[Bug c++/34870] New: template not instantiated for argument-dependent lookup

[Bug c++/34870] New: template not instantiated for argument-dependent lookup

[dragan at plusplus dot co dot yu]

This code should be legal:

template <typename T>
struct Foo
{
    template <typename Z>
    friend void func(const Foo &) {}
};

void check(const Foo<int> & x)
{
    // Foo<int> weird;  // uncomment this line and all works

    func<int>(x);    // <-- GCC issues an ERROR
}

After a brief discussion on gcc@gcc.gnu.org, it has been concluded that this
sample code should work. Apparently, 'func' should have been found by
argument-dependent lookup, instantiating 'Foo<int>' in the process.

Here are links to backup these claims, as specified in the discussion by people
involved:

- C++ Standard
  - 3.4.2 [basic.lookup.koenig]
  - 14.6.5 [temp.inject]
  - 7.3.1.2 [namespace.memdef] p3
- Vandevoorde and Josuttis' C++ Templates, section 9.2.2
- http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_closed.html#34

(gcc@gcc.gnu.org thread 'A simple sample code involving templates, friends and
lookup')


-- 
           Summary: template not instantiated for argument-dependent lookup
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: dragan at plusplus dot co dot yu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34870

[Bug c++/34870] template not instantiated for argument-dependent lookup

[dragan at plusplus dot co dot yu]

------- Comment #1 from dragan at plusplus dot co dot yu  2008-01-19 11:39 -------
Created an attachment (id=14974)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=14974&action=view)
a simple test case (the same as in the bug description)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34870

[Bug c++/34870] template not instantiated for argument-dependent lookup

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |rejects-valid
   Last reconfirmed|0000-00-00 00:00:00         |2008-01-21 10:04:52
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34870

[Bug c++/34870] template not instantiated for argument-dependent lookup

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2008-12-30 05:45 -------
*** Bug 34827 has been marked as a duplicate of this bug. ***


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu dot
                   |                            |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34870

[Bug c++/34870] template not instantiated for argument-dependent lookup

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2008-12-30 11:44 -------
*** Bug 34827 has been marked as a duplicate of this bug. ***


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34870

[Bug c++/34870] template not instantiated for argument-dependent lookup

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2008-12-30 11:44 -------
IMHO the friend declaration isn't a declaration for func.
At least it shouldn't inject the name into Foo<T>.

EDG agrees with me here:

icpc -S t.C -strict_ansi
t.C(12): error: identifier "func" is undefined
    func<int>(x);
    ^

t.C(12): error: type name is not allowed
    func<int>(x);
         ^

compilation aborted for t.C (code 2)


with and without the "weird" decl.  Which is IMHO correct.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|rejects-valid               |accepts-invalid


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34870

[Bug c++/34870] argument-dependent lookup wronly finds friend declaration

[dragan at plusplus dot co dot yu]

------- Comment #5 from dragan at plusplus dot co dot yu  2008-12-30 13:20 -------
The standard says that the friend declaration should inject the name 'func'
into the enclosing namespace, but in a way that it can be found only by ADL.

Here is a test case without templates:

struct Foo
{
    friend void func(const Foo &) {}
};

void check(const Foo & x)
{
    func(x);   <-- ADL, no error
    ::func(x); <-- not ADL, GCC issue an error
}

GCC handles this case correctly. The problem is it doesn't work
when templates come to play.

I personally find this behavior of great value. It reduces name clobbering.
I can for example do:
struct Foo {
    template <typename Type>
    friend bool is(const Foo & foo);
};
... and not clobber any namespace with a function of such non-unique name 'is'.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34870

[Bug c++/34870] argument-dependent lookup wronly finds friend declaration

[jason at gcc dot gnu dot org]

------- Comment #6 from jason at gcc dot gnu dot org  2009-01-15 23:12 -------
3.4.2 begins "When an unqualified name is used as the postfix-expression in a
function call...."  The call func<int>(x) does not get argument-dependent
lookup because func<int> is not an unqualified name, it's a template-id.  The
testcase should be rejected with or without the declaration of weird.


