confusion on #[serde(default)] between struct and field

[Geal]

The #[serde(default)] attribute can be set on the struct and on the filed:

• on the field (what we're using in config right now): fills the field if not present with its Default implementation
• on the struct: fills any fields that are not present with the value from the struct's Default implementation

This was confusing to me because in some cases, I did not get the default values I was expecting. Example:

#[derive(Deserialize)]
struct Parent {
  #[serde(default)]
  thing: Thing,
  other: u8,
}

#[derive(Default, Deserialize)]
struct Thing {
  #[serde(default = "enable_true")]
  enabled: bool,
}

fn enable_true() -> bool {
  true
}

With this code, if I deserialize { "thing": { }, "other": 0, }, I end up with enabled = true because the enabled field is not present, so we use the enabled_true function to fill it, but if I deserialize { "other": 0 }, then thing is not present, so we use its Default implementation, which will set enabled = false.

Proposal: let's move to #[serde(default)] on the struct everywhere, with a custom Default implementation for the struct if we need some specific default values.