[Bug c++/94255] New: template specialization in different namespace causes crash

[Bug c++/94255] New: template specialization in different namespace causes crash

[vince.a.bridgers at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94255

            Bug ID: 94255
           Summary: template specialization in different namespace causes
                    crash
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vince.a.bridgers at gmail dot com
  Target Milestone: ---

I encountered this issue using gcc/g++ 6.2.0, then 8.2.0, the tried trunk that
I built on rhel7. g++ crashes when trying to compile code with template
specialization in different namespace. I know this is incorrect code, but I
wouldn't expect g++ to crash. For reference, clang 8.0.0 compiles this and
gives an error. 


----
Last git hash in log

commit 9def91e9f2a7051c9c146f16c1a10d1b25d33b47
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Mar 19 22:56:20 2020 +0100

---
Configure step for custom, trunk build ... 

../gcc/configure --enable-languages=c,c++ --disable-multilib
--prefix=<home>/gcc-install

----
$ g++ --version
g++ (GCC) 10.0.1 20200319 (experimental)
Copyright (C) 2020 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

----
$ g++ gcc-test.cpp 
gcc-test.cpp:15:38: error: specialization of ‘template<class T, class EnablerT>
struct clang::DynTypedNode::BaseConverter’ in different namespace
[-fpermissive]
   15 |     template <> struct DynTypedNode::BaseConverter<int, void> : public
ValueConverter<int> {};
      |                                      ^~~~~~~~~~~~~~~~~~~~~~~~
gcc-test.cpp:5:60: note:   from definition of ‘template<class T, class
EnablerT> struct clang::DynTypedNode::BaseConverter’
    5 |     template <typename T, typename EnablerT = void> struct
BaseConverter;
      |                                                           
^~~~~~~~~~~~~
g++: internal compiler error: Segmentation fault signal terminated program
cc1plus
Please submit a full bug report,
with preprocessed source if appropriate.
See <https://gcc.gnu.org/bugs/> for instructions.

----
cat test.cpp  ... 

namespace clang {
  class DynTypedNode {
  private:
    template <typename T, typename EnablerT = void> struct BaseConverter;
    template <typename T> struct ValueConverter {};
  };
  namespace ast_type_traits {
    using DynTypedNode = ::clang::DynTypedNode;
  }; // end namespace ast_type_traits
}; // end namespace clang

namespace clang {
  namespace ast_type_traits {
    template <> struct DynTypedNode::BaseConverter<int, void> : public
ValueConverter<int> {};
  }; // end namespace ast_type_traits
}; // end namespace clang

int main(void) {
    return 0;
}

---
cat gcc-test.ii ...

# 1 "gcc-test.cpp"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 1 "<command-line>" 2
# 1 "gcc-test.cpp"

namespace clang {
  class DynTypedNode {
  private:
    template <typename T, typename EnablerT = void> struct BaseConverter;
    template <typename T> struct ValueConverter {};
  };
  namespace ast_type_traits {
    using DynTypedNode = ::clang::DynTypedNode;
  };
};

namespace clang {
  namespace ast_type_traits {
    template <> struct DynTypedNode::BaseConverter<int, void> : public
ValueConverter<int> {};
  };
};

int main(void) {
    return 0;
}


----
$ clang --version
clang version 8.0.0 (tags/RELEASE_800/final)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /app/vbuild/RHEL7-x86_64/clang/8.0.0/bin


$ clang test.cpp 
gcc-test.cpp:15:38: error: class template specialization of 'BaseConverter' not
in class 'DynTypedNode' or an enclosing namespace
    template <> struct DynTypedNode::BaseConverter<int, void> : public
ValueConverter<int> {};
                                     ^
gcc-test.cpp:5:60: note: explicitly specialized declaration is here
    template <typename T, typename EnablerT = void> struct BaseConverter;
                                                           ^
1 error generated.

