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89b59cb5c3
Technically, env() should not be an ASF. (😱) This is why some tests
still fail - env() as specced is expected to have its syntax checked
fully at parse-time, whereas ASFs are not properly syntax-checked until
later. However, I think this approach was worth doing for a few reasons:
- env() behaves like an ASF otherwise. (It is replaced with a set of
arbitrary component-values that are not known until computed-value
time.)
- env() was defined before the ASF concept existed, so I strongly
suspect it will be updated in the future to match that definition,
with a couple of adjustments. (eg, env() is allowed in some extra
places compared to var() and attr().)
- This was much quicker and easier to implement (under 3 hours in total)
compared to the greater amount of work to implement a whole separate
system just for env().
- Most of these tests are marked tentative, and the spec definition of
env() is still somewhat in flux, so failing some is not a huge deal.
If in the future I turn out to be wrong on this, we can convert it to
its own special thing.
477 lines
24 KiB
C++
477 lines
24 KiB
C++
/*
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* Copyright (c) 2025, Sam Atkins <sam@ladybird.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <LibWeb/CSS/Parser/ArbitrarySubstitutionFunctions.h>
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#include <LibWeb/CSS/Parser/Parser.h>
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#include <LibWeb/CSS/Parser/Syntax.h>
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#include <LibWeb/CSS/Parser/SyntaxParsing.h>
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#include <LibWeb/CSS/PropertyName.h>
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#include <LibWeb/CSS/StyleComputer.h>
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#include <LibWeb/CSS/StyleValues/NumberStyleValue.h>
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#include <LibWeb/CSS/StyleValues/UnresolvedStyleValue.h>
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#include <LibWeb/DOM/Document.h>
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#include <LibWeb/DOM/Element.h>
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namespace Web::CSS::Parser {
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bool SubstitutionContext::operator==(SubstitutionContext const& other) const
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{
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return dependency_type == other.dependency_type
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&& first == other.first
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&& second == other.second;
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}
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String SubstitutionContext::to_string() const
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{
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StringView type_name = [this] {
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switch (dependency_type) {
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case DependencyType::Property:
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return "Property"sv;
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case DependencyType::Attribute:
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return "Attribute"sv;
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case DependencyType::Function:
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return "Function"sv;
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}
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VERIFY_NOT_REACHED();
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}();
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return MUST(String::formatted("{} {} {}", type_name, first, second));
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}
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void GuardedSubstitutionContexts::guard(SubstitutionContext& context)
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{
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for (auto& existing_context : m_contexts) {
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if (existing_context == context) {
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existing_context.is_cyclic = true;
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context.is_cyclic = true;
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return;
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}
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}
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m_contexts.append(context);
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}
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void GuardedSubstitutionContexts::unguard(SubstitutionContext const& context)
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{
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[[maybe_unused]] auto const was_removed = m_contexts.remove_first_matching([context](auto const& other) {
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return context == other;
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});
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VERIFY(was_removed);
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}
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Optional<ArbitrarySubstitutionFunction> to_arbitrary_substitution_function(FlyString const& name)
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{
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if (name.equals_ignoring_ascii_case("attr"sv))
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return ArbitrarySubstitutionFunction::Attr;
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if (name.equals_ignoring_ascii_case("env"sv))
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return ArbitrarySubstitutionFunction::Env;
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if (name.equals_ignoring_ascii_case("var"sv))
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return ArbitrarySubstitutionFunction::Var;
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return {};
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}
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bool contains_guaranteed_invalid_value(Vector<ComponentValue> const& values)
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{
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for (auto const& value : values) {
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if (value.contains_guaranteed_invalid_value())
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return true;
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}
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return false;
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}
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// https://drafts.csswg.org/css-values-5/#replace-an-attr-function
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static Vector<ComponentValue> replace_an_attr_function(DOM::AbstractElement& element, GuardedSubstitutionContexts& guarded_contexts, ArbitrarySubstitutionFunctionArguments const& arguments)
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{
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// 1. Let el be the element that the style containing the attr() function is being applied to.
