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Rust 1.30: importing derive macro with use works or fails depending on whether unrelated dependency is present #55386
Description
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
Activity
sfackler commentedon Oct 26, 2018
ron enables serde's
serde_derivefeature 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.