Problem
Running a command, e.g. cargo metadata or cargo check with the --manifest-path set to equal an absolute Windows long-style path causes an error:

The filename, directory name, or volume label syntax is incorrect. (os error 123)

Steps

1. Create a project anywhere and note its path. Let's pretend it's C:\Path
2. Run a cargo command with mainfest-path set to that path as a long absolute path: cargo metadata --manifest-path \\?\C:\Path\Cargo.toml
3. Note the failure.

Notes

Output of cargo version: cargo 1.47.0-nightly (ab32ee8 2020-08-10)

May be related to #7986, #7420, #7643