[Bug c++/94255] template specialization in different namespace causes crash

[vince.a.bridgers at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94255

--- Comment #1 from Vince Bridgers <vince.a.bridgers at gmail dot com> ---
The corrected code successfully compiles. Basically, making sure the template
specialization is in the correct namespace. 

namespace clang {
  class DynTypedNode {
  private:
    template <typename T, typename EnablerT = void> struct BaseConverter;
    template <typename T> struct ValueConverter {};
  };
  namespace ast_type_traits {
    using DynTypedNode = ::clang::DynTypedNode;
  }; // end namespace ast_type_traits
}; // end namespace clang

namespace clang {
  //namespace ast_type_traits {
    template <> struct DynTypedNode::BaseConverter<int, void> : public
ValueConverter<int> {};
  //}; // end namespace ast_type_traits
}; // end namespace clang

int main(void) {
    return 0;
}

[Bug c++/94255] template specialization in different namespace causes crash

[xerofoify at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94255

Nicholas Krause <xerofoify at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at redhat dot com,
                   |                            |xerofoify at gmail dot com

--- Comment #2 from Nicholas Krause <xerofoify at gmail dot com> ---
I've managed to track this down to what appears to me to be a issue in:
tree
push_inner_scope (tree inner)
{
  tree outer = current_scope ();
  if (!outer)
    outer = current_namespace;

  push_inner_scope_r (outer, inner);
  return outer;
}


I'm not certain if we should just check against NULL_TREE for outer or do we
need to also check against DECL_NAMESPACE as well. CCing Jason Merrill to take
a look at this with his comments.

[Bug c++/94255] template specialization in different namespace causes crash

[xerofoify at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94255

--- Comment #3 from Nicholas Krause <xerofoify at gmail dot com> ---
I've managed to track this down to what appears to me to be a issue in:
tree
push_inner_scope (tree inner)
{
  tree outer = current_scope ();
  if (!outer)
    outer = current_namespace;

  push_inner_scope_r (outer, inner);
  return outer;
}


I'm not certain if we should just check against NULL_TREE for outer or do we
need to also check against DECL_NAMESPACE as well. CCing Jason Merrill to take
a look at this with his comments.

[Bug c++/94255] template specialization in different namespace causes crash

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94255

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
                 CC|                            |mpolacek at gcc dot gnu.org
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2020-03-27

--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Confirmed, started with r0-113135-g28704289327e4295928663b5bab7953718f71bc1

[Bug c++/94255] template specialization in different namespace causes crash

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94255

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |mpolacek at gcc dot gnu.org

--- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Testing a patch.

[Bug c++/94255] template specialization in different namespace causes crash

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94255

--- Comment #6 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Patch approved for GCC 11:
https://gcc.gnu.org/pipermail/gcc-patches/2020-April/544081.html

[Bug c++/94255] template specialization in different namespace causes crash

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94255

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:21968d4ae067e3fa1c1728c8db26478e8ac8ad0b

commit r11-175-g21968d4ae067e3fa1c1728c8db26478e8ac8ad0b
Author: Marek Polacek <polacek@redhat.com>
Date:   Fri Apr 17 23:48:11 2020 -0400

    c++: Fix crash with template spec in different namespace [PR94255]

    This is an ICE on invalid, because we're specializing S::foo in the
    wrong namespace.  cp_parser_class_specifier_1 parses S::foo in M
    and then it tries to push the nested-name-specifier of foo, which is
    S.  By that, we're breaking the assumption of push_inner_scope that
    the pushed scope must be a scope nested inside current scope: current
    scope is M, but the namespace context of S is N, and N is not nested
    in M, so we fell into an infinite loop in push_inner_scope_r.

    (cp_parser_class_head called check_specialization_namespace which already
    gave a permerror.)

            PR c++/94255
            * parser.c (cp_parser_class_specifier_1): Check that the scope is
            nested inside current scope before pushing it.

            * g++.dg/template/spec41.C: New test.

[Bug c++/94255] template specialization in different namespace causes crash

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94255

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #8 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Fixed in GCC 11.