[BUG] Disable UFCS on deduced return type not yet deduced (f: () x.f();)

[JohelEGP]

Title: Disable UFCS on deduced return type not yet deduced (f: () x.f();).

Minimal reproducer (https://cpp2.godbolt.org/z/x8GsWo7cT):

#include <ranges>
arity: @struct type = {
  range: type == std::ranges::iota_view<i16, i16>;
  value: range = ();
  begin: (this) -> _ = {
    return std::ranges::iterator_t<range>(); // Deduce.
    return value.begin(); // OK.
    return begin(); // Recurses.
  }
  // error: function 'end' with deduced return type cannot be used before it is defined
  end: (this) value.end();
}
main: () = { }

Commands:

cppfront main.cpp2
clang++18 -std=c++23 -stdlib=libc++ -lc++abi -pedantic-errors -Wall -Wextra -Wconversion -Werror=unused-result -Werror=unused-value -Werror=unused-parameter -I . main.cpp

Expected result: For arity::end to be well-formed by not naming itself in its body.

Actual result and error:

Cpp2 lowered to Cpp1:

//=== Cpp2 type declarations ====================================================


#include "cpp2util.h"

#line 1 "/app/example.cpp2"

#line 2 "/app/example.cpp2"
class arity;
  

//=== Cpp2 type definitions and function declarations ===========================

#line 1 "/app/example.cpp2"
#include <ranges>
class arity {
#line 3 "/app/example.cpp2"
  public: using range = std::ranges::iota_view<cpp2::i16,cpp2::i16>;
  public: range value {}; 
  public: [[nodiscard]] auto begin() const& -> auto;

#line 10 "/app/example.cpp2"
  // error: function 'end' with deduced return type cannot be used before it is defined
  public: [[nodiscard]] auto end() const& -> auto;
};
auto main() -> int;

//=== Cpp2 function definitions =================================================

#line 1 "/app/example.cpp2"

#line 5 "/app/example.cpp2"
  [[nodiscard]] auto arity::begin() const& -> auto{
    return std::ranges::iterator_t<range>(); // Deduce.
    return CPP2_UFCS(begin)(value); // OK.
    return begin(); // Recurses.
  }

  [[nodiscard]] auto arity::end() const& -> auto { return CPP2_UFCS(end)(value);  }

auto main() -> int{}

Output:

main.cpp2:11:69: error: function 'end' with deduced return type cannot be used before it is defined
   11 |   [[nodiscard]] auto arity::end() const& -> auto { return CPP2_UFCS(end)(value);  }
      |                                                                     ^
main.cpp2:11:29: note: 'end' declared here
   11 |   [[nodiscard]] auto arity::end() const& -> auto { return CPP2_UFCS(end)(value);  }
      |                             ^

See also:

• [BUG] Variable with placeholder type can't share name with member call in initializer #550
• [BUG] Disable UFCS if the function needs to be captured #863
• [BUG] Disable UFCS on function named after variable being initialized with CTAD #864