[Bug libstdc++/105422] New: filesystem::copy does not throw exceptions when a subdirectory exists

["mpie@msc-ge.com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105422

            Bug ID: 105422
           Summary: filesystem::copy does not throw exceptions when a
                    subdirectory exists
           Product: gcc
           Version: 11.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mpie@msc-ge.com
  Target Milestone: ---

Created attachment 52895
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52895&action=edit
Example file to reproduce behaviour

Hi,

in Ubuntu 21.10 a recursive filesystem::copy() does correctly throw an
exception if a file can't be read. But it will not throw an exception if there
is an empty subdirectory. The destination will therefore miss a file without a
report. Also the error code will be empty.

See the output of the attached copy_bug.cpp

$ c++ copy_bug.cpp -o copy_bug --std=c++17
$ ./copy_bug

Copytest with withSubDir=0
Exception: filesystem error: cannot copy: Permission denied [test/source]
[test/dest]
Error code: Permission denied
Copytest with withSubDir=1

$ tree -p test       
test
├── [drwxrwxr-x]  dest
│   └── [drwxrwxr-x]  subdir
├── [drwxrwxr-x]  dest_ec
│   └── [drwxrwxr-x]  subdir
└── [drwxrwxr-x]  source
    ├── [drwxrwxr-x]  subdir
    └── [----------]  test.txt