cargo vendor outputs directory with \\?\ on Windows if it previously existed

[agashlin]

Problem

When using the builtin cargo vendor in 1.37.0, if the path already exists the generated .cargo/config output has a path starting with \\?\, which confuses other tools.

I've seen a few terms used for this kind of path: extended-length paths, UNC paths, NT paths. I'm not sure which is accurate.

Steps

1. In a mingw shell, in a crate with some dependencies, mkdir vendor
2. cargo vendor
3. Output includes:

[source.vendored-sources]
directory = "\\\\?\\<basedir>\\vendor"

Possible Solution(s)
With cargo-vendor 0.1.23 (exposed by downgrading to 1.36.0 with rustup default 1.36.0) this was not the case, it would output directory = "<basedir>\\vendor"

This is the case whether or not the directory existed already. With the subcommand in 1.37.0, the above issue happens if the directory already existed, but if it did not then it just says directory = "vendor". This is probably coming from the GetFinalPathNameByHandleW() call inside sys::fs::canonicalize(), but I haven't dug into cargo yet to see why this is being used.

I think something similar was caught and fixed early in cargo-vendor: alexcrichton/cargo-vendor#71 (comment)

Notes

Output of cargo version:

cargo 1.37.0 (9edd089 2019-08-02)

[ehuss]

Thanks for the report! I think this is essentially the same as #7316, so I'm going to close in favor of that (though I'm going to steal your title for the other issue).

[agashlin]

Oops, I should have looked a little harder, thanks for the link!