cargo build --manifest-path <long-path> doesn't work on Windows

[stepancheg]

cargo build --manifest-path <very-long-path>

doesn't work on Windows: reports

error: manifest path `<very-long-path>` does not exist

Script which reproduces the problem: https://github.com/stepancheg/test-win-long-paths/blob/master/test.sh
Failed job on GitHub actions: https://github.com/stepancheg/test-win-long-paths/runs/1532597301

Why it is important

rustc has certain problems with long paths on Windows, which I need to reproduce. I tried to reproduce them with cargo and encountered this issue.

In certain build systems and certain CI environments build paths may be quite long. It is constant pain on Windows.

[ehuss]

There are several issues open for this (such as #7986, which explains a little why this is very difficult), and recent PRs such as #8874, #8881, #8964.

Last time I checked, the MSVC linker didn't support long paths, so even if Cargo supported them, it would likely still not work.
(Though that information may be outdated, it has been a long time since I've tried.)

[ehuss]

Closing as a duplicate of #7986.

[dylni]

When #6198 is fixed, you can use a verbatim path instead (\\?\long\path). There's a PR open to fix it: #8881