[Bug c++/17971] New: [3.4/4.0 regression] Invalid default parameter not diagnosed.

[Bug c++/17971] New: [3.4/4.0 regression] Invalid default parameter not diagnosed.

[reichelt at gcc dot gnu dot org]

Since PR 16929 got a little confusing, I'm opening a new PR for the
following problem:

Since gcc 3.4.0 we accept the following invalid code snippet. The invalid
default parameter "a" is not even diagnosed at instantiation time.
(This is different from PT 17011 - also a spin-off from PR16929 -
which is just a QoI issue.)

===========================================
template<typename> struct A {};

template<typename T> struct B
{
    A<T> a;

    void foo(A<T> = a);
};

template struct B<int>;
===========================================

With 3.3.5 and before we got a decent error message:
bug.cc:7: error: invalid use of member `B<T>::a'

-- 
           Summary: [3.4/4.0 regression] Invalid default parameter not
                    diagnosed.
           Product: gcc
           Version: 3.4.3
            Status: UNCONFIRMED
          Keywords: accepts-invalid
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: reichelt at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org,mark at codesourcery dot
                    com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17971

[Bug c++/17971] [3.4/4.0 regression] Invalid default parameter not diagnosed.

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-10-13 12:22 -------
Confirmed.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2004-10-13 12:22:03
               date|                            |
   Target Milestone|---                         |3.4.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17971

[Bug c++/17971] [3.4/4.0 regression] Invalid default parameter not diagnosed.

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2004-10-13 12:50 -------
I'm not sure this is a bug: the standard quite unmistakably says that 
default arguments aren't evaluated unless used. Now, if I try to 
use the default argument in your testcase, like so 
------------------ 
template<typename> struct A {}; 
 
template<typename T> struct B 
{ 
    A<T> a; 
 
    void foo(A<T> = a); 
}; 
 
void bar () 
{ 
  B<int>().foo(); 
} 
-------------------------- 
then I do get a sensible error: 
g/x> /home/bangerth/bin/gcc-4.0-pre/bin/c++ -c x.cc 
x.cc:5: error: invalid use of non-static data member `B<int>::a' 
x.cc:12: error: from this location 
 
Can you say why the compiler should diagnose this earlier rather than 
later, given what the standard says? 
 
For reference: 
14.7.2/9 says 
  An explicit instantiation does not  constitute  a  use  of  a  default 
  argument, so default argument instantiation is not done.  [Example: 
 
     char* p = 0; 
     template<class T> T g(T = &p); 
     template int g<int>(int);       // OK even though &p isn't an int. 
 
   --end example] 
and there are more places like this. 
 
W. 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17971

[Bug c++/17971] [3.4/4.0 regression] Invalid default parameter not diagnosed.

[mmitchel at gcc dot gnu dot org]

------- Additional Comments From mmitchel at gcc dot gnu dot org  2004-11-01 00:45 -------
Postponed until GCC 3.4.4.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|3.4.3                       |3.4.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17971

[Bug c++/17971] [3.4/4.0 regression] Invalid default parameter not diagnosed.

[lerdsuwa at gcc dot gnu dot org]

------- Additional Comments From lerdsuwa at gcc dot gnu dot org  2004-11-28 06:03 -------
Under investigate.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |lerdsuwa at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17971

[Bug c++/17971] [3.4/4.0 regression] Invalid default parameter not diagnosed.

[lerdsuwa at gcc dot gnu dot org]

------- Additional Comments From lerdsuwa at gcc dot gnu dot org  2004-12-03 10:25 -------
Patch submitted:
  http://gcc.gnu.org/ml/gcc-patches/2004-12/msg00255.html

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17971

[Bug c++/17971] [3.4/4.0 regression] Invalid default parameter not diagnosed.

[lerdsuwa at gcc dot gnu dot org]

------- Additional Comments From lerdsuwa at gcc dot gnu dot org  2004-12-04 07:06 -------
Fixed in 3.4 branch and mainline.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17971