Cargo: Publishing with a crates.io mirror has a confusing error message

[ehuss]

Problem
If one is using a mirror of crates.io, the error message you get when you attempt to publish is confusing. It says:

error: crates cannot be published to crates.io with dependencies sourced from other
registries either publish `bitflags` on crates.io or pull it into this repository
and specify it with a path and version
(crate `bitflags` is pulled from registry `https://github.com/rust-lang/crates.io-index`)

The last line clearly says that it is from "crates.io".

Steps

1. Check out crates.io index (https://github.com/rust-lang/crates.io-index)
2. Create a project with a dependency from crates.io.
3. Add a .cargo/config file to set up the mirror:

[source.crates-io]
replace-with="mirror"

[source.mirror]
registry = "file:///path/to/crates.io-index"

1. cargo publish --dry-run

Possible Solution(s)

• Display a better error message, possibly instructing the user to disable the mirror.
• Detect that a mirror is being used, and allow it to proceed. This seems like it could be tricky.

Notes

• cargo 1.34.0-nightly (5c6aa46e6 2019-02-22)
• Reported by user "calidion" on Discord #crates-io

[clearloop]

Same problem, annotated ~/.cargo/config temporarily.

# [source.crates-io]
# registry = "https://github.com/rust-lang/crates.io-index"
# replace-with = 'ustc'
# [source.ustc]
# registry = "git://mirrors.ustc.edu.cn/crates.io-index"

[chengyuhui]

Connection to GitHub is basically trash for some ISPs in China, so a mirror is sometimes required. Having to comment out ~/.cargo/config every time I need to publish a crate can be annoying.