Support crate package renaming

[mjbshaw]

Crates can now be renamed in the dependencies section. Attempting to do this with the current version of serde fails. Example:

Cargo.toml:

cargo-features = ["rename-dependency"]

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

[dependencies]
sd = { git = "https://github.com/serde-rs/serde", package = "serde_derive" }
sj = { git = "https://github.com/serde-rs/json", package = "serde_json" }

src/main.rs:

#[macro_use]
extern crate sd;
extern crate sj;

#[derive(Serialize, Deserialize, Debug)]
struct Point {
    x: i32,
    y: i32,
}

fn main() {
    let point = Point { x: 1, y: 2 };

    // Convert the Point to a JSON string.
    let serialized = sj::to_string(&point).unwrap();

    // Prints serialized = {"x":1,"y":2}
    println!("serialized = {}", serialized);

    // Convert the JSON string back to a Point.
    let deserialized: Point = sj::from_str(&serialized).unwrap();

    // Prints deserialized = Point { x: 1, y: 2 }
    println!("deserialized = {:?}", deserialized);
}

Output of cargo run:

   Compiling demo v0.1.0 (file:///private/tmp/demo)
error[E0463]: can't find crate for `_serde`
 --> src/main.rs:5:21
  |
5 | #[derive(Serialize, Deserialize, Debug)]
  |                     ^^^^^^^^^^^ can't find crate

error: aborting due to previous error

For more information about this error, try `rustc --explain E0463`.
error: Could not compile `demo`.

To learn more, run the command again with --verbose.

I imagine supporting this will require new features to be added to Rust's procedural macros.

Cargo and Rust versions:

$ cargo --version
cargo 1.28.0-nightly (e2348c2db 2018-06-07)
$ rustc --version
rustc 1.28.0-nightly (e3bf634e0 2018-06-28)

[dtolnay]

Currently serde_derive requires that you list serde in Cargo.toml as well (see https://serde.rs/derive.html) which is missing in yours. So the failure you see is from there being no serde in Cargo.toml, not directly because of the serde_derive or serde_json rename.

In the case that serde really needs to be renamed, I would prefer to track this under #953. Thanks!

[mjbshaw]

Thanks! Sorry I overlooked #953.