[Bug libstdc++/104883] New: <system_error> should define all std::errc enumerators

[Bug libstdc++/104883] New: <system_error> should define all std::errc enumerators

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104883

            Bug ID: 104883
           Summary: <system_error> should define all std::errc enumerators
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

Currently we only define std::errc enumerators when the OS defines the
corresponding errno macro:

#ifdef EOVERFLOW
      value_too_large =                         EOVERFLOW,
#endif


Which causes errors when we rely on that being present, e.g. for AVR:

/home/jwakely/src/gcc/build-avr/avr/libstdc++-v3/include/charconv: In function
‘std::to_chars_result std::__detail::__to_chars(char*, char*, _Tp, int)’:
/home/jwakely/src/gcc/build-avr/avr/libstdc++-v3/include/charconv:132:28:
error: ‘value_too_large’ is not a member of ‘std::errc’; did you mean
‘file_too_large’?
  132 |           __res.ec = errc::value_too_large;
      |                            ^~~~~~~~~~~~~~~
      |                            file_too_large


And src/filesystem/ops-common.h does this to workaround the fact that
std::errc::not_supported isn't always defined:

  inline error_code
  __unsupported() noexcept
  {
#if defined ENOTSUP
    return std::make_error_code(std::errc::not_supported);
#elif defined EOPNOTSUPP
    // This is supposed to be for socket operations
    return std::make_error_code(std::errc::operation_not_supported);
#else
    return std::make_error_code(std::errc::invalid_argument);
#endif
  }


We should consider defining all the enumerators unconditionally, picking values
outside the range used by the OS for <errno.h> constants, e.g.

#ifdef EOVERFLOW
      value_too_large =                         EOVERFLOW,
#else
      value_too_large =                         1001,
#endif

The tricky part is picking a value range that doesn't clash with the OS. For
the OS-specific headers such as config/os/mingw32-w64/error_constants.h we can
just inspect <errno.h> and make an educated choice. For
config/os/generic/error_constants.h maybe we want to do something in configure
or with the preprocessor to find the largest value among all the errno macros
that *are* defined, and add 100. Or just take a gamble and assume the OS uses
small numbers and we can start from 1000, or 32000, or something.

[Bug libstdc++/104883] <system_error> should define all std::errc enumerators

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104883

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
From PR 1007008 comment 2:

-- >8 --
We could do something like this for each enumerator:

#ifdef EFOO
   foo = EFOO,
#else
   foo = _GLIBCXX_ERRC_ORIGIN + __LINE__,
#endif


Where _GLIBCXX_ERRC_ORIGIN is some value intended to be higher than the highest
errno value on the OS. We only need fewer than 100 errc enumerators so
INT_MAX/2 might be OK.

We can use #line to set the __LINE__ to a fixed value in the file, so that the
constants don't change if we add/remove lines before the errc definition.
-- >8 --

We can use a default _GLIBCXX_ERRC_ORIGIN value, and allow it to be overridden
in config/os/*/os_defines.h if the default doesn't work.

[Bug libstdc++/104883] <system_error> should define all std::errc enumerators

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104883

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2022-09-22
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |redi at gcc dot gnu.org

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Created attachment 53613
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53613&action=edit
Generate error_constants.h from <errno.h>

    Instead of having several very similar target-specific headers with
    slightly different sets of enumerators, generate the error_constants.h
    file as part of the build. This ensures that all enumerators are always
    defined, with the value from the corresponding errno macro if present,
    or a libstdc++-specific alternative value.

    The libstdc++-specific values will be values greater than the positive
    integer _GLIBCXX_ERRC_ORIGIN, which defaults to 9999 but can be set in
    os_defines.h if a more suitable value exists for the OS (e.g. ELAST
    could be used for BSD targets).


The advantage of doing this is that we get a header that can be used
freestanding, but with values that match the hosted errno.h (if one exists on
the target).

[Bug libstdc++/104883] <system_error> should define all std::errc enumerators

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104883

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:

https://gcc.gnu.org/g:2d2e163d12f64a5e68f9e0381751ed9d5d6d3617

commit r13-5638-g2d2e163d12f64a5e68f9e0381751ed9d5d6d3617
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Jan 31 22:16:31 2023 +0000

    libstdc++: Fix build failures for avr

    The abr-libc <errno.h> does not define EOVERFLOW, which means that
    std::errc::value_too_large is not defined, and so <charconv> cannot be
    compiled. Define value_too_large for avr with a value that does not
    clash with any that is defined in <errno.h>. This is a kluge to fix
    bootstrap for avr; it can be removed after PR libstdc++/104883 is
    resolved.

    The avr-libc <errno.h> fails to meet the C and POSIX requirements that
    each error macro has a distinct integral value, and is usable in #if
    directives. Add a special case for avr to system_error.cc so that only
    the valid errors are recognized. Also disable the errno checks in
    std::filesystem::remove_all that assume a meaningful value for errno.

    On avr-libc <unistd.h> exists but does not define the POSIX functions
    needed by std::filesystem, so _GLIBCXX_HAVE_UNISTD_H is not sufficient
    to check for basic POSIX APIs. Check !defined __AVR__ as well as
    _GLIBCXX_HAVE_UNISTD_H before using those functions. This is a kluge and
    we should really have a specific macro that says the required functions
    are available.

    libstdc++-v3/ChangeLog:

            * config/os/generic/error_constants.h (errc::value_too_large)
            [__AVR__]: Define.
            * src/c++11/system_error.cc
            (system_category::default_error_condition) [__AVR__]: Only match
            recognize values equal to EDOM, ERANGE, ENOSYS and EINTR.
            * src/c++17/fs_ops.cc (fs::current_path) [__AVR__]: Do not check
            for ENOENT etc. in switch.
            (fs::remove_all) [__AVR__]: Likewise.
            * src/filesystem/ops-common.h [__AVR__]: Do not use POSIX open,
            close etc.

