Investigate YAML as allowed configuration file syntax

[Shadow53]

It seems to be a common request, based on anecdotal evidence from announcing the last couple of releases on Reddit.

I initially chose TOML as the configuration file syntax because it is unambiguous, commonly used among and outside of Rust projects, and more readable than JSON.

From my understanding, YAML has ambiguity (different parsers can parse the same YAML differently) and can be frustrating to use with certain configuration structures, Still, I am willing to consider the feature if I feel it should add something.

For this issue, I am going to take my current configuration (which should be sufficiently long and complex to make the comparison) and translate it to YAML. If I feel there is a significant improvement in readability and/or writability, I may consider also supporting YAML config files.

[Shadow53]

I made the translation, and I have mixed feelings.

• YAML is more succinct than TOML when it comes to nested maps (tables). This is especially clear with hoards containing many piles, where hoard.hoard_name is repeated for every pile label.
• TOML can be more succinct for shallow values, since a table/map can be condensed onto one line using {}.
• YAML seems to be less strict about certain things, e,g, strings do not need to be quoted, except for when they do. This can make the configuration file easier to write, but opens up the possibility of accidentally using the wrong data type.
• Some structures can look weird in YAML. The combinator structure of 2-D arrays makes more sense to me in TOML:

  item = [["foo", "bar"], ["baz", "quux"]]  # (foo AND bar) OR (baz AND quux)

  than they do in YAML:

  item:
      - - foo
        - bar
      - - baz
        - quux

• I showed both the TOML and YAML versions to my wife (a non-programmer), with no context beyond that they were the same document in two formats, and asked which she would prefer for reading and writing. She preferred the YAML.

[Shadow53]

While I personally prefer TOML and will continue using it myself, the vocal preference toward YAML and the relative simplicity in adding support for it has me leaning toward adding it for more people to be able to use hoard.

I have a few remaining concerns:

• If I want to test YAML support, the most direct method will be to maintain two separate configuration files for integration test purposes. This may lead to a desync between the two files, which I would prefer not to have.
  • I could use yj to ensure that they are equivalent structures.
  • Running tests on both files would double the already long test duration.
• The use of env1|env2|env3 as key values for piles may or may not parse correctly from YAML, since I do not see a syntax like TOML for quoting keys. This will be the first thing to test when implementing. If it does not parse correctly, I will not support YAML.