LuciferYang opened a new pull request, #9616:
URL: https://github.com/apache/paimon/pull/9616
### Purpose
close #9615
`BaseVariantReader.RowReader`'s constructor unboxed a map lookup straight
into an `int`:
```java
fieldInputIndices[i] =
schema.objectSchemaMap != null
? schema.objectSchemaMap.get(targetFields.get(i).name())
: -1;
```
`objectSchemaMap` holds only the fields the file actually shredded, so
reading a struct whose fields are not all shredded threw a
`NullPointerException` while the reader was being built, taking the whole scan
with it. Shredding is inferred per data file by default, so the same query can
work on one file and fail on the next.
`getOrDefault(name, -1)` is all it takes, because -1 is the convention the
rest of the class already speaks. The field's own comment says "or -1 if it
doesn't exist in object `typed_value`", `VariantSchema` documents the same
thing for its indices, and `readFromTyped` carries the branch that reads such a
field out of the untyped value:
```java
} else if (unshreddedObject != null) {
...
GenericVariant unshreddedField =
unshreddedObject.getFieldByKey(fieldName);
```
Since the constructor could never produce -1, that branch and the
`needUnshreddedObject` flag guarding it were both dead code. This makes them
reachable, which is the behavior the class was written for.
I checked the other lookups in `org.apache.paimon.data.variant` while I was
there: they all take the result as an `Integer` and null-check it, or go
through `containsKey`, so this was the only site.
### Tests
`BaseVariantReaderTest.testRowReaderWithUnshreddedTargetField` builds a
shredding schema covering only field `a`, asks for `struct<a int, b string>`,
and reads a row back. `b` is asserted to come through as `"hello"`, which is
only reachable through the unshredded branch, so the test covers the revived
path rather than just the absence of the crash. A second case reads `{"a":
27}`, where the file has no untyped value at all, and expects `b` to be null.
Against the unfixed reader the test fails with a `NullPointerException` out
of `BaseVariantReader.create`.
`mvn -pl paimon-common -Dtest=BaseVariantReaderTest test` on JDK 8: 1 test,
0 failures. `spotless:check` and `checkstyle:check` on paimon-common are clean.
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