`cargo test --features dep/feat` does not imply `--features dep` in beta

[tspiteri]

In rustc 1.50.0, cargo --features dep/feat also seems to imply --features dep, but this does not seem to be the case in 1.51.0-beta.6.

For example, for two library crates foo and bar.

foo/Cargo.toml:

[package]
name = "foo"
version = "0.1.0"
edition = "2018"

[features]
foof = []

bar/Cargo.toml:

[package]
name = "bar"
version = "0.1.0"
edition = "2018"

[dependencies.foo]
path = "../foo"
optional = true

This works with stable rustc 1.50.0 (cb75ad5db 2021-02-10):

$ cargo +stable test --features foo/foof -p foo

This gives an error with beta rustc 1.51.0-beta.6 (6a1835ad7 2021-03-12):

$ cargo +beta test --features foo/foof -p foo
error: package ID specification `foo` did not match any packages

I don't know if this used to work unintentionally up to 1.50.0 and the "glitch got fixed" in the beta.

@rustbot modify labels: +regression-from-stable-to-beta -regression-untriaged

[JohnTitor]

This is a cargo issue, @rust-lang/cargo could someone check and transfer it?

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[ehuss]

Transferred to rust-lang/cargo.

I think this was unintended, as part of #8997.