`cargo new` generates gitignore file that ignores non-root `Cargo.lock`s, causing errors with `cargo vendor`

[ashpil]

The default gigignore template generates a line with Cargo.lock rather than /Cargo.lock, causing necessary Cargo.locks in non-root directories to be ignored.

This becomes an issue if one uses cargo vendor to vendor deps - as the gitignore file ignores the dependencies' Cargo.locks, which one is required to have to build without error.

[weihanglo]

I've traced down the issue:

1. The original implementation did ignore root /Cargo.lock. Ignore Cargo.lock for libs in cargo-new #321
2. Someday one wanted to support both gitignore and hgingore's syntax and removed the leading slash. new: use .{git,hg}ignore syntax that's also understood by Mercurial #1247
3. Later, one found that we should not ignore target other than under root directory and added /target back. Ignore only root target directory #4099
4. It turns out that the syntax is not compatible between gitignore and hgignore. Therefore, one started to use hgignore special syntax to handle Cargo.lock. new: fix hgignore for real #4342

In terms of vendoring, personally I believe this should be fixed, especially when cargo start supporting artifact dependencies. Though checking out Cargo.lock into version control system for lib target is not recommended.

[Eh2406]

With that explanation I am +1 on fixing this. Thanks @weihanglo for the writeup!