Using serde_yaml with one or more strings and globset

help
1

I'm brand new to serde, and I'm having trouble figuring out how to accomplish a deserialize task at hand.

I have a YAML config file, with a map entry called 'selection'. The value of this entry is either 1) a single string, or 2) a list of strings. Some examples:

selection: *.flac
----
selection:
    - *.mp3
    - *.jpg
    - *.mkv

I'd like to use serde_yaml to deserialize this config file (no serialization needed), process the one or more strings as glob patterns, and create a GlobSet object. However, I'm having trouble with figuring out the custom deserialization. I've found examples of both coercing single values and lists of values into lists, and converting a value to a new value, but not both together. How would I go about this?

Some issues I've faced:

  1. GlobSet isn't deserializable, so I'd need to use custom deserialization logic.
  2. I'd like to use my existing error handling, using the failure crate.
2

One simple workaround is not to deserialize into your final structure, but a simpler one, and then post-process it.

selection could be an enum with either Vec<String> or String. Serde will know out of the box how to deserialize that much. And then parse the globs yourself, and copy them to the final struct.

3

Might this example be along the lines of what you're looking for? They delegate deserialization of a field to a function that runs different logic depending on whether the value is a string of a struct - if you replaced their visit_map with a visit_seq, and added your GlobSet parsing into those visitor methods, that might get you where you're wanting to go.

That said, I agree with @kornel that sometimes it's wise to just use an intermediate structure if deserializing directly ends up being too complex :slight_smile: