Implicit features due to target-specific optional dependencies are not added in current version

[obi1kenobi]

@obi1kenobi Upgrading to v0.18 results in a failing semver check despite this crate not having received any significant changes. Could you look into this?

Originally posted by @thomaseizinger in libp2p/rust-libp2p#3469 (comment)

Affected crate: libp2p_uds version 0.17, repro commit 5b4eab7bafe6cba8fea6c806027ea680662b7cc6

Its Cargo.toml contains the following block:

[target.'cfg(all(unix, not(target_os = "emscripten")))'.dependencies]
async-std = { version = "1.6.2", optional = true }
libp2p-core = { version = "0.38.0", path = "../../core" }
log = "0.4.1"
futures = "0.3.1"
tokio = { version = "1.15", default-features = false, features = ["net"], optional = true }

This implicitly defines features named async-std and tokio. These features are enabled in the baseline, but for some reason are not enabled in the "current":

[dependencies.libp2p-uds]
path = "/.../rust-libp2p/transports/uds"
features = []
default-features = false

[obi1kenobi]

@tonowak would you mind taking a look at this, since you're much more familiar with this code?

I'm surprised that our feature-detection code seems to detect different features when loading a crate's information via the registry (as in the baseline) versus from a local Cargo.toml manifest (as in the current version).

[obi1kenobi]

I'll release this in a patch version in the morning (my time), because releasing right before going to bed sounds like a recipe for staying up for half the night, just like deploying prod at 5pm on a Friday 😅

[obi1kenobi]

Released in https://github.com/obi1kenobi/cargo-semver-checks/releases/tag/v0.18.2 — sorry for the inconvenience and thanks for bearing with us while we fixed this!