hicpp-use-nullptr does not make sense with spaceship operator

[pavelkryukov]

Bugzilla Link	46235
Resolution	FIXED
Resolved on	Feb 09, 2021 14:27
Version	unspecified
OS	All
CC	@dermojo,@maxim-banaev
Fixed by commit(s)	98146c1

Extended Description

Hello

With the following input:

#include

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

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

and command line:

clang-tidy-10 -checks='hicpp-use-nullptr' tidy20.cpp -- -std=c++20

Clang-Tidy generates following output which does not make sense:

./tidy20.cpp:5:56: warning: use nullptr [hicpp-use-nullptr]
constexpr auto operator<=>(const A&) const = default;
^
nullptr
./tidy20.cpp:8:31: warning: use nullptr [hicpp-use-nullptr]
bool foo(A x, A y) { return x < y; }
^
nullptr

[pavelkryukov]

godbolt.org: https://godbolt.org/z/3Ca-Zn

[llvmbot]

Looking at the AST it's fairly easy to see why this warning is generated

In the defaulted function definition:

| | | | -ImplicitCastExpr <col:56> 'std::__1::_CmpUnspecifiedParam':'void (std::__1::_CmpUnspecifiedType::*)()' <NullToMemberPointer> | | | | -IntegerLiteral col:56 'int' 0

In foo(A, A):

-ImplicitCastExpr <col:31> 'std::__1::_CmpUnspecifiedParam':'void (std::__1::_CmpUnspecifiedType::*)()' <NullToMemberPointer> -IntegerLiteral col:31 'int' 0

Basically part of the spaceship operator comparison expands to

if (R cmp = static_cast(op); cmp != 0) return cmp;

It seems that the 0 is being cast to a member pointer for the comparison which ultimately results in this warning.

[llvmbot]

*** Bug llvm/llvm-bugzilla-archive#46636 has been marked as a duplicate of this bug. ***

[llvmbot]

*** Bug llvm/llvm-bugzilla-archive#49089 has been marked as a duplicate of this bug. ***

[llvmbot]

Should be fixed in 98146c1

[pavelkryukov]

Thank you!

[llvmbot]

mentioned in issue llvm/llvm-bugzilla-archive#46636

[llvmbot]

mentioned in issue llvm/llvm-bugzilla-archive#49089

[llvmbot]

mentioned in issue llvm/llvm-bugzilla-archive#50582