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/* 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
//! Support for [custom properties for cascading variables][custom].
//!
use crate::applicable_declarations::CascadePriority;
use crate::media_queries::Device;
use crate::properties::{CSSWideKeyword, CustomDeclaration, CustomDeclarationValue};
use crate::selector_map::{PrecomputedHashMap, PrecomputedHashSet, PrecomputedHasher};
use crate::Atom;
use cssparser::{
CowRcStr, Delimiter, Parser, ParserInput, SourcePosition, Token, TokenSerializationType,
};
use indexmap::IndexMap;
use selectors::parser::SelectorParseErrorKind;
use servo_arc::Arc;
use smallvec::SmallVec;
use std::borrow::Cow;
use std::cmp;
use std::collections::hash_map::Entry;
use std::fmt::{self, Write};
use std::hash::BuildHasherDefault;
use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};
/// The environment from which to get `env` function values.
///
/// TODO(emilio): If this becomes a bit more complex we should probably move it
/// to the `media_queries` module, or something.
#[derive(Debug, MallocSizeOf)]
pub struct CssEnvironment;
type EnvironmentEvaluator = fn(device: &Device) -> VariableValue;
struct EnvironmentVariable {
name: Atom,
evaluator: EnvironmentEvaluator,
}
macro_rules! make_variable {
($name:expr, $evaluator:expr) => {{
EnvironmentVariable {
name: $name,
evaluator: $evaluator,
}
}};
}
fn get_safearea_inset_top(device: &Device) -> VariableValue {
VariableValue::pixels(device.safe_area_insets().top)
}
fn get_safearea_inset_bottom(device: &Device) -> VariableValue {
VariableValue::pixels(device.safe_area_insets().bottom)
}
fn get_safearea_inset_left(device: &Device) -> VariableValue {
VariableValue::pixels(device.safe_area_insets().left)
}
fn get_safearea_inset_right(device: &Device) -> VariableValue {
VariableValue::pixels(device.safe_area_insets().right)
}
fn get_content_preferred_color_scheme(device: &Device) -> VariableValue {
use crate::gecko::media_features::PrefersColorScheme;
let prefers_color_scheme = unsafe {
crate::gecko_bindings::bindings::Gecko_MediaFeatures_PrefersColorScheme(
device.document(),
/* use_content = */ true,
)
};
VariableValue::ident(match prefers_color_scheme {
PrefersColorScheme::Light => "light",
PrefersColorScheme::Dark => "dark",
})
}
fn get_scrollbar_inline_size(device: &Device) -> VariableValue {
VariableValue::pixels(device.scrollbar_inline_size().px())
}
static ENVIRONMENT_VARIABLES: [EnvironmentVariable; 4] = [
make_variable!(atom!("safe-area-inset-top"), get_safearea_inset_top),
make_variable!(atom!("safe-area-inset-bottom"), get_safearea_inset_bottom),
make_variable!(atom!("safe-area-inset-left"), get_safearea_inset_left),
make_variable!(atom!("safe-area-inset-right"), get_safearea_inset_right),
];
macro_rules! lnf_int {
($id:ident) => {
unsafe {
crate::gecko_bindings::bindings::Gecko_GetLookAndFeelInt(
crate::gecko_bindings::bindings::LookAndFeel_IntID::$id as i32,
)
}
};
}
macro_rules! lnf_int_variable {
($atom:expr, $id:ident, $ctor:ident) => {{
fn __eval(_: &Device) -> VariableValue {
VariableValue::$ctor(lnf_int!($id))
}
make_variable!($atom, __eval)
}};
}
static CHROME_ENVIRONMENT_VARIABLES: [EnvironmentVariable; 7] = [
lnf_int_variable!(
atom!("-moz-gtk-csd-titlebar-radius"),
TitlebarRadius,
int_pixels
),
lnf_int_variable!(atom!("-moz-gtk-csd-menu-radius"), GtkMenuRadius, int_pixels),
lnf_int_variable!(
atom!("-moz-gtk-csd-close-button-position"),
GTKCSDCloseButtonPosition,
integer
),
lnf_int_variable!(
atom!("-moz-gtk-csd-minimize-button-position"),
GTKCSDMinimizeButtonPosition,
integer
),
lnf_int_variable!(
atom!("-moz-gtk-csd-maximize-button-position"),
GTKCSDMaximizeButtonPosition,
integer
),
make_variable!(
atom!("-moz-content-preferred-color-scheme"),
get_content_preferred_color_scheme
),
make_variable!(
atom!("scrollbar-inline-size"),
get_scrollbar_inline_size
),
];
impl CssEnvironment {
#[inline]
fn get(&self, name: &Atom, device: &Device) -> Option<VariableValue> {
if let Some(var) = ENVIRONMENT_VARIABLES.iter().find(|var| var.name == *name) {
return Some((var.evaluator)(device));
}
if !device.chrome_rules_enabled_for_document() {
return None;
}
let var = CHROME_ENVIRONMENT_VARIABLES
.iter()
.find(|var| var.name == *name)?;
Some((var.evaluator)(device))
}
}
/// A custom property name is just an `Atom`.
