firefox/servo/components/style/stylesheets/supports_rule.rs

/* 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/. */

//! [@supports rules](https://drafts.csswg.org/css-conditional-3/#at-supports)

use crate::font_face::{FontFaceSourceFormatKeyword, FontFaceSourceTechFlags};
use crate::parser::ParserContext;
use crate::properties::{PropertyDeclaration, PropertyId, SourcePropertyDeclaration};
use crate::selector_parser::{SelectorImpl, SelectorParser};
use crate::shared_lock::{DeepCloneWithLock, Locked};
use crate::shared_lock::{SharedRwLock, SharedRwLockReadGuard, ToCssWithGuard};
use crate::str::CssStringWriter;
use crate::stylesheets::{CssRuleType, CssRules};
use cssparser::parse_important;
use cssparser::{Delimiter, Parser, SourceLocation, Token};
use cssparser::{ParseError as CssParseError, ParserInput};
#[cfg(feature = "gecko")]
use malloc_size_of::{MallocSizeOfOps, MallocUnconditionalShallowSizeOf};
use selectors::parser::{Selector, SelectorParseErrorKind};
use servo_arc::Arc;
use std::fmt::{self, Write};
use std::str;
use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};

/// An [`@supports`][supports] rule.
///
/// [supports]: https://drafts.csswg.org/css-conditional-3/#at-supports
#[derive(Debug, ToShmem)]
pub struct SupportsRule {
    /// The parsed condition
    pub condition: SupportsCondition,
    /// Child rules
    pub rules: Arc<Locked<CssRules>>,
    /// The result of evaluating the condition
    pub enabled: bool,
    /// The line and column of the rule's source code.
    pub source_location: SourceLocation,
}

impl SupportsRule {
    /// Measure heap usage.
    #[cfg(feature = "gecko")]
    pub fn size_of(&self, guard: &SharedRwLockReadGuard, ops: &mut MallocSizeOfOps) -> usize {
        // Measurement of other fields may be added later.
        self.rules.unconditional_shallow_size_of(ops) +
            self.rules.read_with(guard).size_of(guard, ops)
    }
}

impl ToCssWithGuard for SupportsRule {
    fn to_css(&self, guard: &SharedRwLockReadGuard, dest: &mut CssStringWriter) -> fmt::Result {
        dest.write_str("@supports ")?;
        self.condition.to_css(&mut CssWriter::new(dest))?;
        self.rules.read_with(guard).to_css_block(guard, dest)
    }
}

impl DeepCloneWithLock for SupportsRule {
    fn deep_clone_with_lock(
        &self,
        lock: &SharedRwLock,
        guard: &SharedRwLockReadGuard,
    ) -> Self {
        let rules = self.rules.read_with(guard);
        SupportsRule {
            condition: self.condition.clone(),
            rules: Arc::new(lock.wrap(rules.deep_clone_with_lock(lock, guard))),
            enabled: self.enabled,
            source_location: self.source_location.clone(),
        }
    }
}

/// An @supports condition
///
/// <https://drafts.csswg.org/css-conditional-3/#at-supports>
#[derive(Clone, Debug, ToShmem)]
pub enum SupportsCondition {
    /// `not (condition)`
    Not(Box<SupportsCondition>),
    /// `(condition)`
    Parenthesized(Box<SupportsCondition>),
    /// `(condition) and (condition) and (condition) ..`
    And(Vec<SupportsCondition>),
    /// `(condition) or (condition) or (condition) ..`
    Or(Vec<SupportsCondition>),
    /// `property-ident: value` (value can be any tokens)
    Declaration(Declaration),
    /// A `selector()` function.
    Selector(RawSelector),
    /// `font-format(<font-format>)`
    FontFormat(FontFaceSourceFormatKeyword),
    /// `font-tech(<font-tech>)`
    FontTech(FontFaceSourceTechFlags),
    /// `(any tokens)` or `func(any tokens)`
    FutureSyntax(String),
}

impl SupportsCondition {
    /// Parse a condition
    ///
    /// <https://drafts.csswg.org/css-conditional/#supports_condition>
    pub fn parse<'i, 't>(input: &mut Parser<'i, 't>) -> Result<Self, ParseError<'i>> {
        if input.try_parse(|i| i.expect_ident_matching("not")).is_ok() {
            let inner = SupportsCondition::parse_in_parens(input)?;
            return Ok(SupportsCondition::Not(Box::new(inner)));
        }

        let in_parens = SupportsCondition::parse_in_parens(input)?;

        let location = input.current_source_location();
        let (keyword, wrapper) = match input.next() {
            // End of input
            Err(..) => return Ok(in_parens),
            Ok(&Token::Ident(ref ident)) => {
                match_ignore_ascii_case! { &ident,
                    "and" => ("and", SupportsCondition::And as fn(_) -> _),
                    "or" => ("or", SupportsCondition::Or as fn(_) -> _),
                    _ => return Err(location.new_custom_error(SelectorParseErrorKind::UnexpectedIdent(ident.clone())))
                }
            },
            Ok(t) => return Err(location.new_unexpected_token_error(t.clone())),
        };

        let mut conditions = Vec::with_capacity(2);
        conditions.push(in_parens);
        loop {
            conditions.push(SupportsCondition::parse_in_parens(input)?);
            if input
                .try_parse(|input| input.expect_ident_matching(keyword))
                .is_err()
            {
                // Did not find the expected keyword.
                // If we found some other token, it will be rejected by
                // `Parser::parse_entirely` somewhere up the stack.
                return Ok(wrapper(conditions));
            }
        }
    }

