LibWeb: Implement first draft of CSS syntax highlighting :^)

This works at the Token level, which is quick and easy but has
drawbacks: We don't know when something is a property name or a value,
or if something is part of a selector. But, this works for now.

Userland/Libraries/LibSyntax/Highlighter.h

@@ -16,6 +16,7 @@ namespace Syntax {
 
 enum class Language {
     Cpp,
+    CSS,
     GML,
     HTML,
     INI,

Userland/Libraries/LibWeb/CMakeLists.txt

@@ -49,6 +49,7 @@ set(SOURCES
     CSS/StyleSheetList.cpp
     CSS/StyleValue.cpp
     CSS/Supports.cpp
+    CSS/SyntaxHighlighter/SyntaxHighlighter.cpp
     CSS/ValueID.cpp
     CSS/ValueID.h
     Cookie/ParsedCookie.cpp

Userland/Libraries/LibWeb/CSS/SyntaxHighlighter/SyntaxHighlighter.cpp

@@ -0,0 +1,160 @@
+/*
+ * Copyright (c) 2021, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Debug.h>
+#include <LibWeb/CSS/Parser/Tokenizer.h>
+#include <LibWeb/CSS/SyntaxHighlighter/SyntaxHighlighter.h>
+
+namespace Web::CSS {
+
+bool SyntaxHighlighter::is_identifier(u64 token) const
+{
+    return static_cast<CSS::Token::Type>(token) == CSS::Token::Type::Ident;
+}
+
+bool SyntaxHighlighter::is_navigatable(u64) const
+{
+    return false;
+}
+
+void SyntaxHighlighter::rehighlight(Palette const& palette)
+{
+    dbgln_if(SYNTAX_HIGHLIGHTING_DEBUG, "(CSS::SyntaxHighlighter) starting rehighlight");
+    auto text = m_client->get_text();
+
+    Vector<GUI::TextDocumentSpan> spans;
+
+    auto highlight = [&](auto start_line, auto start_column, auto end_line, auto end_column, Gfx::TextAttributes attributes, CSS::Token::Type type) {
+        if (start_line > end_line || (start_line == end_line && start_column >= end_column)) {
+            dbgln_if(SYNTAX_HIGHLIGHTING_DEBUG, "(CSS::SyntaxHighlighter) discarding ({}-{}) to ({}-{}) because it has zero or negative length", start_line, start_column, end_line, end_column);
+            return;
+        }
+        dbgln_if(SYNTAX_HIGHLIGHTING_DEBUG, "(CSS::SyntaxHighlighter) highlighting ({}-{}) to ({}-{}) with color {}", start_line, start_column, end_line, end_column, attributes.color);
+        spans.empend(
+            GUI::TextRange {
+                { start_line, start_column },
+                { end_line, end_column },
+            },
+            move(attributes),
+            static_cast<u64>(type),
+            false);
+    };
+
+    CSS::Tokenizer tokenizer { text, "utf-8" };
+    auto tokens = tokenizer.parse();
+    for (auto const& token : tokens) {
+        if (token.is(Token::Type::EndOfFile))
+            break;
+
+        switch (token.type()) {
+        case Token::Type::Ident:
+            highlight(token.start_position().line, token.start_position().column, token.end_position().line, token.end_position().column, { palette.syntax_identifier(), {} }, token.type());
+            break;
+
+        case Token::Type::String:
+            highlight(token.start_position().line, token.start_position().column, token.end_position().line, token.end_position().column, { palette.syntax_string(), {} }, token.type());
+            break;
+
+        case Token::Type::Whitespace:
+            // CSS doesn't produce comment tokens, they're just included as part of whitespace.
+            highlight(token.start_position().line, token.start_position().column, token.end_position().line, token.end_position().column, { palette.syntax_comment(), {} }, token.type());
+            break;
+
+        case Token::Type::AtKeyword:
+            highlight(token.start_position().line, token.start_position().column, token.end_position().line, token.end_position().column, { palette.syntax_keyword(), {} }, token.type());
+            break;
+
+        case Token::Type::Function:
+            // Function tokens include the opening '(', so we split that into two tokens for highlighting purposes.
+            highlight(token.start_position().line, token.start_position().column, token.end_position().line, token.end_position().column - 1, { palette.syntax_keyword(), {} }, token.type());
+            highlight(token.end_position().line, token.end_position().column - 1, token.end_position().line, token.end_position().column, { palette.syntax_punctuation(), {} }, Token::Type::OpenParen);
+            break;
+
+        case Token::Type::Url:
+            // An Url token is a `url()` function with its parameter string unquoted.
+            // url
+            highlight(token.start_position().line, token.start_position().column, token.start_position().line, token.start_position().column + 3, { palette.syntax_keyword(), {} }, token.type());
+            // (
