[Bug c++/101850] New: Initialising a std::string variable to itself does not fail at compile time, but throws std::bad_alloc at run time

[prasantabehera at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101850

            Bug ID: 101850
           Summary: Initialising a std::string variable to itself does not
                    fail at compile time, but throws std::bad_alloc at run
                    time
           Product: gcc
           Version: 8.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: prasantabehera at hotmail dot com
  Target Milestone: ---

Version info:
=============
~$ g++ --version
g++ (Ubuntu 8.4.0-1ubuntu1~18.04) 8.4.0
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

~$ gcc --version
gcc (Ubuntu 8.4.0-1ubuntu1~18.04) 8.4.0
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Sample Program:
===============
~$ cat t.cpp
#include <string>

int main() {
  std::string s = s;
  return 0;
}

Problem Description:
====================
The above program tries to initialise a string with itself which is wrong!
However g++ does not show any compile time error, but the resulting binary
fails at run time throwing std::bad_alloc as shown below.

~$ g++ t.cpp
~$ ./a.out
terminate called after throwing an instance of 'std::bad_alloc'
  what():  std::bad_alloc
Aborted (core dumped)

gcc however shows a link time error which is slightly better.

~$ gcc t.cpp
/tmp/cc30YkgH.o: In function `main':
t.cpp:(.text+0x27): undefined reference to `std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char>
>::basic_string(std::__cxx11::basic_string<char, std::char_traits<char>,
std::allocator<char> > const&)'
t.cpp:(.text+0x38): undefined reference to `std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char> >::~basic_string()'
collect2: error: ld returned 1 exit status

I think the coding error should be caught at the compile time by g++. 

Also, the problem is same with any generic C++ class/struct:

#include <string>

struct M {
  std::string s;
};

int main() {
  // std::string s = s;
  M m = m;
  return 0;
}

Also checked with g++ version 7.5.0, to see the same behavior.