Vecs containing Option types are removed from output

[evie-calico]

If a vector contains an option type, and any of its entries are None, the vector is completely removed from the output. I believe this is because toml tries not to output anything for None values, but this chokes when trying to insert a gap with nothing in it.

If you create an enum with the same structure as Option, toml uses a different format that correctly handles "gaps" (shown in the below example); I believe this should be used for vectors of options.

Example on Rust Playground

[evie-calico]

The issue seems to be here

The ? bubbles all errors up, including UnsupportedNone, despite it having a special meaning. This causes the entire array to be removed. At the very least, UnsupportedNone should be transformed into another error:

let value = value.serialize(super::ValueSerializer {}).map_err(|e| {
    if let Error::UnsupportedNone = e {
        Error::UnsupportedType(Some("None is unsupported in vectors"))
    } else {
        e
    }
})?;

But supporting None in Vectors seems worth it :)

[epage]

There are two different ways to look at this bug

The first is that we should be skipping None values in arrays like we do with maps.

The other is that we should more generally error.

I lean towards erroring because gaps may be significant and we wouldn't be able to represent that while having a table without a value can be represented (I misremembered the code).

If you create an enum with the same structure as Option, toml uses a different format that correctly handles "gaps" (shown in the below example); I believe this should be used for vectors of options.

In the enum case, there is a meaningful way of defining "gaps" based on the definition of your enum. With options, there isn't any.