[SPARK-59108][4.2][SQL] Fix Avro positional matching under column pruning

[LuciferYang]

What changes were proposed in this pull request?

Backport of c809c283c2d (#58409) to branch-4.2. The Avro fix comes over as it landed; the two gate removals that PR also carried are not here, because neither gate exists on this branch.

AvroDeserializer now takes the schema its Catalyst schema was projected from, and under positionalFieldMatching it resolves a Catalyst field against that field's position in the data schema rather than its position in the projection. AvroUtils.AvroSchemaHelper takes the resulting positions; with none it keeps using a field's own position, which is what every caller whose Catalyst schema is not a projection needs (from_avro, the write path, the state-store encoder).

Two read call sites pass the data schema on this branch: AvroPartitionReaderFactory on the V2 path and AvroFileFormat.buildReader on V1. Master has a third, AvroFileFormat.readArchive, which does not exist here. A nested record keeps resolving by its own positions, since neither read path prunes nested fields: FileScanBuilder.supportsNestedSchemaPruning is false and AvroScanBuilder does not override it, and SchemaPruning.canPruneDataSchema covers only Parquet and ORC.

ORC already does this for orc.force.positional.evolution: OrcUtils.requestedColumnIds maps the required schema through dataSchema.fieldIndex(name), which makes its positional path projection-independent. Avro decodes the whole record whatever the projection asks for, so nothing extra is read.

Master retired two gates that kept avro out of scan merging, and neither is on this branch: SPARK-57205 (#58340) withheld the SCAN_MERGING capability from AvroTable, and SPARK-59107 (#58411) named avro in DataSourceUtils.isProjectionSensitiveRead. So there is no predicate to change, no AvroTable.supportsScanMerging to turn on, no test to delete, and docs/sql-performance-tuning.md has no "Merging Subplans" section stating the old behaviour. That also means subplan merging can widen an avro projection here with nothing in front of it, which makes the position mapping worth more on this branch than on 4.3, not less.

One shape stays broken, with or without this change: recursiveFieldMaxDepth makes SchemaConverters drop a field it will not recurse into, so the data schema is a gapped view of the Avro schema and positional matching misaligns from the gap onwards. The code records that where the positions are computed.

Why are the changes needed?

With positionalFieldMatching=true the deserializer is built from the projected read schema while the Avro side stays the full Avro schema, and AvroUtils.AvroSchemaHelper.getAvroField pairs Catalyst field i with Avro field i, so a column-pruned read takes the wrong Avro field and returns wrong values with no error. Measured on a file whose fields a, b, c hold id, 100 * id, 10000 * id for ids 0 to 4, read with the option on:

sql("SELECT sum(a), sum(b), sum(c) FROM t").show()  // 10, 1000, 100000 -- all correct
sql("SELECT sum(c) FROM t").show()                  // 10       -- should be 100000
sql("SELECT sum(b) FROM t").show()                  // 10       -- should be 1000
sql("SELECT sum(a), sum(c) FROM t").show()          // 10, 1000 -- sum(c) should be 100000

Only a projection that is a prefix of the file's field list comes back right, so a column's value depends on which other columns the query selects. Both read paths behave the same way. Whether the failure is silent depends on the types of the mispaired fields: matching types return wrong values, as above, and incompatible ones fail the read with a schema-incompatibility error instead. A pushed filter is evaluated inside the deserializer, so the wrong pairing can also drop rows rather than only return wrong values for them.

A pruned projection is all it takes, so this does not depend on scan merging. Merging only makes it easier to reach without asking for it, and on this branch nothing keeps an avro relation out of it.

Does this PR introduce any user-facing change?

Yes, a bug fix on the Avro read path, both V1 and V2, and every 4.2.x release shipped the bug: positional matching has resolved against the projection since 3.2.0 (SPARK-34365). A read that sets positionalFieldMatching and prunes columns now returns the values of the columns it asked for. A query whose projection is a prefix of the Avro field list is unaffected, which is why the option's existing tests need no change. A read that used to land on a type-compatible neighbouring field now pairs with its own field and fails when the two types do not match, so a query that returned values before this change can return an error instead. That is the point of the fix rather than a side effect, but it is the shape most likely to be reported as a regression. The "Cannot find field at position N" message that positional matching raises now names the position it looked for rather than the position within the projection, which are the same number for an unprojected read. Nothing changes when the option is off, which is the default, and nothing changes on the write path or in from_avro.

How was this patch tested?

Five new tests in AvroSuite, so each runs on both read paths (AvroV1Suite and AvroV2Suite extend it): the renamed-schema shape from the description, with each one-column and two-column projection whose values the fix changes, the ones it leaves alone being the prefixes of the field list, a pushed filter under both settings of spark.sql.avro.filterPushdown.enabled, count(1), and mixed-case names under both case-sensitivity settings; a partition column sitting between two data columns in the schema; a nested record, which must keep resolving by its own positions, together with the avroSchema option supplying the Avro side; a projection that reaches past the end of the Avro schema, which reads null; and a mispaired type, which fails the read rather than returning a neighbouring field's values. One test in AvroSchemaHelperSuite for the helper itself. Master's AvroArchiveReadBase case is not here, since this branch has no archive reader.

One more test, in AvroV1Suite, for a merged read. The file has three columns and the two scalar aggregates read the last two, so the merged projection is a proper subset of the data schema and the read has to resolve against that schema to answer [100, 1000]; the scan is one widened FileSourceScanExec reading both columns. Unlike master's version it pins only AQE, since the strictness flags matter to a predicate that does not exist on this branch, and it has no AvroV2Suite twin, since avro never declares SCAN_MERGING here.

Mutation check, measured on this branch: with the position mapping disabled, 11 cases fail, the five SPARK-59108 shapes on each read path and the new merge test, which answers [10, 100] where the file has [100, 1000].

Regression, measured on this branch: the whole avro module, 404 tests, and avro/scalastyle, avro/Test/scalastyle, sql/scalastyle and catalyst/scalastyle. RocksDBStateEncoderSuite and StateStoreSuite, which also build an AvroDeserializer, were run on master rather than here; nothing in this backport differs from the master commit in that path. The existing positionalFieldMatching tests (SPARK-34365) needed no change, because their projections cover the whole schema.

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