[Bug c++/94510] New: nullptr_t implicitly cast to zero twice in std::array

[kndevl at outlook dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94510

            Bug ID: 94510
           Summary: nullptr_t implicitly cast to zero twice in std::array
           Product: gcc
           Version: 9.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kndevl at outlook dot com
  Target Milestone: ---

`std::array<int, 3> arr{ nullptr, 0, 0 };` is expected to fail to compile
similar to how `std::array<int, 3> arr{ nullptr, 0, 1 };` fails. What I infer
is that if all elements are effectively zero, type conversions are not checked.
This makes sense if a variable of static storage duration is initialized to
zero and std::array constructor can ignore the arguments in the initializer if
all arguments are implicitly zero. 

Is there anything on the C++ standard that allows this optimization I am
missing here?

# This works fine, as expected

`g++ -save-temps -c not-bug.cpp`

> not-bug.cpp: In function ‘void test()’:
> not-bug.cpp:4:43: error: cannot convert ‘std::nullptr_t’ to ‘int’ in initialization
>     4 |     std::array<int, 3> arr{ nullptr, 0, 1 };

# This compiles fine, but this should error out

`g++ -save-temps -c bug.cpp`


I built the tip of gcc yesterday. It had the same bug.
Any pointers on how I can go about debugging this? 
- Does type checking happen during GENERIC stage?
- How do I print the source string corresponding to a TREE struct?