Unstable dependency selection and rebuilding

[jwilm]

I've got a project with workspaces that looks roughly like

├── Cargo.lock
├── Cargo.toml
├── push
│   └── Cargo.toml
├── src
└── util
    └── Cargo.toml

util has a dependency on postgres with the uuid feature. I've recently upgraded postgres to support uuid 0.3. Since a new version hasn't been cut, I've added postgres to my .cargo/config. There's a package in my project that depends on uuid 0.2 internally; this may be important. Now, whenever I run cargo build from the push folder, there's a change that postgres decides to switch between 0.2 and 0.3 of uuid thereby triggering rebuilds of postgres, util, and my push crate.

Here's some fingerprint logs demonstrating the behavior:

One run

INFO:cargo::ops::cargo_rustc::fingerprint: fingerprint error for postgres v0.11.10 (file:///home/jwilm/code/rust-postgres): new (uuid v0.2.3) != old (uuid v0.3.1)

Some number of runs later (varies)

INFO:cargo::ops::cargo_rustc::fingerprint: fingerprint error for postgres v0.11.10 (file:///home/jwilm/code/rust-postgres): new (uuid v0.3.1) != old (uuid v0.2.3)

Other fingerprint logs are a result of postgres deciding to rebuild, and there's nothing to suggest why it chose a different uuid abrubtly. The Cargo.lock file does not appear to change.

I've tried setting a workspace in rust-postgres/Cargo.toml to no effect. The rust-postgres uuid dependency looks like this:

uuid = { version = ">= 0.1, < 0.4", optional = true }

which does allow for other versions. In my project Cargo.toml files, only uuid 0.3 is ever specified other than in third-party dependencies which use 0.2 internally.

rustc/cargo versions:

jwilm@jwilm-desk ➜  ~/code/onepush/push  rustc -V
rustc 1.13.0-nightly (3c5a0fa45 2016-08-22)
jwilm@jwilm-desk ➜  ~/code/onepush/push  cargo -V
cargo 0.13.0-nightly (41b2177 2016-08-22)

[alexcrichton]

Hm, sounds fishy! Do you have any paths overrides in .cargo/config in play?

[jwilm]

Only for rust-postgres, but there's nothing changing over there to warrant a rebuild.

paths = ["/home/jwilm/code/rust-postgres"]

[alexcrichton]

Ah that'd do it, if you remove that is the build deterministic?

There's a couple of known bugs in Cargo where paths can cause nondeterministic compiles.

[jwilm]

Well, it's a deterministic failure. I need the path override so that another dependency uses my version of rust-postgres. Should this just be closed with a reference to one of those issues?

[alexcrichton]

I'd recommend using [replace] for overriding for now, otherwise I believe this is #2041

[lilith]

@alexcrichton Is there a nightly build available which supports combining workspaces and [replace]? Do I just have a bad build here?.

[alexcrichton]

@nathanaeljones I'll comment more on that issue

[alexcrichton]

I believe we've since implemented warnings for paths overrides that are likely to cause fishy compilations, so I'm going to close this.