Test schema: allow src property to either be a string or array of strings

[catamorphism]

This makes the test schema consistent with the schema in https://github.com/unicode-org/conformance/blob/main/schema/message_fmt2/testgen_schema.json

[eemeli]

This was previously proposed, discussed, and rejected in #767 (comment). What has changed since then?

[mradbourne]

@eemeli I think we deferred the decision on how to implement the string-array src because we didn't have an immediate use-case.

To recap previous discussion, we were deciding between these two options:

{
    src: string | string[]
}

and:

{
    src: string
} | {
    srcs: string[]
}

My preferred approach is what @catamorphism has proposed in this PR. Semantically, we're talking about a single "source" in both cases (a string array would still represent one "source") so I think it makes sense for the JSON to use a single property.

My understanding is that the drawback for this approach is the extra code required to deserialize the JSON using libraries such as Gson for Java. Are there still concerns around deserialization (e.g. in unicode-org/conformance executors)?

(A third option would be to make src a string[] in all cases but I don't feel there is a need to add more [] to the test JSON because the single-string values are more common.)

[catamorphism]

There's a workaround for Java that I implemented in ICU4J when I did the test unification. So I think the objection in #767 (comment) is no longer relevant (@mihnita ?)

[aphillips]

Ping @mihnita

I'm inclined to follow what the test suite folks say here, but I don't see any approving reviews...

[mradbourne]

It sounds like the deserialization concern is addressed, plus schema consistency with unicode-org/conformance makes sense.

[eemeli]

Why does it make sense to apply this change to make the test schemas consistent? If there is a reason for consistency, why have two different schemas to start with?

I don't object to the change, I'm just getting a sense that either there ought to be one schema that works both here and for the ICU conformance tests, or that there shouldn't be a need to adjust this schema due to requirements of the ICU conformance tests.

[aphillips]

Per the 2024-11-11 teleconference, I'm labeling this for 47 so that it is not required for 46.1. We should resolve this issue as soon as practical, but not block on it for shipping.

[eemeli]

These line splits are weird. Is that intentional?

[eemeli]

This results in a data model error. The same applies to all further array-of-strings sources as well.

[mihnita]

adjust this schema due to requirements of the ICU conformance tests.

It is not for ICU, it is in general.
ICU can parse standard json, same as everybody else.
Being able to split a string on multiple lines is for the readability of the json and has nothing to do with ICU.

[aphillips]

Per our rules, this does not qualify for fast-track. What's more, it's not exactly fast-track if we're holding it for 47 😸