[Bug c++/49470] New: no matching constructor for initialization errors not detected in g++

[Bug c++/49470] New: no matching constructor for initialization errors not detected in g++

[howarth at nitro dot med.uc.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49470

           Summary: no matching constructor for initialization errors not
                    detected in g++
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: howarth@nitro.med.uc.edu


Currently g++ doesn't warn or error on invalid code such as...

template <class T> class Array1D {
  Array1D(int n, T *a);
};
template<typename T>
struct A {
  Array1D<int> x;
  A() : x(1, (const int*)0) {}
};

for which clang++ produces the error...

[MacPro:~] howarth% clang++ -c invalid.cc
invalid.cc:7:9: error: no matching constructor for initialization of
'Array1D<int>'
  A() : x(1, (const int*)0) {}
        ^ ~~~~~~~~~~~~~~~~
invalid.cc:2:3: note: candidate constructor not viable: 2nd argument ('const
int *') would lose const qualifier
  Array1D(int n, T *a);
  ^
invalid.cc:1:26: note: candidate constructor (the implicit copy constructor)
not viable: requires 1 argument, but 2 were provided
template <class T> class Array1D {
                         ^
1 error generated.

[Bug c++/49470] no matching constructor for initialization errors not detected in g++

[howarth at nitro dot med.uc.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49470

--- Comment #1 from Jack Howarth <howarth at nitro dot med.uc.edu> 2011-06-20 03:12:23 UTC ---
This test case originates from http://llvm.org/bugs/show_bug.cgi?id=9627.

[Bug c++/49470] no matching constructor for initialization errors not detected in g++

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49470

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-06-20 10:06:13 UTC ---
If you instantiate the template you get an error.

There are LOTS of things clang diagnoses in uninstantiated templates that g++
doesn't

[Bug c++/49470] no matching constructor for initialization errors not detected in g++

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49470

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
           Severity|normal                      |enhancement

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-06-20 10:26:56 UTC ---
The summary isn't very relevant, the problem has nothing to do with
constructors, it's just that g++ doesn't check before instantiation whether no
valid specialization can be formed for a template.

14.6 [temp.res] p7:
If no valid specialization can be generated for a template definition, and that
template is not instantiated, the template definition is ill-formed, no
diagnostic required. ... [ Note: If a template is instantiated, errors will be
diagnosed according to the other rules in this Standard. Exactly when these
errors are diagnosed is a quality of implementation issue. —end note ]

[Bug c++/49470] optional diagnostic not given for invalid mem-initializer in uninstantiated template

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49470

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.06.22 20:44:17
            Summary|no matching constructor for |optional diagnostic not
                   |initialization errors not   |given for invalid
                   |detected in g++             |mem-initializer in
                   |                            |uninstantiated template
     Ever Confirmed|0                           |1