Multiple rlib candidates found on beta/nightly, but not stable

[djc]

Askama has a Cargo workspace with multiple crates in it. Previously, all of the crates just referenced each other by path. However, last night I published them to crates.io, so now I need conventional dependency specifications. As I did this, my testing with cargo test --all (specifically, the doctests, apparently) started to fail with this error:

See here: https://travis-ci.org/djc/askama/builds/202002221

(As reported in #cargo, @brson asked me to file a bug about it.)

[alexcrichton]

Taking a look now, but note that even if you've published crates it's still best to use path dependencies to pick up local changes. You'll just need to annotate the dependency with an extra version = "..." that you'd otherwise write in for crates.io (example)

[alexcrichton]

This looks like a regression in Cargo, it's passing two --extern askama=... flags to rustdoc --test

[alexcrichton]

Correction, Cargo's always done that, apparently rustdoc is just now reading it...

[alexcrichton]

I've sent a PR to Cargo to fix this: rust-lang/cargo#3721

I'm not really sure what the regression was here between stable/beta, but we may as well backport it to beta on Cargo to get that fix in.