rust - cargo .toml : how to conditionally enable a dependency feature?

Question

在我的项目中，我有 2 个功能:myfeatureA 和 myfeatureB。

我希望其中一个依赖于具有 rt 和 sync 功能的 tokio，另一个依赖于 tokio 仅具有 sync 功能。

我在Cargo.toml中尝试了此配置:

[dependencies]
tokio = { version = "1.32", features = ["rt", "sync"], optional = true }

[features]
myfeatureA = ["dep:tokio"]
myfeatureB = ["dep:tokio/sync"]

$ cargo build --features=myfeatureB
error: failed to parse manifest at `[...]/myproject/Cargo.toml`

Caused by:
  feature `myfeatureB` includes `dep:tokio/sync` with both `dep:` and `/`
  To fix this, remove the `dep:` prefix.

所以，我删除了 dep: 前缀(这是这个 other question 提供的解决方案，但它不起作用):

[features]
myfeatureA = ["dep:tokio"]
myfeatureB = ["tokio/sync"]

$ cargo build --features=myfeatureB
error: Package `myproject v0.1.0 ([...]/myproject)` does not have feature `tokio`. It has an optional dependency with that name, but that dependency uses the "dep:" syntax in the features table, so it does not have an implicit feature with that name.

如何使 myfeatureB 依赖于 tokio 仅具有 sync 功能？

Answer 1

这已在 issue #10788 中报道过，已在 Rust 1.72.0 中修复。现在您可以使用第二种方法(无 dep:)。

对于以前的版本，根本不要使用 dep:，即使对于其他功能也是如此。不过，这会创建一个名为 tokio 的功能。