[SPARK-15983][SQL] Removes FileFormat.prepareRead

## What changes were proposed in this pull request?

Interface method `FileFormat.prepareRead()` was added in #12088 to handle a special case in the LibSVM data source.

However, the semantics of this interface method isn't intuitive: it returns a modified version of the data source options map. Considering that the LibSVM case can be easily handled using schema metadata inside `inferSchema`, we can remove this interface method to keep the `FileFormat` interface clean.

## How was this patch tested?

Existing tests.

Author: Cheng Lian <lian@databricks.com>

Closes #13698 from liancheng/remove-prepare-read.

2 files changed, 1 insertions, 15 deletions

diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/DataSource.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/DataSource.scala
index d3273025b6..7f3683fc98 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/DataSource.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/DataSource.scala
@@ -386,9 +386,6 @@ case class DataSource(
               "It must be specified manually")
         }
 
-        val enrichedOptions =
-          format.prepareRead(sparkSession, caseInsensitiveOptions, fileCatalog.allFiles())
-
         HadoopFsRelation(
           sparkSession,
           fileCatalog,
@@ -396,7 +393,7 @@ case class DataSource(
           dataSchema = dataSchema.asNullable,
           bucketSpec = bucketSpec,
           format,
-          enrichedOptions)
+          caseInsensitiveOptions)
 
       case _ =>
         throw new AnalysisException(
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/fileSourceInterfaces.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/fileSourceInterfaces.scala
index 641c5cb02b..4ac555be7f 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/fileSourceInterfaces.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/fileSourceInterfaces.scala
@@ -26,7 +26,6 @@ import org.apache.hadoop.io.compress.{CompressionCodecFactory, SplittableCompres
 import org.apache.hadoop.mapred.{FileInputFormat, JobConf}
 import org.apache.hadoop.mapreduce.{Job, TaskAttemptContext}
 
-import org.apache.spark.SparkContext
 import org.apache.spark.annotation.Experimental
 import org.apache.spark.internal.Logging
 import org.apache.spark.sql._
@@ -187,15 +186,6 @@ trait FileFormat {
       files: Seq[FileStatus]): Option[StructType]
 
   /**
-   * Prepares a read job and returns a potentially updated data source option [[Map]]. This method
-   * can be useful for collecting necessary global information for scanning input data.
-   */
-  def prepareRead(
-      sparkSession: SparkSession,
-      options: Map[String, String],
-      files: Seq[FileStatus]): Map[String, String] = options
-
-  /**
    * Prepares a write job and returns an [[OutputWriterFactory]].  Client side job preparation can
    * be put here.  For example, user defined output committer can be configured here
    * by setting the output committer class in the conf of spark.sql.sources.outputCommitterClass.
@@ -454,7 +444,6 @@ private[sql] object HadoopFsRelation extends Logging {
     logInfo(s"Listing leaf files and directories in parallel under: ${paths.mkString(", ")}")
 
     val sparkContext = sparkSession.sparkContext
-    val sqlConf = sparkSession.sessionState.conf
     val serializableConfiguration = new SerializableConfiguration(hadoopConf)
     val serializedPaths = paths.map(_.toString)