Cannot declare different version of dependencies in mutually exclusive targets

[wagenet]

Maintainer's update

• This is fixed for registry dependencies but not git dependencies

---

That's a mouthful, but here's an example:

[target.'cfg(not(target_os = "linux"))'.dependencies]
nix = "0.5.0"

[target.'cfg(target_os = "linux")'.dependencies]
nix = "0.4.3"

Unfortunately, right now this isn't allowed as it's considered a duplicate declaration per #2491.

The use case for this is that FreeBSD requires a newer version of nix to work. However, Linuxes with glibc 2.5 require an older version of nix.

My very ugly workaround is to fork nix and rename it. Then I can use cfg to import the correct crate in the source.

[alexcrichton]

Yeah unfortunately Cargo doesn't handle this case very well in general (depending on two versions of a library). If this works at all I'd be pretty surprised!

[wagenet]

It works, but only if the libraries are forked an renamed to avoid actual duplicate names.

[alexcrichton]

Yeah Cargo should definitely have built-in support for that kind of operation.

[TheNeikos]

Interesting, there is this test:

cargo/tests/cfg.rs

Line 232 in be010b5

fn ignore_version_from_other_platform() {

That seems to test exactly that, and it checks for success

[damaex]

I somewhat have an equal problem with the feature-dependencies for mysql-crate:

[target.'cfg(any(unix, macos))'.dependencies.mysql]
version = "*"
default-features = false
features = ["socket"]

[target.'cfg(windows)'.dependencies.mysql]
version = "*"
default-features = false
features = ["pipe"]

[alexcrichton]

@TheNeikos oh interesting! @wagenet maybe this was fixed in nightly at some point? Or perhaps you could gist the exact error?

@damaex ah I think that my actually be an unrelated failure (e.g. another bug in Cargo). Enabling separate features for different targets unfortunately isn't supported right now.

[wagenet]

@alexcrichton looks like you're right about this being fixed on the latest nightly. Thanks!

[wagenet]

Looks like there are still issues around git dependencies. This doesn't work:

[target.'cfg(not(target_os = "linux"))'.dependencies]
nix     = "0.5.0"
pidfile = { git = "https://github.com/wagenet/pidfile-rust", rev = "a0fe92915e419938d8d33f5cefb6e8f50b89d174" }

[target.'cfg(target_os = "linux")'.dependencies]
nix     = "0.4.3"
pidfile = { git = "https://github.com/carllerche/pidfile-rust", rev = "7516edfc9af2c0480e9f187c87de8cf6323c1ee3" }

It complains about pidfile being a duplicate, but not nix.

[wagenet]

Initial work on a PR to fix this here: #3275

[Eh2406]

Note that #6179 (comment) may provide a workaround by using --minimal-cargo-lock to build only for the current platform.

[wagenet]

See #6212.

[alexcrichton]

I don't personally know how we'd solve this today or whether it's easily solvable, but PRs to implement it are of course always welcome!

[RalfJung]

Looks like a duplicate of #2524.

[ehuss]

@RalfJung I don't see this as a duplicate. The issue here is that two different targets using git dependencies does not work. #2524 is about using different features.

[RalfJung]

Sorry for that then, seems I didn't understand what this bug is about.