/*******************************************************************\

Module: C++ Language Type Checking

Author: Daniel Kroening, kroening@cs.cmu.edu

\*******************************************************************/

/// \file
/// C++ Language Type Checking

#include "cpp_typecheck.h"

#ifdef DEBUG
#include <iostream>
#endif

#include <util/arith_tools.h>
#include <util/c_types.h>
#include <util/std_types.h>
#include <util/symbol_table_base.h>

#include <ansi-c/c_qualifiers.h>

#include "cpp_declarator_converter.h"
#include "cpp_name.h"
#include "cpp_type2name.h"
#include "cpp_util.h"

#include <algorithm>

bool cpp_typecheckt::has_const(const typet &type)
{
  if(type.id()==ID_const)
    return true;
  else if(type.id()==ID_merged_type)
  {
    for(const typet &subtype : to_type_with_subtypes(type).subtypes())
    {
      if(has_const(subtype))
        return true;
    }

    return false;
  }
  else
    return false;
}

bool cpp_typecheckt::has_volatile(const typet &type)
{
  if(type.id()==ID_volatile)
    return true;
  else if(type.id()==ID_merged_type)
  {
    for(const typet &subtype : to_type_with_subtypes(type).subtypes())
    {
      if(has_volatile(subtype))
        return true;
    }

    return false;
  }
  else
    return false;
}

bool cpp_typecheckt::has_auto(const typet &type)
{
  if(type.id() == ID_auto)
    return true;
  else if(
    type.id() == ID_merged_type || type.id() == ID_frontend_pointer ||
    type.id() == ID_pointer)
  {
    for(const typet &subtype : to_type_with_subtypes(type).subtypes())
    {
      if(has_auto(subtype))
        return true;
    }

    return false;
  }
  else
    return false;
}

cpp_scopet &cpp_typecheckt::tag_scope(
  const irep_idt &base_name,
  bool has_body,
  bool tag_only_declaration)
{
  // The scope of a compound identifier is difficult,
  // and is different from C.
  //
  // For instance:
  // class A { class B {} }   --> A::B
  // class A { class B; }     --> A::B
  // class A { class B *p; }  --> ::B
  // class B { }; class A { class B *p; } --> ::B
  // class B { }; class A { class B; class B *p; } --> A::B

  // If there is a body, or it's a tag-only declaration,
  // it's always in the current scope, even if we already have
  // it in an upwards scope.

  if(has_body || tag_only_declaration)
    return cpp_scopes.current_scope();

  // No body. Not a tag-only-declaration.
  // Check if we have it already. If so, take it.

  // we should only look for tags, but we don't
  const auto id_set =
    cpp_scopes.current_scope().lookup(base_name, cpp_scopet::RECURSIVE);

  for(const auto &id : id_set)
    if(id->is_class())
      return static_cast<cpp_scopet &>(id->get_parent());

  // Tags without body that we don't have already
  // and that are not a tag-only declaration go into
  // the global scope of the namespace.
  return cpp_scopes.get_global_scope();
}

void cpp_typecheckt::typecheck_compound_type(
  struct_union_typet &type)
{
  // first save qualifiers
  c_qualifierst qualifiers(type);

  // now clear them from the type
  type.remove(ID_C_constant);
  type.remove(ID_C_volatile);
  type.remove(ID_C_restricted);

  // get the tag name
  bool has_tag=type.find(ID_tag).is_not_nil();
  irep_idt base_name;
  cpp_scopet *dest_scope=nullptr;
  bool has_body=type.find(ID_body).is_not_nil();
  bool tag_only_declaration=type.get_bool(ID_C_tag_only_declaration);
  bool is_union = type.id() == ID_union;

  if(!has_tag)
  {
    // most of these should be named by now; see
    // cpp_declarationt::name_anon_struct_union()

    base_name=std::string("#anon_")+std::to_string(++anon_counter);
    type.set(ID_C_is_anonymous, true);
    dest_scope=&cpp_scopes.current_scope();
  }
  else
  {
    const cpp_namet &cpp_name=
      to_cpp_name(type.find(ID_tag));

    // scope given?
    if(cpp_name.is_simple_name())
    {
      base_name=cpp_name.get_base_name();

      // anonymous structs always go into the current scope
      if(type.get_bool(ID_C_is_anonymous))
        dest_scope=&cpp_scopes.current_scope();
      else
        dest_scope=&tag_scope(base_name, has_body, tag_only_declaration);
    }
    else
    {
      cpp_save_scopet cpp_save_scope(cpp_scopes);
      cpp_typecheck_resolvet cpp_typecheck_resolve(*this);
      cpp_template_args_non_tct t_args;
      dest_scope=
        &cpp_typecheck_resolve.resolve_scope(cpp_name, base_name, t_args);
    }
  }

  // The identifier 'tag-X' matches what the C front-end does!
  // The hyphen is deliberate to avoid collisions with other
  // identifiers.
  const irep_idt symbol_name=
    dest_scope->prefix+
    "tag-"+id2string(base_name)+
    dest_scope->suffix;

  // check if we have it already

  if(const auto maybe_symbol=symbol_table.lookup(symbol_name))
  {
    // we do!
    const symbolt &symbol=*maybe_symbol;

    if(has_body)
    {
      if(
        symbol.type.id() == type.id() &&
        to_struct_union_type(symbol.type).is_incomplete())
      {
        // a previously incomplete struct/union becomes complete
        symbolt &writeable_symbol = symbol_table.get_writeable_ref(symbol_name);
        writeable_symbol.type.swap(type);
        typecheck_compound_body(writeable_symbol);
      }
      else if(symbol.type.get_bool(ID_C_is_anonymous))
      {
        // we silently ignore
      }
      else
      {
        error().source_location=type.source_location();
        error() << "compound tag '" << base_name << "' declared previously\n"
                << "location of previous definition: " << symbol.location
                << eom;
        throw 0;
      }
    }
    else if(symbol.type.id() != type.id())
    {
      error().source_location = type.source_location();
      error() << "redefinition of '" << symbol.pretty_name << "'"
              << " as different kind of tag" << eom;
      throw 0;
    }
  }
  else
  {
    // produce new symbol
    type_symbolt symbol{symbol_name, type, ID_cpp};
    symbol.base_name=base_name;
    symbol.location=type.source_location();
    symbol.module=module;
    symbol.pretty_name=
      cpp_scopes.current_scope().prefix+
      id2string(symbol.base_name)+
      cpp_scopes.current_scope().suffix;
    symbol.type.set(
      ID_tag, cpp_scopes.current_scope().prefix+id2string(symbol.base_name));

