c++/6307: gcc looses const qualifier, thus rejecting valid code.

[pthomas@suse.de]

>Number:         6307
>Category:       c++
>Synopsis:       gcc looses const qualifier, thus rejecting valid code.
>Confidential:   no
>Severity:       critical
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          rejects-legal
>Submitter-Id:   net
>Arrival-Date:   Mon Apr 15 07:16:01 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     Philipp Thomas, SuSE Linux Ag
>Release:        3.1 20020408 (prerelease)
>Organization:
>Environment:
i486-suse-linux
>Description:
When compiling the attached test case, gcc fails with

gcc31_bug_const.cc: In member function `int Collision::automatic_shift()':
gcc31_bug_const.cc:38: invalid conversion from `int (*)(int* const&, int*
   const&)' to `int (*)(int*&, int*&)'
gcc31_bug_const.cc:38:   initializing argument 1 of `void
   Link_array<T>::sort(int (*)(T*&, T*&), int, int) [with T = int]'
gcc31_bug_const.cc: In member function `void Link_array<T>::sort(int (*)(T*&,
   T*&), int, int) [with T = int]':
gcc31_bug_const.cc:38:   instantiated from here
gcc31_bug_const.cc:29: invalid conversion from `int (*)(int* const&, int*
   const&)' to `int (*)(int*&, int*&)'
gcc31_bug_const.cc:29:   initializing argument 1 of `void
   Link_array<T>::sort(int (*)(T*&, T*&), int, int) [with T = int]'

AFAICS, this is valid code and gcc looses the const somewhere.
>How-To-Repeat:
Compile attached file with c++.
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:
----gnatsweb-attachment----
Content-Type: text/plain; name="gcc31_bug_const.cc"
Content-Disposition: inline; filename="gcc31_bug_const.cc"

template<class T>
class Link_array
{
public:
  Link_array () {}
  Link_array (Link_array<T> const &src) {}
  // quicksort.
  void sort (int (*compare) (T *const&,T *const&),
	     int lower = -1, int upper = -1);
};

class Note_column
{
public:
  static int shift_compare (int *const &, int *const &) {};
};

class Collision			// interface
{
public:
  int automatic_shift ();
};

template<class T> void
Link_array<T>::sort (int (*compare) (T *const&,T *const&),
		int lower, int upper) 
{
  int last = lower;
  sort (compare, lower, last-1);
}

int
Collision::automatic_shift ()
{
  int d = 1;
  Link_array<int> clashes;

  clashes.sort (Note_column::shift_compare);
  return 1;
}

int main()
{
  return 0;
}