[Bug c++/102482] New: Winit-list-lifetime false positive for temporaries with std::initializer_list

[federico.kircheis at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102482

            Bug ID: 102482
           Summary: Winit-list-lifetime false positive for temporaries
                    with std::initializer_list
           Product: gcc
           Version: 11.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: federico.kircheis at gmail dot com
  Target Milestone: ---

Following program


----
#include <initializer_list>

struct span {
    span(std::initializer_list<int> il) noexcept : begin(il.begin()),
size(il.size()) {}
    const int* begin;
    std::size_t size;
};


int foo(span sp){
        return sp.begin[0];
}

int main() {
    return foo(span(std::initializer_list<int>{}));
}
----


triggers

warning: initializing 'span::begin' from 'std::initializer_list<int>::begin'
does not extend the lifetime of the underlying array [-Winit-list-lifetime]

with no compiler flags except "--std=c++20"

(https://godbolt.org/z/ocaxh46oW)


While the warning is true, the code is completely safe, but the warnings seems
to imply that foo will access a dangling pointer.

Strangely, it does not diagnose anything on


----
#include <vector>

struct span {
    span(std::vector<int> il) noexcept : begin(il.data()), size(il.size()) {}
    const int* begin;
    std::size_t size;
};


int foo(span sp){
        return sp.begin[0];
}

int main() {
    return foo(span(std::vector<int>{}));
}
----

(https://godbolt.org/z/raMoTohvc)

where the lifetime rules are the same.

so I assume the warning is std::initializer_list specific.