[Bug c++/57543] New: decltype needs eplicity 'this' pointer in member function declaration of template class with trailing return type

[Bug c++/57543] New: decltype needs eplicity 'this' pointer in member function declaration of template class with trailing return type

[mitchnull+gcc at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57543

            Bug ID: 57543
           Summary: decltype needs eplicity 'this' pointer in member
                    function declaration of template class with trailing
                    return type
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mitchnull+gcc at gmail dot com

Created attachment 30268
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=30268&action=edit
decltype-implicit-this.cpp

When using trailing return-type for member functions of a template class, the
'this' pointer must be explicitly mentioned. This should not be necessary (The
implicit 'this' works with a non-template class).

Example:

emplate <typename T>
struct DecltypeConstThis {

    T f() const { return T{}; }

    auto g() -> decltype(this->f()) { return this->f(); }
    auto h() const  ->  decltype(f()) { return f(); } // this should work the
same as g() above (with implicit 'this')

};

struct Working {
    int f() const { return 0; }
    auto h() const -> decltype(f()) { return 0; }
};


int main() {

    Working w;
    w.h();

    DecltypeConstThis<int> d;
    d.g();
    d.h();

    return 0;
}

compiler output:

[mitch@deneb src]$ g++ -std=c++11 -o decltype-implicit-this
decltype-implicit-this.cpp 
decltype-implicit-this.cpp: In instantiation of ‘struct
DecltypeConstThis<int>’:
decltype-implicit-this.cpp:22:28:   required from here
decltype-implicit-this.cpp:7:36: error: cannot call member function ‘T
DecltypeConstThis<T>::f() const [with T = int]’ without object
     auto h() const  ->  decltype(f()) { return f(); } // this should work the
same as g() above (with implicit 'this')
                                    ^
decltype-implicit-this.cpp: In function ‘int main()’:
decltype-implicit-this.cpp:24:7: error: ‘struct DecltypeConstThis<int>’ has no
member named ‘h’
     d.h();
       ^

ps: possibly related to bug #54359
>From gcc-bugs-return-423907-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Thu Jun 06 12:43:36 2013
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idT370

Tobias Burnus <burnus at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |ice-on-valid-code, patch
                 CC|                            |burnus at gcc dot gnu.org
   Target Milestone|---                         |4.7.4
            Summary|error: non-trivial          |[4.7 Regression] error:
                   |conversion in unary         |non-trivial conversion in
                   |operation                   |unary operation

--- Comment #4 from Tobias Burnus <burnus at gcc dot gnu.org> ---
The bug was solved in August 2012 on the GCC 4.8 trunk; however, as it is a
regression, it should have been backported to the GCC 4.7 branch.

[Bug c++/57543] decltype needs explicit 'this' pointer in member function declaration of template class with trailing return type

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57543

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2013-06-06
             Blocks|                            |54366
     Ever confirmed|0                           |1

[Bug c++/57543] decltype needs explicit 'this' pointer in member function declaration of template class with trailing return type

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57543

Daniel Krügler <daniel.kruegler at googlemail dot com> changed:

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

--- Comment #1 from Daniel Krügler <daniel.kruegler at googlemail dot com> ---
This problem still exists for gcc 4.9.0 20130519 (experimental)
>From gcc-bugs-return-424031-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Sat Jun 08 15:12:09 2013
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From: "glisse at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/57524] internal compiler error on dump translation unit
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idW524

Marc Glisse <glisse at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|2013-06-05 00:00:00         |2013-06-08
     Ever confirmed|0                           |1
      Known to fail|                            |4.7.3, 4.8.0

--- Comment #9 from Marc Glisse <glisse at gcc dot gnu.org> ---
Calling cc1plus directly, I can reproduce with trunk. The failing assert in
timevar.c is:

  /* Don't allow the same timing variable to be started more than
     once.  */
  gcc_assert (!tv->standalone);


/usr/include/boost/variant/detail/hash_variant.hpp:33:24: internal compiler
error: in timevar_start, at timevar.c:343
0xcce161 timevar_start(timevar_id_t)
    /data/repos/gcc/trunk/gcc/timevar.c:343
0x7cfa85 push_using_directive
    /data/repos/gcc/trunk/gcc/cp/name-lookup.c:5652
0x7cfa34 push_using_directive_1
    /data/repos/gcc/trunk/gcc/cp/name-lookup.c:5641
0x7cfa91 push_using_directive
    /data/repos/gcc/trunk/gcc/cp/name-lookup.c:5653
0x7ca70e do_using_directive(tree_node*)
    /data/repos/gcc/trunk/gcc/cp/name-lookup.c:3933
0x7ca7a7 parse_using_directive(tree_node*, tree_node*)
    /data/repos/gcc/trunk/gcc/cp/name-lookup.c:3957
0x6ddce4 cp_parser_using_directive
    /data/repos/gcc/trunk/gcc/cp/parser.c:15732
0x6d5ceb cp_parser_block_declaration
    /data/repos/gcc/trunk/gcc/cp/parser.c:10670
0x6d53df cp_parser_declaration_statement
    /data/repos/gcc/trunk/gcc/cp/parser.c:10344
0x6d2e33 cp_parser_statement
    /data/repos/gcc/trunk/gcc/cp/parser.c:9107
0x6d371b cp_parser_statement_seq_opt
    /data/repos/gcc/trunk/gcc/cp/parser.c:9379
0x6d361e cp_parser_compound_statement
    /data/repos/gcc/trunk/gcc/cp/parser.c:9333
0x6e1e23 cp_parser_function_body
    /data/repos/gcc/trunk/gcc/cp/parser.c:18066
0x6e20b0 cp_parser_ctor_initializer_opt_and_function_body
    /data/repos/gcc/trunk/gcc/cp/parser.c:18102
0x6e8f28 cp_parser_function_definition_after_declarator
    /data/repos/gcc/trunk/gcc/cp/parser.c:22080
0x6eab72 cp_parser_late_parsing_for_member
    /data/repos/gcc/trunk/gcc/cp/parser.c:22730
0x6e36cc cp_parser_class_specifier_1
    /data/repos/gcc/trunk/gcc/cp/parser.c:18825
0x6e3795 cp_parser_class_specifier
    /data/repos/gcc/trunk/gcc/cp/parser.c:18849
0x6da899 cp_parser_type_specifier
    /data/repos/gcc/trunk/gcc/cp/parser.c:13861
0x6d66b4 cp_parser_decl_specifier_seq
    /data/repos/gcc/trunk/gcc/cp/parser.c:11152

