[SPARK-48739][SQL] Disable writing collated data to file formats that don't support them in non managed tables

[stefankandic]

What changes were proposed in this pull request?

Disable writing collated types to data sources that don't support them. However, spark managed tables should still work as the schema is in HMS and not in the file itself.

Why are the changes needed?

Right now, when users write a collated type directly to json, text, orc.. they will not see that collation when reading back.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

Added new UTs

Was this patch authored or co-authored using generative AI tooling?

No.

[stefankandic]

@cloud-fan Please take a look when you find the time

[allisonwang-db]

Shall we combine this with the data.schema.foreach check mentioned above?

[cloud-fan]

For internal file source API, I think we can simply update FileFormat#supportDataType in certain formats such as CSV to return false for string with collation. So no new API is needed.

For data source v1, we can add a new API to CreatableRelationProvider, like supportsStringCollation. Ideally this is not needed as we already have CreatableRelationProvider#supportsDataType. But string collation is special as it's still StringType and existing v1 data sources may mistakenly support it if they do case _: StringType => true

UPDATE: actually CreatableRelationProvider#supportsDataType is newly added in spark 4.0 (not released yet). We can change it to not support string with collation, so that all existing v1 sources won't support string with collation, unless they override supportsDataType to explicitly support it.

[stefankandic]

@cloud-fan

For internal file source API, I think we can simply update FileFormat#supportDataType in certain formats such as CSV to return false for string with collation. So no new API is needed.

This would mean that we wouldn't be able to create spark managed tables with collations for those formats. Is that something that we want to do?

[cloud-fan]

This would mean that we wouldn't be able to create spark managed tables with collations for those formats. Is that something that we want to do?

To confirm the goal of this PR: we want to have a new API for file sources to indicate that a type is supported only with a catalog? I think we should be more specific about this, as there are many APIs to use a file source:

1. read a path with a user-specified schema
2. write to a path
3. create external table with a path
4. create managed table