[Bug c++/21631] New: Diagnostic for misdefined copy constructor is not particularly clear

[Bug c++/21631] New: Diagnostic for misdefined copy constructor is not particularly clear

[pkoning at equallogic dot com]

If I define a copy constructor as T(T&) rather than the correct T(const T&),
I'll end up with messages of the form:

| > keyed_obj.hh:159: error: no matching function for call to
'CxnIndex::CxnIndex(CxnIndex)'
| > Indeces.hh:150: note: candidates are: CxnIndex::CxnIndex(CxnIndex&)

which is baffling to most users because usually an argument of type T& is
acceptable for a call with a type T argument.  It doesn't help that there isn't
a call in the source code -- the compiler generated a copy constructor
reference, for reasons that may not be obvious from reading the source.

It would be helpful if the compiler could guide the user to the fix, perhaps by
doing one or both of the following:

a. Warn on the declaration of T(T&) with a message along the lines of "that
looks like a copy constructor, but it really should be T(const T&)"

b. In the message I quoted above, mention that a T(const T&) is needed and was
not supplied.

-- 
           Summary: Diagnostic for misdefined copy constructor is not
                    particularly clear
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pkoning at equallogic dot com
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i386-netbsd
  GCC host triplet: i386-netbsd
GCC target triplet: mipsel-netbsdelf


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21631

[Bug c++/21631] diagnostic for a non constant reference when passed a non lvalue (copy constructor)

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-05-17 20:00 -------
Confirmed, simple example:
struct f
{
  f(f&);
};
int g(void)
{
  f a = f();
}

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
           Keywords|                            |diagnostic
   Last reconfirmed|0000-00-00 00:00:00         |2005-05-17 20:00:40
               date|                            |
            Summary|Diagnostic for misdefined   |diagnostic for a non
                   |copy constructor is not     |constant reference when
                   |particularly clear          |passed a non lvalue (copy
                   |                            |constructor)


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21631

[Bug c++/21631] diagnostic for a non constant reference when passed a non lvalue (copy constructor)

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-05-17 20:17 -------
Note T(T&) is still a copy constructor, just not one which takes a constant reference.
Also note:
it really bolls down to this testcase:
int  f(int&);
int f();
int g(void)
{
  return f(1);
}

If we get rid of the second f function, we get a good warning.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21631

[Bug c++/21631] diagnostic for a non constant reference when passed a non lvalue (copy constructor)

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
   Last reconfirmed|2005-05-17 20:00:40         |2005-09-17 03:57:49
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21631

[Bug c++/21631] diagnostic for a non constant reference when passed a non lvalue (copy constructor)

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=21631

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |jason at gcc dot gnu.org
         Resolution|---                         |FIXED
           Assignee|unassigned at gcc dot gnu.org      |jason at gcc dot gnu.org
   Target Milestone|---                         |4.10.0

--- Comment #4 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed on trunk.

[Bug c++/21631] diagnostic for a non constant reference when passed a non lvalue (copy constructor)

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=21631

--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Wed May 14 16:48:07 2014
New Revision: 210436

URL: http://gcc.gnu.org/viewcvs?rev=210436&root=gcc&view=rev
Log:
    PR c++/20332
    PR c++/21631
    * call.c (reference_binding): Treat lvalue/rvalue mismatch and
    dropped cv-quals as a bad conversion.
    (convert_like_real) [ck_ref_bind]: Explain them.
    (compare_ics): Check badness before stripping reference
    bindings.  Handle comparing bad reference bindings.
    * typeck.c (comp_cv_qualification): Add overload that just takes
    integers.
    * cp-tree.h: Declare it.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/diag2.C
    trunk/gcc/testsuite/g++.dg/diagnostic/ref1.C
    trunk/gcc/testsuite/g++.dg/diagnostic/ref2.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/call.c
    trunk/gcc/cp/cp-tree.h
    trunk/gcc/cp/typeck.c
    trunk/gcc/testsuite/g++.dg/conversion/op4.C
    trunk/gcc/testsuite/g++.dg/cpp0x/overloadn.C
    trunk/gcc/testsuite/g++.dg/expr/cond9.C
    trunk/gcc/testsuite/g++.dg/init/synth2.C
    trunk/gcc/testsuite/g++.dg/lookup/two-stage4.C
    trunk/gcc/testsuite/g++.dg/overload/arg3.C
    trunk/gcc/testsuite/g++.dg/overload/conv-op1.C
    trunk/gcc/testsuite/g++.dg/overload/copy1.C
    trunk/gcc/testsuite/g++.dg/overload/volatile1.C
    trunk/gcc/testsuite/g++.dg/rtti/dyncast6.C
    trunk/gcc/testsuite/g++.dg/template/copy1.C
    trunk/gcc/testsuite/g++.old-deja/g++.benjamin/15800-1.C
    trunk/gcc/testsuite/g++.old-deja/g++.brendan/cvt3.C
    trunk/gcc/testsuite/g++.old-deja/g++.bugs/900514_03.C
    trunk/gcc/testsuite/g++.old-deja/g++.eh/ctor1.C
    trunk/gcc/testsuite/g++.old-deja/g++.jason/temporary2.C
    trunk/gcc/testsuite/g++.old-deja/g++.law/cvt20.C
    trunk/gcc/testsuite/g++.old-deja/g++.law/enum4.C
    trunk/gcc/testsuite/g++.old-deja/g++.law/init8.C
    trunk/gcc/testsuite/g++.old-deja/g++.law/operators9.C
    trunk/gcc/testsuite/g++.old-deja/g++.mike/net8.C
    trunk/gcc/testsuite/g++.old-deja/g++.mike/p1989.C
    trunk/gcc/testsuite/g++.old-deja/g++.mike/p2431.C
    trunk/gcc/testsuite/g++.old-deja/g++.mike/p438.C
    trunk/gcc/testsuite/g++.old-deja/g++.mike/p701.C
    trunk/gcc/testsuite/g++.old-deja/g++.other/crash24.C
    trunk/gcc/testsuite/g++.old-deja/g++.other/volatile1.C
    trunk/gcc/testsuite/g++.old-deja/g++.pt/auto_ptr.C
    trunk/gcc/testsuite/g++.old-deja/g++.pt/t05.C
    trunk/libstdc++-v3/testsuite/20_util/forward/1_neg.cc