual => cmp == Ordering::Equal || cmp == Ordering::Less,
+        }
+    }
+
+    fn parse<'i>(input: &mut Parser<'i, '_>) -> Result<Self, ParseError<'i>> {
+        let location = input.current_source_location();
+        let operator = match *input.next()? {
+            Token::Delim('=') => return Ok(Operator::Equal),
+            Token::Delim('>') => Operator::GreaterThan,
+            Token::Delim('<') => Operator::LessThan,
+            ref t => return Err(location.new_unexpected_token_error(t.clone())),
+        };
+
+        // https://drafts.csswg.org/mediaqueries-4/#mq-syntax:
+        //
+        //     No whitespace is allowed between the “<” or “>”
+        //     <delim-token>s and the following “=” <delim-token>, if it’s
+        //     present.
+        //
+        // TODO(emilio): Maybe we should ignore comments as well?
+        // https://github.com/w3c/csswg-drafts/issues/6248
+        let parsed_equal = input
+            .try_parse(|i| {
+                let t = i.next_including_whitespace().map_err(|_| ())?;
+                if !matches!(t, Token::Delim('=')) {
+                    return Err(());
+                }
+                Ok(())
+            })
+            .is_ok();
+
+        if !parsed_equal {
+            return Ok(operator);
+        }
+
+        Ok(match operator {
+            Operator::GreaterThan => Operator::GreaterThanEqual,
+            Operator::LessThan => Operator::LessThanEqual,
+            _ => unreachable!(),
+        })
+    }
+}
+
+#[derive(Clone, Debug, MallocSizeOf, ToShmem, PartialEq)]
+enum QueryFeatureExpressionKind {
+    /// Just the media feature name.
+    Empty,
+
+    /// A single value.
+    Single(QueryExpressionValue),
+
+    /// Legacy range syntax (min-*: value) or so.
+    LegacyRange(LegacyRange, QueryExpressionValue),
+
+    /// Modern range context syntax:
+    /// https://drafts.csswg.org/mediaqueries-5/#mq-range-context
+    Range {
+        left: Option<(Operator, QueryExpressionValue)>,
+        right: Option<(Operator, QueryExpressionValue)>,
+    },
+}
+
+impl QueryFeatureExpressionKind {
+    /// Evaluate a given range given an optional query value and a value from
+    /// the browser.
+    fn evaluate<T>(
+        &self,
+        context_value: T,
+        mut compute: impl FnMut(&QueryExpressionValue) -> T,
+    ) -> bool
+    where
+        T: PartialOrd + Zero,
+    {
+        match *self {
+            Self::Empty => return !context_value.is_zero(),
+            Self::Single(ref value) => {
+                let value = compute(value);
+                let cmp = match context_value.partial_cmp(&value) {
+                    Some(c) => c,
+                    None => return false,
+                };
+                cmp == Ordering::Equal
+            },
+            Self::LegacyRange(ref range, ref value) => {
+                let value = compute(value);
+                let cmp = match context_value.partial_cmp(&value) {
+                    Some(c) => c,
+                    None => return false,
+                };
+                cmp == Ordering::Equal ||
+                    match range {
+                        LegacyRange::Min => cmp == Ordering::Greater,
+                        LegacyRange::Max => cmp == Ordering::Less,
+                    }
+            },
+            Self::Range {
+                ref left,
+                ref right,
+            } => {
+                debug_assert!(left.is_some() || right.is_some());
+                if let Some((ref op, ref value)) = left {
+                    let value = compute(value);
+                    let cmp = match value.partial_cmp(&context_value) {
+                        Some(c) => c,
+                        None => return false,
+                    };
+                    if !op.evaluate(cmp) {
+                        return false;
+                    }
+                }
+                if let Some((ref op, ref value)) = right {
+                    let value = compute(value);
+                    let cmp = match context_value.partial_cmp(&value) {
+                        Some(c) => c,
+                        None => return false,
+                    };
+                    if !op.evaluate(cmp) {
+                        return false;
+                    }
+                }
+                true
+            },
+        }
+    }
+
+    /// Non-ranged features only need to compare to one value at most.
