[Bug 1995569] Re: std::experimental::filesystem missing exception specification noexcept build error regression (libstdc++-11-dev 11.3.0-1ubuntu1~22.04 upgrade)

[Launchpad Bug Tracker]

[Expired for gcc-11 (Ubuntu) because there has been no activity for 60
days.]

** Changed in: gcc-11 (Ubuntu)
       Status: Incomplete => Expired

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https://bugs.launchpad.net/bugs/1995569

Title:
  std::experimental::filesystem missing exception specification noexcept
  build error regression (libstdc++-11-dev 11.3.0-1ubuntu1~22.04
  upgrade)

Status in gcc-11 package in Ubuntu:
  Expired

Bug description:
  Summary:
  On Ubuntu 22.04.1 LTS using clang 11, I'm newly (REGRESSION) getting build errors on std::experimental::filesystem consumption cases:

  .
  .
  .
  In file included from ............./../../Compiler/StdFileSystem.h:37:
  In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/experimental/filesystem:38:
  /usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/experimental/bits/fs_path.h:1209:9: error: 'begin' is missing exception specification 'noexcept'
    path::begin() const

  
  This very likely has been introduced by (dpkg.log)
  2022-10-27 13:18:37 upgrade libstdc++-11-dev:amd64 11.2.0-19ubuntu1 11.3.0-1ubuntu1~22.04


  
  Details:
  No issues seen (working build) until very recently.
  Analysis:
  extraction of
  libstdc++-11-dev_11.2.0-19ubuntu1_amd64.deb
  ( http://security.ubuntu.com/ubuntu/pool/main/g/gcc-11/ ), where
  usr/include/c++/11/experimental/bits/fs_path.h
  has:
      // iterators
      class iterator;
      typedef iterator const_iterator;

      iterator begin() const;
  .
  .
  .
    inline path::iterator
    path::begin() const
    {
      if (_M_type == _Type::_Multi)
        return iterator(this, _M_cmpts.begin());
      return iterator(this, false);
    }

  
  , as opposed to 11.3.0-1ubuntu1~22.04:

      // iterators
      class iterator;
      typedef iterator const_iterator;

      iterator begin() const noexcept;
  .
  .
  .
    inline path::iterator
    path::begin() const
    {
      if (_M_type == _Type::_Multi)
        return iterator(this, _M_cmpts.begin());
      return iterator(this, false);
    }

  
  (witness "noexcept" specification newly added, but
  INCONSISTENTLY:
  at declaration location only, and missing at implementation site)

  
  Apparently fixed by
  git://gcc.gnu.org/git/gcc.git commit
  42eff613d0c10f "libstdc++: Add 'noexcept' to path::iterator members"
  (but currently published for gcc >= 12 release tags only!).

  A workaround might be
  applying
  -Wno-missing-exception-spec
  ( https://clang.llvm.org/docs/DiagnosticsReference.html )
  in all std::experimental::filesystem consumption cases (only!).
  Or being forced to
  instead actively (source / config modification) switch to
  std::filesystem (which
  does not seem to have this INCONSISTENCY bug, in
  /usr/include/c++/11/bits/fs_path.h
  ).


  $ lsb_release -rd
  Description:    Ubuntu 22.04.1 LTS
  Release:        22.04

  $ apt-cache policy libstdc++-11-dev
  libstdc++-11-dev:
    Installed: 11.3.0-1ubuntu1~22.04
    Candidate: 11.3.0-1ubuntu1~22.04
    Version table:
   *** 11.3.0-1ubuntu1~22.04 500
          500 http://de.archive.ubuntu.com/ubuntu jammy-updates/main amd64 Packages
          500 http://security.ubuntu.com/ubuntu jammy-security/main amd64 Packages
          100 /var/lib/dpkg/status
       11.2.0-19ubuntu1 500
          500 http://de.archive.ubuntu.com/ubuntu jammy/main amd64 Packages

  
  Thank you for all your awesome service efforts!

  P.S.: I got
  "In what package did you find this bug?"
  "libstdc++-11-dev" does not exist in Ubuntu. Please choose a different package. If you're unsure, please select "I don't know"
  ( at https://launchpad.net/ubuntu/+source/gcc-11/+filebug )
  Though libstdc++-11-dev clearly *is* a "package".
  --> this process is overly confusing, thus
  possibly should be corrected.

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