blocking_kind customization does not compile

[Tradias]

With the "recent" blocking_kind rework there are several places in the code that look like this (godbolt):

namespace unifex
{
inline constexpr struct blocking_t {
    auto operator()() const { return ""; }
} blocking;

namespace _let_v
{
struct _sender {
  static constexpr int blocking = 1;

  friend auto tag_invoke(const _sender& sender) noexcept {
    const char* v = blocking();  // error: called object type 'int' is not a function or function pointer
  }
};
}
}

For example in let_value.hpp:

libunifex/include/unifex/let_value.hpp

Lines 384 to 386 in 2358687

	friend constexpr blocking_kind tag_invoke(tag_t<unifex::blocking>, const type& sender) noexcept {
	// get the runtime blocking_kind for the predecessor
	blocking_kind pred = blocking(sender.pred_);

I don't understand how your pipeline even managed to compile libunifex. This godbolt example does not: https://godbolt.org/z/6MdYYM586

Proposed solution:

blocking_kind pred = unifex::blocking(sender.pred_);

[ispeters]

I don't understand how your pipeline even managed to compile libunifex.

Excellent question! The only guesses I have are old, non-conformant compilers, or maybe we're not invoking the broken code.