///
/// Note that this does not include the `--` prefix
pub type Name = Atom;
/// Parse a custom property name.
///
pub fn parse_name(s: &str) -> Result<&str, ()> {
if s.starts_with("--") && s.len() > 2 {
Ok(&s[2..])
} else {
Err(())
}
}
/// A value for a custom property is just a set of tokens.
///
/// We preserve the original CSS for serialization, and also the variable
/// references to other custom property names.
#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToShmem)]
pub struct VariableValue {
css: String,
first_token_type: TokenSerializationType,
last_token_type: TokenSerializationType,
/// Whether a variable value has a reference to an environment variable.
///
/// If this is the case, we need to perform variable substitution on the
/// value.
references_environment: bool,
/// Custom property names in var() functions.
references: Box<[Name]>,
}
impl ToCss for SpecifiedValue {
fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
where
W: Write,
{
dest.write_str(&self.css)
}
}
/// A map from CSS variable names to CSS variable computed values, used for
/// resolving.
///
/// A consistent ordering is required for CSSDeclaration objects in the
/// DOM. CSSDeclarations expose property names as indexed properties, which
/// need to be stable. So we keep an array of property names which order is
/// determined on the order that they are added to the name-value map.
///
/// The variable values are guaranteed to not have references to other
/// properties.
pub type CustomPropertiesMap =
IndexMap<Name, Arc<VariableValue>, BuildHasherDefault<PrecomputedHasher>>;
/// Both specified and computed values are VariableValues, the difference is
/// whether var() functions are expanded.
pub type SpecifiedValue = VariableValue;
/// Both specified and computed values are VariableValues, the difference is
/// whether var() functions are expanded.
pub type ComputedValue = VariableValue;
/// A struct holding information about the external references to that a custom
/// property value may have.
#[derive(Default)]
struct VarOrEnvReferences {
custom_property_references: PrecomputedHashSet<Name>,
references_environment: bool,
}
impl VariableValue {
fn empty() -> Self {
Self {
css: String::new(),
last_token_type: TokenSerializationType::nothing(),
first_token_type: TokenSerializationType::nothing(),
references: Default::default(),
references_environment: false,
}
}
fn push<'i>(
&mut self,
input: &Parser<'i, '_>,
css: &str,
css_first_token_type: TokenSerializationType,
css_last_token_type: TokenSerializationType,
) -> Result<(), ParseError<'i>> {
/// Prevent values from getting terribly big since you can use custom
/// properties exponentially.
///
/// This number (2MB) is somewhat arbitrary, but silly enough that no
/// reasonable page should hit it. We could limit by number of total
/// substitutions, but that was very easy to work around in practice
/// (just choose a larger initial value and boom).
const MAX_VALUE_LENGTH_IN_BYTES: usize = 2 * 1024 * 1024;
if self.css.len() + css.len() > MAX_VALUE_LENGTH_IN_BYTES {
return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
}
// This happens e.g. between two subsequent var() functions:
// `var(--a)var(--b)`.
//
// In that case, css_*_token_type is nonsensical.
if css.is_empty() {
return Ok(());
}
self.first_token_type.set_if_nothing(css_first_token_type);
// If self.first_token_type was nothing,
// self.last_token_type is also nothing and this will be false:
if self
.last_token_type
.needs_separator_when_before(css_first_token_type)
{
self.css.push_str("/**/")
}
self.css.push_str(css);
self.last_token_type = css_last_token_type;
Ok(())
}
fn push_from<'i>(
&mut self,
input: &Parser<'i, '_>,
position: (SourcePosition, TokenSerializationType),
last_token_type: TokenSerializationType,
) -> Result<(), ParseError<'i>> {
self.push(
input,
input.slice_from(position.0),
position.1,
last_token_type,
)
}
fn push_variable<'i>(
&mut self,
input: &Parser<'i, '_>,
variable: &ComputedValue,
) -> Result<(), ParseError<'i>> {
debug_assert!(variable.references.is_empty());
self.push(
input,
&variable.css,
variable.first_token_type,
variable.last_token_type,
)
}
/// Parse a custom property value.