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// Let first arg be the first <declaration-value> in arguments.
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// Let second arg be the <declaration-value>? passed after the comma, or null if there was no comma.
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auto const& first_argument = arguments.first();
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auto const second_argument = arguments.get(1);
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FlyString attribute_name;
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struct RawString { };
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Variant<Empty, NonnullOwnPtr<SyntaxNode>, RawString> syntax;
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Optional<FlyString> unit_name;
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auto failure = [&] -> Vector<ComponentValue> {
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// This is step 6, but defined here for convenience.
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// 1. If second arg is null, and syntax was omitted, return an empty CSS <string>.
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if (!second_argument.has_value() && syntax.has<Empty>())
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return { Token::create_string({}) };
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// 2. If second arg is null, return the guaranteed-invalid value.
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if (!second_argument.has_value())
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return { ComponentValue { GuaranteedInvalidValue {} } };
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// 3. Substitute arbitrary substitution functions in second arg, and return the result.
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return substitute_arbitrary_substitution_functions(element, guarded_contexts, second_argument.value());
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};
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// 2. Substitute arbitrary substitution functions in first arg, then parse it as <attr-name> <attr-type>?.
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// If that returns failure, jump to the last step (labeled FAILURE).
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// Otherwise, let attr name and syntax be the results of parsing (with syntax being null if <attr-type> was
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// omitted), processed as specified in the definition of those arguments.
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auto substituted = substitute_arbitrary_substitution_functions(element, guarded_contexts, first_argument);
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TokenStream first_argument_tokens { substituted };
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// <attr-name> = [ <ident-token>? '|' ]? <ident-token>
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// FIXME: Support optional attribute namespace
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if (!first_argument_tokens.next_token().is(Token::Type::Ident))
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return failure();
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attribute_name = first_argument_tokens.consume_a_token().token().ident();
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first_argument_tokens.discard_whitespace();
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// <attr-type> = type( <syntax> ) | raw-string | <attr-unit>
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if (first_argument_tokens.next_token().is(Token::Type::Ident)) {
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auto const& syntax_ident = first_argument_tokens.next_token().token().ident();
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if (syntax_ident.equals_ignoring_ascii_case("raw-string"sv)) {
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first_argument_tokens.discard_a_token(); // raw-string
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syntax = RawString {};
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} else if (syntax_ident == "%"sv
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|| Angle::unit_from_name(syntax_ident).has_value()
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|| Flex::unit_from_name(syntax_ident).has_value()
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|| Frequency::unit_from_name(syntax_ident).has_value()
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|| Length::unit_from_name(syntax_ident).has_value()
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|| Resolution::unit_from_name(syntax_ident).has_value()
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|| Time::unit_from_name(syntax_ident).has_value()) {
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syntax = TypeSyntaxNode::create("number"_fly_string).release_nonnull<SyntaxNode>();
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unit_name = first_argument_tokens.consume_a_token().token().ident();
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} else {
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return failure();
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}
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} else if (first_argument_tokens.next_token().is_function("type"sv)) {
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auto const& type_function = first_argument_tokens.consume_a_token().function();
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if (auto parsed_syntax = parse_as_syntax(type_function.value)) {
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syntax = parsed_syntax.release_nonnull();
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} else {
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return failure();
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}
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}
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first_argument_tokens.discard_whitespace();
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if (first_argument_tokens.has_next_token())
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return failure();
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// 3. If attr name exists as an attribute on el, let attr value be its value; otherwise jump to the last step (labeled FAILURE).
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// FIXME: Attribute namespaces
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auto attribute_value = element.element().get_attribute(attribute_name);
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if (!attribute_value.has_value())
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return failure();
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// 4. If syntax is null or the keyword raw-string, return a CSS <string> whose value is attr value.
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// NOTE: No parsing or modification of any kind is performed on the value.
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if (syntax.visit(
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[](Empty) { return true; },
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[](RawString) { return true; },
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[](auto&) { return false; })) {
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return { Token::create_string(*attribute_value) };
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}
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// 5. Substitute arbitrary substitution functions in attr value, with «"attribute", attr name» as the substitution
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// context, then parse with a <syntax> attr value, with syntax and el. If that succeeds, return the result;
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// otherwise, jump to the last step (labeled FAILURE).
