[llvm-bugs] [Bug 44325] New: Wzero-as-null-pointer-constant warns when using `operator<=>`

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=44325

            Bug ID: 44325
           Summary: Wzero-as-null-pointer-constant warns when using
                    `operator<=>`
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: david at doublewise.net
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org,
                    neeilans at live.com, richard-llvm at metafoo.co.uk

```
#include <compare>

auto b = 1 <=> 2 < 0;
```

Outputs:

```
<source>:3:20: warning: zero as null pointer constant
[-Wzero-as-null-pointer-constant]

auto b = 1 <=> 2 < 0;

                   ^

                   nullptr

1 warning generated.

Compiler returned: 0
```




See it live: https://godbolt.org/z/9a8cnD



Technically, the warning is accurate. User code has a literal `0` that is being
passed to a function accepting a `nullptr`. However, this is an implementation
detail of the standard library and the intended interface for use (users should
not use `nullptr` there), so we should not warn users for doing so (and
definitely should not direct them to change their code).

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