pub fn parse<'i, 't>(input: &mut Parser<'i, 't>) -> Result<Arc<Self>, ParseError<'i>> {
let mut references = VarOrEnvReferences::default();
let (first_token_type, css, last_token_type) =
parse_self_contained_declaration_value(input, Some(&mut references))?;
let custom_property_references = references
.custom_property_references
.into_iter()
.collect::<Vec<_>>()
.into_boxed_slice();
let mut css = css.into_owned();
css.shrink_to_fit();
Ok(Arc::new(VariableValue {
css,
first_token_type,
last_token_type,
references: custom_property_references,
references_environment: references.references_environment,
}))
}
/// Create VariableValue from an int.
fn integer(number: i32) -> Self {
Self::from_token(Token::Number {
has_sign: false,
value: number as f32,
int_value: Some(number),
})
}
/// Create VariableValue from an int.
fn ident(ident: &'static str) -> Self {
Self::from_token(Token::Ident(ident.into()))
}
/// Create VariableValue from a float amount of CSS pixels.
fn pixels(number: f32) -> Self {
// No way to get TokenSerializationType::Dimension without creating
// Token object.
Self::from_token(Token::Dimension {
has_sign: false,
value: number,
int_value: None,
unit: CowRcStr::from("px"),
})
}
/// Create VariableValue from an integer amount of CSS pixels.
fn int_pixels(number: i32) -> Self {
Self::from_token(Token::Dimension {
has_sign: false,
value: number as f32,
int_value: Some(number),
unit: CowRcStr::from("px"),
})
}
fn from_token(token: Token) -> Self {
let token_type = token.serialization_type();
let mut css = token.to_css_string();
css.shrink_to_fit();
VariableValue {
css,
first_token_type: token_type,
last_token_type: token_type,
references: Default::default(),
references_environment: false,
}
}
}
/// Parse the value of a non-custom property that contains `var()` references.
pub fn parse_non_custom_with_var<'i, 't>(
input: &mut Parser<'i, 't>,
) -> Result<(TokenSerializationType, Cow<'i, str>), ParseError<'i>> {
let (first_token_type, css, _) = parse_self_contained_declaration_value(input, None)?;
Ok((first_token_type, css))
}
fn parse_self_contained_declaration_value<'i, 't>(
input: &mut Parser<'i, 't>,
references: Option<&mut VarOrEnvReferences>,
) -> Result<(TokenSerializationType, Cow<'i, str>, TokenSerializationType), ParseError<'i>> {
let start_position = input.position();
let mut missing_closing_characters = String::new();
let (first, last) =
parse_declaration_value(input, references, &mut missing_closing_characters)?;
let mut css: Cow<str> = input.slice_from(start_position).into();
if !missing_closing_characters.is_empty() {
// Unescaped backslash at EOF in a quoted string is ignored.
if css.ends_with("\\") && matches!(missing_closing_characters.as_bytes()[0], b'"' | b'\'') {
css.to_mut().pop();
}
css.to_mut().push_str(&missing_closing_characters);
}
Ok((first, css, last))
}
fn parse_declaration_value<'i, 't>(
input: &mut Parser<'i, 't>,
references: Option<&mut VarOrEnvReferences>,
missing_closing_characters: &mut String,
) -> Result<(TokenSerializationType, TokenSerializationType), ParseError<'i>> {
input.parse_until_before(Delimiter::Bang | Delimiter::Semicolon, |input| {
parse_declaration_value_block(input, references, missing_closing_characters)
})
}
/// Like parse_declaration_value, but accept `!` and `;` since they are only
/// invalid at the top level
fn parse_declaration_value_block<'i, 't>(
input: &mut Parser<'i, 't>,
mut references: Option<&mut VarOrEnvReferences>,
missing_closing_characters: &mut String,
) -> Result<(TokenSerializationType, TokenSerializationType), ParseError<'i>> {
input.skip_whitespace();
let mut token_start = input.position();
let mut token = match input.next_including_whitespace_and_comments() {
Ok(token) => token,
Err(_) => {
return Ok((
TokenSerializationType::nothing(),
TokenSerializationType::nothing(),
));
},
};
let first_token_type = token.serialization_type();
loop {
macro_rules! nested {
() => {
input.parse_nested_block(|input| {
parse_declaration_value_block(
input,
references.as_mut().map(|r| &mut **r),
missing_closing_characters,
)
})?