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auto parser = Parser::create(ParsingParams { element.element().document() }, attribute_value.value());
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auto unsubstituted_values = parser.parse_as_list_of_component_values();
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auto substituted_values = substitute_arbitrary_substitution_functions(element, guarded_contexts, unsubstituted_values,
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SubstitutionContext { SubstitutionContext::DependencyType::Attribute, attribute_name.to_string() });
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auto parsed_value = parse_with_a_syntax(ParsingParams { element.document() }, substituted_values, *syntax.get<NonnullOwnPtr<SyntaxNode>>(), element);
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if (parsed_value->is_guaranteed_invalid())
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return failure();
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if (unit_name.has_value()) {
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// https://drafts.csswg.org/css-values-5/#ref-for-typedef-attr-type%E2%91%A0
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// If given as an <attr-unit> value, the value is first parsed as if type(<number>) was specified, then the
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// resulting numeric value is turned into a dimension with the corresponding unit, or a percentage if % was
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// given. Values that fail to parse as a <number> trigger fallback.
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// FIXME: The spec is ambiguous about what we should do for non-number-literals.
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// Chromium treats them as invalid, so copy that for now.
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// Spec issue: https://github.com/w3c/csswg-drafts/issues/12479
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if (!parsed_value->is_number())
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return failure();
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return { Token::create_dimension(parsed_value->as_number().number(), unit_name.release_value()) };
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}
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return parsed_value->tokenize();
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// 6. FAILURE:
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// NB: Step 6 is a lambda defined at the top of the function.
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}
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// https://drafts.csswg.org/css-env/#substitute-an-env
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static Vector<ComponentValue> replace_an_env_function(DOM::AbstractElement& element, GuardedSubstitutionContexts& guarded_contexts, ArbitrarySubstitutionFunctionArguments const& arguments)
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{
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// AD-HOC: env() is not defined as an ASF (and was defined before the ASF concept was), but behaves a lot like one.
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// So, this is a combination of the spec's "substitute an env()" algorithm linked above, and the "replace a FOO function()" algorithms.
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auto const& first_argument = arguments.first();
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auto const second_argument = arguments.get(1);
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// AD-HOC: Substitute ASFs in the first argument.
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auto substituted_first_argument = substitute_arbitrary_substitution_functions(element, guarded_contexts, first_argument);
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// AD-HOC: Parse the arguments.
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// env() = env( <custom-ident> <integer [0,∞]>*, <declaration-value>? )
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TokenStream first_argument_tokens { substituted_first_argument };
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first_argument_tokens.discard_whitespace();
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auto& name_token = first_argument_tokens.consume_a_token();
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if (!name_token.is(Token::Type::Ident))
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return { ComponentValue { GuaranteedInvalidValue {} } };
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auto& name = name_token.token().ident();
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first_argument_tokens.discard_whitespace();
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Vector<i64> indices;
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// FIXME: Are non-literal <integer>s allowed here?
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while (first_argument_tokens.has_next_token()) {
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auto& maybe_integer = first_argument_tokens.consume_a_token();
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if (!maybe_integer.is(Token::Type::Number))
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return { ComponentValue { GuaranteedInvalidValue {} } };
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auto& number = maybe_integer.token().number();
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if (number.is_integer() && number.integer_value() >= 0)
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indices.append(number.integer_value());
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else
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return { ComponentValue { GuaranteedInvalidValue {} } };
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first_argument_tokens.discard_whitespace();
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}
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// 1. If the name provided by the first argument of the env() function is a recognized environment variable name,
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// the number of supplied integers matches the number of dimensions of the environment variable referenced by
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// that name, and values of the indices correspond to a known sub-value, replace the env() function by the value
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// of the named environment variable.
