Dual versions of defmt causes links error when it should not

[korken89]

Hi all,

I'm looking to add to all the crates I maintain so it support defmt 0.2 and 0.3, but I get a links error even though the dependencies are optional.
If you do the same for cortex-m which also uses the links argument it does however work!

Something is being done in defmt which breaks optional dependencies - not sure what.
This does however block us from supporting both 0.2 and 0.3, which would allow us to do a non-breaking release of crates with 0.3 support.

Not working Cargo.toml (run in empty project):

[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

Working Cargo.toml (run in empty project):

[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 = "cortex-m"
version = "0.6"
optional = true

[dependencies.defmt03]
package = "cortex-m"
version = "0.7"
optional = true

[jonas-schievink]

Duplicate of #426, I believe

[korken89]

Seems like it, that's unfortunate.
I don't want to release new major versions just due to this, but maybe there's no way around it.

[korken89]

Here is the root cargo issue as well: rust-lang/cargo#5969

[korken89]

Are there any issues with specifying a range of versions for defmt for libraries?
E.g.:

[dependencies.defmt]
version = ">=0.2,<0.4"
optional = true

This seems to work in my experiments in heapless, but I'm not sure if this has unintended consequences.

[Urhengulas]

Hi @korken89, let's move the discussion to #426, in order to scatter it not too much.