[Bug c++/101803] New: CTAD fails for nested designated initializers

[Bug c++/101803] New: CTAD fails for nested designated initializers

[h2+bugs at fsfe dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101803

            Bug ID: 101803
           Summary: CTAD fails for nested designated initializers
           Product: gcc
           Version: 11.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: h2+bugs at fsfe dot org
  Target Milestone: ---

See the code below. Two initializing statements fail to build, although they
shouldn't influence CTAD of the outer type at all (IMHO).

struct Inner
{
    int i = 0;
};

struct Outer2
{
    Inner s{};
};

template <typename T = int>
struct Outer
{
    Inner s{};
};

int main()
{
    Outer2 o21{ .s = {} };                // works
    Outer2 o22{ .s = Inner{ .i = 1} };    // works
    Outer2 o23{ .s = { .i = 1} };         // works

    Outer2 o24{ .s{} };                   // works
    Outer2 o25{ .s{Inner{ .i = 1} } };    // works
    Outer2 o26{ .s{ .i = 1} };            // works

    Outer o1{ .s = {} };                // works
    Outer o2{ .s = Inner{ .i = 1} };    // works
//    Outer o3{ .s = { .i = 1} };         // does not

    Outer o4{ .s{} };                   // works
    Outer o5{ .s{Inner{ .i = 1} } };    // works
//    Outer o6{ .s{ .i = 1} };            // does not
}

[Bug c++/101803] CTAD fails for nested designated initializers

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101803

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ppalka at gcc dot gnu.org
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2021-08-18
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org

--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed on trunk so far by r12-2991 (which incorrectly refers to PR101820 instead
of this PR)

[Bug c++/101803] CTAD fails for nested designated initializers

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101803

--- 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:4285ca3e1c4a6c9540dcdf1c4a71b99aba9bbfe8

commit r12-3024-g4285ca3e1c4a6c9540dcdf1c4a71b99aba9bbfe8
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Aug 19 09:07:02 2021 -0400

    c++: Fix PR number in testcase [PR101803]

    Also clarify the description of CONSTRUCTOR_BRACES_ELIDED_P.

            PR c++/101803

    gcc/cp/ChangeLog:

            * cp-tree.h (CONSTRUCTOR_IS_PAREN_INIT): Clarify comment.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp2a/class-deduction-aggr12.C: Fix PR number.

[Bug c++/101803] CTAD fails for nested designated initializers

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101803

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:dc867191914eff2993312fc25c48db4b7c6289e9

commit r11-9079-gdc867191914eff2993312fc25c48db4b7c6289e9
Author: Patrick Palka <ppalka@redhat.com>
Date:   Wed Aug 18 08:37:45 2021 -0400

    c++: aggregate CTAD and brace elision [PR101344]

    Here the problem is ultimately that collect_ctor_idx_types always
    recurses into an eligible sub-CONSTRUCTOR regardless of whether the
    corresponding pair of braces was elided in the original initializer.
    This causes us to reject some completely-braced forms of aggregate
    CTAD as in the first testcase below, because collect_ctor_idx_types
    effectively assumes that the original initializer is always minimally
    braced (and so the aggregate deduction candidate is given a function
    type that's incompatible with the original completely-braced initializer).

    In order to fix this, collect_ctor_idx_types needs to somehow know the
    shape of the original initializer when iterating over the reshaped
    initializer.  To that end this patch makes reshape_init flag sub-ctors
    that were built to undo brace elision in the original ctor, so that
    collect_ctor_idx_types that determine whether to recurse into a sub-ctor
    by simply inspecting this flag.

    This happens to also fix PR101820, which is about aggregate CTAD using
    designated initializers, for much the same reasons.

    A curious case is the "intermediately-braced" initialization of 'e3'
    (which we reject) in the first testcase below.  It seems to me we're
    behaving as specified here (according to [over.match.class.deduct]/1)
    because the initializer element x_1={1, 2, 3, 4} corresponds to the
    subobject e_1=E::t, hence the type T_1 of the first function parameter
    of the aggregate deduction candidate is T(&&)[2][2], but T can't be
    deduced from x_1 using this parameter type (as opposed to say T(&&)[4]).

            PR c++/101344
            PR c++/101803

    gcc/cp/ChangeLog:

            * cp-tree.h (CONSTRUCTOR_BRACES_ELIDED_P): Define.
            * decl.c (reshape_init_r): Set it.
            * pt.c (collect_ctor_idx_types): Recurse into a sub-CONSTRUCTOR
            iff CONSTRUCTOR_BRACES_ELIDED_P.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp2a/class-deduction-aggr11.C: New test.
            * g++.dg/cpp2a/class-deduction-aggr12.C: New test.

    (cherry picked from commit be4a4fb516688d7cfe28a80a4aa333f4ecf0b518)

[Bug c++/101803] CTAD fails for nested designated initializers

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101803

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
   Target Milestone|---                         |11.3
         Resolution|---                         |FIXED

--- Comment #4 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 11.3 and 12.

[Bug c++/101803] CTAD fails for nested designated initializers

[h2+bugs at fsfe dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101803

--- Comment #5 from Hannes Hauswedell <h2+bugs at fsfe dot org> ---
Thanks a lot for the fix! Any chance this will make into the 10.x branch?

[Bug c++/101803] CTAD fails for nested designated initializers

[h2+bugs at fsfe dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101803

--- Comment #6 from Hannes Hauswedell <h2+bugs at fsfe dot org> ---
Since it seems like 10.4 is around the corner... any chance this will make it?

Thanks a lot!

[Bug c++/101803] CTAD fails for nested designated initializers

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101803

--- Comment #7 from Patrick Palka <ppalka at gcc dot gnu.org> ---
(In reply to Hannes Hauswedell from comment #6)
> Since it seems like 10.4 is around the corner... any chance this will make
> it?
> 
> Thanks a lot!

Unfortunately I don't think so :/ the patch doesn't apply cleanly to the 10
branch because it depends on PR93976 / P2082R1.  And we tend to backport
non-regression C++20 bugfixes only to the latest release, which in this case
was GCC 11.

[Bug c++/101803] CTAD fails for nested designated initializers

[h2+bugs at fsfe dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101803

--- Comment #8 from Hannes Hauswedell <h2+bugs at fsfe dot org> ---
OK, thank you anyway!