LibCpp: Introduce DummyASTNode

This allows us to use pase_* methods inside match_* methods,
without adding any actual AST nodes to the m_nodes list.

Userland/Libraries/LibCpp/AST.h

@@ -78,6 +78,7 @@ public:
     virtual bool is_type() const { return false; }
     virtual bool is_declaration() const { return false; }
     virtual bool is_name() const { return false; }
+    virtual bool is_dummy_node() const { return false; }
 
 protected:
     ASTNode(ASTNode* parent, Optional<Position> start, Optional<Position> end, const String& filename)
@@ -756,4 +757,15 @@ public:
 
     NonnullRefPtrVector<Expression> m_expressions;
 };
+
+class DummyAstNode : public ASTNode {
+public:
+    DummyAstNode(ASTNode* parent, Optional<Position> start, Optional<Position> end, const String& filename)
+    : ASTNode(parent, start, end, filename)
+    {
+    }
+    virtual bool is_dummy_node() const override { return true; }
+    virtual const char* class_name() const override { return "DummyAstNode"; }
+    virtual void dump(size_t) const override { }
+};
 }

Userland/Libraries/LibCpp/Parser.cpp

@@ -263,7 +263,7 @@ Parser::TemplatizedMatchResult Parser::match_type()
 
     if (!match_name())
         return TemplatizedMatchResult::NoMatch;
-    parse_name(*m_root_node);
+    parse_name(get_dummy_node());
 
     if (peek(Token::Type::Less).has_value()) {
         if (match_template_arguments()) {
@@ -287,7 +287,7 @@ bool Parser::match_template_arguments()
     while (!eof() && peek().type() != Token::Type::Greater) {
         if (match_type() == TemplatizedMatchResult::NoMatch)
             return false;
-        parse_type(*m_root_node);
+        parse_type(get_dummy_node());
     }
 
     return peek().type() == Token::Type::Greater;
@@ -320,7 +320,7 @@ bool Parser::match_variable_declaration()
     }
 
     VERIFY(m_root_node);
-    parse_type(*m_root_node);
+    parse_type(get_dummy_node());
 
     // Identifier
     if (!peek(Token::Type::Identifier).has_value()) {
@@ -668,7 +668,7 @@ bool Parser::match_function_declaration()
     if (match_type() == TemplatizedMatchResult::NoMatch)
         return false;
     VERIFY(m_root_node);
-    parse_type(*m_root_node);
+    parse_type(get_dummy_node());
 
     if (!peek(Token::Type::Identifier).has_value())
         return false;
@@ -888,7 +888,7 @@ RefPtr<ASTNode> Parser::node_at(Position pos) const
     auto index = index_of_node_at(pos);
     if (!index.has_value())
         return nullptr;
-    return m_nodes[index.value()];
+    return m_state.nodes[index.value()];
 }
 
 Optional<size_t> Parser::index_of_node_at(Position pos) const
@@ -902,12 +902,12 @@ Optional<size_t> Parser::index_of_node_at(Position pos) const
         return Position { node.end().line - node.start().line, node.start().line != node.end().line ? 0 : node.end().column - node.start().column };
     };
 
-    for (size_t node_index = 0; node_index < m_nodes.size(); ++node_index) {
-        auto& node = m_nodes[node_index];
+    for (size_t node_index = 0; node_index < m_state.nodes.size(); ++node_index) {
+        auto& node = m_state.nodes[node_index];
         if (node.start() > pos || node.end() < pos)
             continue;
 
-        if (!match_node_index.has_value() || (node_span(node) < node_span(m_nodes[match_node_index.value()])))
+        if (!match_node_index.has_value() || (node_span(node) < node_span(m_state.nodes[match_node_index.value()])))
             match_node_index = node_index;
     }
     return match_node_index;
@@ -945,12 +945,12 @@ Parser::TemplatizedMatchResult Parser::match_function_call()
     ScopeGuard state_guard = [this] { load_state(); };
     if (!match_name())
         return TemplatizedMatchResult::NoMatch;
-    parse_name(*m_root_node);
+    parse_name(get_dummy_node());
 
     bool is_templatized = false;
     if (match_template_arguments()) {
         is_templatized = true;
-        parse_template_arguments(*m_root_node);
+        parse_template_arguments(get_dummy_node());
     }
 
     if (!match(Token::Type::LeftParen))
@@ -1408,7 +1408,7 @@ bool Parser::match_c_style_cast_expression()
 
     if (match_type() == TemplatizedMatchResult::NoMatch)
         return false;
-    parse_type(*m_root_node);
+    parse_type(get_dummy_node());
 
     if (consume().type() != Token::Type::RightParen)
         return false;

Userland/Libraries/LibCpp/Parser.h

@@ -155,6 +155,7 @@ private:
     struct State {
         size_t token_index { 0 };
         Vector<String> errors;
+        NonnullRefPtrVector<ASTNode> nodes;
     };
 
     void error(StringView message = {});
@@ -164,7 +165,9 @@ private:
     create_ast_node(ASTNode& parent, const Position& start, Optional<Position> end, Args&&... args)
     {
         auto node = adopt(*new T(&parent, start, end, m_filename, forward<Args>(args)...));
-        m_nodes.append(node);
+        if(!parent.is_dummy_node()) {
+            m_state.nodes.append(node);
+        }
         return node;
     }
 
@@ -172,11 +175,19 @@ private:
     create_root_ast_node(const Position& start, Position end)
     {
         auto node = adopt(*new TranslationUnit(nullptr, start, end, m_filename));
-        m_nodes.append(node);
+        m_state.nodes.append(node);
         m_root_node = node;
         return node;
     }
 
+
+    DummyAstNode& get_dummy_node()
+    {
+        static NonnullRefPtr<DummyAstNode> dummy  = adopt(*new DummyAstNode(nullptr, {}, {}, {}));
+        return dummy;
+    }
+
+
     bool match_attribute_specification();
     void consume_attribute_specification();
     bool match_ellipsis();
@@ -191,7 +202,6 @@ private:
     State m_state;
     Vector<State> m_saved_states;
     RefPtr<TranslationUnit> m_root_node;
-    NonnullRefPtrVector<ASTNode> m_nodes;
 
     Vector<TokenAndPreprocessorDefinition> m_replaced_preprocessor_tokens;
 };