};
}
macro_rules! check_closed {
($closing:expr) => {
if !input.slice_from(token_start).ends_with($closing) {
missing_closing_characters.push_str($closing)
}
};
}
let last_token_type = match *token {
Token::Comment(_) => {
let serialization_type = token.serialization_type();
let token_slice = input.slice_from(token_start);
if !token_slice.ends_with("*/") {
missing_closing_characters.push_str(if token_slice.ends_with('*') {
"/"
} else {
"*/"
})
}
serialization_type
},
Token::BadUrl(ref u) => {
let e = StyleParseErrorKind::BadUrlInDeclarationValueBlock(u.clone());
return Err(input.new_custom_error(e));
},
Token::BadString(ref s) => {
let e = StyleParseErrorKind::BadStringInDeclarationValueBlock(s.clone());
return Err(input.new_custom_error(e));
},
Token::CloseParenthesis => {
let e = StyleParseErrorKind::UnbalancedCloseParenthesisInDeclarationValueBlock;
return Err(input.new_custom_error(e));
},
Token::CloseSquareBracket => {
let e = StyleParseErrorKind::UnbalancedCloseSquareBracketInDeclarationValueBlock;
return Err(input.new_custom_error(e));
},
Token::CloseCurlyBracket => {
let e = StyleParseErrorKind::UnbalancedCloseCurlyBracketInDeclarationValueBlock;
return Err(input.new_custom_error(e));
},
Token::Function(ref name) => {
if name.eq_ignore_ascii_case("var") {
let args_start = input.state();
input.parse_nested_block(|input| {
parse_var_function(input, references.as_mut().map(|r| &mut **r))
})?;
input.reset(&args_start);
} else if name.eq_ignore_ascii_case("env") {
let args_start = input.state();
input.parse_nested_block(|input| {
parse_env_function(input, references.as_mut().map(|r| &mut **r))
})?;
input.reset(&args_start);
}
nested!();
check_closed!(")");
Token::CloseParenthesis.serialization_type()
},
Token::ParenthesisBlock => {
nested!();
check_closed!(")");
Token::CloseParenthesis.serialization_type()
},
Token::CurlyBracketBlock => {
nested!();
check_closed!("}");
Token::CloseCurlyBracket.serialization_type()
},
Token::SquareBracketBlock => {
nested!();
check_closed!("]");
Token::CloseSquareBracket.serialization_type()
},
Token::QuotedString(_) => {
let serialization_type = token.serialization_type();
let token_slice = input.slice_from(token_start);
let quote = &token_slice[..1];
debug_assert!(matches!(quote, "\"" | "'"));
if !(token_slice.ends_with(quote) && token_slice.len() > 1) {
missing_closing_characters.push_str(quote)
}
serialization_type
},
Token::Ident(ref value) |
Token::AtKeyword(ref value) |
Token::Hash(ref value) |
Token::IDHash(ref value) |
Token::UnquotedUrl(ref value) |
Token::Dimension {
unit: ref value, ..
} => {
let serialization_type = token.serialization_type();
let is_unquoted_url = matches!(token, Token::UnquotedUrl(_));
if value.ends_with("�") && input.slice_from(token_start).ends_with("\\") {
// Unescaped backslash at EOF in these contexts is interpreted as U+FFFD
// Check the value in case the final backslash was itself escaped.
// Serialize as escaped U+FFFD, which is also interpreted as U+FFFD.
// (Unescaped U+FFFD would also work, but removing the backslash is annoying.)
missing_closing_characters.push_str("�")
}
if is_unquoted_url {
check_closed!(")");
}
serialization_type
},
_ => token.serialization_type(),
};
token_start = input.position();
token = match input.next_including_whitespace_and_comments() {
Ok(token) => token,
Err(..) => return Ok((first_token_type, last_token_type)),
};
}
}
fn parse_fallback<'i, 't>(input: &mut Parser<'i, 't>) -> Result<(), ParseError<'i>> {
// Exclude `!` and `;` at the top level
input.parse_until_before(Delimiter::Bang | Delimiter::Semicolon, |input| {
// Skip until the end.