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if (auto environment_variable = environment_variable_from_string(name);
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environment_variable.has_value() && indices.size() == environment_variable_dimension_count(*environment_variable)) {
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auto result = element.document().environment_variable_value(*environment_variable, indices);
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if (result.has_value())
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return result.release_value();
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}
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// 2. Otherwise, if the env() function has a fallback value as its second argument, replace the env() function by
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// the fallback value. If there are any env() references in the fallback, substitute them as well.
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// AD-HOC: Substitute all ASFs in the result.
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if (second_argument.has_value())
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return substitute_arbitrary_substitution_functions(element, guarded_contexts, second_argument.value());
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// 3. Otherwise, the property or descriptor containing the env() function is invalid at computed-value time.
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return { ComponentValue { GuaranteedInvalidValue {} } };
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}
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// https://drafts.csswg.org/css-variables-1/#replace-a-var-function
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static Vector<ComponentValue> replace_a_var_function(DOM::AbstractElement& element, GuardedSubstitutionContexts& guarded_contexts, ArbitrarySubstitutionFunctionArguments const& arguments)
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{
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// 1. Let el be the element that the style containing the var() function is being applied to.
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// Let first arg be the first <declaration-value> in arguments.
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// Let second arg be the <declaration-value>? passed after the comma, or null if there was no comma.
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auto const& first_argument = arguments.first();
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auto const second_argument = arguments.get(1);
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// 2. Substitute arbitrary substitution functions in first arg, then parse it as a <custom-property-name>.
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// If parsing returned a <custom-property-name>, let result be the computed value of the corresponding custom
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// property on el. Otherwise, let result be the guaranteed-invalid value.
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auto substituted_first_argument = substitute_arbitrary_substitution_functions(element, guarded_contexts, first_argument);
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TokenStream name_tokens { substituted_first_argument };
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name_tokens.discard_whitespace();
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auto& name_token = name_tokens.consume_a_token();
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name_tokens.discard_whitespace();
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Vector<ComponentValue> result;
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if (name_tokens.has_next_token() || !name_token.is(Token::Type::Ident) || !is_a_custom_property_name_string(name_token.token().ident())) {
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result = { ComponentValue { GuaranteedInvalidValue {} } };
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} else {
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// Look up the value of the custom property
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auto& custom_property_name = name_token.token().ident();
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auto custom_property_value = StyleComputer::compute_value_of_custom_property(element, custom_property_name, guarded_contexts);
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if (custom_property_value->is_guaranteed_invalid()) {
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result = { ComponentValue { GuaranteedInvalidValue {} } };
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} else if (custom_property_value->is_unresolved()) {
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result = custom_property_value->as_unresolved().values();
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} else {
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dbgln_if(CSS_PARSER_DEBUG, "Custom property `{}` is an unsupported type: {}", custom_property_name, to_underlying(custom_property_value->type()));
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result = { ComponentValue { GuaranteedInvalidValue {} } };
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}
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}
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// FIXME: 3. If the custom property named by the var()’s first argument is animation-tainted, and the var() is being used
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// in a property that is not animatable, set result to the guaranteed-invalid value.
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// 4. If result contains the guaranteed-invalid value, and second arg was provided, set result to the result of substitute arbitrary substitution functions on second arg.
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if (contains_guaranteed_invalid_value(result) && second_argument.has_value())
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result = substitute_arbitrary_substitution_functions(element, guarded_contexts, second_argument.value());
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// 5. Return result.
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return result;
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}
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static ErrorOr<void> substitute_arbitrary_substitution_functions_step_2(DOM::AbstractElement& element, GuardedSubstitutionContexts& guarded_contexts, TokenStream<ComponentValue>& source, Vector<ComponentValue>& dest)
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{
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// Step 2 of https://drafts.csswg.org/css-values-5/#substitute-arbitrary-substitution-function
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// 2. For each arbitrary substitution function func in values (ordered via a depth-first pre-order traversal) that
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// is not nested in the contents of another arbitrary substitution function:
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while (source.has_next_token()) {
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auto const& value = source.consume_a_token();
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if (value.is_function()) {
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auto const& source_function = value.function();
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if (auto maybe_function_id = to_arbitrary_substitution_function(source_function.name); maybe_function_id.has_value()) {
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auto function_id = maybe_function_id.release_value();
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// FIXME: 1. Substitute early-invoked functions in func’s contents, and let early result be the result.
