Optional dependencies with links cause failure even when not used

[korken89]

Problem

As a dependency I want 2 versions of a crate, but the crate uses the links attribute as only one is allowed.
If I rename the 2 versions of a crate and use the package and set optional = true the links check still fails, even though none of the optional dependencies are enabled.

I'd expect this to work with only one of the 2 enabled, but fail with a links error if both were enabled.
And it seems from here that this should be allowed: https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#renaming-dependencies-in-cargotoml
With the line Depend on multiple versions of a crate.

Steps

Use the following Cargo.toml in an empty project and run cargo build to show the issue:

[package]
name = "dual-defmt"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]

[dependencies.defmt02]
package = "defmt"
version = "0.2"
optional = true

[dependencies.defmt03]
package = "defmt"
version = "0.3"
optional = true

Possible Solution(s)

No response

Notes

No response

Version

cargo 1.56.0 (4ed5d137b 2021-10-04)
release: 1.56.0
commit-hash: 4ed5d137baff5eccf1bae5a7b2ae4b57efad4a7d
commit-date: 2021-10-04

[Eh2406]

The root of your problem is that a lockfile is generated with all features enabled. Features are supposed to be additive.
In this case, if you have a different project in a different workspace that depends on your example it will work.

[ehuss]

Closing as a duplicate of #5969, which contains a deeper discussion of this situation.