Allow dependencies that only apply to specific cargo targets (bin, example, etc.)

[tbu-]

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Past RFCs

• Allow specifying dependencies for individual artifacts rfcs#2887
• Allow specifying features of the implicit lib dependency rfcs#3020
• Cargo target features rfcs#3374

Related requests

• Automatically enable required-features #4663

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Use case: I have a library that also produces an executable. The executable needs env_logger in order to be able to log, the library shouldn't carry that dependency though, as it pulls in all sorts of crates (e.g. regex (?)).

[pwoolcoc]

@tbu- I have a branch with this mostly working, I'm trying to get it cleaned up and committed "soon"

[tbu-]

Sounds great!

[marjakm]

Any updates?

[alexbool]

+1, would be great to have it

[gyscos]

Also consider as possible filters for dependencies:

• Examples
• Integration tests
• Benchmarks

Also, should it be per-binary (when multiple are provided)?

[hauleth]

@gyscos all of that can fall into dev-dependencies bucket. I see no reason for giving ability to set dependency only for benchmarks or something.

[azerupi]

@alexcrichton is this a desired feature? Would a PR proposing this get merged?

My personal opinion is that it would be useful for libraries exposing a little cli alongside of a lib (e.g. pulldown-cmark) because it would allow them to, for example, pull in an argument parser (e.g. Clap) without imposing that dependency on all the library users and without the need to create a separate crate for the small binary.

Also, should it be per-binary (when multiple are provided)?

What is your opinion on this and how should it be represented in Cargo.toml?

[fulmicoton]

Would love to have this.

[alexcrichton]

@azerupi yeah I suspect Cargo will end up with something like this eventually, it's certainly a well motivated feature! I wouldn't got he route of dependencies-per-binary yet, though, as we don't similarly also have things like dependencies-per-example or dependencies-per-test

[alexreg]

Any progress on this yet?