[Bug libstdc++/83626] New: std::experimental::filesystem::remove_all throws exception instead of returning 0 if path doesn't exist

[chillermillerlong at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83626

            Bug ID: 83626
           Summary: std::experimental::filesystem::remove_all throws
                    exception instead of returning 0 if path doesn't exist
           Product: gcc
           Version: 7.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: chillermillerlong at hotmail dot com
  Target Milestone: ---

The current std::experimental::filesystem::remove_all() implementation seems to
throw an exception if the specified path does not exist. I may be
misunderstanding the standard, but § 30.10.15.31 in the latest C++17 draft says
that the function "Recursively deletes the contents of p if it exists, then
deletes file p itself" and returns "The number of files removed". It seems to
me that the function should return 0 if the path does not exist. (Indeed, this
is how boost::filesystem::remove_all() behaves.)

The following sample program demonstrates the behavior.

    #include <experimental/filesystem>
    #include <iostream>

    namespace fs = std::experimental::filesystem;

    int main(int argc, char *argv[])
    {
        std::cout << "Deleted " << fs::remove_all(argv[1]) << " paths\n";
    }

If I pass it a path that doesn't exist, it throws an exception:

    $ g++ fs.cpp -std=c++17 -lstdc++fs
    $ ./a.out /tmp/non-existent
    terminate called after throwing an instance of
'std::experimental::filesystem::v1::__cxx11::filesystem_error'
      what():  filesystem error: cannot remove all: No such file or directory
[/tmp/non-existent]
    [1]    9386 abort (core dumped)  ./a.out /tmp/non-existent