Auto merge of #5361 - derekdreery:issue_5345, r=matklad

Fix issue 5345

Fixes #5345.

Also adds some docs and Debug impls.

diff --cc src/cargo/core/compiler/context/mod.rs
Simple merge

diff --cc src/cargo/core/package.rs
Simple merge

diff --cc src/cargo/ops/cargo_compile.rs
Simple merge