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From: "Marc.van-Leeuwen at math dot univ-poitiers.fr" <sourceware-bugzilla@sourceware.org>
To: gdb-prs@sourceware.org
Subject: [Bug c++/17098] New: In program using unique_ptr, identifier 'tuple'
 cannot be used (problem with variadic templates?)
Date: Sat, 28 Jun 2014 10:17:00 -0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=17098

            Bug ID: 17098
           Summary: In program using unique_ptr, identifier 'tuple' cannot
                    be used (problem with variadic templates?)
           Product: gdb
           Version: unknown
            Status: NEW
          Severity: normal
          Priority: P2
         Component: c++
          Assignee: unassigned at sourceware dot org
          Reporter: Marc.van-Leeuwen at math dot univ-poitiers.fr

Created attachment 7662
  --> https://sourceware.org/bugzilla/attachment.cgi?id=7662&action=edit
preprocessed input from sample program, file mini.ii

When running gdb on a program using an instance of the unique_ptr class
template, the identifier 'tuple' can no longer be accessed in any way, as
otherwise valid expressions now give a syntax error. A minimal example:

mini.cpp:

    #include <memory>

    int main()
    {
      std::unique_ptr<int> p;
    }

compile this with gcc (version 4.8.1) using the command

    g++ -std=c++11 -ggdb -o mini mini.cpp

now run gdb and ask to print the (nonexistent) variable 'tuple'

    $ gdb mini
    GNU gdb (GDB) 7.6.1-ubuntu
    Copyright (C) 2013 Free Software Foundation, Inc.
    License GPLv3+: GNU GPL version 3 or later
<http://gnu.org/license/gpl.html>
    This is free software: you are free to change and redistribute it.
    There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
    and "show warranty" for details.
    This GDB was configured as "x86_64-linux-gnu".
    For bug reporting instructions, please see:
    <http://www.gnu.org/software/gdb/bugs/>...
    Reading symbols from /home/marc/atlas/sources/stand-alone/mini...done.
    (gdb) p tuple
    A syntax error in expression, near `'.
    (gdb) 

Whereas in a program not using any unique_ptr (for instance the above program
after removing the unique statement in 'main') one would correctly get

    (gdb) p tuple
    No symbol "tuple" in current context.

It seems that 'tuple' has changed its syntax category for gdb, making any
access to variables/fields called 'tuple' impossible. I stumbled on this when
debugging a program that actually used a field of that name, but the bug does
not appear to depend on that circumstance.


Looking and the (attached) preprocessed input, it seems that the problem might
be that 'tuple' is defined as a variadic template class:

    template<typename...>
      class tuple;

and later

    template<typename... _Elements>
      class tuple : public _Tuple_impl<0, _Elements...>
      { ... };

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