    // move early, must be visible before doing body
    symbolt *new_symbol;

    if(symbol_table.move(symbol, new_symbol))
    {
      error().source_location=symbol.location;
      error() << "cpp_typecheckt::typecheck_compound_type: "
              << "symbol_table.move() failed" << eom;
      throw 0;
    }

    // put into dest_scope
    cpp_idt &id=cpp_scopes.put_into_scope(*new_symbol, *dest_scope);

    id.id_class=cpp_idt::id_classt::CLASS;
    id.is_scope=true;
    id.prefix=cpp_scopes.current_scope().prefix+
              id2string(new_symbol->base_name)+
              cpp_scopes.current_scope().suffix+"::";
    id.class_identifier=new_symbol->name;
    id.id_class=cpp_idt::id_classt::CLASS;

    if(has_body)
      typecheck_compound_body(*new_symbol);
    else
    {
      struct_union_typet new_type(new_symbol->type.id());
      new_type.set(ID_tag, new_symbol->base_name);
      new_type.make_incomplete();
      new_type.add_source_location() = type.source_location();
      new_symbol->type.swap(new_type);
    }
  }

  if(is_union)
  {
    // create union tag
    union_tag_typet tag_type(symbol_name);
    qualifiers.write(tag_type);
    type.swap(tag_type);
  }
  else
  {
    // create struct tag
    struct_tag_typet tag_type(symbol_name);
    qualifiers.write(tag_type);
    type.swap(tag_type);
  }
}

void cpp_typecheckt::typecheck_compound_declarator(
  const symbolt &symbol,
  const cpp_declarationt &declaration,
  cpp_declaratort &declarator,
  struct_typet::componentst &components,
  const irep_idt &access,
  bool is_static,
  bool is_typedef,
  bool is_mutable)
{
  bool is_cast_operator=
    declaration.type().id()=="cpp-cast-operator";

  if(is_cast_operator)
  {
    PRECONDITION(
      declarator.name().get_sub().size() == 2 &&
      declarator.name().get_sub().front().id() == ID_operator);

    typet type=static_cast<typet &>(declarator.name().get_sub()[1]);
    declarator.type().add_subtype() = type;

    cpp_namet::namet name("(" + cpp_type2name(type) + ")");
    declarator.name().get_sub().back().swap(name);
  }

  typet final_type=
    declarator.merge_type(declaration.type());

  // this triggers template elaboration
  elaborate_class_template(final_type);

  typecheck_type(final_type);

  if(final_type.id() == ID_empty)
  {
    error().source_location = declaration.type().source_location();
    error() << "void-typed member not permitted" << eom;
    throw 0;
  }

  cpp_namet cpp_name;
  cpp_name.swap(declarator.name());

  irep_idt base_name;

  if(cpp_name.is_nil())
  {
    // Yes, there can be members without name.
    base_name=irep_idt();
  }
  else if(cpp_name.is_simple_name())
  {
    base_name=cpp_name.get_base_name();
  }
  else
  {
    error().source_location=cpp_name.source_location();
    error() << "declarator in compound needs to be simple name"
            << eom;
    throw 0;
  }

  bool is_method=!is_typedef && final_type.id()==ID_code;
  bool is_constructor=declaration.is_constructor();
  bool is_destructor=declaration.is_destructor();
  bool is_virtual=declaration.member_spec().is_virtual();
  bool is_explicit=declaration.member_spec().is_explicit();
  bool is_inline=declaration.member_spec().is_inline();

  final_type.set(ID_C_member_name, symbol.name);

  // first do some sanity checks

  if(is_virtual && !is_method)
  {
    error().source_location=cpp_name.source_location();
    error() << "only methods can be virtual" << eom;
    throw 0;
  }

  if(is_inline && !is_method)
  {
    error().source_location=cpp_name.source_location();
    error() << "only methods can be inlined" << eom;
    throw 0;
  }

  if(is_virtual && is_static)
  {
    error().source_location=cpp_name.source_location();
    error() << "static methods cannot be virtual" << eom;
    throw 0;
  }

  if(is_cast_operator && is_static)
  {
    error().source_location=cpp_name.source_location();
    error() << "cast operators cannot be static" << eom;
    throw 0;
  }

  if(is_constructor && is_virtual)
  {
    error().source_location=cpp_name.source_location();
    error() << "constructors cannot be virtual" << eom;
    throw 0;
  }

  if(!is_constructor && is_explicit)
  {
    error().source_location=cpp_name.source_location();
    error() << "only constructors can be explicit" << eom;
    throw 0;
  }

  if(is_constructor && base_name != symbol.base_name)
  {
    error().source_location=cpp_name.source_location();
    error() << "member function must return a value or void" << eom;
    throw 0;
  }

  if(is_destructor &&
     base_name!="~"+id2string(symbol.base_name))
  {
    error().source_location=cpp_name.source_location();
    error() << "destructor with wrong name" << eom;
    throw 0;
  }

  // now do actual work

  irep_idt identifier;

  // the below is a temporary hack
  // if(is_method || is_static)
  if(id2string(cpp_scopes.current_scope().prefix).find("#anon")==
     std::string::npos ||
     is_method || is_static)
  {
    // Identifiers for methods include the scope prefix.
    // Identifiers for static members include the scope prefix.
    identifier=
      cpp_scopes.current_scope().prefix+
      id2string(base_name);
  }
  else
  {
    // otherwise, we keep them simple
    identifier=base_name;
  }

  struct_typet::componentt component(identifier, final_type);
  component.set(ID_access, access);
  component.set_base_name(base_name);
  component.set_pretty_name(base_name);
  component.add_source_location()=cpp_name.source_location();

  if(cpp_name.is_operator())
  {
    component.set(ID_is_operator, true);
    component.type().set(ID_C_is_operator, true);
  }

  if(is_cast_operator)
    component.set(ID_is_cast_operator, true);

  if(declaration.member_spec().is_explicit())
    component.set(ID_is_explicit, true);

