cfg parameters for dependencies

[trevex]

I started using cargo recently and noticed that I am unable to pass cfg parameters to dependencies. Although this might be a fairly rare use-case it would help to configure dependencies, i.e.
imagine an ORM for mysql, a use case for cfg would be to specify the mysql connector (Sun Connector, libmysqlclient, libdrizzle), where multiple are available.
In an application using the ORM library, it might be desired to pick the mysql client library.

Therefore it would be nice to be able to specify cfg parameters

[dependencies.*]
cfg = "USE_DRIZZLE"

[alexcrichton]

This is definitely planned! There will be support for a package to expose a number of features which can be selected upon and each feature will be able to pass flags to the compiler.

[trevex]

Good to hear 👍

[huonw]

(Just being planned doesn't mean this shouldn't be open. :) )

[rail44]

Is it going to come with [[bin]] section?
I mean, is

[[bin]]
name = "foo"
cfg = "bar"

allowed?

[metajack]

This is blocking a Servo move to Cargo. Specifically rust-alert has conditional dependencies for some platforms. On OS X it needs rust-cocoa and rust-core-foundation, but has no dependencies on Linux.

https://github.com/servo/rust-alert

[alexcrichton]

I believe this is now aptly covered by #385, so I'm going to close this in favor of that issue.