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LibWeb: Add basic support for the attr() CSS function

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CSS Values and Units Module Level 5 defines attr as:
  `attr(<q-name> <attr-type>?, <declaration-value>?)`

This implementation does not contain support for the type argument,
effectively supporting `attr(<q-name>, <declaration-value>?)`
This commit is contained in:
Simon Wanner 2022-03-29 23:33:50 +02:00 • committed by Andreas Kling
parent ba6ba67fa0
commit 6437f5da36
4 changed files with 56 additions and 19 deletions
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35
Userland/Libraries/LibWeb/CSS/StyleComputer.cpp
View file

@ -495,7 +495,7 @@ static RefPtr<StyleValue> get_custom_property(DOM::Element const& element, FlySt
bool StyleComputer::expand_unresolved_values(DOM::Element& element, StringView property_name, HashMap<FlyString, NonnullRefPtr<PropertyDependencyNode>>& dependencies, Vector<StyleComponentValueRule> const& source, Vector<StyleComponentValueRule>& dest, size_t source_start_index) const
{
// FIXME: Do this better!
// We build a copy of the tree of StyleComponentValueRules, with all var()s replaced with their contents.
// We build a copy of the tree of StyleComponentValueRules, with all var()s and attr()s replaced with their contents.
// This is a very naive solution, and we could do better if the CSS Parser could accept tokens one at a time.
// Arbitrary large value chosen to avoid the billion-laughs attack.
@ -553,6 +553,35 @@ bool StyleComputer::expand_unresolved_values(DOM::Element& element, StringView p
return false;
continue;
}
} else if (value.function().name().equals_ignoring_case("attr"sv)) {
// https://drafts.csswg.org/css-values-5/#attr-substitution
auto const& attr_contents = value.function().values();
if (attr_contents.is_empty())
return false;
auto const& attr_name_token = attr_contents.first();
if (!attr_name_token.is(Token::Type::Ident))
return false;
auto attr_name = attr_name_token.token().ident();
auto attr_value = element.get_attribute(attr_name);
// 1. If the attr() function has a substitution value, replace the attr() function by the substitution value.
if (!attr_value.is_null()) {
// FIXME: attr() should also accept an optional type argument, not just strings.
dest.empend(Token::of_string(attr_value));
continue;
}
// 2. Otherwise, if the attr() function has a fallback value as its last argument, replace the attr() function by the fallback value.
// If there are any var() or attr() references in the fallback, substitute them as well.
if (attr_contents.size() > 2 && attr_contents[1].is(Token::Type::Comma)) {
if (!expand_unresolved_values(element, property_name, dependencies, attr_contents, dest, 2))
return false;
continue;
}
// 3. Otherwise, the property containing the attr() function is invalid at computed-value time.
return false;
}
auto const& source_function = value.function();
@ -580,9 +609,9 @@ bool StyleComputer::expand_unresolved_values(DOM::Element& element, StringView p
RefPtr<StyleValue> StyleComputer::resolve_unresolved_style_value(DOM::Element& element, PropertyID property_id, UnresolvedStyleValue const& unresolved) const
{
// Unresolved always contains a var(), unless it is a custom property's value, in which case we shouldn't be trying
// Unresolved always contains a var() or attr(), unless it is a custom property's value, in which case we shouldn't be trying
// to produce a different StyleValue from it.
VERIFY(unresolved.contains_var());
VERIFY(unresolved.contains_var_or_attr());
Vector<StyleComponentValueRule> expanded_values;
HashMap<FlyString, NonnullRefPtr<PropertyDependencyNode>> dependencies;