+    fn non_ranged_value(&self) -> Option<&QueryExpressionValue> {
+        match *self {
+            Self::Empty => None,
+            Self::Single(ref v) => Some(v),
+            Self::LegacyRange(..) | Self::Range { .. } => {
+                debug_assert!(false, "Unexpected ranged value in non-ranged feature!");
+                None
+            },
+        }
+    }
+}
+
+/// A feature expression contains a reference to the feature, the value the
+/// query contained, and the range to evaluate.
+#[derive(Clone, Debug, MallocSizeOf, ToShmem, PartialEq)]
+pub struct QueryFeatureExpression {
+    feature_type: FeatureType,
+    feature_index: usize,
+    kind: QueryFeatureExpressionKind,
+}
+
+impl ToCss for QueryFeatureExpression {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: fmt::Write,
+    {
+        dest.write_str("(")?;
+
+        match self.kind {
+            QueryFeatureExpressionKind::Empty => self.write_name(dest)?,
+            QueryFeatureExpressionKind::Single(ref v) |
+            QueryFeatureExpressionKind::LegacyRange(_, ref v) => {
+                self.write_name(dest)?;
+                dest.write_str(": ")?;
+                v.to_css(dest, self)?;
+            },
+            QueryFeatureExpressionKind::Range {
+                ref left,
+                ref right,
+            } => {
+                if let Some((ref op, ref val)) = left {
+                    val.to_css(dest, self)?;
+                    dest.write_char(' ')?;
+                    op.to_css(dest)?;
+                    dest.write_char(' ')?;
+                }
+                self.write_name(dest)?;
+                if let Some((ref op, ref val)) = right {
+                    dest.write_char(' ')?;
+                    op.to_css(dest)?;
+                    dest.write_char(' ')?;
+                    val.to_css(dest, self)?;
+                }
+            },
+        }
+        dest.write_char(')')
+    }
+}
+
+fn consume_operation_or_colon<'i>(
+    input: &mut Parser<'i, '_>,
+) -> Result<Option<Operator>, ParseError<'i>> {
+    if input.try_parse(|input| input.expect_colon()).is_ok() {
+        return Ok(None);
+    }
+    Operator::parse(input).map(|op| Some(op))
+}
+
+#[allow(unused_variables)]
+fn disabled_by_pref(feature: &Atom, context: &ParserContext) -> bool {
+    #[cfg(feature = "gecko")]
+    {
+        if *feature == atom!("forced-colors") {
+            // forced-colors is always enabled in the ua and chrome. On
+            // the web it is hidden behind a preference, which is defaulted
+            // to 'true' as of bug 1659511.
+            return !context.in_ua_or_chrome_sheet() &&
+                !static_prefs::pref!("layout.css.forced-colors.enabled");
+        }
+        // prefers-contrast is always enabled in the ua and chrome. On
+        // the web it is hidden behind a preference.
+        if *feature == atom!("prefers-contrast") {
+            return !context.in_ua_or_chrome_sheet() &&
+                !static_prefs::pref!("layout.css.prefers-contrast.enabled");
+        }
+    }
+    false
+}
+
+impl QueryFeatureExpression {
+    fn new(
+        feature_type: FeatureType,
+        feature_index: usize,
+        kind: QueryFeatureExpressionKind,
+    ) -> Self {
+        debug_assert!(feature_index < feature_type.features().len());
+        Self {
+            feature_type,
+            feature_index,
+            kind,
+        }
+    }
+
+    fn write_name<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: fmt::Write,
+    {
+        let feature = self.feature();
+        if feature.flags.contains(FeatureFlags::WEBKIT_PREFIX) {
+            dest.write_str("-webkit-")?;
+        }
+
+        if let QueryFeatureExpressionKind::LegacyRange(range, _) = self.kind {
+            match range {
+                LegacyRange::Min => dest.write_str("min-")?,
+                LegacyRange::Max => dest.write_str("max-")?,
+            }
+        }
+
+        // NB: CssStringWriter not needed, feature names are under control.
+        write!(dest, "{}", feature.name)?;
+
+        Ok(())
+    }
+
+    fn feature(&self) -> &'static QueryFeatureDescription {
+        &self.feature_type.features()[self.feature_index]
+    }
+
+    /// Returns the feature flags for our feature.