while input.next_including_whitespace_and_comments().is_ok() {}
Ok(())
})
}
// If the var function is valid, return Ok((custom_property_name, fallback))
fn parse_var_function<'i, 't>(
input: &mut Parser<'i, 't>,
references: Option<&mut VarOrEnvReferences>,
) -> Result<(), ParseError<'i>> {
let name = input.expect_ident_cloned()?;
let name = parse_name(&name).map_err(|()| {
input.new_custom_error(SelectorParseErrorKind::UnexpectedIdent(name.clone()))
})?;
if input.try_parse(|input| input.expect_comma()).is_ok() {
parse_fallback(input)?;
}
if let Some(refs) = references {
refs.custom_property_references.insert(Atom::from(name));
}
Ok(())
}
fn parse_env_function<'i, 't>(
input: &mut Parser<'i, 't>,
references: Option<&mut VarOrEnvReferences>,
) -> Result<(), ParseError<'i>> {
// TODO(emilio): This should be <custom-ident> per spec, but no other
input.expect_ident()?;
if input.try_parse(|input| input.expect_comma()).is_ok() {
parse_fallback(input)?;
}
if let Some(references) = references {
references.references_environment = true;
}
Ok(())
}
/// A struct that takes care of encapsulating the cascade process for custom
/// properties.
pub struct CustomPropertiesBuilder<'a> {
seen: PrecomputedHashSet<&'a Name>,
may_have_cycles: bool,
custom_properties: Option<CustomPropertiesMap>,
inherited: Option<&'a Arc<CustomPropertiesMap>>,
reverted: PrecomputedHashMap<&'a Name, (CascadePriority, bool)>,
device: &'a Device,
}
impl<'a> CustomPropertiesBuilder<'a> {
/// Create a new builder, inheriting from a given custom properties map.
pub fn new(inherited: Option<&'a Arc<CustomPropertiesMap>>, device: &'a Device) -> Self {
Self {
seen: PrecomputedHashSet::default(),
reverted: Default::default(),
may_have_cycles: false,
custom_properties: None,
inherited,
device,
}
}
/// Cascade a given custom property declaration.
pub fn cascade(&mut self, declaration: &'a CustomDeclaration, priority: CascadePriority) {
let CustomDeclaration {
ref name,
ref value,
} = *declaration;
if let Some(&(reverted_priority, is_origin_revert)) = self.reverted.get(&name) {
if !reverted_priority.allows_when_reverted(&priority, is_origin_revert) {
return;
}
}
let was_already_present = !self.seen.insert(name);
if was_already_present {
return;
}
if !self.value_may_affect_style(name, value) {
return;
}
if self.custom_properties.is_none() {
self.custom_properties = Some(match self.inherited {
Some(inherited) => (**inherited).clone(),
None => CustomPropertiesMap::default(),
});
}
let map = self.custom_properties.as_mut().unwrap();
match *value {
CustomDeclarationValue::Value(ref unparsed_value) => {
let has_references = !unparsed_value.references.is_empty();
self.may_have_cycles |= has_references;
// If the variable value has no references and it has an
// environment variable here, perform substitution here instead
// of forcing a full traversal in `substitute_all` afterwards.
let value = if !has_references && unparsed_value.references_environment {
let result = substitute_references_in_value(unparsed_value, &map, &self.device);
match result {
Ok(new_value) => new_value,
Err(..) => {
map.remove(name);
return;
},
}
} else {
(*unparsed_value).clone()
};
map.insert(name.clone(), value);
},
CustomDeclarationValue::CSSWideKeyword(keyword) => match keyword {
CSSWideKeyword::RevertLayer | CSSWideKeyword::Revert => {
let origin_revert = keyword == CSSWideKeyword::Revert;
self.seen.remove(name);
self.reverted.insert(name, (priority, origin_revert));
},
CSSWideKeyword::Initial => {
map.remove(name);
},
// handled in value_may_affect_style
CSSWideKeyword::Unset | CSSWideKeyword::Inherit => unreachable!(),
},
}
}
fn value_may_affect_style(&self, name: &Name, value: &CustomDeclarationValue) -> bool {
match *value {
CustomDeclarationValue::CSSWideKeyword(CSSWideKeyword::Unset) |
CustomDeclarationValue::CSSWideKeyword(CSSWideKeyword::Inherit) => {
// Custom properties are inherited by default. So
// explicit 'inherit' or 'unset' means we can just use
// any existing value in the inherited CustomPropertiesMap.
