maintaining order when deserializing to maps

[samuelcolvin]

Continuation from #269, but that was a long time ago.

That issue refers to linked-hash-map however that crate is in maintenance mode and as far as I can tell it doesn't seem to support deserializing.

Running

extern crate linked_hash_map;
use linked_hash_map::LinkedHashMap as Map;

fn main() {
    let s = r#"{"x": 1, "y": 2}"#;
    let deserialized: Map<String, i32> = serde_json::from_str(&s).unwrap();
    println!("deserialized = {:?}", deserialized);
}

with rust rustc 1.34.0 (91856ed52 2019-04-10) gives:

cargo run
   Compiling serde v1.0.90
   Compiling ryu v0.2.7
   Compiling itoa v0.4.3
   Compiling linked-hash-map v0.5.2
   Compiling serde_json v1.0.39
   Compiling donkey-make v0.1.1 (/home/samuel/code/donkey-make)
error[E0277]: the trait bound `linked_hash_map::LinkedHashMap<std::string::String, i32>: serde::de::Deserialize<'_>` is not satisfied
 --> src/main.rs:6:42
  |
6 |     let deserialized: Map<String, i32> = serde_json::from_str(&s).unwrap();
  |                                          ^^^^^^^^^^^^^^^^^^^^ the trait `serde::de::Deserialize<'_>` is not implemented for `linked_hash_map::LinkedHashMap<std::string::String, i32>`
  |
  = note: required by `serde_json::de::from_str`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.
error: Could not compile `donkey-make`.

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

I've also tried indexmap which seems to be still support however I get a similar error.

[dtolnay]

You need to opt into their serde impls.

[dependencies]
linked-hash-map = { version = "0.5", features = ["serde_impl"] }

[samuelcolvin]

thanks, I was being dumb.

indexmap also supports serde it turns out:

[dependencies]
indexmap = {version = "1.0.2", features = ["serde-1"]}

Might be worth adding to docs.