Breaking change in mapping entry order in release 0.8.19

Before release 0.8.19 (replacing LinkedHashMap with IndexMap, commit b450e9808bd4f591a292a99e72342ad713a65a43), iteration order of serde_yaml::Mapping entries was preserved when an entry was .remove()d.

Starting with release 0.8.19, iteration order changes when removing an entry other than the last entry. For my use case, this is a breaking change.

Example code to reproduce:

extern crate serde; // 1.0.130
extern crate serde_yaml; // 0.8.21

use serde::Serialize;

#[derive(Serialize)]
struct Data {
    a: String,
    b: String,
    c: String,
}

fn main() {
    let structure = Data {
        a: "foo".to_string(),
        b: "bar".to_string(),
        c: "baz".to_string(),
    };

    let mut yaml = serde_yaml::to_value(&structure).unwrap();
    let yaml = yaml.as_mapping_mut().unwrap();

    let yaml_str = serde_yaml::to_string(&yaml).unwrap();
    assert_eq!(yaml_str, r#"---
a: foo
b: bar
c: baz
"#);

    yaml.remove(&serde_yaml::Value::String("a".to_string()));

    let yaml_str = serde_yaml::to_string(&yaml).unwrap();
    assert_eq!(yaml_str, r#"---
b: bar
c: baz
"#);

}

Playground link: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=594665a2b82c1887d66e511b72932220

The output is:

thread 'main' panicked at 'assertion failed: `(left == right)`
  left: `"---\nc: baz\nb: bar\n"`,
 right: `"---\nb: bar\nc: baz\n"`', src/main.rs:33:5

Notice how the remaining mapping entries have swapped positions.

dtolnay / serde-yaml

Breaking change in mapping entry order in release 0.8.19 #221