return false;
},
_ => {},
}
let existing_value = self
.custom_properties
.as_ref()
.and_then(|m| m.get(name))
.or_else(|| self.inherited.and_then(|m| m.get(name)));
match (existing_value, value) {
(None, &CustomDeclarationValue::CSSWideKeyword(CSSWideKeyword::Initial)) => {
// The initial value of a custom property is the same as it
// not existing in the map.
return false;
},
(Some(existing_value), &CustomDeclarationValue::Value(ref value)) => {
// Don't bother overwriting an existing inherited value with
// the same specified value.
if existing_value == value {
return false;
}
},
_ => {},
}
true
}
fn inherited_properties_match(&self, map: &CustomPropertiesMap) -> bool {
let inherited = match self.inherited {
Some(inherited) => inherited,
None => return false,
};
if inherited.len() != map.len() {
return false;
}
for name in self.seen.iter() {
if inherited.get(*name) != map.get(*name) {
return false;
}
}
true
}
/// Returns the final map of applicable custom properties.
///
/// If there was any specified property, we've created a new map and now we
/// need to remove any potential cycles, and wrap it in an arc.
///
/// Otherwise, just use the inherited custom properties map.
pub fn build(mut self) -> Option<Arc<CustomPropertiesMap>> {
let mut map = match self.custom_properties.take() {
Some(m) => m,
None => return self.inherited.cloned(),
};
if self.may_have_cycles {
substitute_all(&mut map, &self.seen, self.device);
}
// Some pages apply a lot of redundant custom properties, see e.g.
// haven't really changed, and save some memory by reusing the inherited
// map in that case.
if self.inherited_properties_match(&map) {
return self.inherited.cloned();
}
map.shrink_to_fit();
Some(Arc::new(map))
}
}
/// Resolve all custom properties to either substituted, invalid, or unset
/// (meaning we should use the inherited value).
///
/// It does cycle dependencies removal at the same time as substitution.
fn substitute_all(
custom_properties_map: &mut CustomPropertiesMap,
seen: &PrecomputedHashSet<&Name>,
device: &Device,
) {
// The cycle dependencies removal in this function is a variant
// of Tarjan's algorithm. It is mostly based on the pseudo-code
// listed in
// title=Tarjan%27s_strongly_connected_components_algorithm&oldid=801728495
/// Struct recording necessary information for each variable.
#[derive(Debug)]
struct VarInfo {
/// The name of the variable. It will be taken to save addref
/// when the corresponding variable is popped from the stack.
/// This also serves as a mark for whether the variable is
/// currently in the stack below.
name: Option<Name>,
/// If the variable is in a dependency cycle, lowlink represents
/// a smaller index which corresponds to a variable in the same
/// strong connected component, which is known to be accessible
/// from this variable. It is not necessarily the root, though.
lowlink: usize,
}
/// Context struct for traversing the variable graph, so that we can
/// avoid referencing all the fields multiple times.
#[derive(Debug)]
struct Context<'a> {
/// Number of variables visited. This is used as the order index
/// when we visit a new unresolved variable.
count: usize,
/// The map from custom property name to its order index.
index_map: PrecomputedHashMap<Name, usize>,
/// Information of each variable indexed by the order index.
var_info: SmallVec<[VarInfo; 5]>,
/// The stack of order index of visited variables. It contains
/// all unfinished strong connected components.
stack: SmallVec<[usize; 5]>,
map: &'a mut CustomPropertiesMap,
/// To resolve the environment to substitute `env()` variables.
device: &'a Device,
}
/// This function combines the traversal for cycle removal and value
/// substitution. It returns either a signal None if this variable
/// has been fully resolved (to either having no reference or being
/// marked invalid), or the order index for the given name.
///
/// When it returns, the variable corresponds to the name would be
/// in one of the following states:
/// * It is still in context.stack, which means it is part of an
/// potentially incomplete dependency circle.
/// * It has been removed from the map. It can be either that the
/// substitution failed, or it is inside a dependency circle.
/// When this function removes a variable from the map because
/// of dependency circle, it would put all variables in the same
/// strong connected component to the set together.
/// * It doesn't have any reference, because either this variable
/// doesn't have reference at all in specified value, or it has
/// been completely resolved.