  // either blank, const, volatile, or const volatile
  const typet &method_qualifier=
    static_cast<const typet &>(declarator.add(ID_method_qualifier));

  if(is_static)
  {
    component.set(ID_is_static, true);
    component.type().set(ID_C_is_static, true);
  }

  if(is_typedef)
    component.set(ID_is_type, true);

  if(is_mutable)
    component.set(ID_is_mutable, true);

  exprt &value=declarator.value();
  irept &initializers=declarator.member_initializers();

  if(is_method)
  {
    if(
      value.id() == ID_code &&
      to_code(value).get_statement() == ID_cpp_delete)
    {
      value.make_nil();
      component.set(ID_access, ID_noaccess);
    }

    component.set(ID_is_inline, declaration.member_spec().is_inline());

    // the 'virtual' name of the function
    std::string virtual_name = id2string(component.get_base_name()) +
                               id2string(function_identifier(component.type()));

    if(has_const(method_qualifier))
      virtual_name+="$const";

    if(has_volatile(method_qualifier))
      virtual_name += "$volatile";

    if(to_code_type(component.type()).return_type().id() == ID_destructor)
      virtual_name="@dtor";

    // The method may be virtual implicitly.
    std::set<irep_idt> virtual_bases;

    for(const auto &comp : components)
    {
      if(comp.get_bool(ID_is_virtual))
      {
        if(comp.get(ID_virtual_name) == virtual_name)
        {
          is_virtual=true;
          const code_typet &code_type=to_code_type(comp.type());
          DATA_INVARIANT(
            !code_type.parameters().empty(), "must have parameters");
          const typet &pointer_type=code_type.parameters()[0].type();
          DATA_INVARIANT(
            pointer_type.id() == ID_pointer, "this must be pointer");
          virtual_bases.insert(
            to_pointer_type(pointer_type).base_type().get(ID_identifier));
        }
      }
    }

    if(!is_virtual)
    {
      typecheck_member_function(
        symbol, component, initializers,
        method_qualifier, value);

      if(!value.is_nil() && !is_static)
      {
        error().source_location=cpp_name.source_location();
        error() << "no initialization allowed here" << eom;
        throw 0;
      }
    }
    else // virtual
    {
      component.type().set(ID_C_is_virtual, true);
      component.type().set(ID_C_virtual_name, virtual_name);

      // Check if it is a pure virtual method
      if(value.is_not_nil() && value.is_constant())
      {
        mp_integer i;
        to_integer(to_constant_expr(value), i);
        if(i!=0)
        {
          error().source_location = declarator.name().source_location();
          error() << "expected 0 to mark pure virtual method, got " << i << eom;
          throw 0;
        }
        component.set(ID_is_pure_virtual, true);
        value.make_nil();
      }

      typecheck_member_function(
        symbol,
        component,
        initializers,
        method_qualifier,
        value);

      // get the virtual-table symbol type
      irep_idt vt_name="virtual_table::"+id2string(symbol.name);

      if(!symbol_table.has_symbol(vt_name))
      {
        // first time: create a virtual-table symbol type
        type_symbolt vt_symb_type{vt_name, struct_typet(), ID_cpp};
        vt_symb_type.base_name="virtual_table::"+id2string(symbol.base_name);
        vt_symb_type.pretty_name=vt_symb_type.base_name;
        vt_symb_type.module=module;
        vt_symb_type.location=symbol.location;
        vt_symb_type.type.set(ID_name, vt_symb_type.name);

        const bool failed=!symbol_table.insert(std::move(vt_symb_type)).second;
        CHECK_RETURN(!failed);

        // add a virtual-table pointer
        struct_typet::componentt compo(
          id2string(symbol.name) + "::@vtable_pointer",
          pointer_type(struct_tag_typet(vt_name)));
        compo.set_base_name("@vtable_pointer");
        compo.set_pretty_name(id2string(symbol.base_name) + "@vtable_pointer");
        compo.set(ID_is_vtptr, true);
        compo.set(ID_access, ID_public);
        components.push_back(compo);
        put_compound_into_scope(compo);
      }

      typet &vt=symbol_table.get_writeable_ref(vt_name).type;
      INVARIANT(vt.id()==ID_struct, "Virtual tables must be stored as struct");
      struct_typet &virtual_table=to_struct_type(vt);

      component.set(ID_virtual_name, virtual_name);
      component.set(ID_is_virtual, is_virtual);

      // add an entry to the virtual table
      struct_typet::componentt vt_entry(
        id2string(vt_name) + "::" + virtual_name,
        pointer_type(component.type()));
      vt_entry.set_base_name(virtual_name);
      vt_entry.set_pretty_name(virtual_name);
      vt_entry.set(ID_access, ID_public);
      vt_entry.add_source_location()=symbol.location;
      virtual_table.components().push_back(vt_entry);

      // take care of overloading
      while(!virtual_bases.empty())
      {
        irep_idt virtual_base=*virtual_bases.begin();

        // a new function that does 'late casting' of the 'this' parameter
        symbolt func_symb{
          id2string(component.get_name()) + "::" + id2string(virtual_base),
          component.type(),
          symbol.mode};
        func_symb.base_name = component.get_base_name();
        func_symb.pretty_name = component.get_base_name();
        func_symb.module=module;
        func_symb.location=component.source_location();

        // change the type of the 'this' pointer
        code_typet &code_type=to_code_type(func_symb.type);
        code_typet::parametert &this_parameter = code_type.parameters().front();
        to_pointer_type(this_parameter.type())
          .base_type()
          .set(ID_identifier, virtual_base);

