LibWeb: Implement CSS parsing convenience functions

These mostly match the API in `DeprecatedCSSParser.h`. The exception is
that `parse_selector()` returns a `SelectorList` instead of just one
`Selector`. The only uses of that are in
`ParentNode::query_selector[_all]()` which should be matching against a
list, according to the spec.

`parse_html_length()` is an odd case. It's used for `width="200"` cases
in HTML, so is not really CSS related, but does produce a StyleValue.
The values allowed in `width/height` in HTML vary per element, but they
are a lot more restricted than in CSS, so it's slightly inappropriate to
use the CSS parser for them, even though it's convenient.

We also ignore a few functions:

- `parse_line_width()`
- `parse_line_style()`
- `parse_color()`

These are all only used in `StyleResolver`, when it is given a property
value as a String. That won't happen once the old parser is removed.

2 files changed, 63 insertions, 0 deletions

diff --git a/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp b/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp
index c367dd1b95..509c5594b0 100644
--- a/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp
+++ b/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp
@@ -1777,6 +1777,13 @@ RefPtr<StyleValue> Parser::parse_box_shadow_value(ParsingContext const& context,
     return BoxShadowStyleValue::create(offset_x, offset_y, blur_radius, color);
 }
 
+RefPtr<StyleValue> Parser::parse_as_css_value(PropertyID property_id)
+{
+    auto component_values = parse_as_list_of_component_values();
+    auto tokens = TokenStream(component_values);
+    return parse_css_value(property_id, tokens);
+}
+
 RefPtr<StyleValue> Parser::parse_css_value(PropertyID property_id, TokenStream<StyleComponentValueRule>& tokens)
 {
     Vector<StyleComponentValueRule> component_values;
@@ -2405,3 +2412,46 @@ OwnPtr<CalculatedStyleValue::CalcSum> Parser::parse_calc_sum(ParsingContext cons
 }
 
 }
+
+namespace Web {
+
+RefPtr<CSS::CSSStyleSheet> parse_css(CSS::ParsingContext const& context, StringView const& css)
+{
+    if (css.is_empty())
+        return CSS::CSSStyleSheet::create({});
+    CSS::Parser parser(context, css);
+    return parser.parse_as_stylesheet();
+}
+
+RefPtr<CSS::CSSStyleDeclaration> parse_css_declaration(CSS::ParsingContext const& context, StringView const& css)
+{
+    if (css.is_empty())
+        return CSS::CSSStyleDeclaration::create({}, {});
+    CSS::Parser parser(context, css);
+    return parser.parse_as_list_of_declarations();
+}
+
+RefPtr<CSS::StyleValue> parse_css_value(CSS::ParsingContext const& context, StringView const& string, CSS::PropertyID property_id)
+{
+    if (string.is_empty())
+        return {};
+    CSS::Parser parser(context, string);
+    return parser.parse_as_css_value(property_id);
+}
+
+Optional<CSS::SelectorList> parse_selector(CSS::ParsingContext const& context, StringView const& selector_text)
+{
+    CSS::Parser parser(context, selector_text);
+    return parser.parse_as_selector();
+}
+
+RefPtr<CSS::StyleValue> parse_html_length(DOM::Document const& document, StringView const& string)
+{
+    auto integer = string.to_int();
+    if (integer.has_value())
+        return CSS::LengthStyleValue::create(CSS::Length::make_px(integer.value()));
+    // FIXME: The const_cast is a hack.
+    return parse_css_value(CSS::ParsingContext(const_cast<DOM::Document&>(document)), string);
+}
+
+}
diff --git a/Userland/Libraries/LibWeb/CSS/Parser/Parser.h b/Userland/Libraries/LibWeb/CSS/Parser/Parser.h
index 2e2f35a34d..ffe7d7c223 100644
--- a/Userland/Libraries/LibWeb/CSS/Parser/Parser.h
+++ b/Userland/Libraries/LibWeb/CSS/Parser/Parser.h
@@ -93,6 +93,8 @@ public:
     Optional<SelectorList> parse_as_selector();
     Optional<SelectorList> parse_as_relative_selector();
 
+    RefPtr<StyleValue> parse_as_css_value(PropertyID);
+
     // FIXME: These want to be private, but StyleResolver still uses them for now.
     RefPtr<StyleValue> parse_css_value(PropertyID, TokenStream<StyleComponentValueRule>&);
     static RefPtr<StyleValue> parse_css_value(ParsingContext const&, PropertyID, StyleComponentValueRule const&);
@@ -206,3 +208,14 @@ private:
 };
 
 }
+
+namespace Web {
+
+RefPtr<CSS::CSSStyleSheet> parse_css(CSS::ParsingContext const&, StringView const&);
+RefPtr<CSS::CSSStyleDeclaration> parse_css_declaration(CSS::ParsingContext const&, StringView const&);
+RefPtr<CSS::StyleValue> parse_css_value(CSS::ParsingContext const&, StringView const&, CSS::PropertyID property_id = CSS::PropertyID::Invalid);
+Optional<CSS::SelectorList> parse_selector(CSS::ParsingContext const&, StringView const&);
+
+RefPtr<CSS::StyleValue> parse_html_length(DOM::Document const&, StringView const&);
+
+}