/// * There is no such variable at all.
fn traverse<'a>(name: &Name, context: &mut Context<'a>) -> Option<usize> {
// Some shortcut checks.
let (name, value) = {
let value = context.map.get(name)?;
// Nothing to resolve.
if value.references.is_empty() {
debug_assert!(
!value.references_environment,
"Should've been handled earlier"
);
return None;
}
// Whether this variable has been visited in this traversal.
let key;
match context.index_map.entry(name.clone()) {
Entry::Occupied(entry) => {
return Some(*entry.get());
},
Entry::Vacant(entry) => {
key = entry.key().clone();
entry.insert(context.count);
},
}
// Hold a strong reference to the value so that we don't
// need to keep reference to context.map.
(key, value.clone())
};
// Add new entry to the information table.
let index = context.count;
context.count += 1;
debug_assert_eq!(index, context.var_info.len());
context.var_info.push(VarInfo {
name: Some(name),
lowlink: index,
});
context.stack.push(index);
let mut self_ref = false;
let mut lowlink = index;
for next in value.references.iter() {
let next_index = match traverse(next, context) {
Some(index) => index,
// There is nothing to do if the next variable has been
// fully resolved at this point.
None => {
continue;
},
};
let next_info = &context.var_info[next_index];
if next_index > index {
// The next variable has a larger index than us, so it
// must be inserted in the recursive call above. We want
// to get its lowlink.
lowlink = cmp::min(lowlink, next_info.lowlink);
} else if next_index == index {
self_ref = true;
} else if next_info.name.is_some() {
// The next variable has a smaller order index and it is
// in the stack, so we are at the same component.
lowlink = cmp::min(lowlink, next_index);
}
}
context.var_info[index].lowlink = lowlink;
if lowlink != index {
// This variable is in a loop, but it is not the root of
// this strong connected component. We simply return for
// now, and the root would remove it from the map.
//
// This cannot be removed from the map here, because
// otherwise the shortcut check at the beginning of this
// function would return the wrong value.
return Some(index);
}
// This is the root of a strong-connected component.
let mut in_loop = self_ref;
let name;
loop {
let var_index = context
.stack
.pop()
.expect("The current variable should still be in stack");
let var_info = &mut context.var_info[var_index];
// We should never visit the variable again, so it's safe
// to take the name away, so that we don't do additional
// reference count.
let var_name = var_info
.name
.take()
.expect("Variable should not be poped from stack twice");
if var_index == index {
name = var_name;
break;
}
// Anything here is in a loop which can traverse to the
// variable we are handling, so remove it from the map, it's invalid
// at computed-value time.
context.map.remove(&var_name);
in_loop = true;
}
if in_loop {
// This variable is in loop. Resolve to invalid.
context.map.remove(&name);
return None;
}
// Now we have shown that this variable is not in a loop, and all of its
// dependencies should have been resolved. We can start substitution
// now.
let result = substitute_references_in_value(&value, &context.map, &context.device);
match result {
Ok(computed_value) => {
context.map.insert(name, computed_value);
},
Err(..) => {
// This is invalid, reset it to the guaranteed-invalid value.
context.map.remove(&name);
},
}
// All resolved, so return the signal value.
None
}
// Note that `seen` doesn't contain names inherited from our parent, but
// those can't have variable references (since we inherit the computed
// variables) so we don't want to spend cycles traversing them anyway.
for name in seen {
let mut context = Context {
count: 0,
index_map: PrecomputedHashMap::default(),
stack: SmallVec::new(),
var_info: SmallVec::new(),
map: custom_properties_map,
device,
};
traverse(name, &mut context);
}
}
/// Replace `var()` and `env()` functions in a pre-existing variable value.
fn substitute_references_in_value<'i>(
value: &'i VariableValue,
custom_properties: &CustomPropertiesMap,
device: &Device,
) -> Result<Arc<ComputedValue>, ParseError<'i>> {
debug_assert!(!value.references.is_empty() || value.references_environment);
let mut input = ParserInput::new(&value.css);
let mut input = Parser::new(&mut input);
let mut position = (input.position(), value.first_token_type);
let mut computed_value = ComputedValue::empty();
let last_token_type = substitute_block(
&mut input,
&mut position,
&mut computed_value,
custom_properties,
device,
)?;
computed_value.push_from(&input, position, last_token_type)?;
computed_value.css.shrink_to_fit();
Ok(Arc::new(computed_value))
}
/// Replace `var()` functions in an arbitrary bit of input.
///
/// If the variable has its initial value, the callback should return `Err(())`
/// and leave `partial_computed_value` unchanged.
