LibGUI+HackStudio: Move syntax highlighting from HackStudio to LibGUI

This patch introduces the GUI::SyntaxHighlighter class, which can be
attached to a GUI::TextEditor to provide syntax highlighting.

The C++ syntax highlighting from HackStudio becomes a new class called
GUI::CppSyntaxHighlighter. This will make it possible to get C++ syntax
highlighting in any app that uses a GUI::TextEditor. :^)

Sidenote: It does feel a bit weird having a C++ lexer in a GUI toolkit
library, and we'll probably end up moving this out to a separate place
as this functionality grows larger.

Libraries/LibGUI/CppSyntaxHighlighter.cpp

@@ -0,0 +1,147 @@
+#include <LibGUI/CppLexer.h>
+#include <LibGUI/CppSyntaxHighlighter.h>
+#include <LibGUI/TextEditor.h>
+
+namespace GUI {
+
+struct TextStyle {
+    Color color;
+    const Gfx::Font* font { nullptr };
+};
+
+static TextStyle style_for_token_type(CppToken::Type type)
+{
+    switch (type) {
+    case CppToken::Type::Keyword:
+        return { Color::Black, &Gfx::Font::default_bold_fixed_width_font() };
+    case CppToken::Type::KnownType:
+        return { Color::from_rgb(0x929200), &Gfx::Font::default_bold_fixed_width_font() };
+    case CppToken::Type::Identifier:
+        return { Color::from_rgb(0x000092) };
+    case CppToken::Type::DoubleQuotedString:
+    case CppToken::Type::SingleQuotedString:
+    case CppToken::Type::Number:
+        return { Color::from_rgb(0x920000) };
+    case CppToken::Type::PreprocessorStatement:
+        return { Color::from_rgb(0x009292) };
+    case CppToken::Type::Comment:
+        return { Color::from_rgb(0x009200) };
+    default:
+        return { Color::Black };
+    }
+}
+
+void CppSyntaxHighlighter::rehighlight()
+{
+    ASSERT(m_editor);
+    auto text = m_editor->text();
+    CppLexer lexer(text);
+    auto tokens = lexer.lex();
+
+    Vector<GUI::TextDocumentSpan> spans;
+    for (auto& token : tokens) {
+#ifdef DEBUG_SYNTAX_HIGHLIGHTING
+        dbg() << token.to_string() << " @ " << token.m_start.line << ":" << token.m_start.column << " - " << token.m_end.line << ":" << token.m_end.column;
+#endif
+        GUI::TextDocumentSpan span;
+        span.range.set_start({ token.m_start.line, token.m_start.column });
+        span.range.set_end({ token.m_end.line, token.m_end.column });
+        auto style = style_for_token_type(token.m_type);
+        span.color = style.color;
+        span.font = style.font;
+        span.is_skippable = token.m_type == CppToken::Type::Whitespace;
+        span.data = (void*)token.m_type;
+        spans.append(span);
+    }
+    m_editor->document().set_spans(spans);
+
+    m_has_brace_buddies = false;
+    highlight_matching_token_pair();
+
+    m_editor->update();
+}
+
+void CppSyntaxHighlighter::highlight_matching_token_pair()
+{
+    ASSERT(m_editor);
+    auto& document = m_editor->document();
+
+    enum class Direction {
+        Forward,
+        Backward,
+    };
+
+    auto find_span_of_type = [&](int i, CppToken::Type type, CppToken::Type not_type, Direction direction) {
+        int nesting_level = 0;
+        bool forward = direction == Direction::Forward;
+        for (forward ? ++i : --i; forward ? (i < document.spans().size()) : (i >= 0); forward ? ++i : --i) {
+            auto& span = document.spans().at(i);
+            auto span_token_type = (CppToken::Type)((uintptr_t)span.data);
+            if (span_token_type == not_type) {
+                ++nesting_level;
+            } else if (span_token_type == type) {
+                if (nesting_level-- <= 0)
+                    return i;
+            }
+        }
+        return -1;
+    };
+
+    auto make_buddies = [&](int index0, int index1) {
+        auto& buddy0 = const_cast<GUI::TextDocumentSpan&>(document.spans()[index0]);
+        auto& buddy1 = const_cast<GUI::TextDocumentSpan&>(document.spans()[index1]);
+        m_has_brace_buddies = true;
+        m_brace_buddies[0].index = index0;
+        m_brace_buddies[1].index = index1;
+        m_brace_buddies[0].span_backup = buddy0;
+        m_brace_buddies[1].span_backup = buddy1;
+        buddy0.background_color = Color::DarkCyan;
+        buddy1.background_color = Color::DarkCyan;
+        buddy0.color = Color::White;
+        buddy1.color = Color::White;
+        m_editor->update();
+    };
+
+    struct MatchingTokenPair {
+        CppToken::Type open;
+        CppToken::Type close;
+    };
+
+    MatchingTokenPair pairs[] = {
+        { CppToken::Type::LeftCurly, CppToken::Type::RightCurly },
+        { CppToken::Type::LeftParen, CppToken::Type::RightParen },
+        { CppToken::Type::LeftBracket, CppToken::Type::RightBracket },
+    };
+
+    for (int i = 0; i < document.spans().size(); ++i) {
+        auto& span = const_cast<GUI::TextDocumentSpan&>(document.spans().at(i));
+        auto token_type = (CppToken::Type)((uintptr_t)span.data);
+
+        for (auto& pair : pairs) {
+            if (token_type == pair.open && span.range.start() == m_editor->cursor()) {
+                auto buddy = find_span_of_type(i, pair.close, pair.open, Direction::Forward);
+                if (buddy != -1)
+                    make_buddies(i, buddy);
+                return;
+            }
+        }
+
+        auto right_of_end = span.range.end();
+        right_of_end.set_column(right_of_end.column() + 1);
+
+        for (auto& pair : pairs) {
+            if (token_type == pair.close && right_of_end == m_editor->cursor()) {
+                auto buddy = find_span_of_type(i, pair.open, pair.close, Direction::Backward);
+                if (buddy != -1)
+                    make_buddies(i, buddy);
+                return;
+            }
+        }
+    }
+}
+
+CppSyntaxHighlighter::~CppSyntaxHighlighter()
+{
+}
+
+}