[Bug libstdc++/97654] New: std::filesystem::copy() can't overwrite existing symlink

[Bug libstdc++/97654] New: std::filesystem::copy() can't overwrite existing symlink

[devl@adrian-ebeling.de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97654

            Bug ID: 97654
           Summary: std::filesystem::copy() can't overwrite existing
                    symlink
           Product: gcc
           Version: 9.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: devl@adrian-ebeling.de
  Target Milestone: ---

Created attachment 49480
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49480&action=edit
Full output with -v

std::filesystem::copy() with copy_options = copy_symlinks | overwrite_existing
does not overwrite existing symlinks. Instead it produces the following error:

terminate called after throwing an instance of
'std::filesystem::__cxx11::filesystem_error'
  what():  filesystem error: cannot copy: Invalid argument [link] [link_copy]

Using gcc-9.3.0 on Ubuntu focal.
Here's a simple shell script that creates the source files and produces the
error:

#!/bin/bash

# Create a regular file and two links to it
touch dest
ln -sf dest link
ln -sf dest link_copy


# Create a cpp program that uses std::filesystem to copy "link" to "link_copy",
# overwriting the existing link_copy

cat <<EOF > copyLink.cpp
#include <filesystem>
int main() {
    using namespace std::filesystem;
    copy("link", "link_copy",
         copy_options::copy_symlinks | copy_options::overwrite_existing);
}
EOF

#compile and run
g++ -v --save-temps -std=c++17  copyLink.cpp -o copyLink
./copyLink

[Bug libstdc++/97654] std::filesystem::copy() can't overwrite existing symlink

[devl@adrian-ebeling.de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97654

--- Comment #1 from devl@adrian-ebeling.de ---
Created attachment 49481
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49481&action=edit
intermediate files

.ii and .s files

[Bug libstdc++/97654] std::filesystem::copy() can't overwrite existing symlink

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97654

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to devl from comment #0)
> Created attachment 49480 [details]
> Full output with -v
> 
> std::filesystem::copy() with copy_options = copy_symlinks |
> overwrite_existing does not overwrite existing symlinks. Instead it produces
> the following error:
> 
> terminate called after throwing an instance of
> 'std::filesystem::__cxx11::filesystem_error'
>   what():  filesystem error: cannot copy: Invalid argument [link] [link_copy]

I think that's the behaviour specified by the standard, see [fs.op.copy] p4
bullet (4.6).

Or the equivalent description at
https://en.cppreference.com/w/cpp/filesystem/copy

  If from is a symbolic link, then 

  - If copy_options::skip_symlink is present in options, does nothing.
  - Otherwise, if to does not exist and copy_options::copy_symlinks is present
in options, then behaves as if copy_symlink(from, to)
  - Otherwise, reports an error

[Bug libstdc++/97654] std::filesystem::copy() can't overwrite existing symlink

[devl@adrian-ebeling.de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97654

devl@adrian-ebeling.de changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #3 from devl@adrian-ebeling.de ---
I suppose you're right.
If is_­symlink(f), the overwrite_existing flag is not taken into account,
according to the standard.

Sounds like a standard oversight to me, though.

Sigh, I guess I just have to manually delete the destination beforehand if it's
a symlink. The thing is I have to copy a whole bunch of files and only some of
them are symlinks.

Thanks for your help.