+            highlight(token.start_position().line, token.start_position().column + 3, token.start_position().line, token.start_position().column + 4, { palette.syntax_punctuation(), {} }, Token::Type::OpenParen);
+            // <string>
+            highlight(token.start_position().line, token.start_position().column + 4, token.end_position().line, token.end_position().column - 1, { palette.syntax_string(), {} }, Token::Type::String);
+            // )
+            highlight(token.end_position().line, token.end_position().column - 1, token.end_position().line, token.end_position().column, { palette.syntax_punctuation(), {} }, Token::Type::CloseParen);
+            break;
+
+        case Token::Type::Number:
+        case Token::Type::Dimension:
+        case Token::Type::Percentage:
+            highlight(token.start_position().line, token.start_position().column, token.end_position().line, token.end_position().column, { palette.syntax_number(), {} }, token.type());
+            break;
+
+        case Token::Type::Delim:
+        case Token::Type::Colon:
+        case Token::Type::Comma:
+        case Token::Type::Semicolon:
+        case Token::Type::OpenCurly:
+        case Token::Type::OpenParen:
+        case Token::Type::OpenSquare:
+        case Token::Type::CloseCurly:
+        case Token::Type::CloseParen:
+        case Token::Type::CloseSquare:
+            highlight(token.start_position().line, token.start_position().column, token.end_position().line, token.end_position().column, { palette.syntax_punctuation(), {} }, token.type());
+            break;
+
+        case Token::Type::CDO:
+        case Token::Type::CDC:
+            highlight(token.start_position().line, token.start_position().column, token.end_position().line, token.end_position().column, { palette.syntax_comment(), {} }, token.type());
+            break;
+
+        case Token::Type::Hash:
+            // FIXME: Hash tokens can be ID selectors or colors, we don't know which without parsing properly.
+            highlight(token.start_position().line, token.start_position().column, token.end_position().line, token.end_position().column, { palette.syntax_number(), {} }, token.type());
+            break;
+
+        case Token::Type::Invalid:
+        case Token::Type::BadUrl:
+        case Token::Type::BadString:
+            // FIXME: Error highlighting color in palette?
+            highlight(token.start_position().line, token.start_position().column, token.end_position().line, token.end_position().column, { Color(Color::NamedColor::Red), {}, false, true }, token.type());
+            break;
+
+        case Token::Type::EndOfFile:
+        default:
+            break;
+        }
+    }
+
+    if constexpr (SYNTAX_HIGHLIGHTING_DEBUG) {
+        dbgln("(CSS::SyntaxHighlighter) list of all spans:");
+        for (auto& span : spans)
+            dbgln("{}, {} - {}", span.range, span.attributes.color, span.data);
+        dbgln("(CSS::SyntaxHighlighter) end of list");
+    }
+
+    m_client->do_set_spans(move(spans));
+    m_has_brace_buddies = false;
+    highlight_matching_token_pair();
+    m_client->do_update();
+}
+
+Vector<Syntax::Highlighter::MatchingTokenPair> SyntaxHighlighter::matching_token_pairs_impl() const
+{
+    static Vector<Syntax::Highlighter::MatchingTokenPair> pairs;
+    if (pairs.is_empty()) {
+        pairs.append({ static_cast<u64>(CSS::Token::Type::OpenCurly), static_cast<u64>(CSS::Token::Type::CloseCurly) });
+        pairs.append({ static_cast<u64>(CSS::Token::Type::OpenParen), static_cast<u64>(CSS::Token::Type::CloseParen) });
+        pairs.append({ static_cast<u64>(CSS::Token::Type::OpenSquare), static_cast<u64>(CSS::Token::Type::CloseSquare) });
+        pairs.append({ static_cast<u64>(CSS::Token::Type::CDO), static_cast<u64>(CSS::Token::Type::CDC) });
+    }
+    return pairs;
+}
+
+bool SyntaxHighlighter::token_types_equal(u64 token0, u64 token1) const
+{
+    return token0 == token1;
+}
+
+}

Userland/Libraries/LibWeb/CSS/SyntaxHighlighter/SyntaxHighlighter.h

@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) 2021, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibSyntax/Highlighter.h>
+
+namespace Web::CSS {
+
+class SyntaxHighlighter : public Syntax::Highlighter {
+public:
+    SyntaxHighlighter() = default;
+    virtual ~SyntaxHighlighter() override = default;
+
+    virtual bool is_identifier(u64) const override;
+    virtual bool is_navigatable(u64) const override;
+
+    virtual Syntax::Language language() const override { return Syntax::Language::CSS; }
+    virtual void rehighlight(Palette const&) override;
+
+protected:
+    virtual Vector<MatchingTokenPair> matching_token_pairs_impl() const override;
+    virtual bool token_types_equal(u64, u64) const override;
+};
+
+}