Yaml merge keys

This crate implements support for the Merge Key Language-Independent Type for YAML draft specification for YAML documents from the yaml-rust and serde_yaml (with the serde_yaml feature) crates.

When a mapping in a YAML document contains a << key, its value should be either a mapping or a sequence of mappings. For each mapping, it is merged into the parent mapping where the parent mapping wins conflicts (so that it may override keys from the merge set).

lib.rs:

YAML Merge Keys

The YAML Merge Key extension is not supported by the core YAML crate, but can be implemented after parsing. This crate transforms a parsed YAML document and merges dictionaries together.

Usage

This crate provides a function which implements the YAML Merge Key extension. Given a YAML document from yaml-rust (or serde_yaml with the serde_yaml feature), it will return a YAML document with the merge keys removed and merged into their owning dictionaries.

use yaml_rust::YamlLoader;
use yaml_merge_keys::merge_keys;

// YAML document contents.
let raw = "\
ref: &ref
    merged_key: merged
    added_key: merged
dict:
    <<: *ref
    top_key: given
    merged_key: given
";
let merged = "\
ref:
    merged_key: merged
    added_key: merged
dict:
    top_key: given
    merged_key: given
    added_key: merged
";

// Parse the YAML documents.
let raw_yaml = YamlLoader::load_from_str(raw).unwrap().remove(0);
let merged_yaml = YamlLoader::load_from_str(merged).unwrap().remove(0);

// Merge the keys.
let merged_keys = merge_keys(raw_yaml).unwrap();

// The keys have been merged.
assert_eq!(merged_keys, merged_yaml);

// Using `serde_yaml` is also supported with the feature.
#[cfg(feature = "serde_yaml")]
{
    use yaml_merge_keys::merge_keys_serde;

    let raw_yaml = serde_yaml::from_str(raw).unwrap();
    let merged_yaml: serde_yaml::Value = serde_yaml::from_str(merged).unwrap();

    let merged_keys = merge_keys_serde(raw_yaml).unwrap();

    assert_eq!(merged_keys, merged_yaml);
}

Example

---
- &CENTER { x: 1, y: 2 }
- &LEFT { x: 0, y: 2 }
- &BIG { r: 10 }
- &SMALL { r: 1 }

# All the following maps are equal:

- # Explicit keys
  x: 1
  y: 2
  r: 10
  label: center/big

- # Merge one map
  << : *CENTER
  r: 10
  label: center/big

- # Merge multiple maps
  << : [ *CENTER, *BIG ]
  label: center/big

- # Override
  << : [ *BIG, *LEFT, *SMALL ]
  x: 1
  label: center/big