[Bug c++/87293] New: An object with invalid type is treated as if it were of type int when reporting errors

[b7.10110111 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87293

            Bug ID: 87293
           Summary: An object with invalid type is treated as if it were
                    of type int when reporting errors
           Product: gcc
           Version: 8.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: b7.10110111 at gmail dot com
  Target Milestone: ---

Consider the following C++ code:

//--------------------------------
#include <memory>
int main()
{
    std::shared_ptr<dbl> p(new double{5.3});
}
//--------------------------------

Here, g++ emits the following messages:
------------------BEGIN---------------------
test.cpp: In function ‘int main()’:
test.cpp:4:21: error: ‘dbl’ was not declared in this scope
     std::shared_ptr<dbl> p(new double{5.3});
                     ^~~
test.cpp:4:24: error: template argument 1 is invalid
     std::shared_ptr<dbl> p(new double{5.3});
                        ^
test.cpp:4:43: error: invalid conversion from ‘double*’ to ‘int’ [-fpermissive]
     std::shared_ptr<dbl> p(new double{5.3});
                                           ^
-----------------END-----------------------

The first error is correct: there's no dbl type. But the last error makes no
sense at all. There's nothing in the code which could imply that the type of
`p` could be `int`: even if there were no type present, C++ is not C89 to imply
`int` by default.

Moreover, if we add a line which uses `p` in another erroneous way, e.g.
"struct S{}s=p;", g++ again thinks that `p` is of type `int` ("error:
conversion from ‘int’ to non-scalar type ‘main()::S’ requested").