Diagnose dangling assignments for std::initializer_list.

[hokein]

See the example below, it would be nice for clang to diagnose this case.

https://godbolt.org/z/W3dhEzY6M

#include <vector>
using namespace std;

int main() 
{
  // Good: Initializing an initializer_list object from the array extends the
  // lifetime of the array exactly like binding a reference to a temporary.
  initializer_list<int> a = {1, 2, 3};

  // Dangerous! the lifetime of the backing array is not extended for assignments.
  // 
  // A holds dangling pointers into backing array which are destroyed at the end of full expression.
  a = {2, 3, 4};
  for (int i : a) {
    i;
  }
}

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Haojian Wu (hokein)

See the example below, it would be nice for clang to diagnose this case.

https://godbolt.org/z/W3dhEzY6M

#include <vector>
using namespace std;

int main() 
{
  // Good: Initializing an initializer_list object from the array extends the
  // lifetime of the array exactly like binding a reference to a temporary.
  initializer_list<int> a = {1, 2, 3};

  // Dangerous! the lifetime of the backing array is not extended for assignments.
  // 
  // A holds dangling pointers into backing array which are destroyed at the end of full expression.
  a = {2, 3, 4};
  for (int i : a) {
    i;
  }
}

[hokein]

gcc implements this warning -Winit-list-lifetime: https://godbolt.org/z/M4bxvjG46