        // create symbols for the parameters
        code_typet::parameterst &args=code_type.parameters();
        std::size_t i=0;
        for(auto &arg : args)
        {
          irep_idt param_base_name = arg.get_base_name();

          if(param_base_name.empty())
            param_base_name = "arg" + std::to_string(i++);

          symbolt arg_symb{
            id2string(func_symb.name) + "::" + id2string(param_base_name),
            arg.type(),
            symbol.mode};
          arg_symb.base_name = param_base_name;
          arg_symb.pretty_name = param_base_name;
          arg_symb.location=func_symb.location;

          arg.set_identifier(arg_symb.name);

          // add the parameter to the symbol table
          const bool failed=!symbol_table.insert(std::move(arg_symb)).second;
          CHECK_RETURN(!failed);
        }

        // do the body of the function
        typecast_exprt late_cast(
          lookup(args[0].get_identifier()).symbol_expr(),
          to_code_type(component.type()).parameters()[0].type());

        side_effect_expr_function_callt expr_call(
          symbol_exprt(component.get_name(), component.type()),
          {late_cast},
          uninitialized_typet{},
          source_locationt{});
        expr_call.arguments().reserve(args.size());

        for(const auto &arg : args)
        {
          expr_call.arguments().push_back(
            lookup(arg.get_identifier()).symbol_expr());
        }

        if(code_type.return_type().id()!=ID_empty &&
           code_type.return_type().id()!=ID_destructor)
        {
          expr_call.type()=to_code_type(component.type()).return_type();

          func_symb.value = code_blockt{{code_frontend_returnt(
            already_typechecked_exprt{std::move(expr_call)})}};
        }
        else
        {
          func_symb.value = code_blockt{{code_expressiont(
            already_typechecked_exprt{std::move(expr_call)})}};
        }

        // add this new function to the list of components

        struct_typet::componentt new_compo=component;
        new_compo.type()=func_symb.type;
        new_compo.set_name(func_symb.name);
        components.push_back(new_compo);

        // add the function to the symbol table
        {
          const bool failed=!symbol_table.insert(std::move(func_symb)).second;
          CHECK_RETURN(!failed);
        }

        put_compound_into_scope(new_compo);

        // next base
        virtual_bases.erase(virtual_bases.begin());
      }
    }
  }

  if(is_static && !is_method) // static non-method member
  {
    // add as global variable to symbol_table
    symbolt static_symbol{identifier, component.type(), symbol.mode};
    static_symbol.base_name = component.get_base_name();
    static_symbol.is_lvalue=true;
    static_symbol.is_static_lifetime=true;
    static_symbol.location=cpp_name.source_location();
    static_symbol.is_extern=true;

    // TODO: not sure about this: should be defined separately!
    dynamic_initializations.push_back(static_symbol.name);

    symbolt *new_symbol;
    if(symbol_table.move(static_symbol, new_symbol))
    {
      error().source_location=cpp_name.source_location();
      error() << "redeclaration of static member '" << static_symbol.base_name
              << "'" << eom;
      throw 0;
    }

    if(value.is_not_nil())
    {
      if(cpp_is_pod(new_symbol->type))
      {
        new_symbol->value.swap(value);
        c_typecheck_baset::do_initializer(*new_symbol);
      }
      else
      {
        symbol_exprt symexpr = symbol_exprt::typeless(new_symbol->name);

        exprt::operandst ops;
        ops.push_back(value);
        auto defcode = cpp_constructor(source_locationt(), symexpr, ops);
        CHECK_RETURN(defcode.has_value());

        new_symbol->value.swap(defcode.value());
      }
    }
  }

  // array members must have fixed size
  check_fixed_size_array(component.type());

  put_compound_into_scope(component);

  components.push_back(component);
}

/// check that an array has fixed size
void cpp_typecheckt::check_fixed_size_array(typet &type)
{
  if(type.id()==ID_array)
  {
    array_typet &array_type=to_array_type(type);

    if(array_type.size().is_not_nil())
    {
      if(array_type.size().id() == ID_symbol)
      {
        const symbol_exprt &s = to_symbol_expr(array_type.size());
        const symbolt &symbol = lookup(s.identifier());

        if(cpp_is_pod(symbol.type) && symbol.type.get_bool(ID_C_constant))
          array_type.size() = symbol.value;
      }

      make_constant_index(array_type.size());
    }

    // recursive call for multi-dimensional arrays
    check_fixed_size_array(array_type.element_type());
  }
}

void cpp_typecheckt::put_compound_into_scope(
  const struct_union_typet::componentt &compound)
{
  const irep_idt &base_name=compound.get_base_name();
  const irep_idt &name=compound.get_name();

  // nothing to do if no base_name (e.g., an anonymous bitfield)
  if(base_name.empty())
    return;

  if(compound.type().id()==ID_code)
  {
    // put the symbol into scope
    cpp_idt &id=cpp_scopes.current_scope().insert(base_name);
    id.id_class = compound.get_bool(ID_is_type) ? cpp_idt::id_classt::TYPEDEF
                                                : cpp_idt::id_classt::SYMBOL;
    id.identifier=name;
    id.class_identifier=cpp_scopes.current_scope().identifier;
    id.is_member=true;
    id.is_constructor =
      to_code_type(compound.type()).return_type().id() == ID_constructor;
    id.is_method=true;
    id.is_static_member=compound.get_bool(ID_is_static);

    // create function block-scope in the scope
    cpp_idt &id_block=
      cpp_scopes.current_scope().insert(
        irep_idt(std::string("$block:") + base_name.c_str()));

    id_block.id_class=cpp_idt::id_classt::BLOCK_SCOPE;
    id_block.identifier=name;
    id_block.class_identifier=cpp_scopes.current_scope().identifier;
    id_block.is_method=true;
    id_block.is_static_member=compound.get_bool(ID_is_static);

    id_block.is_scope=true;
    id_block.prefix = compound.get_string(ID_prefix);
    cpp_scopes.id_map[id.identifier]=&id_block;
  }
  else
  {
    // check if it's already there
    const auto id_set =
      cpp_scopes.current_scope().lookup(base_name, cpp_scopet::SCOPE_ONLY);

    for(const auto &id_it : id_set)
    {
      const cpp_idt &id=*id_it;