+    pub fn feature_flags(&self) -> FeatureFlags {
+        self.feature().flags
+    }
+
+    /// Parse a feature expression of the form:
+    ///
+    /// ```
+    /// (media-feature: media-value)
+    /// ```
+    pub fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+        feature_type: FeatureType,
+    ) -> Result<Self, ParseError<'i>> {
+        input.expect_parenthesis_block()?;
+        input.parse_nested_block(|input| {
+            Self::parse_in_parenthesis_block(context, input, feature_type)
+        })
+    }
+
+    fn parse_feature_name<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+        feature_type: FeatureType,
+    ) -> Result<(usize, Option<LegacyRange>), ParseError<'i>> {
+        let mut flags = FeatureFlags::empty();
+        let location = input.current_source_location();
+        let ident = input.expect_ident()?;
+
+        if context.in_ua_or_chrome_sheet() {
+            flags.insert(FeatureFlags::CHROME_AND_UA_ONLY);
+        }
+
+        let mut feature_name = &**ident;
+        if starts_with_ignore_ascii_case(feature_name, "-webkit-") {
+            feature_name = &feature_name[8..];
+            flags.insert(FeatureFlags::WEBKIT_PREFIX);
+        }
+
+        let range = if starts_with_ignore_ascii_case(feature_name, "min-") {
+            feature_name = &feature_name[4..];
+            Some(LegacyRange::Min)
+        } else if starts_with_ignore_ascii_case(feature_name, "max-") {
+            feature_name = &feature_name[4..];
+            Some(LegacyRange::Max)
+        } else {
+            None
+        };
+
+        let atom = Atom::from(string_as_ascii_lowercase(feature_name));
+        let (feature_index, feature) = match feature_type.find_feature(&atom) {
+            Some((i, f)) => (i, f),
+            None => {
+                return Err(location.new_custom_error(
+                    StyleParseErrorKind::MediaQueryExpectedFeatureName(ident.clone()),
+                ))
+            },
+        };
+
+        if disabled_by_pref(&feature.name, context) ||
+            !flags.contains(feature.flags.parsing_requirements()) ||
+            (range.is_some() && !feature.allows_ranges())
+        {
+            return Err(location.new_custom_error(
+                StyleParseErrorKind::MediaQueryExpectedFeatureName(ident.clone()),
+            ));
+        }
+
+        Ok((feature_index, range))
+    }
+
+    /// Parses the following range syntax:
+    ///
+    ///   (feature-value <operator> feature-name)
+    ///   (feature-value <operator> feature-name <operator> feature-value)
+    fn parse_multi_range_syntax<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+        feature_type: FeatureType,
+    ) -> Result<Self, ParseError<'i>> {
+        let start = input.state();
+
+        // To parse the values, we first need to find the feature name. We rely
+        // on feature values for ranged features not being able to be top-level
+        // <ident>s, which holds.
+        let feature_index = loop {
+            // NOTE: parse_feature_name advances the input.
+            if let Ok((index, range)) = Self::parse_feature_name(context, input, feature_type) {
+                if range.is_some() {
+                    // Ranged names are not allowed here.
+                    return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
+                }
+                break index;
+            }
+            if input.is_exhausted() {
+                return Err(start
+                    .source_location()
+                    .new_custom_error(StyleParseErrorKind::UnspecifiedError));
+            }
+        };
+
+        input.reset(&start);
+
+        let feature = &feature_type.features()[feature_index];
+        let left_val = QueryExpressionValue::parse(feature, context, input)?;
+        let left_op = Operator::parse(input)?;
+
+        {
+            let (parsed_index, _) = Self::parse_feature_name(context, input, feature_type)?;
+            debug_assert_eq!(
+                parsed_index, feature_index,
+                "How did we find a different feature?"
+            );
+        }
+
+        let right_op = input.try_parse(Operator::parse).ok();
+        let right = match right_op {
+            Some(op) => {
+                if !left_op.is_compatible_with(op) {
+                    return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
+                }
+                Some((op, QueryExpressionValue::parse(feature, context, input)?))
+            },
+            None => None,
+        };
+        Ok(Self::new(
+            feature_type,
+            feature_index,
+            QueryFeatureExpressionKind::Range {
+                left: Some((left_op, left_val)),
+                right,
+            },
+        ))
+    }
+
+    /// Parse a feature expression where we've already consumed the parenthesis.