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auto const& early_result = source_function.value;
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// 2. If early result contains the guaranteed-invalid value, replace func in values with the guaranteed-invalid
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// value and continue.
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if (contains_guaranteed_invalid_value(early_result)) {
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dest.empend(GuaranteedInvalidValue {});
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continue;
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}
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// 3. Parse early result according to func’s argument grammar. If this returns failure, replace func in values
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// with the guaranteed-invalid value and continue; otherwise, let arguments be the result.
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auto maybe_arguments = parse_according_to_argument_grammar(function_id, early_result);
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if (!maybe_arguments.has_value()) {
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dest.empend(GuaranteedInvalidValue {});
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continue;
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}
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auto arguments = maybe_arguments.release_value();
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// 4. Replace an arbitrary substitution function for func, given arguments, as defined by that function.
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// Let result be the returned list of component values.
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auto result = replace_an_arbitrary_substitution_function(element, guarded_contexts, function_id, arguments);
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// 5. If result contains the guaranteed-invalid value, replace func in values with the guaranteed-invalid value.
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// Otherwise, replace func in values with result.
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if (contains_guaranteed_invalid_value(result)) {
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dest.empend(GuaranteedInvalidValue {});
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} else {
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// NB: Because we're doing this in one pass recursively, we now need to substitute any ASFs in result.
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TokenStream result_stream { result };
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Vector<ComponentValue> result_after_processing;
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TRY(substitute_arbitrary_substitution_functions_step_2(element, guarded_contexts, result_stream, result_after_processing));
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// NB: Protect against the billion-laughs attack by limiting to an arbitrary large number of tokens.
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// https://drafts.csswg.org/css-values-5/#long-substitution
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if (source.remaining_token_count() + result_after_processing.size() > 16384) {
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dest.clear();
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dest.empend(GuaranteedInvalidValue {});
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return Error::from_string_literal("Stopped expanding arbitrary substitution functions: maximum length reached.");
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}
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dest.extend(result_after_processing);
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}
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continue;
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}
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Vector<ComponentValue> function_values;
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TokenStream source_function_contents { source_function.value };
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TRY(substitute_arbitrary_substitution_functions_step_2(element, guarded_contexts, source_function_contents, function_values));
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dest.empend(Function { source_function.name, move(function_values) });
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continue;
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}
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if (value.is_block()) {
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auto const& source_block = value.block();
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TokenStream source_block_values { source_block.value };
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Vector<ComponentValue> block_values;
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TRY(substitute_arbitrary_substitution_functions_step_2(element, guarded_contexts, source_block_values, block_values));
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dest.empend(SimpleBlock { source_block.token, move(block_values) });
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continue;
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}
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dest.empend(value);
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}
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return {};
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}
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// https://drafts.csswg.org/css-values-5/#substitute-arbitrary-substitution-function
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Vector<ComponentValue> substitute_arbitrary_substitution_functions(DOM::AbstractElement& element, GuardedSubstitutionContexts& guarded_contexts, Vector<ComponentValue> const& values, Optional<SubstitutionContext> context)
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{
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// To substitute arbitrary substitution functions in a sequence of component values values, given an optional
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// substitution context context:
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// 1. Guard context for the remainder of this algorithm. If context is marked as a cyclic substitution context,
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// return the guaranteed-invalid value.