    /// Parses a functional supports condition.
    fn parse_functional<'i, 't>(
        function: &str,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self, ParseError<'i>> {
        match_ignore_ascii_case! { function,
            "selector" => {
                let pos = input.position();
                consume_any_value(input)?;
                Ok(SupportsCondition::Selector(RawSelector(
                    input.slice_from(pos).to_owned()
                )))
            },
            "font-format" if static_prefs::pref!("layout.css.font-tech.enabled") => {
                let kw = FontFaceSourceFormatKeyword::parse(input)?;
                Ok(SupportsCondition::FontFormat(kw))
            },
            "font-tech" if static_prefs::pref!("layout.css.font-tech.enabled") => {
                let flag = FontFaceSourceTechFlags::parse_one(input)?;
                Ok(SupportsCondition::FontTech(flag))
            },
            _ => {
                Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError))
            },
        }
    }

    /// Parses an `@import` condition as per
    /// https://drafts.csswg.org/css-cascade-5/#typedef-import-conditions
    pub fn parse_for_import<'i, 't>(input: &mut Parser<'i, 't>) -> Result<Self, ParseError<'i>> {
        input.expect_function_matching("supports")?;
        input.parse_nested_block(parse_condition_or_declaration)
    }

    /// <https://drafts.csswg.org/css-conditional-3/#supports_condition_in_parens>
    fn parse_in_parens<'i, 't>(input: &mut Parser<'i, 't>) -> Result<Self, ParseError<'i>> {
        // Whitespace is normally taken care of in `Parser::next`, but we want to not include it in
        // `pos` for the SupportsCondition::FutureSyntax cases.
        input.skip_whitespace();
        let pos = input.position();
        let location = input.current_source_location();
        match *input.next()? {
            Token::ParenthesisBlock => {
                let nested = input
                    .try_parse(|input| input.parse_nested_block(parse_condition_or_declaration));
                if let Ok(nested) = nested {
                    return Ok(Self::Parenthesized(Box::new(nested)));
                }
            },
            Token::Function(ref ident) => {
                let ident = ident.clone();
                let nested = input.try_parse(|input| {
                    input.parse_nested_block(|input| {
                        SupportsCondition::parse_functional(&ident, input)
                    })
                });
                if nested.is_ok() {
                    return nested;
                }
            },
            ref t => return Err(location.new_unexpected_token_error(t.clone())),
        }
        input.parse_nested_block(consume_any_value)?;
        Ok(SupportsCondition::FutureSyntax(
            input.slice_from(pos).to_owned(),
        ))
    }

    /// Evaluate a supports condition
    pub fn eval(&self, cx: &ParserContext) -> bool {
        match *self {
            SupportsCondition::Not(ref cond) => !cond.eval(cx),
            SupportsCondition::Parenthesized(ref cond) => cond.eval(cx),
            SupportsCondition::And(ref vec) => vec.iter().all(|c| c.eval(cx)),
            SupportsCondition::Or(ref vec) => vec.iter().any(|c| c.eval(cx)),
            SupportsCondition::Declaration(ref decl) => decl.eval(cx),
            SupportsCondition::Selector(ref selector) => selector.eval(cx),
            SupportsCondition::FontFormat(ref format) => eval_font_format(format),
            SupportsCondition::FontTech(ref tech) => eval_font_tech(tech),
            SupportsCondition::FutureSyntax(_) => false,
        }
    }
}

#[cfg(feature = "gecko")]
fn eval_font_format(kw: &FontFaceSourceFormatKeyword) -> bool {
    use crate::gecko_bindings::bindings;
    unsafe { bindings::Gecko_IsFontFormatSupported(*kw) }
}

#[cfg(feature = "gecko")]
fn eval_font_tech(flag: &FontFaceSourceTechFlags) -> bool {
    use crate::gecko_bindings::bindings;
    unsafe { bindings::Gecko_IsFontTechSupported(*flag) }
}

#[cfg(feature = "servo")]
fn eval_font_format(_: &FontFaceSourceFormatKeyword) -> bool {
    false
}

#[cfg(feature = "servo")]
fn eval_font_tech(_: &FontFaceSourceTechFlags) -> bool {
    false
}