///
/// Otherwise, it should push the value of the variable (with its own `var()` functions replaced)
/// to `partial_computed_value` and return `Ok(last_token_type of what was pushed)`
///
/// Return `Err(())` if `input` is invalid at computed-value time.
/// or `Ok(last_token_type that was pushed to partial_computed_value)` otherwise.
fn substitute_block<'i>(
input: &mut Parser<'i, '_>,
position: &mut (SourcePosition, TokenSerializationType),
partial_computed_value: &mut ComputedValue,
custom_properties: &CustomPropertiesMap,
device: &Device,
) -> Result<TokenSerializationType, ParseError<'i>> {
let mut last_token_type = TokenSerializationType::nothing();
let mut set_position_at_next_iteration = false;
loop {
let before_this_token = input.position();
let next = input.next_including_whitespace_and_comments();
if set_position_at_next_iteration {
*position = (
before_this_token,
match next {
Ok(token) => token.serialization_type(),
Err(_) => TokenSerializationType::nothing(),
},
);
set_position_at_next_iteration = false;
}
let token = match next {
Ok(token) => token,
Err(..) => break,
};
match token {
Token::Function(ref name)
if name.eq_ignore_ascii_case("var") || name.eq_ignore_ascii_case("env") =>
{
let is_env = name.eq_ignore_ascii_case("env");
partial_computed_value.push(
input,
input.slice(position.0..before_this_token),
position.1,
last_token_type,
)?;
input.parse_nested_block(|input| {
// parse_var_function() / parse_env_function() ensure neither .unwrap() will fail.
let name = {
let name = input.expect_ident().unwrap();
if is_env {
Atom::from(&**name)
} else {
Atom::from(parse_name(&name).unwrap())
}
};
let env_value;
let value = if is_env {
if let Some(v) = device.environment().get(&name, device) {
env_value = v;
Some(&env_value)
} else {
None
}
} else {
custom_properties.get(&name).map(|v| &**v)
};
if let Some(v) = value {
last_token_type = v.last_token_type;
partial_computed_value.push_variable(input, v)?;
// Skip over the fallback, as `parse_nested_block` would return `Err`
// if we don't consume all of `input`.
// FIXME: Add a specialized method to cssparser to do this with less work.
while input.next().is_ok() {}
} else {
input.expect_comma()?;
input.skip_whitespace();
let after_comma = input.state();
let first_token_type = input
.next_including_whitespace_and_comments()
.ok()
.map_or_else(TokenSerializationType::nothing, |t| {
t.serialization_type()
});
input.reset(&after_comma);
let mut position = (after_comma.position(), first_token_type);
last_token_type = substitute_block(
input,
&mut position,
partial_computed_value,
custom_properties,
device,
)?;
partial_computed_value.push_from(input, position, last_token_type)?;
}
Ok(())
})?;
set_position_at_next_iteration = true
},
Token::Function(_) |
Token::ParenthesisBlock |
Token::CurlyBracketBlock |
Token::SquareBracketBlock => {
input.parse_nested_block(|input| {
substitute_block(
input,
position,
partial_computed_value,
custom_properties,
device,
)
})?;
// It's the same type for CloseCurlyBracket and CloseSquareBracket.
last_token_type = Token::CloseParenthesis.serialization_type();
},
_ => last_token_type = token.serialization_type(),
}
}
// FIXME: deal with things being implicitly closed at the end of the input. E.g.
// ```html
// <div style="--color: rgb(0,0,0">
// <p style="background: var(--color) var(--image) top left; --image: url('a.png"></p>
// </div>
// ```
Ok(last_token_type)
}
/// Replace `var()` and `env()` functions for a non-custom property.
///
/// Return `Err(())` for invalid at computed time.
pub fn substitute<'i>(
input: &'i str,
first_token_type: TokenSerializationType,
computed_values_map: Option<&Arc<CustomPropertiesMap>>,
device: &Device,
) -> Result<String, ParseError<'i>> {
let mut substituted = ComputedValue::empty();
let mut input = ParserInput::new(input);
let mut input = Parser::new(&mut input);
let mut position = (input.position(), first_token_type);
let empty_map = CustomPropertiesMap::default();
let custom_properties = match computed_values_map {
Some(m) => &**m,
None => &empty_map,
};
let last_token_type = substitute_block(
&mut input,
&mut position,
&mut substituted,
&custom_properties,
device,
)?;
substituted.push_from(&input, position, last_token_type)?;
Ok(substituted.css)
}