[Bug c++/29229] New: g++ fails to find dependent name in template from instantiation context

[Bug c++/29229] New: g++ fails to find dependent name in template from instantiation context

[debian-gcc at lists dot debian dot org]

[forwarded from http://bugs.debian.org/385992]

  Matthias

bug submitter writes:

It appears that g++ no longer finds a dependent name when it is the
template function itself.

    $cat -n test.cpp
         1  template <class C> void f(C *p)
         2  { f(*p); }
         3
         4  void f(int i)
         5  { i++; }
         6
         7  int main(int argc, char**)
         8  { f(&argc); }
    $g++-4.0 -o test test.cpp
    $g++-4.1 -o test test.cpp
    test.cpp: In function 'void f(C*) [with C = int]':
    test.cpp:8:   instantiated from here
    test.cpp:2: error: no matching function for call to 'f(int&)'
    $

To my understanding from the C++ standard, g++-4.0 behaves correctly.

My reasoning:

    In f(*p), f is a dependent name according to clause 14.6.2, para 1.

    The point of instantiation is f(&argc).

    In f(*p), f is an unqualified-id but not a template-id, so 14.6.4.2
    applies: only functions with external linkage will be found.  However,
    f(int) has external linkage.

    Name lookup (3.4, 3.4.2) does not distinguish between the different
    contexts for the case of an instantiated instantiation.

So, the lookup of f in f(*p) should consider f<C>(C*) and f(int) together,
and select f(int) from them.

When f(int) and its call in the template are renamed to something else,
the lookup succeeds. I do not know of a reason for having template f
hide the existence of function f.

g++ -v output for upstream:

    $g++-4.1 -v -o test test.cpp
    Using built-in specs.
    Target: i486-linux-gnu
    Configured with: ../src/configure -v
--enable-languages=c,c++,fortran,objc,obj-c++,treelang --prefix=/usr
--enable-shared --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --enable-nls
--program-suffix=-4.1 --enable-__cxa_atexit --enable-clocale=gnu
--enable-libstdcxx-debug --enable-mpfr --with-tune=i686
--enable-checking=release i486-linux-gnu
    Thread model: posix
    gcc version 4.1.2 20060814 (prerelease) (Debian 4.1.1-11)
     /usr/lib/gcc/i486-linux-gnu/4.1.2/cc1plus -quiet -v -D_GNU_SOURCE test.cpp
-quiet -dumpbase test.cpp -mtune=i686 -auxbase test -version -o
/home/vzweije/tmp/ccgs0DVY.s
    ignoring nonexistent directory "/usr/local/include/i486-linux-gnu"
    ignoring nonexistent directory
"/usr/lib/gcc/i486-linux-gnu/4.1.2/../../../../i486-linux-gnu/include"
    ignoring nonexistent directory "/usr/include/i486-linux-gnu"
    #include "..." search starts here:
    #include <...> search starts here:
     /usr/lib/gcc/i486-linux-gnu/4.1.2/../../../../include/c++/4.1.2
    
/usr/lib/gcc/i486-linux-gnu/4.1.2/../../../../include/c++/4.1.2/i486-linux-gnu
     /usr/lib/gcc/i486-linux-gnu/4.1.2/../../../../include/c++/4.1.2/backward
     /usr/local/include
     /usr/lib/gcc/i486-linux-gnu/4.1.2/include
     /usr/include
    End of search list.
    GNU C++ version 4.1.2 20060814 (prerelease) (Debian 4.1.1-11)
(i486-linux-gnu)
            compiled by GNU C version 4.1.2 20060814 (prerelease) (Debian
4.1.1-11).
    GGC heuristics: --param ggc-min-expand=46 --param ggc-min-heapsize=31550
    Compiler executable checksum: af253f4d4c50ecb6c5ed3e2466348eaf
    test.cpp: In function 'void f(C*) [with C = int]':
    test.cpp:8:   instantiated from here
    test.cpp:2: error: no matching function for call to 'f(int&)'
    $


-- 
           Summary: g++ fails to find dependent name in template from
                    instantiation context
           Product: gcc
           Version: 4.1.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: debian-gcc at lists dot debian dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29229

[Bug c++/29229] g++ fails to find dependent name in template from instantiation context

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2006-09-25 22:54 -------
You are incorrect.  This code is invalid because argument dependent namelookup
does not have an effect on fundumental types.

This sentence is where it goes wrong:
    Name lookup (3.4, 3.4.2) does not distinguish between the different
    contexts for the case of an instantiated instantiation.

14.6.4.2/1 says:
For the part of the lookup using unqualified name lookup (3.4.1), only function
declarations with external linkage from the template definition context are
found.

see the template definition context, so it does distinguish.

*** This bug has been marked as a duplicate of 2922 ***


-- 

pinskia at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29229