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if (context.has_value()) {
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guarded_contexts.guard(context.value());
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if (context->is_cyclic)
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return { ComponentValue { GuaranteedInvalidValue {} } };
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}
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ScopeGuard const guard { [&] {
|
||
if (context.has_value())
|
||
guarded_contexts.unguard(context.value());
|
||
} };
|
||
|
||
// 2. For each arbitrary substitution function func in values (ordered via a depth-first pre-order traversal) that
|
||
// is not nested in the contents of another arbitrary substitution function:
|
||
Vector<ComponentValue> new_values;
|
||
TokenStream source { values };
|
||
auto maybe_error = substitute_arbitrary_substitution_functions_step_2(element, guarded_contexts, source, new_values);
|
||
if (maybe_error.is_error())
|
||
return { ComponentValue { GuaranteedInvalidValue {} } };
|
||
|
||
// 3. If context is marked as a cyclic substitution context, return the guaranteed-invalid value.
|
||
// NOTE: Nested arbitrary substitution functions may have marked context as cyclic in step 2.
|
||
if (context.has_value() && context->is_cyclic)
|
||
return { ComponentValue { GuaranteedInvalidValue {} } };
|
||
|
||
// 4. Return values.
|
||
return new_values;
|
||
}
|
||
|
||
Optional<ArbitrarySubstitutionFunctionArguments> parse_according_to_argument_grammar(ArbitrarySubstitutionFunction function, Vector<ComponentValue> const& values)
|
||
{
|
||
// Equivalent to `<declaration-value> , <declaration-value>?`, used by multiple argument grammars.
|
||
auto parse_declaration_value_then_optional_declaration_value = [](Vector<ComponentValue> const& values) -> Optional<ArbitrarySubstitutionFunctionArguments> {
|
||
TokenStream tokens { values };
|
||
|
||
auto first_argument = Parser::parse_declaration_value(tokens, Parser::StopAtComma::Yes);
|
||
if (!first_argument.has_value())
|
||
return OptionalNone {};
|
||
|
||
if (!tokens.has_next_token())
|
||
return ArbitrarySubstitutionFunctionArguments { first_argument.release_value() };
|
||
|
||
if (!tokens.next_token().is(Token::Type::Comma))
|
||
return {};
|
||
|
||
tokens.discard_a_token(); // ,
|
||
|
||
auto second_argument = Parser::parse_declaration_value(tokens, Parser::StopAtComma::No);
|
||
if (tokens.has_next_token())
|
||
return OptionalNone {};
|
||
return ArbitrarySubstitutionFunctionArguments { first_argument.release_value(), second_argument.value_or({}) };
|
||
};
|
||
|
||
switch (function) {
|
||
case ArbitrarySubstitutionFunction::Attr:
|
||
// https://drafts.csswg.org/css-values-5/#attr-notation
|
||
// <attr-args> = attr( <declaration-value> , <declaration-value>? )
|
||
return parse_declaration_value_then_optional_declaration_value(values);
|
||
case ArbitrarySubstitutionFunction::Env:
|
||
// https://drafts.csswg.org/css-env/#env-function
|
||
// AD-HOC: This doesn't have an argument-grammar definition.
|
||
// However, it follows the same format of "some CVs, then an optional comma and a fallback".
|
||
return parse_declaration_value_then_optional_declaration_value(values);
|
||
case ArbitrarySubstitutionFunction::Var:
|
||
// https://drafts.csswg.org/css-variables/#funcdef-var
|
||
// <var-args> = var( <declaration-value> , <declaration-value>? )
|
||
return parse_declaration_value_then_optional_declaration_value(values);
|
||
}
|
||
VERIFY_NOT_REACHED();
|
||
}
|
||
|
||
// https://drafts.csswg.org/css-values-5/#replace-an-arbitrary-substitution-function
|
||
Vector<ComponentValue> replace_an_arbitrary_substitution_function(DOM::AbstractElement& element, GuardedSubstitutionContexts& guarded_contexts, ArbitrarySubstitutionFunction function, ArbitrarySubstitutionFunctionArguments const& arguments)
|
||
{
|
||
switch (function) {
|
||
case ArbitrarySubstitutionFunction::Attr:
|
||
return replace_an_attr_function(element, guarded_contexts, arguments);
|
||
case ArbitrarySubstitutionFunction::Env:
|
||
return replace_an_env_function(element, guarded_contexts, arguments);
|
||
case ArbitrarySubstitutionFunction::Var:
|
||
return replace_a_var_function(element, guarded_contexts, arguments);
|
||
}
|
||
VERIFY_NOT_REACHED();
|
||
}
|
||
|
||
}
|