"unexpected "error": '8:1: 8:33: multiple matching crates for deny_public_fields [E0464]'" after Cargo update

[SimonSapin]

Servo’s CI failed after updating Cargo: servo/servo#16601 (comment)

CC @nox

I suspect that the issue is using -L path/to/directory whereas Cargo uses --extern name=path/to/file.rlib. I tried to reproduce outside of Servo but failed.

Attempted steps:

• rustup update nightly
• rustup update nightly-2017-04-21
• Use this branch master...SimonSapin:dep
• cd test-project
• cargo +nightly test
• cargo +nightly-2017-04-21 test

[laumann]

I'm not sure what to do about this. If the issue is using --extern instead of -L then maybe https://github.com/servo/servo/blob/234951e4b6d66891cd0cc9705f42e3ca16d9e3d5/tests/compiletest/helper/lib.rs#L26 needs changing.

But if there are multiple matching crates, does that mean that Cargo started adding dependencies that weren't added before? Maybe the dependencies added with config.target_rustcflags is obsolete?

[SimonSapin]

I filed this in case you had another idea, but unfortunately I believe there isn’t much to do as long as compiletest-rs works by calling rustc. To properly work with Cargo’s dependency management it should generate Cargo.toml files and call cargo instead, but that’s beyond a mere bugfix and almost sounds like a rewrite.