[Bug c++/32066] New: member/type lookup doesn't work properly with templates

[Bug c++/32066] New: member/type lookup doesn't work properly with templates

[andrew dot stubbs at st dot com]

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The following is adapted from the example from the C++ standard, clause 14.6/4
(actually it's the updated version from DR345):

      1     struct A {
      2       struct X { };
      3       static int X; 
      4     } ; 
      5     template<class T> void f(T t) {
      6       typename T::X x;  // invalid
      7       T::X y;           // invalid
      8       int z = T::X;     // OK
      9     }
     10     void foo() {
     11       A a;   
     12       f(a);  // error: T::X refers to the data member A::X not 
     13              // the struct A::X.
     14     }

I've removed the `B' class from the example, made A::X static (so that T::X may
be used to reference it), and added lines 7 and 8. According to the standard,
clause 14.6/4, all the `T::X' should find the data member X, *not* the type
member X, regardless of the `typename' keyword.

In this case, however, GCC 4.1.1 has not done this, and gives the following
diagnostics:

t.cxx: In function ‘void f(T)’:
t.cxx:7: error: expected `;' before ‘y’

Line 6 has been compiled OK; `T::X' has found the type.
Line 7 has been rejected correctly; `T::X' has not found a type, which means
the `typename' keyword in line 6 was significant.
Line 8 has been compiled correctly; `T::X' has found the data member.


-- 
           Summary: member/type lookup doesn't work properly with templates
           Product: gcc
           Version: 4.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: andrew dot stubbs at st dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32066

[Bug c++/32066] member/type lookup doesn't work properly with templates

[christian dot bruel at st dot com]

------- Comment #1 from christian dot bruel at st dot com  2009-12-07 08:13 -------
I'm wondering if this is not an application of the name hiding rule described
in the IEC 14882:1998 (3.3.7) that says here that the class name T::X is hidden
by the object static int T::X i, so T::X y refers to the object's name not the
class. Making the test invalid. Not certain, just a thought.

This could be reduced as 

struct A
{
#ifdef X_MEMBER
  static int X;
#endif
#ifdef X_NAME
  struct X { }; 
#endif
} ; 

void foo(void)
{ 
#ifdef X_NAME
  A::X y;  
#endif
#ifdef X_MEMBER
  A::X = 1;
#endif
} 

if both X_NAME and X_MEMBER are defined the line A::X y; becomes invalid.


-- 

christian dot bruel at st dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |christian dot bruel at st
                   |                            |dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32066

[Bug c++/32066] member/type lookup doesn't work properly with templates

[redi at gcc dot gnu dot org]

------- Comment #2 from redi at gcc dot gnu dot org  2009-12-07 15:11 -------
(In reply to comment #1)
> I'm wondering if this is not an application of the name hiding rule described
> in the IEC 14882:1998 (3.3.7) that says here that the class name T::X is hidden
> by the object static int T::X i, so T::X y refers to the object's name not the
> class.

Exactly. The point is that the standard says "The usual qualified name
lookup (3.4.3) is used to find the qualified-id even in the presence of
typename."


> Making the test invalid. Not certain, just a thought.

The test is supposed to be invalid, but should give an error on line 6 and line
7, GCC only gives an error on line 7.

> This could be reduced as  ...

Your reduced version is irrelevant because it's not a template and there's no
"typename" keyword. GCC gets that right, but doesn't get the original report
right.

The test can be reduced to this, which should not compile:

struct A {
  struct X { };
  int X;
};
template<class T> void f(T t) {
  typename T::X x;
}
void foo() {
  A a;
  f(a); // error: T::X refers to the data member A::X not the struct A::X
}


-- 

redi at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |accepts-invalid
      Known to fail|                            |4.1.2 4.4.2
   Last reconfirmed|0000-00-00 00:00:00         |2009-12-07 15:11:25
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32066

[Bug c++/32066] member/type lookup doesn't work properly with templates

[christian dot bruel at st dot com]

------- Comment #3 from christian dot bruel at st dot com  2009-12-07 16:41 -------
> The test can be reduced to this, which should not compile:
> 
> struct A {
>   struct X { };
>   int X;
> };
> template<class T> void f(T t) {
>   typename T::X x;
> }
> void foo() {
>   A a;
>   f(a); // error: T::X refers to the data member A::X not the struct A::X
> }
> 

OK. note that with the original tests, 'int X' was declared static.
That makes the case a little bit different since 3.3.7.2 refers to "object,
function or enumerator", not class member. 

So variants of this case have declarations:

struct A {
  struct X { };
  enum x {a, b, c} X;
};

and 

struct A {
  struct X { };
  void X();
};


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32066

[Bug c++/32066] member/type lookup doesn't work properly with templates

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=32066

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |schaub.johannes@googlemail.
                   |                            |com

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 48920 has been marked as a duplicate of this bug. ***

[Bug c++/32066] member/type lookup doesn't work properly with templates

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=32066

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |daniel.kruegler@googlemail.
                   |                            |com

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 58590 has been marked as a duplicate of this bug. ***