"type annotations required" errors in 1.28 beta

[emilyalbini]

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<_>`

• mles-client regressed from stable to beta (build log) cc @jq-rs
• ogrep regressed from stable to beta (build log) cc @kriomant
• openml regressed from stable to beta (build log) cc @mbillingr
• screeps-api regressed from stable to beta (build log) cc @daboross
• tokio-dns-unofficial regressed from stable to beta (build log) cc @sbstp
• 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 (mbillingr/openml-rust@96d7877) 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.

[emilyalbini]

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 b559710, probably #50170. cc @rust-lang/libs, I've closed #50954 as a duplicate of this bug.