      // the name is already in the scope
      // this is ok if they belong to different categories
      if(!id.is_class() && !id.is_enum())
      {
        error().source_location=compound.source_location();
        error() << "'" << base_name << "' already in compound scope" << eom;
        throw 0;
      }
    }

    // put into the scope
    cpp_idt &id=cpp_scopes.current_scope().insert(base_name);
    id.id_class=compound.get_bool(ID_is_type)?
      cpp_idt::id_classt::TYPEDEF:
      cpp_idt::id_classt::SYMBOL;
    id.identifier=name;
    id.class_identifier=cpp_scopes.current_scope().identifier;
    id.is_member=true;
    id.is_method=false;
    id.is_static_member=compound.get_bool(ID_is_static);
  }
}

void cpp_typecheckt::typecheck_friend_declaration(
  symbolt &symbol,
  cpp_declarationt &declaration)
{
  // A friend of a class can be a function/method,
  // or a struct/class/union type.

  if(declaration.is_template())
  {
    error().source_location=declaration.type().source_location();
    error() << "friend template not supported" << eom;
    throw 0;
  }

  // we distinguish these whether there is a declarator
  if(declaration.declarators().empty())
  {
    typet &ftype=declaration.type();

    // must be struct or union
    if(ftype.id()!=ID_struct && ftype.id()!=ID_union)
    {
      error().source_location=declaration.type().source_location();
      error() << "unexpected friend" << eom;
      throw 0;
    }

    if(ftype.find(ID_body).is_not_nil())
    {
      error().source_location=declaration.type().source_location();
      error() << "friend declaration must not have compound body" << eom;
      throw 0;
    }

    cpp_save_scopet saved_scope(cpp_scopes);
    cpp_scopes.go_to_global_scope();
    typecheck_type(ftype);
    symbol.type.add(ID_C_friends).move_to_sub(ftype);

    return;
  }

  // It should be a friend function.
  // Do the declarators.

#ifdef DEBUG
  std::cout << "friend declaration: " << declaration.pretty() << '\n';
#endif

  for(auto &sub_it : declaration.declarators())
  {
#ifdef DEBUG
    std::cout << "decl: " << sub_it.pretty() << "\n with value "
              << sub_it.value().pretty() << '\n';
    std::cout << "  scope: " << cpp_scopes.current_scope().prefix << '\n';
#endif

    if(sub_it.value().is_not_nil())
      declaration.member_spec().set_inline(true);

    cpp_declarator_convertert cpp_declarator_converter(*this);
    cpp_declarator_converter.is_friend = true;
    const symbolt &conv_symb = cpp_declarator_converter.convert(
      declaration.type(),
      declaration.storage_spec(),
      declaration.member_spec(),
      sub_it);
    exprt symb_expr = cpp_symbol_expr(conv_symb);
    symbol.type.add(ID_C_friends).move_to_sub(symb_expr);
  }
}

void cpp_typecheckt::typecheck_compound_body(symbolt &symbol)
{
  cpp_save_scopet saved_scope(cpp_scopes);

  // enter scope of compound
  cpp_scopes.set_scope(symbol.name);

  PRECONDITION(symbol.type.id() == ID_struct || symbol.type.id() == ID_union);

  struct_union_typet &type=
    to_struct_union_type(symbol.type);

  // pull the base types in
  if(!type.find(ID_bases).get_sub().empty())
  {
    if(type.id()==ID_union)
    {
      error().source_location=symbol.location;
      error() << "union types must not have bases" << eom;
      throw 0;
    }

    typecheck_compound_bases(to_struct_type(type));
  }

  exprt &body=static_cast<exprt &>(type.add(ID_body));
  struct_union_typet::componentst &components=type.components();

  symbol.type.set(ID_name, symbol.name);

  // default access
  irep_idt access = type.default_access();

  bool found_ctor=false;
  bool found_dtor=false;

  // we first do everything _but_ the constructors

  Forall_operands(it, body)
  {
    if(it->id()==ID_cpp_declaration)
    {
      cpp_declarationt &declaration=
        to_cpp_declaration(*it);

      if(declaration.member_spec().is_friend())
      {
        typecheck_friend_declaration(symbol, declaration);
        continue; // done
      }

      if(declaration.is_template())
      {
        // remember access mode
        declaration.set(ID_C_access, access);
        convert_template_declaration(declaration);
        continue;
      }

      if(declaration.type().id().empty())
        continue;

      bool is_typedef=declaration.is_typedef();

      // is it tag-only?
      if(declaration.type().id()==ID_struct ||
         declaration.type().id()==ID_union ||
         declaration.type().id()==ID_c_enum)
        if(declaration.declarators().empty())
          declaration.type().set(ID_C_tag_only_declaration, true);

      declaration.name_anon_struct_union();
      typecheck_type(declaration.type());

      bool is_static=declaration.storage_spec().is_static();
      bool is_mutable=declaration.storage_spec().is_mutable();

      if(declaration.storage_spec().is_extern() ||
         declaration.storage_spec().is_auto() ||
         declaration.storage_spec().is_register())
      {
        error().source_location=declaration.storage_spec().location();
        error() << "invalid storage class specified for field" << eom;
        throw 0;
      }

      // anonymous member?
      if(
        declaration.declarators().empty() &&
        ((declaration.type().id() == ID_struct_tag &&
          follow_tag(to_struct_tag_type(declaration.type()))
            .get_bool(ID_C_is_anonymous)) ||
         (declaration.type().id() == ID_union_tag &&
          follow_tag(to_union_tag_type(declaration.type()))
            .get_bool(ID_C_is_anonymous)) ||
         declaration.type().get_bool(ID_C_is_anonymous)))
      {
        // we only allow this on struct/union types
        if(
          declaration.type().id() != ID_union_tag &&
          declaration.type().id() != ID_struct_tag)
        {
          error().source_location=declaration.type().source_location();
          error() << "member declaration does not declare anything"
                  << eom;
          throw 0;
        }

        convert_anon_struct_union_member(
          declaration, access, components);

        continue;
      }

      // declarators
      for(auto &declarator : declaration.declarators())
      {
        // Skip the constructors until all the data members
        // are discovered
        if(declaration.is_destructor())
          found_dtor=true;

        if(declaration.is_constructor())
        {
          found_ctor=true;
          continue;
        }

        typecheck_compound_declarator(
          symbol,
          declaration, declarator, components,
          access, is_static, is_typedef, is_mutable);
      }
    }
    else if(it->id()=="cpp-public")
      access=ID_public;
    else if(it->id()=="cpp-private")
      access=ID_private;
    else if(it->id()=="cpp-protected")
      access=ID_protected;
    else
    {
    }
  }

