Evaluate constant conditional expressions

Signed-off-by: Roberto Raggi <[email protected]>

Author: robertoraggi

src/parser/cxx/ast_interpreter.cc

@@ -122,6 +122,18 @@ struct ASTInterpreter::NewPlacementResult {};
 
 struct ASTInterpreter::NestedNamespaceSpecifierResult {};
 
+struct ASTInterpreter::ToBool {
+  ASTInterpreter& interp;
+
+  auto operator()(const StringLiteral*) const -> std::optional<bool> {
+    return true;
+  }
+
+  auto operator()(const auto& value) const -> std::optional<bool> {
+    return bool(value);
+  }
+};
+
 struct ASTInterpreter::UnitVisitor {
   ASTInterpreter& accept;
 
@@ -2193,10 +2205,17 @@ auto ASTInterpreter::ExpressionVisitor::operator()(BinaryExpressionAST* ast)
 auto ASTInterpreter::ExpressionVisitor::operator()(
     ConditionalExpressionAST* ast) -> ExpressionResult {
   auto conditionResult = accept(ast->condition);
-  auto iftrueExpressionResult = accept(ast->iftrueExpression);
-  auto iffalseExpressionResult = accept(ast->iffalseExpression);
 
-  return ExpressionResult{std::nullopt};
+  if (!conditionResult.has_value()) return std::nullopt;
+
+  if (accept.toBool(conditionResult.value())) {
+    auto result = accept(ast->iftrueExpression);
+    return result;
+  }
+
+  auto result = accept(ast->iffalseExpression);
+
+  return result;
 }
 
 auto ASTInterpreter::ExpressionVisitor::operator()(YieldExpressionAST* ast)
@@ -3176,4 +3195,8 @@ auto ASTInterpreter::evaluate(ExpressionAST* ast) -> std::optional<ConstValue> {
   return result;
 }
 
+auto ASTInterpreter::toBool(const ConstValue& value) -> std::optional<bool> {
+  return std::visit(ToBool{*this}, value);
+}
+
 }  // namespace cxx

src/parser/cxx/ast_interpreter.h

@@ -43,6 +43,8 @@ class ASTInterpreter {
 
   [[nodiscard]] auto evaluate(ExpressionAST* ast) -> std::optional<ConstValue>;
 
+  [[nodiscard]] auto toBool(const ConstValue& value) -> std::optional<bool>;
+
  private:
   using ExpressionResult = std::optional<ConstValue>;
 
@@ -116,6 +118,9 @@ class ASTInterpreter {
   struct AttributeSpecifierVisitor;
   struct AttributeTokenVisitor;
 
+  // ops
+  struct ToBool;
+
   // run on the base nodes
   [[nodiscard]] auto operator()(UnitAST* ast) -> UnitResult;
   [[nodiscard]] auto operator()(DeclarationAST* ast) -> DeclarationResult;