"type annotations required" errors in 1.28 beta

[pietroalbini]

A bunch of crates failed to compile in 1.28 beta with error messages like these:

type annotations required: cannot resolve `std::io::Error: std::convert::From<_>`
type annotations required: cannot resolve `std::borrow::Cow<'_, str>: std::convert::From<&_>`'`
type annotations required: cannot resolve `std::string::String: std::convert::AsRef<_>`

• [x] mles-client regressed from stable to beta (build log) cc @jq-rs
• [ ] ogrep regressed from stable to beta (build log) cc @kriomant
• [x] openml regressed from stable to beta (build log) cc @mbillingr
• [ ] screeps-api regressed from stable to beta (build log) cc @daboross
• [x] tokio-dns-unofficial regressed from stable to beta (build log) cc @sbstp
• [x] topgrade regressed from stable to beta (build log) cc @r-darwish
• [ ] travis regressed from stable to beta (build log) cc @softprops

Also, the following crates are failing because they depend on tokio-dns-unofficial:

• tokio-postgres regressed from stable to beta (build log)
• tokio-tungstenite regressed from stable to beta (build log)
• GitHub repo grotsev/http_port regressed from stable to beta (build log)

[mbillingr]

I fixed this in openml (https://github.com/mbillingr/openml-rust/commit/96d7877e4e35365bf3c4e9e9ab7273f610ff7ad7) by changing Cow::from(self.as_ref()) to Cow::from(self.as_str()) (self is of type String). This is probably how it should have been written anyway.

[sbstp]

I don't see any errors in the build log of my crate. The fold issue was spotted and fixed a few weeks ago here. It seems like the issue in other crates is because they depend on old versions.

Any clue why this breaking change started happening? I don't think I can release a 0.1.2.

[pietroalbini]

I don't see any errors in the build log of my crate.

Copy-pasted the link for the wrong version, sorry. This is the one for 0.1.1.

Any clue why this breaking change started happening? I don't think I can release a 0.1.2.

I haven't investigated this yet. If it's a bug in the compiler we'll get this fixed before 1.28 reaches stable.

[sbstp]

Is it possible to backport the fix? The current version is 0.3.1, is cargo able to publish a 0.1.2 version that's semver compatible with the broken version? I guess I could yank that version, but the existing dependencies will still continue to break.

[sfackler]

You can publish a 0.1.2

[sbstp]

Alright, I've released 0.1.2 and it seems to have fixed the issue.

[r-darwish]

I also changed my code to as_str as it makes more sense.

@pietroalbini this process of checking the beta compiler by compiling actual crates is awesome. Is there any place in which I can read more about how it works?

[mbillingr]

@r-darwish I think crater is the tool in use.

[Mark-Simulacrum]

This is caused by b559710e58427213d6f82008206c22cf3d76b4c4, probably https://github.com/rust-lang/rust/pull/50170. cc @rust-lang/libs, I've closed https://github.com/rust-lang/rust/issues/50954 as a duplicate of this bug.

[pietroalbini]

Ping @rust-lang/libs, any news on this?

[alexcrichton]

We'll be discussing this in this week's triage meeting

[alexcrichton]

The conclusion of said discussion is that we're going to leave this as-is, but if any crates have difficulty updating we're more than willing to help!

[jq-rs]

Mles-client build is failing due to dependencies, thus it should work now as the dependencies are fixed. Just made a build with nightly, runs smoothly. So it was just miscategorized here.