Clang-Tidy: modernize-use-nullptr does not make sense with spaceship operator

[pavelkryukov]

Reopening #45580, as the problem was not solved:

https://godbolt.org/z/3hed7vPvM

#include <compare>

struct A {
  int a;
  constexpr auto operator<=>(const A&) const = default;
};

bool foo(A x, A y) { return x < y; }

Command line:

clang-tidy-13 -checks='hicpp-use-nullptr' tidy20.cpp -- -std=c++20

Output:

<source>:5:56: warning: use nullptr [hicpp-use-nullptr]
    constexpr auto operator<=>(const A&) const = default;
                                                       ^
                                                        nullptr

Also, for strange reasons I cannot escape it with NOLINTNEXTLINE with local clang-tidy-13.
Godbolt's trunk version suppresses warning correctly.

[llvmbot]

@llvm/issue-subscribers-c-20

[llvmbot]

@llvm/issue-subscribers-bug

[llvmbot]

@llvm/issue-subscribers-clang-tidy

[JonasToth]

for the suppression: maybe this check is aliased, did you use NOLINTNEXTLINE(modernize-use-nullptr)? Aliased checks cause the warning to appear multiple times.

[pavelkryukov]

Yes, I did. It did not help :-(

[jensmassberg]

modernize-use-nullptr gives a warning for

#include <compare>

struct A {
  int a;
  constexpr auto operator<=>(const A&) const = default;
};

bool foo(A x, A y) { return x < y; }

but it doesn't warn for

#include <compare>

struct A {
  constexpr auto operator<=>(const A&) const = default;
};

bool foo(A x, A y) { return x < y; }

nor for

namespace std {
struct strong_ordering {
  int n;
  constexpr operator int() const { return n; }
  static const strong_ordering equal, greater, less;
};
constexpr strong_ordering strong_ordering::equal = {0};
constexpr strong_ordering strong_ordering::greater = {1};
constexpr strong_ordering strong_ordering::less = {-1};
} // namespace std

struct A {
  int a;
  constexpr auto operator<=>(const A&) const = default;
};

bool foo(A x, A y) { return x < y; }

The latter one is equivalent to the C++20 test for modernize-use-nullptr .