[Bug c++/14774] New: inaccessible unused copy constructor diagnostic could be more helpful

[mdorey at bluearc dot com]

Compiling:

void h ();

struct B {
private:
  B (B&) {
    h ();
  }
};

struct A {
  A ();

  B b;
};

void f (const A&);

void g () {
  f (A ());
}

Results in:

uncopyable-output-functor.cpp: In function `void g()':
uncopyable-output-functor.cpp:19: error: no matching function for call to
`A::A(const A&)'
uncopyable-output-functor.cpp:10: note: candidates are: A::A(A&)

With:

gcc version 3.4.0 20040320 (prerelease) (Debian)

According to the Standard, section 8.5.3.5, first "Otherwise" clause, this is
correct behaviour.  Whether a copy is taken or whether a reference is bound to
the temporary is implementation-defined (why?) and the copy constructor is
required to be accessible whether or not the copy is actually done.

Requiring the accessibility of a function that's not going to be called (and
isn't in this case) seems a sufficiently uncommon and odd case to me that
perhaps a specific diagnostic would reduce confusion?  I, for one, nearly
submitted a "this is a regression!" bug.

-- 
           Summary: inaccessible unused copy constructor diagnostic could be
                    more helpful
           Product: gcc
           Version: 3.4.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: mdorey at bluearc dot com
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14774