PDGGK opened a new issue, #39749:
URL: https://github.com/apache/beam/issues/39749
### What happened?
`Row#toString` throws for an `ITERABLE` field whose value is a plain
`Iterable`:
```java
Schema schema =
Schema.builder().addStringField("k").addIterableField("vals",
FieldType.STRING).build();
Iterable<String> bare = () -> Arrays.asList("p", "q").iterator();
Row.withSchema(schema).attachValues("k1", bare).toString();
```
```
java.lang.IllegalArgumentException: value type is 'class ...' for field type
'ITERABLE'
at
org.apache.beam.sdk.schemas.SchemaUtils.toPrettyFieldValueString(SchemaUtils.java:273)
```
`toPrettyFieldValueString` requires a `List` before iterating:
```java
if (!(value instanceof List)) {
throw new IllegalArgumentException(...);
}
```
An `ITERABLE` field declares an `Iterable`, so the guard is stricter than
the type it is guarding. The branch below it only iterates and counts — both
available from an `Iterable` once materialised.
`Row#toString` is `SchemaUtils.toPrettyString(this)`, so one unusual field
takes out logging and debugger output for **every** field beside it, which is a
poor trade for a stricter check in a renderer.
### Note on where the fix belongs
There is a reasonable position that a materialised `Row` should always hold
a `List` for `ARRAY`/`ITERABLE`, and that a non-`List` arriving here means a
producer is at fault. That may well be true and worth fixing separately — but
the reproducer above uses only `Schema.builder`,
`Row.withSchema(...).attachValues(...)` and `toString()`, so a value that is
merely `Iterable` does reach the renderer through the public API, and a
`toString()` that throws is hard to defend regardless of who produced the value.
### Issue Priority
Priority: 3 (minor)
### Issue Components
- [x] Component: Java SDK
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