  // Add the default dtor, if needed
  // (we have to do the destructor before building the virtual tables,
  //  as the destructor may be virtual!)

  if((found_ctor || !cpp_is_pod(symbol.type)) && !found_dtor)
  {
    // build declaration
    cpp_declarationt dtor;
    default_dtor(symbol, dtor);

    typecheck_compound_declarator(
      symbol,
      dtor, dtor.declarators()[0], components,
      ID_public, false, false, false);
  }

  // set up virtual tables before doing the constructors
  if(symbol.type.id()==ID_struct)
    do_virtual_table(symbol);

  if(!found_ctor && !cpp_is_pod(symbol.type))
  {
    // it's public!
    exprt cpp_public("cpp-public");
    body.add_to_operands(std::move(cpp_public));

    // build declaration
    cpp_declarationt ctor;
    default_ctor(symbol.type.source_location(), symbol.base_name, ctor);
    body.add_to_operands(std::move(ctor));
  }

  // Reset the access type
  access = type.default_access();

  // All the data members are now known.
  // We now deal with the constructors that we are given.
  Forall_operands(it, body)
  {
    if(it->id()==ID_cpp_declaration)
    {
      cpp_declarationt &declaration=
        to_cpp_declaration(*it);

      if(!declaration.is_constructor())
        continue;

      for(auto &declarator : declaration.declarators())
      {
        #if 0
        irep_idt ctor_base_name=
          declarator.name().get_base_name();
        #endif

        if(declarator.value().is_not_nil()) // body?
        {
          if(declarator.find(ID_member_initializers).is_nil())
            declarator.set(ID_member_initializers, ID_member_initializers);

          if(type.id() == ID_union)
          {
            check_member_initializers(
              {}, type.components(), declarator.member_initializers());
          }
          else
          {
            check_member_initializers(
              to_struct_type(type).bases(),
              type.components(),
              declarator.member_initializers());
          }

          full_member_initialization(
            type,
            declarator.member_initializers());
        }

        // Finally, we typecheck the constructor with the
        // full member-initialization list
        // Shall all be false
        bool is_static=declaration.storage_spec().is_static();
        bool is_mutable=declaration.storage_spec().is_mutable();
        bool is_typedef=declaration.is_typedef();

        typecheck_compound_declarator(
          symbol,
          declaration, declarator, components,
          access, is_static, is_typedef, is_mutable);
      }
    }
    else if(it->id()=="cpp-public")
      access=ID_public;
    else if(it->id()=="cpp-private")
      access=ID_private;
    else if(it->id()=="cpp-protected")
      access=ID_protected;
    else
    {
    }
  }

  if(!cpp_is_pod(symbol.type))
  {
    // Add the default copy constructor
    struct_typet::componentt component;

    if(!find_cpctor(symbol))
    {
      // build declaration
      cpp_declarationt cpctor;
      default_cpctor(symbol, cpctor);
      CHECK_RETURN(cpctor.declarators().size() == 1);

      exprt value(ID_cpp_not_typechecked);
      value.copy_to_operands(cpctor.declarators()[0].value());
      cpctor.declarators()[0].value()=value;

      typecheck_compound_declarator(
        symbol,
        cpctor, cpctor.declarators()[0], components,
        ID_public, false, false, false);
    }

    // Add the default assignment operator
    if(!find_assignop(symbol))
    {
      // build declaration
      cpp_declarationt assignop;
      default_assignop(symbol, assignop);
      CHECK_RETURN(assignop.declarators().size() == 1);

      // The value will be typechecked only if the operator
      // is actually used
      cpp_declaratort declarator;
      assignop.declarators().push_back(declarator);
      assignop.declarators()[0].value() = exprt(ID_cpp_not_typechecked);

      typecheck_compound_declarator(
        symbol,
        assignop, assignop.declarators()[0], components,
        ID_public, false, false, false);
    }
  }

  // clean up!
  symbol.type.remove(ID_body);
}

void cpp_typecheckt::move_member_initializers(
  irept &initializers,
  const code_typet &type,
  exprt &value)
{
  // see if we have initializers
  if(!initializers.get_sub().empty())
  {
    const source_locationt &location=
      static_cast<const source_locationt &>(
        initializers.find(ID_C_source_location));

    if(type.return_type().id() != ID_constructor)
    {
      error().source_location=location;
      error() << "only constructors are allowed to "
              << "have member initializers" << eom;
      throw 0;
    }

    if(value.is_nil())
    {
      error().source_location=location;
      error() << "only constructors with body are allowed to "
              << "have member initializers" << eom;
      throw 0;
    }

    if(to_code(value).get_statement() != ID_block)
      value = code_blockt{{to_code(value)}};

    exprt::operandst::iterator o_it=value.operands().begin();
    for(const auto &initializer : initializers.get_sub())
    {
      o_it =
        value.operands().insert(o_it, static_cast<const exprt &>(initializer));
      o_it++;
    }
  }
}

void cpp_typecheckt::typecheck_member_function(
  const symbolt &compound_symbol,
  struct_typet::componentt &component,
  irept &initializers,
  const typet &method_qualifier,
  exprt &value)
{
  code_typet &type = to_code_type(component.type());

  if(component.get_bool(ID_is_static))
  {
    if(!method_qualifier.id().empty())
    {
      error().source_location=component.source_location();
      error() << "method is static -- no qualifiers allowed" << eom;
      throw 0;
    }
  }
  else
  {
    add_this_to_method_type(compound_symbol, type, method_qualifier);
  }

  if(value.id() == ID_cpp_not_typechecked && value.has_operands())
  {
    move_member_initializers(
      initializers, type, to_multi_ary_expr(value).op0());
  }
  else
    move_member_initializers(initializers, type, value);

  irep_idt f_id=
    function_identifier(component.type());

  const irep_idt identifier=
    cpp_scopes.current_scope().prefix+
    id2string(component.get_base_name())+
    id2string(f_id);

  component.set_name(identifier);
  component.set(ID_prefix, id2string(identifier) + "::");

  if(value.is_not_nil())
    to_code_type(type).set_inlined(true);

  symbolt symbol{identifier, type, compound_symbol.mode};
  symbol.base_name=component.get_base_name();
  symbol.value.swap(value);
  symbol.module=module;
  symbol.location=component.source_location();