/// supports_condition | declaration
/// <https://drafts.csswg.org/css-conditional/#dom-css-supports-conditiontext-conditiontext>
pub fn parse_condition_or_declaration<'i, 't>(
    input: &mut Parser<'i, 't>,
) -> Result<SupportsCondition, ParseError<'i>> {
    if let Ok(condition) = input.try_parse(SupportsCondition::parse) {
        Ok(condition)
    } else {
        Declaration::parse(input).map(SupportsCondition::Declaration)
    }
}

impl ToCss for SupportsCondition {
    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
    where
        W: Write,
    {
        match *self {
            SupportsCondition::Not(ref cond) => {
                dest.write_str("not ")?;
                cond.to_css(dest)
            },
            SupportsCondition::Parenthesized(ref cond) => {
                dest.write_char('(')?;
                cond.to_css(dest)?;
                dest.write_char(')')
            },
            SupportsCondition::And(ref vec) => {
                let mut first = true;
                for cond in vec {
                    if !first {
                        dest.write_str(" and ")?;
                    }
                    first = false;
                    cond.to_css(dest)?;
                }
                Ok(())
            },
            SupportsCondition::Or(ref vec) => {
                let mut first = true;
                for cond in vec {
                    if !first {
                        dest.write_str(" or ")?;
                    }
                    first = false;
                    cond.to_css(dest)?;
                }
                Ok(())
            },
            SupportsCondition::Declaration(ref decl) => decl.to_css(dest),
            SupportsCondition::Selector(ref selector) => {
                dest.write_str("selector(")?;
                selector.to_css(dest)?;
                dest.write_char(')')
            },
            SupportsCondition::FontFormat(ref kw) => {
                dest.write_str("font-format(")?;
                kw.to_css(dest)?;
                dest.write_char(')')
            },
            SupportsCondition::FontTech(ref flag) => {
                dest.write_str("font-tech(")?;
                flag.to_css(dest)?;
                dest.write_char(')')
            },
            SupportsCondition::FutureSyntax(ref s) => dest.write_str(&s),
        }
    }
}

#[derive(Clone, Debug, ToShmem)]
/// A possibly-invalid CSS selector.
pub struct RawSelector(pub String);

impl ToCss for RawSelector {
    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
    where
        W: Write,
    {
        dest.write_str(&self.0)
    }
}

impl RawSelector {
    /// Tries to evaluate a `selector()` function.
    pub fn eval(&self, context: &ParserContext) -> bool {
        let mut input = ParserInput::new(&self.0);
        let mut input = Parser::new(&mut input);
        input
            .parse_entirely(|input| -> Result<(), CssParseError<()>> {
                let parser = SelectorParser {
                    namespaces: &context.namespaces,
                    stylesheet_origin: context.stylesheet_origin,
                    url_data: context.url_data,
                    for_supports_rule: true,
                };

                Selector::<SelectorImpl>::parse(&parser, input)
                    .map_err(|_| input.new_custom_error(()))?;

                Ok(())
            })
            .is_ok()
    }
}

#[derive(Clone, Debug, ToShmem)]
/// A possibly-invalid property declaration
pub struct Declaration(pub String);

impl ToCss for Declaration {
    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
    where
        W: Write,
    {
        dest.write_str(&self.0)
    }
}

/// <https://drafts.csswg.org/css-syntax-3/#typedef-any-value>
fn consume_any_value<'i, 't>(input: &mut Parser<'i, 't>) -> Result<(), ParseError<'i>> {
    input.expect_no_error_token().map_err(|err| err.into())
}

impl Declaration {
    /// Parse a declaration
    pub fn parse<'i, 't>(input: &mut Parser<'i, 't>) -> Result<Declaration, ParseError<'i>> {
        let pos = input.position();
        input.expect_ident()?;
        input.expect_colon()?;
        consume_any_value(input)?;
        Ok(Declaration(input.slice_from(pos).to_owned()))
    }

    /// Determine if a declaration parses
    ///
    /// <https://drafts.csswg.org/css-conditional-3/#support-definition>
    pub fn eval(&self, context: &ParserContext) -> bool {
        debug_assert!(context.rule_types().contains(CssRuleType::Style));

        let mut input = ParserInput::new(&self.0);
        let mut input = Parser::new(&mut input);
        input
            .parse_entirely(|input| -> Result<(), CssParseError<()>> {
                let prop = input.expect_ident_cloned().unwrap();
                input.expect_colon().unwrap();

                let id =
                    PropertyId::parse(&prop, context).map_err(|_| input.new_custom_error(()))?;

                let mut declarations = SourcePropertyDeclaration::default();
                input.parse_until_before(Delimiter::Bang, |input| {
                    PropertyDeclaration::parse_into(&mut declarations, id, &context, input)
                        .map_err(|_| input.new_custom_error(()))
                })?;
                let _ = input.try_parse(parse_important);
                Ok(())
            })
            .is_ok()
    }
}