[Bug c++/113158] New: Erroneous "looser exception specification" error for class template

[Bug c++/113158] New: Erroneous "looser exception specification" error for class template

[sim.f.nilsson at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113158

            Bug ID: 113158
           Summary: Erroneous "looser exception specification" error for
                    class template
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sim.f.nilsson at gmail dot com
  Target Milestone: ---

The following code is not accepted by GCC 13.2.0 (among other versions):

#include <type_traits>

struct base {
    virtual int f() const = 0;
};

template<typename T>
struct derived : base {
    int f() const noexcept(std::is_nothrow_copy_constructible_v<T>) override
    {
        return sizeof(T);
    }
};

int g()
{
    return derived<double>{}.f();
}

I've tested versions 9 through 13 and trunk. Version 9.5 seems to be the last
version that accepts the code. The code is accepted by both Clang and MSVC. To
the best of my knowledge Clang and MSVC are correct to accept the code as
base::f is a "potentially throwing function" without the noexcept specifier.

What flags are used when compiling the code does not seem to influence the
behaviour, but for reference I've mostly used '-Wall -Wextra -O1 -std=c++17' in
comparisons.

The following compiler-explorer link also demonstrates the error:
https://compiler-explorer.com/z/1c48Yr76P

Adding 'noexcept(false)' in the base-class declaration of f, or either
'noexcept' or 'noexcept(false)' to the derived definition, makes GCC accept it.

[Bug c++/113158] [11/12/13/14 Regression] Erroneous "looser exception specification" error for class template

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113158

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Erroneous "looser exception |[11/12/13/14 Regression]
                   |specification" error for    |Erroneous "looser exception
                   |class template              |specification" error for
                   |                            |class template
      Known to work|                            |9.5.0
   Target Milestone|---                         |11.5
      Known to fail|                            |10.1.0

[Bug c++/113158] [11/12/13/14 Regression] Erroneous "looser exception specification" error for class template and depedent noexcept value

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113158

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2023-12-27
            Summary|[11/12/13/14 Regression]    |[11/12/13/14 Regression]
                   |Erroneous "looser exception |Erroneous "looser exception
                   |specification" error for    |specification" error for
                   |class template              |class template and depedent
                   |                            |noexcept value

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.

Reduced testcase:
```
template<typename T>
struct V {
  static constexpr bool t = false;
};
struct base {
    virtual int f() = 0;
};

template<typename T>
struct derived : base {
    int f() noexcept(V<T>::t) override;
};
```

[Bug c++/113158] [11/12/13/14 Regression] Erroneous "looser exception specification" error for class template and depedent noexcept value

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113158

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mpolacek at gcc dot gnu.org,
                   |                            |ppalka at gcc dot gnu.org
           Keywords|needs-bisection             |

--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Started with r10-1280-g78f7607db4c53f

[Bug c++/113158] [11/12/13/14 Regression] Erroneous "looser exception specification" error for class template and depedent noexcept value

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113158

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

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

[Bug c++/113158] [11/12/13/14 Regression] Erroneous "looser exception specification" error for class template and depedent noexcept value

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113158

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
https://gcc.gnu.org/pipermail/gcc-patches/2024-February/645767.html

[Bug c++/113158] [11/12/13/14 Regression] Erroneous "looser exception specification" error for class template and depedent noexcept value

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113158

--- Comment #4 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:876fa432ef4074053fa65b1855e7d43320515576

commit r14-9047-g876fa432ef4074053fa65b1855e7d43320515576
Author: Marek Polacek <polacek@redhat.com>
Date:   Thu Feb 15 17:07:43 2024 -0500

    c++: wrong looser excep spec for dep noexcept [PR113158]

    Here we find ourselves in maybe_check_overriding_exception_spec in
    a template context where we can't instantiate a dependent noexcept.
    That's OK, but we have to defer the checking otherwise we give wrong
    errors.

            PR c++/113158

    gcc/cp/ChangeLog:

            * search.cc (maybe_check_overriding_exception_spec): Defer checking
            when a noexcept couldn't be instantiated & evaluated to false/true.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/noexcept83.C: New test.

[Bug c++/113158] [11/12/13 Regression] Erroneous "looser exception specification" error for class template and depedent noexcept value

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113158

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[11/12/13/14 Regression]    |[11/12/13 Regression]
                   |Erroneous "looser exception |Erroneous "looser exception
                   |specification" error for    |specification" error for
                   |class template and depedent |class template and depedent
                   |noexcept value              |noexcept value

--- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Fixed on trunk so far.