[Bug c++/103346] New: ICE on template specialization via alias template with a non-type parameter pack, and fold expression on lambda calls

[Bug c++/103346] New: ICE on template specialization via alias template with a non-type parameter pack, and fold expression on lambda calls

[ap.vanzanten at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103346

            Bug ID: 103346
           Summary: ICE on template specialization via alias template with
                    a non-type parameter pack, and fold expression on
                    lambda calls
           Product: gcc
           Version: 11.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ap.vanzanten at gmail dot com
  Target Milestone: ---

Command: g++ -std=c++20 <code file>

Code:
----

struct Item {};

template <typename T, T... ts>
struct Sequence;

template <Item... items>
using ItemSequence = Sequence<Item, items...>;

template <Item... items>
constexpr auto f() {
  constexpr auto l = [](Item item) { return item; };
  return ItemSequence<l(items)...>{};
}

----

Output:
----

<source>: In substitution of 'template<Item ...items> using ItemSequence =
Sequence<Item, (const Item)items ...> [with Item ...items = {f::l((const
Item)items)...}]':
<source>:12:34:   required from here
<source>:7:37: internal compiler error: Segmentation fault
    7 | using ItemSequence = Sequence<Item, items...>;
      |                                     ^~~~~
0x1786229 internal_error(char const*, ...)
        ???:0
0xfa6740 strip_array_types(tree_node*)
        ???:0
0x82f438 cp_type_quals(tree_node const*)
        ???:0
0x7e8a1b tsubst_pack_expansion(tree_node*, tree_node*, int, tree_node*)
        ???:0
0x7ef14a tsubst_template_args(tree_node*, tree_node*, int, tree_node*)
        ???:0
0x7ef72c tsubst_argument_pack(tree_node*, tree_node*, int, tree_node*)
        ???:0
0x7ef12c tsubst_template_args(tree_node*, tree_node*, int, tree_node*)
        ???:0
0x7dd7cc tsubst(tree_node*, tree_node*, int, tree_node*)
        ???:0
0x7dd8a7 tsubst(tree_node*, tree_node*, int, tree_node*)
        ???:0
0x7f40b2 instantiate_template(tree_node*, tree_node*, int)
        ???:0
0x7dde4d tsubst(tree_node*, tree_node*, int, tree_node*)
        ???:0
0x7e6702 lookup_template_class(tree_node*, tree_node*, tree_node*, tree_node*,
int, int)
        ???:0
0x80a52d finish_template_type(tree_node*, tree_node*, int)
        ???:0
0x7c47db c_parse_file()
        ???:0
0x896762 c_common_parse_file()
        ???:0
Please submit a full bug report,
...

----

Note the issue is not present when moving the lambda 'l' out of the function
'f' (into global scope), or when removing the 'ItemSequence' alias, and simply
using 'Sequence<Item, items...>' directly.

See also https://godbolt.org/z/Yqnnod4W6 for a live example.

[Bug c++/103346] ICE on template specialization via alias template with a non-type parameter pack, and fold expression on lambda calls

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103346

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-11-22
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
           Keywords|                            |rejects-valid
                 CC|                            |jason at gcc dot gnu.org,
                   |                            |marxin at gcc dot gnu.org

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
Confirmed, started with r9-3836-g4be5c72cf3ea3ee9, it was rejected before the
revision.

[Bug c++/103346] ICE on template specialization via alias template with a non-type parameter pack, and fold expression on lambda calls

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103346

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:49b6b7ac3314843466395c4a194aa178c80e64f5

commit r13-4807-g49b6b7ac3314843466395c4a194aa178c80e64f5
Author: Patrick Palka <ppalka@redhat.com>
Date:   Tue Dec 20 11:09:11 2022 -0500

    c++: NTTP object wrapper substitution fixes [PR103346, ...]

    This patch fixes some issues with substitution into a C++20 template
    parameter object wrapper:

    * The first testcase demonstrates a situation where the same_type_p
      assert in relevant case of tsubst_copy doesn't hold, because (partial)
      substitution of {int,} into the wrapper's TREE_TYPE yields A<int> but
      substitution into the underlying TEMPLATE_PARM_INDEX is a nop due to
      tsubst's level==1/tf_partial early exit tests, hence TREE_TYPE in the
      latter case remains A<T>.  So this patch just gets rid of the assert;
      the type mismatch doesn't seem to be a problem in practice.

    * In the second testcase, dependent substitution into the underlying
      TEMPLATE_PARM_INDEX yields a CALL_EXPR with empty TREE_TYPE, which
      tsubst_copy doesn't expect.  This patch fixes this by handling empty
      TREE_TYPE the same way as a non-const TREE_TYPE.  Moreover, after
      this substitution we're left with a VIEW_CONVERT_EXPR wrapping a
      CALL_EXPR instead of a TEMPLATE_PARM_INDEX, which during the subsequent
      non-dependent substitution tsubst_copy doesn't expect either.  So
      this patch also relaxes tsubst_copy to accept such VIEW_CONVERT_EXPR
      too.

    * In the third testcase, we end up never resolving the call to
      f.modify() because tsubst_copy doesn't do overload resolution.
      This patch fixes this by moving the handling of these
      VIEW_CONVERT_EXPR wrappers from tsubst_copy to tsubst_copy_and_build.
      For good measure tsubst_copy_and_build should also handle
      REF_PARENTHESIZED_P wrappers instead of delegating to tsubst_copy.

            PR c++/103346
            PR c++/104278
            PR c++/102553

    gcc/cp/ChangeLog:

            * pt.cc (tsubst_copy) <case VIEW_CONVERT_EXPR>: Move the
            handling of C++20 template parameter object wrappers to ...
            (tsubst_copy_and_build) <case VIEW_CONVERT_EXPR>: ... here.
            Accept non-TEMPLATE_PARM_INDEX inner operand.  Handle empty
            TREE_TYPE on substituted inner operand.  Remove same_type_p
            assert.  Also handle REF_PARENTHESIZED_P VIEW_CONVERT_EXPRs.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp2a/nontype-class52a.C: New test.
            * g++.dg/cpp2a/nontype-class53.C: New test.
            * g++.dg/cpp2a/nontype-class54.C: New test.
            * g++.dg/cpp2a/nontype-class55.C: New test.

[Bug c++/103346] ICE on template specialization via alias template with a non-type parameter pack, and fold expression on lambda calls

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103346

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |13.0
                 CC|                            |ppalka at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org
             Status|NEW                         |ASSIGNED

[Bug c++/103346] ICE on template specialization via alias template with a non-type parameter pack, and fold expression on lambda calls

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103346

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |13.0

--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 13

[Bug c++/103346] ICE on template specialization via alias template with a non-type parameter pack, and fold expression on lambda calls

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103346

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |iDingDong at outlook dot com

--- Comment #4 from Patrick Palka <ppalka at gcc dot gnu.org> ---
*** Bug 102470 has been marked as a duplicate of this bug. ***