Generate data models from supervisor schema for Go-SDK

[jason810496]

• closes: Use Supervisor Schema to generate Go-SDK Data Models #68064

Why

Same as Java-SDK implementation, we should auto generate the data models that will directly be sent to the Coordinator IPC channel from task-sdk/src/airflow/sdk/execution_time/schema/schema.json. Actually, all the Lang-SDK should follow the generating data models from supervisor schema pattern to avoid the schema drift.

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Was generative AI tooling used to co-author this PR?

• Yes, with help of Claude Code (Opus 4.8) following the guidelines

[uranusjr]

Disclosure: I don’t really understand Go tooling; the reviews are highly assisted by Claude.

[uranusjr]

According to Claude:

The defaults.gen.go approach addresses inbound decoding only. The outbound encoding problem we discussed is still present: GetPreviousTI.MapIndex remains int with omitempty, so sending GetPreviousTI{MapIndex: 0} to the supervisor will silently drop the 0, and the supervisor will apply its default (-1), incorrectly treating a map_index=0 request as unmapped.

The minimal fix is to add a pass in gen/main.go that rewrites any struct field in models.gen.go where:

• the Go type is a concrete integer (int), and
• the schema property has a non-zero default (i.e., defaultLiteral would produce a seed for it)

...from int to *int, and strips omitempty from the tag (since with a pointer, nil already means "absent" and omitempty would be redundant and confusing).

With this type, the call site passes &mapIndex to get it encoded, or nil to omit it. The supervisor receives the explicit 0 and treats it as index 0, not unmapped.

defaults.gen.go would then also need to change: GetPreviousTI.DecodeMsgpack would use a *int pre-seed, which means &-1 as the default pointer. The alias constructor becomes alias{MapIndex: intPtr(-1)} (with a small helper, or inline with new(int) and assignment). Or, since *int + absent key decodes to nil, the decode-side default for GetPreviousTI.MapIndex is just nil — and the call site treats nil the same as -1. That's actually the cleaner outcome: the Go SDK sends nil to mean "unmapped" (which the supervisor interprets as its -1 default), and sends &0 to mean index 0. No decode-side seeding needed at all for that field.

The change to gen/main.go would sit inside writeDefaults (or a new pre-pass before it): scan structs[structName] for int-typed fields whose schema property has a non-zero default, emit an AST rewrite of models.gen.go that changes the field type to *int and strips ,omitempty from the tag. That rewrite would be analogous to the dead-typedef stripping already done in parseModels.