[Bug c++/30431] failure to check for visible declaration of friend function to template class

[vbraun at physics dot upenn dot edu]

------- Comment #4 from vbraun at physics dot upenn dot edu  2007-04-25 16:51 -------
Super-condensed testcase (gcc 4.1.2):

-------------- snip on -----------------
template<typename T> void f() {}
class A
{
  void f() {};
  friend void f<int>();   // line 5
};
-------------- snip off -----------------

[vbraun@galileo test]$ c++4 -Wall -pedantic friendtest.cc
friendtest.cc:5: error: variable or field ‘f’ declared void
friendtest.cc:5: error: ‘f’ is neither function nor member function; cannot be
declared friend
friendtest.cc:5: error: expected ‘;’ before ‘<’ token


The following versions all compile correctly (but do different things):

-------------- snip on -----------------
template<typename T> void f() {}
class A
{
  void f() {};
  friend void ::f<int>();   // Explicitly name scope
};
----------------------------------------
template<typename T> void f() {}
class A
{
  friend void f<int>();   // friend before member
  void f() {};
};
----------------------------------------
template<typename T> void f() {}
class A
{
  void f() {};
  template<typename T> friend void f(); // many-to-many friend
};
----------------------------------------
void f() {}
class A
{
  void f() {};
  friend void f(); // no template
};
-------------- snip off ----------------

Something is wrong with the friend lookup after a member of the same name is
encountered. After seeing the class member f (either data member or member
function), gcc forgets that the template function f is in the current
namespace. 

See also: Discussion for friend lookup rules.
http://std.dkuug.dk/jtc1/sc22/wg21/docs/cwg_defects.html#166
According to this, the code should be valid.

Bug 17122 is a duplicate, but did not see any activity in 1 year.


-- 

vbraun at physics dot upenn dot edu changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |vbraun at physics dot upenn
                   |                            |dot edu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30431