  // move early, it must be visible before doing any value
  symbolt *new_symbol;

  const bool symbol_exists = symbol_table.move(symbol, new_symbol);
  if(symbol_exists && new_symbol->is_weak)
  {
    // there might have been an earlier friend declaration
    *new_symbol = std::move(symbol);
  }
  else if(symbol_exists)
  {
    error().source_location=symbol.location;
    error() << "failed to insert new method symbol: " << symbol.name << '\n'
            << "name of previous symbol: " << new_symbol->name << '\n'
            << "location of previous symbol: " << new_symbol->location << eom;

    throw 0;
  }

  // Is this in a class template?
  // If so, we defer typechecking until used.
  if(cpp_scopes.current_scope().get_parent().is_template_scope())
    deferred_typechecking.insert(new_symbol->name);
  else // remember for later typechecking of body
    add_method_body(new_symbol);
}

void cpp_typecheckt::add_this_to_method_type(
  const symbolt &compound_symbol,
  code_typet &type,
  const typet &method_qualifier)
{
  typet subtype;

  if(compound_symbol.type.id() == ID_union)
    subtype = union_tag_typet(compound_symbol.name);
  else
    subtype = struct_tag_typet(compound_symbol.name);

  if(has_const(method_qualifier))
    subtype.set(ID_C_constant, true);

  if(has_volatile(method_qualifier))
    subtype.set(ID_C_volatile, true);

  code_typet::parametert parameter(pointer_type(subtype));
  parameter.set_identifier(ID_this);
  parameter.set_base_name(ID_this);
  parameter.set_this();
  if(!cpp_scopes.current_scope().get_parent().is_template_scope())
    convert_parameter(compound_symbol.mode, parameter);

  code_typet::parameterst &parameters = type.parameters();
  parameters.insert(parameters.begin(), parameter);
}

void cpp_typecheckt::add_anonymous_members_to_scope(
  const symbolt &struct_union_symbol)
{
  const struct_union_typet &struct_union_type=
    to_struct_union_type(struct_union_symbol.type);

  const struct_union_typet::componentst &struct_union_components=
    struct_union_type.components();

  // do scoping -- the members of the struct/union
  // should be visible in the containing struct/union,
  // and that recursively!

  for(const auto &comp : struct_union_components)
  {
    if(comp.type().id()==ID_code)
    {
      error().source_location=struct_union_symbol.type.source_location();
      error() << "anonymous struct/union member '"
              << struct_union_symbol.base_name
              << "' shall not have function members" << eom;
      throw 0;
    }

    if(comp.get_anonymous())
    {
      const symbolt &symbol=lookup(comp.type().get(ID_identifier));
      // recursive call
      add_anonymous_members_to_scope(symbol);
    }
    else
    {
      const irep_idt &base_name=comp.get_base_name();

      if(cpp_scopes.current_scope().contains(base_name))
      {
        error().source_location=comp.source_location();
        error() << "'" << base_name << "' already in scope" << eom;
        throw 0;
      }

      cpp_idt &id=cpp_scopes.current_scope().insert(base_name);
      id.id_class=cpp_idt::id_classt::SYMBOL;
      id.identifier=comp.get_name();
      id.class_identifier=struct_union_symbol.name;
      id.is_member=true;
    }
  }
}

void cpp_typecheckt::convert_anon_struct_union_member(
  const cpp_declarationt &declaration,
  const irep_idt &access,
  struct_typet::componentst &components)
{
  const struct_union_typet &final_type =
    declaration.type().id() == ID_struct_tag
      ? static_cast<const struct_union_typet &>(
          follow_tag(to_struct_tag_type(declaration.type())))
      : static_cast<const struct_union_typet &>(
          follow_tag(to_union_tag_type(declaration.type())));
  symbolt &struct_union_symbol =
    symbol_table.get_writeable_ref(final_type.get(ID_name));

  if(declaration.storage_spec().is_static() ||
     declaration.storage_spec().is_mutable())
  {
    error().source_location=struct_union_symbol.type.source_location();
    error() << "storage class is not allowed here" << eom;
    throw 0;
  }

  if(!cpp_is_pod(struct_union_symbol.type))
  {
    error().source_location=struct_union_symbol.type.source_location();
    error() << "anonymous struct/union member is not POD" << eom;
    throw 0;
  }

  // produce an anonymous member
  irep_idt base_name="#anon_member"+std::to_string(components.size());

  irep_idt identifier=
    cpp_scopes.current_scope().prefix+
    base_name.c_str();

  typet compound_type;

  if(struct_union_symbol.type.id() == ID_union)
    compound_type = union_tag_typet(struct_union_symbol.name);
  else
    compound_type = struct_tag_typet(struct_union_symbol.name);

  struct_typet::componentt component(identifier, compound_type);
  component.set_access(access);
  component.set_base_name(base_name);
  component.set_pretty_name(base_name);
  component.set_anonymous(true);
  component.add_source_location()=declaration.source_location();

  components.push_back(component);

  add_anonymous_members_to_scope(struct_union_symbol);

  put_compound_into_scope(component);

  struct_union_symbol.type.set(ID_C_unnamed_object, base_name);
}

bool cpp_typecheckt::get_component(
  const source_locationt &source_location,
  const exprt &object,
  const irep_idt &component_name,
  exprt &member)
{
  PRECONDITION(
    object.type().id() == ID_struct_tag || object.type().id() == ID_union_tag);

