zfarrell opened a new pull request, #22499:
URL: https://github.com/apache/datafusion/pull/22499
## Which issue does this PR close?
<!-- No linked issue. Happy to file one if reviewers prefer. -->
- Closes #.
## Rationale for this change
Downstream catalog implementations that resolve schemas asynchronously
cannot reuse `InformationSchemaProvider` — it enumerates schemas via
`CatalogProvider::schema_names()`, which is synchronous, so an
async-only catalog has to provide its own `information_schema.schemata`
view. Today that requires either duplicating the column layout and
the row-building logic, or reaching into private items.
Exposing `InformationSchemataBuilder` and a `schemata_schema()` factory
lets external crates emit byte-for-byte-compatible `schemata` batches
without copy-pasting the contract.
## What changes are included in this PR?
- `pub fn schemata_schema() -> SchemaRef` — extracts the column-layout
factory. `InformationSchemata::new` now calls it instead of inlining
the schema, so there is a single source of truth.
- `InformationSchemataBuilder` becomes `pub` (was private) with a
`Default` impl and a public `new()`. `add_schemata` and `finish` are
bumped to `pub`. The function bodies and parameter types
(`&str` / `Option<&str>`) are unchanged.
- `finish` now returns `Result<RecordBatch>` instead of panicking via
an internal `.unwrap()`. The one internal caller
(`PartitionStream::execute` for `InformationSchemata`) was previously
wrapping `Ok(builder.finish())` and is updated to just
`builder.finish()` since the inner expression now produces the
`Result` directly.
## Are these changes tested?
Yes. A new unit test `schemata_builder_emits_canonical_schema_and_rows`
exercises the public API end-to-end via `Default::default()`, asserts
the produced batch's schema matches `schemata_schema()`, and verifies
the null pattern for `schema_owner`, the three `default_character_set_*`
columns, and `sql_path`. The pre-existing internal users
(`InformationSchemata::new`, `PartitionStream::execute`) continue to
exercise the same code path through the unchanged
`InformationSchemata::builder()` constructor.
## Are there any user-facing changes?
Yes — three new public items in `datafusion-catalog`: `schemata_schema`,
`InformationSchemataBuilder` (with its `new` / `add_schemata` / `finish`
methods + `Default` impl). No existing public API is broken. The
`Result<RecordBatch>` return on `finish` is a first-time-public surface,
not a regression.
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