+    pub fn parse_in_parenthesis_block<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+        feature_type: FeatureType,
+    ) -> Result<Self, ParseError<'i>> {
+        let (feature_index, range) =
+            match input.try_parse(|input| Self::parse_feature_name(context, input, feature_type)) {
+                Ok(v) => v,
+                Err(e) => {
+                    if let Ok(expr) = Self::parse_multi_range_syntax(context, input, feature_type) {
+                        return Ok(expr);
+                    }
+                    return Err(e);
+                },
+            };
+        let operator = input.try_parse(consume_operation_or_colon);
+        let operator = match operator {
+            Err(..) => {
+                // If there's no colon, this is a query of the form
+                // '(<feature>)', that is, there's no value specified.
+                //
+                // Gecko doesn't allow ranged expressions without a
+                // value, so just reject them here too.
+                if range.is_some() {
+                    return Err(
+                        input.new_custom_error(StyleParseErrorKind::RangedExpressionWithNoValue)
+                    );
+                }
+
+                return Ok(Self::new(
+                    feature_type,
+                    feature_index,
+                    QueryFeatureExpressionKind::Empty,
+                ));
+            },
+            Ok(operator) => operator,
+        };
+
+        let feature = &feature_type.features()[feature_index];
+
+        let value = QueryExpressionValue::parse(feature, context, input).map_err(|err| {
+            err.location
+                .new_custom_error(StyleParseErrorKind::MediaQueryExpectedFeatureValue)
+        })?;
+
+        let kind = match range {
+            Some(range) => {
+                if operator.is_some() {
+                    return Err(
+                        input.new_custom_error(StyleParseErrorKind::MediaQueryUnexpectedOperator)
+                    );
+                }
+                QueryFeatureExpressionKind::LegacyRange(range, value)
+            },
+            None => match operator {
+                Some(operator) => {
+                    if !feature.allows_ranges() {
+                        return Err(input
+                            .new_custom_error(StyleParseErrorKind::MediaQueryUnexpectedOperator));
+                    }
+                    QueryFeatureExpressionKind::Range {
+                        left: None,
+                        right: Some((operator, value)),
+                    }
+                },
+                None => QueryFeatureExpressionKind::Single(value),
+            },
+        };
+
+        Ok(Self::new(feature_type, feature_index, kind))
+    }
+
+    /// Returns whether this query evaluates to true for the given device.
+    pub fn matches(&self, context: &computed::Context) -> KleeneValue {
+        macro_rules! expect {
+            ($variant:ident, $v:expr) => {
+                match *$v {
+                    QueryExpressionValue::$variant(ref v) => v,
+                    _ => unreachable!("Unexpected QueryExpressionValue"),
+                }
+            };
+        }
+
+        KleeneValue::from(match self.feature().evaluator {
+            Evaluator::Length(eval) => {
+                let v = eval(context);
+                self.kind
+                    .evaluate(v, |v| expect!(Length, v).to_computed_value(context))
+            },
+            Evaluator::OptionalLength(eval) => {
+                let v = match eval(context) {
+                    Some(v) => v,
+                    None => return KleeneValue::Unknown,
+                };
+                self.kind
+                    .evaluate(v, |v| expect!(Length, v).to_computed_value(context))
+            },
+            Evaluator::Integer(eval) => {
+                let v = eval(context);
+                self.kind.evaluate(v, |v| *expect!(Integer, v))
+            },
+            Evaluator::Float(eval) => {
+                let v = eval(context);
+                self.kind.evaluate(v, |v| *expect!(Float, v))
+            },
+            Evaluator::NumberRatio(eval) => {
+                let ratio = eval(context);
+                // A ratio of 0/0 behaves as the ratio 1/0, so we need to call used_value()
+                // to convert it if necessary.
+                // FIXME: we may need to update here once
+                // https://github.com/w3c/csswg-drafts/issues/4954 got resolved.
+                self.kind
+                    .evaluate(ratio, |v| expect!(NumberRatio, v).used_value())
+            },
+            Evaluator::OptionalNumberRatio(eval) => {
+                let ratio = match eval(context) {
+                    Some(v) => v,
+                    None => return KleeneValue::Unknown,
+                };
+                // See above for subtleties here.
