rebuild dependencies on rust update

[allan-simon]

When I update rust nightly and i try to cargo build again I got these errors

src/xmpp/lib.rs:15:1: 15:18 error: found possibly newer version of crate `std` which `xml` depends on
src/xmpp/lib.rs:15 extern crate xml;
                   ^~~~~~~~~~~~~~~~~
src/xmpp/lib.rs:15:1: 15:18 note: perhaps this crate needs to be recompiled?
src/xmpp/lib.rs:15 extern crate xml;
                   ^~~~~~~~~~~~~~~~~
src/xmpp/lib.rs:15:18: 15:18 note: crate `std` path #1: /usr/lib/rust/rust-nightly/lib/rustlib/i686-unknown-linux-gnu/lib/libstd-4e7c5e5c.rlib
src/xmpp/lib.rs:15:18: 15:18 note: crate `std` path #2: /usr/lib/rust/rust-nightly/lib/rustlib/i686-unknown-linux-gnu/lib/libstd-4e7c5e5c.so
src/xmpp/lib.rs:15:18: 15:18 note: crate `xml` path #1: /home/allan/perso/rust-xmpp-server-stream/target/deps/libxml4e3e5018578ccea9.rlib
error: aborting due to previous error
Could not execute process `rustc src/xmpp/lib.rs --crate-name xmpp --crate-type lib -g -C metadata=rust-xmpp-server-stream:-:0.0.0:-:file:/home/allan/perso/rust-xmpp-server-stream -C extra-filename=59396aea2dc02d0a --out-dir /home/allan/perso/rust-xmpp-server-stream/target -L /home/allan/perso/rust-xmpp-server-stream/target -L /home/allan/perso/rust-xmpp-server-stream/target/deps` (status=101)

however the crate xml is provided as dependency, it would be great if cargo could detect that and rebuild dependencies on version change of rust (as otherwise we need to guess that we have to delete target directory, though I admit it's not a difficult guess )

[alexcrichton]

Cargo does indeed detect when rust was updated, so I'm curious why you're running into this. Could you give some more information about your setup, steps to reproduce, and the version of cargo you're using?

[allan-simon]

it's a bit late, but basically here are the steps

1. I use cargo and rust-nightly from ubuntu's ppa
2. built a first time this project https://github.com/allan-simon/rust-xmpp-server-stream and its dependencies using cargo build not later than 3 days ago (may be 2 days ago)
3. updated my code a little (I assume it should not be of any importance but who knows), the dependencies haven't changed.
4. upgraded today my version of rust (cargo was not updated)
5. runned cargo build again => get that error

[alexcrichton]

Ok, I've gone through that workflow many times recently and cargo has rebuilt when rustc updates. It may have been fixed in a version of cargo later on than you're using. I'm going to close this for now under that assumption, but feel free to reopen if you run into it again!

[nfriedly]

I know this is a super-old ticket, but I ran into a related issue today and came across this when searching for a solution. I eventually figured it out, but hopefully this saves someone else some time and frustration:

If you get the message

note: perhaps this crate needs to be recompiled?

The way you do that is by running cargo clean and then cargo build.