Minor updates: comments, naming

spark/src/main/scala/org/apache/spark/sql/delta/DeltaAnalysis.scala

@@ -949,10 +949,11 @@ class DeltaAnalysis(session: SparkSession)
   }
 
   /**
-   * Returns a mapping of (fromType, toType) to Boolean indicating whether `fromType` is eligible to
-   * be automatically widened to `toType` when ingesting data. If it is, the table schema is updated
-   * to `toType` before ingestion and values are written using their origin `toType` type.
-   * Otherwise, the table type `fromType` is retained and values are downcasted on write.
+   * Returns the type widening mode to use for the given delta table. A type widening mode indicates
+   * for (fromType, toType) tuples whether `fromType` is eligible to be automatically widened to
+   * `toType` when ingesting data. If it is, the table schema is updated to `toType` before
+   * ingestion and values are written using their original `toType` type. Otherwise, the table type
+   * `fromType` is retained and values are downcasted on write.
    */
   private def getTypeWideningMode(
       deltaTable: DeltaTableV2,
@@ -964,7 +965,7 @@ class DeltaAnalysis(session: SparkSession)
 
     if (typeWideningEnabled && schemaEvolutionEnabled) {
       TypeWideningMode.TypeEvolution(
-        uniformIcebergEnabled = UniversalFormat.icebergEnabled(snapshot.metadata))
+        uniformIcebergCompatibleOnly = UniversalFormat.icebergEnabled(snapshot.metadata))
     } else {
       TypeWideningMode.NoTypeWidening
     }

spark/src/main/scala/org/apache/spark/sql/delta/ResolveDeltaMergeInto.scala

@@ -297,7 +297,7 @@ object ResolveDeltaMergeInto {
         target.collectFirst {
           case DeltaTable(index) if TypeWidening.isEnabled(index.protocol, index.metadata) =>
             TypeWideningMode.TypeEvolution(
-              uniformIcebergEnabled = UniversalFormat.icebergEnabled(index.metadata))
+              uniformIcebergCompatibleOnly = UniversalFormat.icebergEnabled(index.metadata))
         }.getOrElse(TypeWideningMode.NoTypeWidening)
 
       // The implicit conversions flag allows any type to be merged from source to target if Spark

spark/src/main/scala/org/apache/spark/sql/delta/TypeWidening.scala

@@ -77,12 +77,12 @@ object TypeWidening {
   def isTypeChangeSupportedForSchemaEvolution(
       fromType: AtomicType,
       toType: AtomicType,
-      uniformIcebergEnabled: Boolean): Boolean =
+      uniformIcebergCompatibleOnly: Boolean): Boolean =
     TypeWideningShims.isTypeChangeSupportedForSchemaEvolution(
       fromType = fromType,
       toType = toType
     ) && (
-      !uniformIcebergEnabled ||
+      !uniformIcebergCompatibleOnly ||
         isTypeChangeSupportedByIceberg(fromType = fromType, toType = toType)
     )
 

spark/src/main/scala/org/apache/spark/sql/delta/TypeWideningMode.scala

@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 package org.apache.spark.sql.delta
 
 import org.apache.spark.sql.types.AtomicType
@@ -21,30 +22,31 @@ import org.apache.spark.sql.types.AtomicType
  * A type widening mode captures a specific set of type changes that are allowed to be applied.
  * Currently:
  *  - NoTypeWidening: No type change is allowed.
- *  - TypeEvolution(uniformIcebergEnabled = true): Type changes that are eligible to be applied
- *    automatically during schema evolution and that are supported by Iceberg are allowed.
- *  - TypeEvolution(uniformIcebergEnabled = false): Type changes that are eligible to be applied
- *    automatically during schema evolution are allowed, even if they are not supported by Iceberg.
+ *  - TypeEvolution(uniformIcebergCompatibleOnly = true): Type changes that are eligible to be
+ *    applied automatically during schema evolution and that are supported by Iceberg are allowed.
+ *  - TypeEvolution(uniformIcebergCompatibleOnly = false): Type changes that are eligible to be
+ *    applied automatically during schema evolution are allowed, even if they are not supported by
+ *    Iceberg.
  */
-trait TypeWideningMode {
+sealed trait TypeWideningMode {
   def shouldWidenType(fromType: AtomicType, toType: AtomicType): Boolean
 }
 
 object TypeWideningMode {
   /**
    * No type change allowed. Typically because type widening and/or schema evolution isn't enabled.
    */
-  object NoTypeWidening extends TypeWideningMode {
+  case object NoTypeWidening extends TypeWideningMode {
     override def shouldWidenType(fromType: AtomicType, toType: AtomicType): Boolean = false
   }
 
   /**
    * Type changes that are eligible to be applied automatically during schema evolution are allowed.
    * Can be restricted to only type changes supported by Iceberg.
    */
-  case class TypeEvolution(uniformIcebergEnabled: Boolean) extends TypeWideningMode {
+  case class TypeEvolution(uniformIcebergCompatibleOnly: Boolean) extends TypeWideningMode {
     override def shouldWidenType(fromType: AtomicType, toType: AtomicType): Boolean =
         TypeWidening.isTypeChangeSupportedForSchemaEvolution(
-          fromType = fromType, toType = toType, uniformIcebergEnabled)
+          fromType = fromType, toType = toType, uniformIcebergCompatibleOnly)
   }
 }

spark/src/main/scala/org/apache/spark/sql/delta/schema/ImplicitMetadataOperation.scala

@@ -222,7 +222,7 @@ object ImplicitMetadataOperation {
 
       val typeWideningMode = if (TypeWidening.isEnabled(txn.protocol, txn.metadata)) {
         TypeWideningMode.TypeEvolution(
-          uniformIcebergEnabled = UniversalFormat.icebergEnabled(txn.metadata))
+          uniformIcebergCompatibleOnly = UniversalFormat.icebergEnabled(txn.metadata))
       } else {
         TypeWideningMode.NoTypeWidening
       }

spark/src/main/scala/org/apache/spark/sql/delta/sources/DeltaSink.scala

@@ -178,7 +178,7 @@ case class DeltaSink(
 
     val typeWideningMode = if (canMergeSchema && TypeWidening.isEnabled(protocol, metadata)) {
         TypeWideningMode.TypeEvolution(
-          uniformIcebergEnabled = UniversalFormat.icebergEnabled(metadata))
+          uniformIcebergCompatibleOnly = UniversalFormat.icebergEnabled(metadata))
       } else {
         TypeWideningMode.NoTypeWidening
       }

spark/src/test/scala/org/apache/spark/sql/delta/schema/SchemaUtilsSuite.scala

@@ -2533,7 +2533,7 @@ class SchemaUtilsSuite extends QueryTest
       mergeSchemas(
         base,
         update,
-        typeWideningMode = TypeWideningMode.TypeEvolution(uniformIcebergEnabled = false),
+        typeWideningMode = TypeWideningMode.TypeEvolution(uniformIcebergCompatibleOnly = false),
         keepExistingType = true
       )
     assert(mergedSchema === expected)