  struct_union_typet final_type =
    object.type().id() == ID_struct_tag
      ? static_cast<const struct_union_typet &>(
          follow_tag(to_struct_tag_type(object.type())))
      : static_cast<const struct_union_typet &>(
          follow_tag(to_union_tag_type(object.type())));

  const struct_union_typet::componentst &components=
    final_type.components();

  for(const auto &component : components)
  {
    member_exprt tmp(object, component.get_name(), component.type());
    tmp.add_source_location()=source_location;

    if(component.get_name()==component_name)
    {
      member.swap(tmp);

      bool not_ok=check_component_access(component, final_type);
      if(not_ok)
      {
        if(disable_access_control)
        {
          member.set(ID_C_not_accessible, true);
          member.set(ID_C_access, component.get(ID_access));
        }
        else
        {
          error().source_location=source_location;
          error() << "member '" << component_name << "' is not accessible ("
                  << component.get(ID_access) << ")" << eom;
          throw 0;
        }
      }

      if(object.get_bool(ID_C_lvalue))
        member.set(ID_C_lvalue, true);

      if(
        object.type().get_bool(ID_C_constant) &&
        !component.get_bool(ID_is_mutable))
      {
        member.type().set(ID_C_constant, true);
      }

      member.add_source_location()=source_location;

      return true; // component found
    }
    else if(
      (component.type().id() == ID_struct_tag &&
       follow_tag(to_struct_tag_type(component.type()))
         .find(ID_C_unnamed_object)
         .is_not_nil()) ||
      (component.type().id() == ID_union_tag &&
       follow_tag(to_union_tag_type(component.type()))
         .find(ID_C_unnamed_object)
         .is_not_nil()) ||
      component.type().find(ID_C_unnamed_object).is_not_nil())
    {
      // could be anonymous union or struct

      if(
        component.type().id() == ID_union_tag ||
        component.type().id() == ID_struct_tag)
      {
        // recursive call!
        if(get_component(source_location, tmp, component_name, member))
        {
          if(check_component_access(component, final_type))
          {
            error().source_location=source_location;
            error() << "member '" << component_name << "' is not accessible"
                    << eom;
            throw 0;
          }

          if(object.get_bool(ID_C_lvalue))
            member.set(ID_C_lvalue, true);

          if(
            object.get_bool(ID_C_constant) &&
            !component.get_bool(ID_is_mutable))
          {
            member.type().set(ID_C_constant, true);
          }

          member.add_source_location()=source_location;
          return true; // component found
        }
      }
    }
  }

  return false; // component not found
}

bool cpp_typecheckt::check_component_access(
  const struct_union_typet::componentt &component,
  const struct_union_typet &struct_union_type)
{
  const irep_idt &access=component.get(ID_access);

  if(access == ID_noaccess)
    return true; // not ok

  if(access==ID_public)
    return false; // ok

  PRECONDITION(access == ID_private || access == ID_protected);

  const irep_idt &struct_identifier=
    struct_union_type.get(ID_name);

  for(cpp_scopet *pscope = &(cpp_scopes.current_scope());
      !(pscope->is_root_scope());
      pscope = &(pscope->get_parent()))
  {
    if(pscope->is_class())
    {
      if(pscope->identifier==struct_identifier)
        return false; // ok

      const struct_typet &scope_struct=
        to_struct_type(lookup(pscope->identifier).type);

      if(subtype_typecast(
        to_struct_type(struct_union_type), scope_struct))
        return false; // ok

      else break;
    }
  }

  // check friendship
  const irept::subt &friends = struct_union_type.find(ID_C_friends).get_sub();

  for(const auto &friend_symb : friends)
  {
    const cpp_scopet &friend_scope =
      cpp_scopes.get_scope(friend_symb.get(ID_identifier));

    for(cpp_scopet *pscope = &(cpp_scopes.current_scope());
        !(pscope->is_root_scope());
        pscope = &(pscope->get_parent()))
    {
      if(friend_scope.identifier==pscope->identifier)
        return false; // ok

      if(pscope->is_class())
        break;
    }
  }

  return true; // not ok
}

void cpp_typecheckt::get_bases(
  const struct_typet &type,
  std::set<irep_idt> &set_bases) const
{
  for(const auto &b : type.bases())
  {
    DATA_INVARIANT(b.id() == ID_base, "base class expression expected");

    const struct_typet &base = to_struct_type(lookup(b.type()).type);

    set_bases.insert(base.get(ID_name));
    get_bases(base, set_bases);
  }
}

void cpp_typecheckt::get_virtual_bases(
  const struct_typet &type,
  std::list<irep_idt> &vbases) const
{
  if(std::find(vbases.begin(), vbases.end(), type.get(ID_name))!=vbases.end())
    return;

  for(const auto &b : type.bases())
  {
    DATA_INVARIANT(b.id() == ID_base, "base class expression expected");

    const struct_typet &base = to_struct_type(lookup(b.type()).type);

    if(b.get_bool(ID_virtual))
      vbases.push_back(base.get(ID_name));

    get_virtual_bases(base, vbases);
  }
}

bool cpp_typecheckt::subtype_typecast(
  const struct_typet &from,
  const struct_typet &to) const
{
  if(from.get(ID_name)==to.get(ID_name))
    return true;

  std::set<irep_idt> bases;

  get_bases(from, bases);

  return bases.find(to.get(ID_name))!=bases.end();
}

void cpp_typecheckt::make_ptr_typecast(
  exprt &expr,
  const pointer_typet &dest_type)
{
  typet src_type=expr.type();

  PRECONDITION(src_type.id() == ID_pointer);

  const struct_typet &src_struct =
    follow_tag(to_struct_tag_type(to_pointer_type(src_type).base_type()));

  const struct_typet &dest_struct =
    follow_tag(to_struct_tag_type(dest_type.base_type()));

  PRECONDITION(
    subtype_typecast(src_struct, dest_struct) ||
    subtype_typecast(dest_struct, src_struct));

  expr = typecast_exprt(expr, dest_type);
}