[SPARK-34246][SQL][FOLLOWUP] Change the definition of findTightestCommonType for backward compatibility

[gengliangwang]

What changes were proposed in this pull request?

Change the definition of findTightestCommonType from

def findTightestCommonType(t1: DataType, t2: DataType): Option[DataType]

to

val findTightestCommonType: (DataType, DataType) => Option[DataType]

Why are the changes needed?

For backward compatibility.
When running a MongoDB connector (built with Spark 3.1.1) with the latest master, there is such an error

java.lang.NoSuchMethodError: org.apache.spark.sql.catalyst.analysis.TypeCoercion$.findTightestCommonType()Lscala/Function2

from https://github.com/mongodb/mongo-spark/blob/master/src/main/scala/com/mongodb/spark/sql/MongoInferSchema.scala#L150

In the previous release, the function was

static public  scala.Function2<org.apache.spark.sql.types.DataType, org.apache.spark.sql.types.DataType, scala.Option<org.apache.spark.sql.types.DataType>> findTightestCommonType ()

After #31349, the function becomes:

static public  scala.Option<org.apache.spark.sql.types.DataType> findTightestCommonType (org.apache.spark.sql.types.DataType t1, org.apache.spark.sql.types.DataType t2)

This PR is to reduce the unnecessary API change.

Does this PR introduce any user-facing change?

Yes, the definition of TypeCoercion.findTightestCommonType is consistent with previous release again.

How was this patch tested?

Existing unit tests

[SparkQA]

Kubernetes integration test starting
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/42857/

[SparkQA]

Kubernetes integration test status failure
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/42857/

[cloud-fan]

Generally speaking, we don't need to keep backward compatibility for internal APIs. But this one is just a small change to avoid breaking a MongoDB connector, which seems worthwhile to me. LGTM

[gengliangwang]

Thanks, merging to master

[SparkQA]

Test build #138335 has finished for PR 32493 at commit f8d7acb.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[maropu]

late lgtm.