--manifest-path forces recompile when using vendoring

[sebastianblunt]

Problem

If vendoring dependencies instead of pulling from crates.io, then using --manifest-path will cause cargo to recompile whenever switching from inside the repo to outside.

Steps

1. I created a minimal repository to reproduce this: https://github.com/sebastianblunt/cargo-6999
2. cd into the repo and run cargo build
3. cd ..
4. cargo build --manifest-path example/Cargo.toml
5. Notice that it will recompile both the dependency and example.

If you go into the example repo and remove/rename the .cargo directory, thereby removing the vendoring, then cargo will not recompile when you do the above.

It does not seem to make any difference whether you use absolute or relative paths in the .cargo/config.

Possible Solution(s)

Notes

Output of cargo version: cargo 1.37.0-nightly (545f35425 2019-05-23)

[ehuss]

Thanks for making the repro! Cargo doesn't read the .cargo/config file when using --manifest-path (it uses the current working directory). I believe this is a dupe of #2930.

[ehuss]

Closing in favor of #2930.