[Bug c++/84434] New: [8 Regression] internal compiler error: tree check: expected var_decl or field_decl or function_decl or type_decl or template_decl, have using_decl in build_deduction_guide, at cp/pt.c:25636

["mpolacek at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84434

            Bug ID: 84434
           Summary: [8 Regression] internal compiler error: tree check:
                    expected var_decl or field_decl or function_decl or
                    type_decl or template_decl, have using_decl in
                    build_deduction_guide, at cp/pt.c:25636
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mpolacek at gcc dot gnu.org
  Target Milestone: ---

namespace std {
template <typename _Tp> using decay_t = _Tp;
template <typename> class optional {};
} // namespace std

class RiskAnalysis {
  struct Context;
  void RunAnalysis(std::optional<Context>) noexcept;
};
namespace ext {
namespace detail::scope_guard {
template <typename Fn> class A {
  Fn m_fn;

public:
  template <typename Fn_> A(Fn_ p1) : m_fn(p1) {}
};
template <typename... Params> class B {
  using callback_type = scope_guard::A<Params...>;
  callback_type callback;

public:
  template <typename... Params_> B(Params_... p1) : callback(p1...) {}
};
template <typename T> struct C { using type = T; };
template <typename T> using unwrap_decay_t = typename C<std::decay_t<T>>::type;
} // namespace detail::scope_guard
template <typename... Params>
struct scope_guard : detail::scope_guard::B<Params...> {
  using base_type = detail::scope_guard::B<Params...>;
  using base_type::base_type;
  ~scope_guard();
};
template <typename... Params>
scope_guard(Params...)
    ->scope_guard<detail::scope_guard::unwrap_decay_t<Params>...>;
} // namespace ext

void RiskAnalysis::RunAnalysis(std::optional<Context>) noexcept {
  ext::scope_guard([] {});
}

$ ./cc1plus -quiet bz.cc -std=c++17
bz.cc: In member function ‘void
RiskAnalysis::RunAnalysis(std::optional<RiskAnalysis::Context>)’:
bz.cc:40:25: internal compiler error: tree check: expected var_decl or
field_decl or function_decl or type_decl or template_decl, have using_decl in
build_deduction_guide, at cp/pt.c:25636
   ext::scope_guard([] {});
                         ^
0x15d5158 tree_check_failed(tree_node const*, char const*, int, char const*,
...)
        /home/marek/src/gcc/gcc/tree.c:9335
0x82674b tree_check5(tree_node*, char const*, int, char const*, tree_code,
tree_code, tree_code, tree_code, tree_code)
        /home/marek/src/gcc/gcc/tree.h:3223
0xa71f40 build_deduction_guide
        /home/marek/src/gcc/gcc/cp/pt.c:25636
0xa74140 do_class_deduction
        /home/marek/src/gcc/gcc/cp/pt.c:25850
0xa74955 do_auto_deduction(tree_node*, tree_node*, tree_node*, int,
auto_deduction_context, tree_node*, int)
        /home/marek/src/gcc/gcc/cp/pt.c:25978
0xb110d1 build_functional_cast(tree_node*, tree_node*, int)
        /home/marek/src/gcc/gcc/cp/typeck2.c:2088
0x9cefcb cp_parser_functional_cast
        /home/marek/src/gcc/gcc/cp/parser.c:27250
0x9a6287 cp_parser_postfix_expression
        /home/marek/src/gcc/gcc/cp/parser.c:6952
0x9a9b63 cp_parser_unary_expression
        /home/marek/src/gcc/gcc/cp/parser.c:8318
0x9aac7f cp_parser_cast_expression
        /home/marek/src/gcc/gcc/cp/parser.c:9086
0x9aad79 cp_parser_binary_expression
        /home/marek/src/gcc/gcc/cp/parser.c:9187
0x9abad7 cp_parser_assignment_expression
        /home/marek/src/gcc/gcc/cp/parser.c:9476
0x9abe74 cp_parser_expression
        /home/marek/src/gcc/gcc/cp/parser.c:9645
0x9aefee cp_parser_expression_statement
        /home/marek/src/gcc/gcc/cp/parser.c:11112
0x9ae8fb cp_parser_statement
        /home/marek/src/gcc/gcc/cp/parser.c:10916
0x9af64d cp_parser_statement_seq_opt
        /home/marek/src/gcc/gcc/cp/parser.c:11255
0x9af543 cp_parser_compound_statement
        /home/marek/src/gcc/gcc/cp/parser.c:11209
0x9c3eaa cp_parser_function_body
        /home/marek/src/gcc/gcc/cp/parser.c:21750
0x9c416d cp_parser_ctor_initializer_opt_and_function_body
        /home/marek/src/gcc/gcc/cp/parser.c:21787
0x9cdad1 cp_parser_function_definition_after_declarator
        /home/marek/src/gcc/gcc/cp/parser.c:26688
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