I would say that there is a misconception. C: does not reference the root directory of a volume. It references the current working directory of that volume.

You should either prohibit this or handle it properly, not silently convert to something else, especially not a root directory. I think the failure mode of converting C: to C:/ is a very bad one:

my $p= path("C:");
unlink $_ for $p->children;
[download]

For UNC paths, I see no such bad failure mode of appending a trailing directory separator.

C: does not reference the root directory of a volume

I understand that. What I'm trying to get guidance on is how likely it is that people would use "C:" and not mean the root directory.

If I understand you correctly, what probably needs to happen is to immediately turn C: into the absolute path for cwd on that volume via getdcwd.

Is that right?

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Yes. I would consider it highly likely that people use the system as documented.

Yes, getcwd getdcwd is the function that needs to get involved to make C: resolve correctly.