[Bug 1831222] [NEW] Concept declaration requiring another concept fails

[Piotr Mikołajczyk]

Public bug reported:

template<typename T>
concept bool Addable = requires (T x, T y) {
    { x + y } -> T;
    { x += y } -> T&;
};

template<typename T>
concept bool SSemiring = requires(typename T::element_t& a, typename T::element_t& b, const Addable* vptr) {

    { a + b } -> typename T::element_t;
    { a * b } -> typename T::element_t;

    { T::zero() } -> typename T::element_t;
    { T::one() } -> typename T::element_t;

    { typename T::element_t{vptr} };

};

produces:
gcc_bug.hpp:10:93: internal compiler error: in synthesize_implicit_template_parm, at cp/parser.c:39065
 concept bool SSemiring = requires(typename T::element_t& a, typename T::element_t& b, const Addable* vptr) {
                                                                                             ^~~~~~~

** Affects: gcc-8 (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: concepts

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https://bugs.launchpad.net/bugs/1831222

Title:
  Concept declaration requiring another concept fails

Status in gcc-8 package in Ubuntu:
  New

Bug description:
  template<typename T>
  concept bool Addable = requires (T x, T y) {
      { x + y } -> T;
      { x += y } -> T&;
  };

  template<typename T>
  concept bool SSemiring = requires(typename T::element_t& a, typename T::element_t& b, const Addable* vptr) {

      { a + b } -> typename T::element_t;
      { a * b } -> typename T::element_t;

      { T::zero() } -> typename T::element_t;
      { T::one() } -> typename T::element_t;

      { typename T::element_t{vptr} };

  };

  produces:
  gcc_bug.hpp:10:93: internal compiler error: in synthesize_implicit_template_parm, at cp/parser.c:39065
   concept bool SSemiring = requires(typename T::element_t& a, typename T::element_t& b, const Addable* vptr) {
                                                                                               ^~~~~~~

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