[Bug c++/21181] New: namespace lookup error message misleading

[Bug c++/21181] New: namespace lookup error message misleading

[tneumann at pi3 dot informatik dot uni-mannheim dot de]

Consider the following C++ code:

class A;
namespace X {
class B { friend class A; };
}
using namespace X;
class A {};
A a;

In the last line the compiler complains that A is undefined. After reading the 
release notes I understamd what happens (although I'm surprised. E.g. Comeau 
accepts the code). 
However the error message is very misleading: The problem is not that A is 
undefined but that X::A is undefined! This is very confusing for users.

-- 
           Summary: namespace lookup error message misleading
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: tneumann at pi3 dot informatik dot uni-mannheim dot de
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21181

[Bug c++/21181] namespace lookup error message misleading

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-04-23 20:38 -------
This is a dup of bug 19403.  The problem is that GCC before 4.0.0, the friend was saying the wrong 
friend was a friend of B.  But in 4.0.0 we get that right but a decided that the class was declared in the 
namespace which is wrong, it should not be injected.  This is all fixed already on the mainline.

*** This bug has been marked as a duplicate of 19403 ***

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |DUPLICATE


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21181

[Bug c++/21181] namespace lookup error message misleading

[Woebbeking at web dot de]

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------- Additional Comments From Woebbeking at web dot de  2005-04-24 15:23 -------
Hi, 
 
he's not complaining about the "new" friend lookup behaviour but about the 
misleading error message. I had two similar cases and it was not easy to find 
out what was going on. Have a look at the attachments. 
 
 
Cheers, 
André 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21181

[Bug c++/21181] namespace lookup error message misleading

[Woebbeking at web dot de]

------- Additional Comments From Woebbeking at web dot de  2005-04-24 16:01 -------
One additional note: if I use a named namespace in the 2nd case it compiles 
fine. Dunno if this is a bug. 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21181

[Bug c++/21181] namespace lookup error message misleading

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-04-24 16:05 -------
(In reply to comment #2)
> Hi, 
>  
> he's not complaining about the "new" friend lookup behaviour but about the 
> misleading error message. I had two similar cases and it was not easy to find 
> out what was going on. Have a look at the attachments. 

That would then be PR 12272, PR 20293, and PR 16093 and a couple other PRs.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21181

[Bug c++/21181] namespace lookup error message misleading

[Woebbeking at web dot de]

------- Additional Comments From Woebbeking at web dot de  2005-04-24 16:17 -------
Are you sure? None of the given PRs uses friend declarations. In my two cases I 
only have to use friend struct ::S1 and all is fine but to find the broken 
friend declarations is PITA. 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21181

[Bug c++/21181] namespace lookup error message misleading

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-04-24 16:20 -------
(In reply to comment #7)
> Are you sure? None of the given PRs uses friend declarations. In my two cases I 
> only have to use friend struct ::S1 and all is fine but to find the broken 
> friend declarations is PITA. 

Yes and that is the correct way otherwise you get the wrong class declared as a friend, again this is a 
dup of bug 19403 which is fixed correctly in 4.1.0 and above in that the friend statement is no longer a 
declaration of a class but just a marking on the class if it exists in the future the class is a friend of the 
other class.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21181

[Bug c++/21181] namespace lookup error message misleading

[Woebbeking at web dot de]

------- Additional Comments From Woebbeking at web dot de  2005-04-24 17:24 -------
I see. Then I'm looking forward to 4.1 :-) 
 
One last thing: is it a bug that the behaviour differs for named namespace in 
my second example? 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21181

[Bug c++/21181] namespace lookup error message misleading

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-04-24 17:27 -------
(In reply to comment #9)
> I see. Then I'm looking forward to 4.1 :-) 
>  
> One last thing: is it a bug that the behaviour differs for named namespace in 
> my second example? 

You second example is about equivant to before GCC fixes the friend bug for declaring the class in the 
namespace:
struct S1
{
    S1();
};

namespace
{
    struct S1;
    struct S2
    {
        friend struct S1;
    };
}

S1::S1()
{
}

So S1 ambiguous in the global namespace.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21181

[Bug c++/21181] namespace lookup error message misleading

[Woebbeking at web dot de]

------- Additional Comments From Woebbeking at web dot de  2005-04-24 19:45 -------
Thanks for enlightening me. 

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21181