+                self.kind
+                    .evaluate(ratio, |v| expect!(NumberRatio, v).used_value())
+            },
+            Evaluator::Resolution(eval) => {
+                let v = eval(context).dppx();
+                self.kind.evaluate(v, |v| {
+                    expect!(Resolution, v).to_computed_value(context).dppx()
+                })
+            },
+            Evaluator::Enumerated { evaluator, .. } => {
+                let computed = self
+                    .kind
+                    .non_ranged_value()
+                    .map(|v| *expect!(Enumerated, v));
+                return evaluator(context, computed)
+            },
+            Evaluator::BoolInteger(eval) => {
+                let computed = self
+                    .kind
+                    .non_ranged_value()
+                    .map(|v| *expect!(BoolInteger, v));
+                let boolean = eval(context);
+                computed.map_or(boolean, |v| v == boolean)
+            },
+        })
+    }
+}
+
+/// A value found or expected in a expression.
+///
+/// FIXME(emilio): How should calc() serialize in the Number / Integer /
+/// BoolInteger / NumberRatio case, as computed or as specified value?
+///
+/// If the first, this would need to store the relevant values.
+///
+/// See: https://github.com/w3c/csswg-drafts/issues/1968
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToShmem)]
+pub enum QueryExpressionValue {
+    /// A length.
+    Length(Length),
+    /// A (non-negative) integer.
+    Integer(u32),
+    /// A floating point value.
+    Float(CSSFloat),
+    /// A boolean value, specified as an integer (i.e., either 0 or 1).
+    BoolInteger(bool),
+    /// A single non-negative number or two non-negative numbers separated by '/',
+    /// with optional whitespace on either side of the '/'.
+    NumberRatio(Ratio),
+    /// A resolution.
+    Resolution(Resolution),
+    /// An enumerated value, defined by the variant keyword table in the
+    /// feature's `mData` member.
+    Enumerated(KeywordDiscriminant),
+}
+
+impl QueryExpressionValue {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>, for_expr: &QueryFeatureExpression) -> fmt::Result
+    where
+        W: fmt::Write,
+    {
+        match *self {
+            QueryExpressionValue::Length(ref l) => l.to_css(dest),
+            QueryExpressionValue::Integer(v) => v.to_css(dest),
+            QueryExpressionValue::Float(v) => v.to_css(dest),
+            QueryExpressionValue::BoolInteger(v) => dest.write_str(if v { "1" } else { "0" }),
+            QueryExpressionValue::NumberRatio(ratio) => ratio.to_css(dest),
+            QueryExpressionValue::Resolution(ref r) => r.to_css(dest),
+            QueryExpressionValue::Enumerated(value) => match for_expr.feature().evaluator {
+                Evaluator::Enumerated { serializer, .. } => dest.write_str(&*serializer(value)),
+                _ => unreachable!(),
+            },
+        }
+    }
+
+    fn parse<'i, 't>(
+        for_feature: &QueryFeatureDescription,
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<QueryExpressionValue, ParseError<'i>> {
+        Ok(match for_feature.evaluator {
+            Evaluator::OptionalLength(..) | Evaluator::Length(..) => {
+                let length = Length::parse_non_negative(context, input)?;
+                QueryExpressionValue::Length(length)
+            },
+            Evaluator::Integer(..) => {
+                let integer = Integer::parse_non_negative(context, input)?;
+                QueryExpressionValue::Integer(integer.value() as u32)
+            },
+            Evaluator::BoolInteger(..) => {
+                let integer = Integer::parse_non_negative(context, input)?;
+                let value = integer.value();
+                if value > 1 {
+                    return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
+                }
+                QueryExpressionValue::BoolInteger(value == 1)
+            },
+            Evaluator::Float(..) => {
+                let number = Number::parse(context, input)?;
+                QueryExpressionValue::Float(number.get())
+            },
+            Evaluator::OptionalNumberRatio(..) | Evaluator::NumberRatio(..) => {
+                use crate::values::specified::Ratio as SpecifiedRatio;
+                let ratio = SpecifiedRatio::parse(context, input)?;
+                QueryExpressionValue::NumberRatio(Ratio::new(ratio.0.get(), ratio.1.get()))
+            },
+            Evaluator::Resolution(..) => {
+                QueryExpressionValue::Resolution(Resolution::parse(context, input)?)
+            },
+            Evaluator::Enumerated { parser, .. } => {
+                QueryExpressionValue::Enumerated(parser(context, input)?)
+            },
+        })
+    }
+}