Rust 1.30: importing derive macro with use works or fails depending on whether unrelated dependency is present

[ghost]

Using Rust 1.30 it is possible to bring macros into scope using use instead of #[macro_use]. I am therefore (perhaps a bit over-zealously) trying to get rid of all instances of #[macro_use] in my crates, when I hit upon what seems to be a strange edge case regarding the following bit of code:

extern crate serde;

use serde::Serialize;

#[derive(Serialize)]
pub enum Foo {
    Bar,
}

Using the following Cargo.toml, which includes a dependency on ron which is not used in the code:

[package]
name = "foo"
version = "0.1.0"

[dependencies]
serde = "1.0.78"
ron = "0.4.0"

This compiles fine:

 % cargo build    
    Finished dev [unoptimized + debuginfo] target(s) in 1.65s

However when I remove the dependency on ron (which itself depends on serde) from my Cargo.toml:

[package]
name = "foo"
version = "0.1.0"

[dependencies]
serde = "1.0.78"

Then I get a compile error:

 % cargo build
   Compiling foo v0.1.0 (/sysroot/home/bram.senders/source/lws-connector-tmp)                  
error: cannot find derive macro `Serialize` in this scope                                      
 --> src/lib.rs:5:10                                                                           
  |                                                                                            
5 | #[derive(Serialize)]                                                                       
  |          ^^^^^^^^^                                                                         
                                                                                               
error: aborting due to previous error                                                          
                                                                                               
error: Could not compile `foo`.                                                                

Meta

 % rustc --version --verbose
rustc 1.30.0 (da5f414c2 2018-10-24)
binary: rustc
commit-hash: da5f414c2c0bfe5198934493f04c676e2b23ff2e
commit-date: 2018-10-24
host: x86_64-unknown-linux-gnu
release: 1.30.0
LLVM version: 8.0

[sfackler]

ron enables serde's serde_derive feature which reexports the derive macros. If you stop depending on ron, that feature stops being activated. You can either directly depend on the serde_derive crate or enable the feature yourself: https://docs.rs/crate/ron/0.4.0/source/Cargo.toml.orig.

[ghost]

Aaah, I see! I had never realized before that a dependant crate could modify which features I can use from another crate. So this is not a bug. Sorry for the noise and thank you very much for the explanation!