[Bug c++/57543] decltype needs explicit 'this' pointer in member function declaration of template class with trailing return type

[d.frey at gmx dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57543

Daniel Frey <d.frey at gmx dot de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |d.frey at gmx dot de

--- Comment #2 from Daniel Frey <d.frey at gmx dot de> ---
Here's another short example which seems to expose the same bug:

template< typename > struct X
{
  void foo() {}

  auto bar() -> decltype( X::foo() ) //1
  {
    return foo();
  }
};

int main()
{
  X<int>().bar();
}

Note that the decltype in //1 causes the problem, not the body of the function.
Changing //1 to decltype(foo()) fails with the same error message, changing it
to either decltype(this->foo()) or decltype(std::declval<X>().foo()) solves the
problem and GCC accepts the code. Also note that Clang compiles all versions
just fine.

The bug seems to occur in unevaluated contexts and only for templates. If you
change the above class X to be a non-template GCC accepts the code as well.

[Bug c++/57543] decltype needs explicit 'this' pointer in member function declaration of template class with trailing return type

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57543

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |paolo.carlini at oracle dot com
   Target Milestone|---                         |4.10.0

--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Mine.

[Bug c++/57543] decltype needs explicit 'this' pointer in member function declaration of template class with trailing return type

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57543

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW
           Assignee|paolo.carlini at oracle dot com    |unassigned at gcc dot gnu.org

[Bug c++/57543] decltype needs explicit 'this' pointer in member function declaration of template class with trailing return type

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57543

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> ---
There is a much more general issue behind this:

  https://gcc.gnu.org/ml/gcc-patches/2014-05/msg02548.html

[Bug c++/57543] decltype needs explicit 'this' pointer in member function declaration of template class with trailing return type

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57543

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |paolo.carlini at oracle dot com

--- Comment #6 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Ok, I have a draft, sorry about the ping-pong ;)

[Bug c++/57543] decltype needs explicit 'this' pointer in member function declaration of template class with trailing return type

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57543

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED
           Assignee|paolo.carlini at oracle dot com    |unassigned at gcc dot gnu.org

--- Comment #8 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Fixed.

[Bug c++/57543] decltype needs explicit 'this' pointer in member function declaration of template class with trailing return type

[paolo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57543

--- Comment #7 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> ---
Author: paolo
Date: Sat May 31 08:51:20 2014
New Revision: 211102

URL: http://gcc.gnu.org/viewcvs?rev=211102&root=gcc&view=rev
Log:
/cp
2014-05-31  Paolo Carlini  <paolo.carlini@oracle.com>

    DR 1227
    PR c++/57543
    * cp-tree.h (TYPE_HAS_LATE_RETURN_TYPE): Add.
    * pt.c (tsubst_function_type): Inject the this parameter; do the
    substitutions in the order mandated by the DR.
    (copy_default_args_to_explicit_spec): Copy TYPE_HAS_LATE_RETURN_TYPE.
    * decl.c (grokdeclarator): Maybe set TYPE_HAS_LATE_RETURN_TYPE.
    (static_fn_type): Copy it.
    * decl2.c (build_memfn_type, change_return_type,
    cp_reconstruct_complex_type): Likewise.
    * parser.c (cp_parser_lambda_declarator_opt): Likewise.
    * tree.c (strip_typedefs): Likewise.
    * typeck.c (merge_types): Likewise.

/testsuite
2014-05-31  Paolo Carlini  <paolo.carlini@oracle.com>

    DR 1227
    PR c++/57543
    * g++.dg/cpp0x/pr57543-1.C: New.
    * g++.dg/cpp0x/pr57543-2.C: Likewise.
    * g++.dg/cpp0x/pr57543-3.C: Likewise.
    * g++.dg/cpp0x/decltype59.C: Likewise.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/decltype59.C
    trunk/gcc/testsuite/g++.dg/cpp0x/pr57543-1.C
    trunk/gcc/testsuite/g++.dg/cpp0x/pr57543-2.C
    trunk/gcc/testsuite/g++.dg/cpp0x/pr57543-3.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/cp-tree.h
    trunk/gcc/cp/decl.c
    trunk/gcc/cp/decl2.c
    trunk/gcc/cp/parser.c
    trunk/gcc/cp/pt.c
    trunk/gcc/cp/tree.c
    trunk/gcc/cp/typeck.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/57543] decltype needs explicit 'this' pointer in member function declaration of template class with trailing return type

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57543

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |yyc1992 at gmail dot com

--- Comment #9 from Jonathan Wakely <redi at gcc dot gnu.org> ---
*** Bug 61400 has been marked as a duplicate of this bug. ***