-- 

jason at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34870

[Bug c++/34870] argument-dependent lookup wrongly finds friend declaration

[jason at gcc dot gnu dot org]

------- Comment #7 from jason at gcc dot gnu dot org  2009-01-16 04:54 -------
Actually, this is still an accepts-invalid bug when weird is uncommented.


-- 

jason at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|INVALID                     |
            Summary|argument-dependent lookup   |argument-dependent lookup
                   |wronly finds friend         |wrongly finds friend
                   |declaration                 |declaration


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34870

[Bug c++/34870] argument-dependent lookup wrongly finds friend declaration

[dragan at plusplus dot co dot yu]

------- Comment #8 from dragan at plusplus dot co dot yu  2009-01-16 21:22 -------
Created an attachment (id=17123)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=17123&action=view)
another test case

I disagree... here is another test case. Semantically, it is the same
as the first one, so there is no reason why "unqualified name" could
not include (among others) an unqualified template-id. Either it is
a defect in standard, or there is a place that says that template-id
can also be qualified or unqualified. This test case eliminates
the template-id, and we're back to my original bug report.

Hm... why do people try to close or invert this bug report?
It is fairly logical and with references to standard,
discussion and defect report...


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34870

[Bug c++/34870] argument-dependent lookup wrongly finds friend declaration

[jason at gcc dot gnu dot org]

------- Comment #9 from jason at gcc dot gnu dot org  2009-03-27 18:34 -------
You're right, a template-id does still get argument-dependent lookup.


-- 

jason at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34870

[Bug c++/34870] argument-dependent lookup wrongly finds friend declaration

[schaub-johannes at web dot de]

------- Comment #10 from schaub-johannes at web dot de  2009-05-17 16:38 -------
A added another bug-report very similar to this that handles the case where the
friend definition is about a template:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40177 . GCC accepts in that case,
while it should reject. 


-- 

schaub-johannes at web dot de changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |schaub-johannes at web dot
                   |                            |de


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34870

[Bug c++/34870] argument-dependent lookup fails to find friend declaration

[jason at gcc dot gnu dot org]

------- Comment #11 from jason at gcc dot gnu dot org  2009-11-05 22:08 -------
The ADL and template-id issue:

  http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#561

but I'm declaring this PR to be about the bug-002.cc testcase, which shows the
real bug here without the distraction of template-ids, which can be dealt with
in PR 40177.


-- 

jason at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jason at gcc dot gnu dot org
                   |dot org                     |
             Status|REOPENED                    |ASSIGNED
           Keywords|accepts-invalid             |rejects-valid
   Last reconfirmed|2008-12-29 18:28:06         |2009-11-05 22:08:19
               date|                            |
            Summary|argument-dependent lookup   |argument-dependent lookup
                   |wrongly finds friend        |fails to find friend
                   |declaration                 |declaration
   Target Milestone|---                         |4.5.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34870

[Bug c++/34870] argument-dependent lookup fails to find friend declaration

[jason at gcc dot gnu dot org]

------- Comment #12 from jason at gcc dot gnu dot org  2009-11-06 03:33 -------
Subject: Bug 34870

Author: jason
Date: Fri Nov  6 03:33:06 2009
New Revision: 153958

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=153958
Log:
        PR c++/34870
        * name-lookup.c (arg_assoc_class): Call complete_type.
        * pt.c (instantiate_class_template): Call uses_template_parms
        instead of dependent_type_p.

Added:
    trunk/gcc/testsuite/g++.dg/lookup/koenig7.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/name-lookup.c
    trunk/gcc/cp/pt.c
    trunk/gcc/testsuite/ChangeLog


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34870

[Bug c++/34870] argument-dependent lookup fails to find friend declaration

[jason at gcc dot gnu dot org]

------- Comment #13 from jason at gcc dot gnu dot org  2009-11-06 04:08 -------
Fixed for 4.5.


-- 

jason at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34870