chenwang-databricks opened a new pull request, #55650:
URL: https://github.com/apache/spark/pull/55650
Add three small public APIs that let v2 catalog connectors (such as the
Unity Catalog Spark connector built on TableViewCatalog) round-trip a Spark
StructField through external storage without reaching for private[sql] helpers
or the singleton-StructType wrap workaround:
- StructField.json / StructField.prettyJson: public counterparts of
DataType.json / DataType.prettyJson, exposing the existing private[sql]
jsonValue.
- StructField.fromJson(String): companion-object parser that mirrors
DataType.fromJson and is the inverse of StructField.json.
- Column.fromStructField(StructField): static factory in the catalog Column
interface that maps a Spark StructField (with metadata) into a connector Column
(with metadataInJSON), symmetric to TableInfo.schema() which already goes the
other way via CatalogV2Util.v2ColumnsToStructType.
Implementation notes:
- DataType.parseStructField is widened from `private` to `private[sql]` so
the new `StructField.fromJson` companion can reuse it. The method remains
internal to spark-sql-api; no public surface change.
- Column.fromStructField mirrors the canonical inverse
CatalogV2Util.structFieldToV2Column: the "comment" key is stripped from the
metadata JSON before being stamped as `metadataInJSON`, because the comment is
exposed separately via Column.comment(). Without the strip, comments would be
duplicated (once in metadataInJSON, once via the dedicated accessor) and
consumers reading `metadataInJSON` directly would see an unexpected "comment"
entry.
- Scaladoc cross-method references are written as plain backticks (e.g.
`StructField.fromJson(String)`) rather than `[[StructField.fromJson]]` so the
Javaunidoc translation step doesn't emit a `{@link StructField.fromJson}` that
javadoc rejects -- javadoc requires `#` as the member separator, which
Scaladoc's `[[...]]` form translates as `.` and javadoc cannot resolve.
- MIMA exclusions in project/MimaExcludes.scala for three sql-api 4.0.0
binary-compat issues introduced by adding a `fromJson(String)` static factory
to StructField's companion object: scalac drops the auto-generated `tupled` and
`curried` Function22 helpers and the AbstractFunction4 parent. None are
documented public API; the removals are safe.
Tests:
- DataTypeSuite covers StructField round-trip via .json / .fromJson with
metric_view-style metadata + comment, and an empty-metadata field.
- CatalogV2UtilSuite covers Column.fromStructField for: (a) a field with
both non-comment metadata and a comment (asserts the comment is NOT in
metadataInJSON), (b) a field with no metadata at all, and (c) a field whose
only metadata was the comment (asserts metadataInJSON is null after the strip).
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