huan233usc opened a new pull request, #746:
URL: https://github.com/apache/iceberg-cpp/pull/746
Part 1 of 4 splitting #730 (column default values, item 2 of #637). The full
end-to-end implementation is in #731, kept open as the proof-of-concept;
this series
lands it in reviewable pieces.
This PR is the **schema foundation** — representing, serializing and
validating v3
column default values. It changes no read or write behavior on its own.
## What's in this PR
- **`SchemaField`** carries `initial-default` / `write-default`, stored as
`std::shared_ptr<const Literal>` (immutable payload shared across copies,
like the
adjacent `type_`; the C++ analog of Java's `final Literal<?>`). Getters
return
`std::optional<std::reference_wrapper<const Literal>>` (the
`Schema::FindFieldByName`
idiom). Copy-preserving modifiers (`WithInitialDefault` /
`WithWriteDefault` /
`WithIdAndType`) ensure reconstruction never silently drops a member.
- **Reconstruction-preservation**: every in-tree site that rebuilds a
`SchemaField`
(`ReassignField`, the `type_util` fresh-id / prune visitors,
`delete_filter`'s
`MergeField`) routes through `WithIdAndType`.
- **JSON serde**: parse/write `initial-default` / `write-default` using the
existing
single-value serialization (all primitive types).
- **`Schema::Validate`**: rejects default values below format v3
(`kMinFormatVersionDefaultValues`), and validates that a default is a
non-null
primitive literal matching the field type.
- **Generic projection**: a column missing from a data file with an
`initial-default`
maps to `FieldProjection::Kind::kDefault` carrying the literal (the
per-format readers
consume this in the follow-up PRs).
## Follow-ups (stacked on this PR)
- read path — Parquet (`literal_util` + parquet projection/materialization)
- read path — Avro
- schema evolution (`UpdateSchema` add/update column defaults)
## Testing
Full suite green. New coverage: schema serde round-trip (incl. nested +
mismatch
rejection), `Schema::Validate` v3 gating for both initial- and
write-default, type
mismatch rejection, generic projection of missing required/optional fields
with
defaults, and id-reassignment preserving defaults. New
`TableMetadataV3Valid.json`
test resource.
This pull request and its description were written by Isaac.
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