Latest released version does not compile

[ia0]

Problem

The cargo library doesn't build at 0.50.0 (latest released version) and 0.52.0. However it does at master.

Steps

1. git checkout 67a00f95b (supposedly 0.50.0) or git checkout 60143816b (supposedly 0.52.0)
2. cargo build --release --lib
3. The following error is displayed:

error[E0283]: type annotations needed
   --> src/cargo/util/config/de.rs:530:63
    |
530 |                 seed.deserialize(Tuple2Deserializer(1i32, env.as_ref()))
    |                                                           ----^^^^^^--
    |                                                           |   |
    |                                                           |   cannot infer type for type parameter `T` declared on the trait `AsRef`
    |                                                           this method call resolves to `&T`
    |
    = note: cannot satisfy `std::string::String: AsRef<_>`
help: use the fully qualified path for the potential candidates
    |
530 |                 seed.deserialize(Tuple2Deserializer(1i32, <std::string::String as AsRef<OsStr>>::as_ref(env)))
    |                                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
530 |                 seed.deserialize(Tuple2Deserializer(1i32, <std::string::String as AsRef<std::path::Path>>::as_ref(env)))
    |                                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
530 |                 seed.deserialize(Tuple2Deserializer(1i32, <std::string::String as AsRef<str>>::as_ref(env)))
    |                                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
530 |                 seed.deserialize(Tuple2Deserializer(1i32, <std::string::String as AsRef<[u8]>>::as_ref(env)))
    |                                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0283`.
error: could not compile `cargo`

To learn more, run the command again with --verbose.

Possible Solution(s)

Bump and release version 0.53.0.

Notes

Output of cargo version: cargo 1.51.0-nightly (c3abcfe8a 2021-01-25)
Output of rustc version: rustc 1.51.0-nightly (04caa632d 2021-01-30)

[est31]

Hitting this issue in the cargo-udeps CI as well. cargo install --locked works, which means it's likely due to a dependency update. If I do the following, I can reproduce the issue on cargo-udeps master:

$ cargo update -p syn -p serde
    Updating serde v1.0.121 -> v1.0.123
    Updating serde_derive v1.0.121 -> v1.0.123
    Updating syn v1.0.59 -> v1.0.60

(It doesn't reproduce without that)

cc @dtolnay

[est31]

Already happens when I do:

$ cargo update -p syn && cargo update -p serde --precise 1.0.122
    Updating crates.io index
    Updating syn v1.0.59 -> v1.0.60
    Updating crates.io index
    Updating serde v1.0.121 -> v1.0.122
    Updating serde_derive v1.0.121 -> v1.0.122

And it does not happen when I run it for syn only, so I suspect it's either due to a serde or serde_derive change, between the 1.0.121 and 1.0.122 versions. changes link.

[est31]

See f097d02 and #9101

[est31]

and serde-rs/serde#1967

[ia0]

I didn't mention in the initial post, but I actually got the issue when building cargo-outdated with cargo install cargo-outdated. So besides serde, this should also break CIs of projects where cargo-outdated is built with the command above. At least it did for https://travis-ci.org/github/ia0/data-encoding/jobs/757173491.

Not sure what is the release policy of cargo but when debugging this I was surprised to see that the latest published version is 0.50.0 while master is past 0.52.0. I was also surprised to see that the issue is not present in master, so the fix should just be to publish a new version.

[est31]

@ia0 release policy of the cargo crate is to release the new version on crates.io whenever there is a new release of rust/rustc. There is also a 6 week beta waiting period. So if the fix arrives in an "ordinary" way it'll take until March 25... hopefully it's realized that this is untenable, but let's see.

[ia0]

Oh I see, that's good to know. Thanks for the info! I guess I'll just disable the cargo outdated test in my CI until this is fixed. This is not a big issue for me. I just felt I had to report it.

[est31]

You can also try if cargo install --locked works for you.

[ia0]

Yes it works, thanks!

[Eh2406]

We discussed it in today's Cargo meeting. We are good to do a patch release of the library when a PR bacporting #9101 is merged.

[est31]

@Eh2406 that'd be awesome!