huan233usc opened a new pull request, #874:
URL: https://github.com/apache/iceberg-cpp/pull/874
## What
Adds an end-to-end test for v3 column default values: write a real Parquet
file, evolve the schema through `UpdateSchema` to add a column with an
`initial-default`, then read the pre-evolution file back using the schema that
evolution actually produced and assert the old rows materialize the default.
## Why
The existing default-value coverage stops short of this seam:
- the read-path tests (`ParquetReaderTest.ReadMissingFieldsWithDefaults`,
the Avro equivalents) build the projected schema **by hand**, so they never
exercise a schema that `UpdateSchema` produced;
- the evolution tests (`UpdateSchemaDefaultValueTest.*`) assert on the
resulting schema but never write or read a data file.
So nothing covered "evolution emits a defaulted field → the reader fills it
for rows written before the column existed", which is the behaviour users
actually depend on.
## How
The test runs on the existing `UpdateSchemaDefaultValueTest` fixture (v3
metadata, in-memory catalog, mock `FileIO`), which already provides a table
plus a writable IO:
1. write `[[1,2,3],[4,5,6]]` to a Parquet file using the table's current
schema (`x`, `y`, `z`);
2. `AddColumn("added", int64(), ..., Literal::Long(42))` and `Commit()`;
3. reload the table, confirm the committed field carries the
`initial-default`;
4. open the original file with the evolved schema and compare against
`[[1,2,3,42],[4,5,6,42]]`.
`parquet::RegisterAll()` is called from `SetUpTestSuite` so the
writer/reader factories are available (the target already builds with
`USE_BUNDLE`).
## Testing
`table_update_test` passes (809 tests). Verified the test is meaningful by
dropping the default from the evolution step, which makes it fail rather than
silently pass.
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