[Bug libstdc++/104883] <system_error> should define all std::errc enumerators

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104883

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #0)
> Which causes errors when we rely on that being present, e.g. for AVR:
> 
> /home/jwakely/src/gcc/build-avr/avr/libstdc++-v3/include/charconv: In
> function ‘std::to_chars_result std::__detail::__to_chars(char*, char*, _Tp,
> int)’:
> /home/jwakely/src/gcc/build-avr/avr/libstdc++-v3/include/charconv:132:28:
> error: ‘value_too_large’ is not a member of ‘std::errc’; did you mean
> ‘file_too_large’?
>   132 |           __res.ec = errc::value_too_large;
>       |                            ^~~~~~~~~~~~~~~
>       |                            file_too_large

This specific problem is now fixed for avr, but the general problem remains.

[Bug libstdc++/104883] <system_error> should define all std::errc enumerators

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104883

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Jonathan Wakely
<redi@gcc.gnu.org>:

https://gcc.gnu.org/g:aa18735f7aa99b40c56b3e3aacb1b28cb805bb90

commit r12-9099-gaa18735f7aa99b40c56b3e3aacb1b28cb805bb90
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Jan 31 22:16:31 2023 +0000

    libstdc++: Fix build failures for avr

    The abr-libc <errno.h> does not define EOVERFLOW, which means that
    std::errc::value_too_large is not defined, and so <charconv> cannot be
    compiled. Define value_too_large for avr with a value that does not
    clash with any that is defined in <errno.h>. This is a kluge to fix
    bootstrap for avr; it can be removed after PR libstdc++/104883 is
    resolved.

    The avr-libc <errno.h> fails to meet the C and POSIX requirements that
    each error macro has a distinct integral value, and is usable in #if
    directives. Add a special case for avr to system_error.cc so that only
    the valid errors are recognized. Also disable the errno checks in
    std::filesystem::remove_all that assume a meaningful value for errno.

    On avr-libc <unistd.h> exists but does not define the POSIX functions
    needed by std::filesystem, so _GLIBCXX_HAVE_UNISTD_H is not sufficient
    to check for basic POSIX APIs. Check !defined __AVR__ as well as
    _GLIBCXX_HAVE_UNISTD_H before using those functions. This is a kluge and
    we should really have a specific macro that says the required functions
    are available.

    libstdc++-v3/ChangeLog:

            * config/os/generic/error_constants.h (errc::value_too_large)
            [__AVR__]: Define.
            * src/c++11/system_error.cc
            (system_category::default_error_condition) [__AVR__]: Only match
            recognize values equal to EDOM, ERANGE, ENOSYS and EINTR.
            * src/c++17/fs_ops.cc (fs::current_path) [__AVR__]: Do not check
            for ENOENT etc. in switch.
            (fs::remove_all) [__AVR__]: Likewise.
            * src/filesystem/ops-common.h [__AVR__]: Do not use POSIX open,
            close etc.

    (cherry picked from commit 2d2e163d12f64a5e68f9e0381751ed9d5d6d3617)

[Bug libstdc++/104883] <system_error> should define all std::errc enumerators

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104883

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Jonathan Wakely
<redi@gcc.gnu.org>:

https://gcc.gnu.org/g:c86ac1a463f97554b1df9ef8a3e18573ef115e35

commit r11-10578-gc86ac1a463f97554b1df9ef8a3e18573ef115e35
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Jan 31 22:16:31 2023 +0000

    libstdc++: Fix build failures for avr

    The avr-libc <errno.h> does not define EOVERFLOW, which means that
    std::errc::value_too_large is not defined, and so <charconv> cannot be
    compiled. Define value_too_large for avr with a value that does not
    clash with any that is defined in <errno.h>. This is a kluge to fix
    bootstrap for avr; it can be removed after PR libstdc++/104883 is
    resolved.

    The avr-libc <errno.h> fails to meet the C and POSIX requirements that
    each error macro has a distinct integral value, and is usable in #if
    directives. Add a special case for avr to system_error.cc so that only
    the valid errors are recognized. Also disable the errno checks in
    std::filesystem::remove_all that assume a meaningful value for errno.

    On avr-libc <unistd.h> exists but does not define the POSIX functions
    needed by std::filesystem, so _GLIBCXX_HAVE_UNISTD_H is not sufficient
    to check for basic POSIX APIs. Check !defined __AVR__ as well as
    _GLIBCXX_HAVE_UNISTD_H before using those functions. This is a kluge and
    we should really have a specific macro that says the required functions
    are available.

    libstdc++-v3/ChangeLog:

            * config/os/generic/error_constants.h (errc::value_too_large)
            [__AVR__]: Define.
            * src/c++11/system_error.cc
            (system_category::default_error_condition) [__AVR__]: Only match
            recognize values equal to EDOM, ERANGE, ENOSYS and EINTR.
            * src/c++17/fs_ops.cc (fs::current_path) [__AVR__]: Do not use
            getcwd.
            * src/filesystem/ops-common.h [__AVR__]: Do not use POSIX open,
            close etc.

    (cherry picked from commit 2d2e163d12f64a5e68f9e0381751ed9d5d6d3617)