[SPARK-27619][SQL][FOLLOWUP] Rename 'spark.sql.legacy.useHashOnMapType' to 'spark.sql.legacy.allowHashOnMapType'

### What changes were proposed in this pull request?
Renamed configuration from `spark.sql.legacy.useHashOnMapType` to `spark.sql.legacy.allowHashOnMapType`.

### Why are the changes needed?
Better readability of configuration.

### Does this PR introduce any user-facing change?
No

### How was this patch tested?
Existing UTs.

Closes #27719 from iRakson/SPARK-27619_FOLLOWUP.

Authored-by: iRakson <raksonrakesh@gmail.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>

docs/sql-migration-guide.md

@@ -224,7 +224,7 @@ license: |
 
   - Since Spark 3.0, when casting string value to integral types(tinyint, smallint, int and bigint), datetime types(date, timestamp and interval) and boolean type, the leading and trailing whitespaces (<= ASCII 32) will be trimmed before converted to these type values, e.g. `cast(' 1\t' as int)` results `1`, `cast(' 1\t' as boolean)` results `true`, `cast('2019-10-10\t as date)` results the date value `2019-10-10`. In Spark version 2.4 and earlier, while casting string to integrals and booleans, it will not trim the whitespaces from both ends, the foregoing results will be `null`, while to datetimes, only the trailing spaces (= ASCII 32) will be removed.
 
-  - Since Spark 3.0, An analysis exception will be thrown when hash expressions are applied on elements of MapType. To restore the behavior before Spark 3.0, set `spark.sql.legacy.useHashOnMapType` to true.
+  - Since Spark 3.0, an analysis exception will be thrown when hash expressions are applied on elements of MapType. To restore the behavior before Spark 3.0, set `spark.sql.legacy.allowHashOnMapType` to `true`.
     
   - Since Spark 3.0, numbers written in scientific notation(e.g. `1E2`) would be parsed as Double. In Spark version 2.4 and earlier, they're parsed as Decimal. To restore the behavior before Spark 3.0, you can set `spark.sql.legacy.exponentLiteralAsDecimal.enabled` to `true`.
 

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/hash.scala

@@ -256,11 +256,11 @@ abstract class HashExpression[E] extends Expression {
       TypeCheckResult.TypeCheckFailure(
         s"input to function $prettyName requires at least one argument")
     } else if (children.exists(child => hasMapType(child.dataType)) &&
-      !SQLConf.get.getConf(SQLConf.LEGACY_USE_HASH_ON_MAPTYPE)) {
+        !SQLConf.get.getConf(SQLConf.LEGACY_ALLOW_HASH_ON_MAPTYPE)) {
       TypeCheckResult.TypeCheckFailure(
         s"input to function $prettyName cannot contain elements of MapType. In Spark, same maps " +
-          "may have different hashcode, thus hash expressions are prohibited on MapType " +
+          "may have different hashcode, thus hash expressions are prohibited on MapType elements." +
-          s"elements. To restore previous behavior set ${SQLConf.LEGACY_USE_HASH_ON_MAPTYPE.key} " +
+          s" To restore previous behavior set ${SQLConf.LEGACY_ALLOW_HASH_ON_MAPTYPE.key} " +
           "to true.")
     } else {
       TypeCheckResult.TypeCheckSuccess

sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala

@@ -2258,7 +2258,7 @@ object SQLConf {
       .booleanConf
       .createWithDefault(false)
 
-  val LEGACY_USE_HASH_ON_MAPTYPE = buildConf("spark.sql.legacy.useHashOnMapType")
+  val LEGACY_ALLOW_HASH_ON_MAPTYPE = buildConf("spark.sql.legacy.allowHashOnMapType")
     .doc("When set to true, hash expressions can be applied on elements of MapType. Otherwise, " +
       "an analysis exception will be thrown.")
     .booleanConf

sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala

@@ -2130,10 +2130,11 @@ class SQLQuerySuite extends QueryTest with SharedSparkSession with AdaptiveSpark
     }
   }
 
-  test("SPARK-27619: when spark.sql.legacy.useHashOnMapType is true, hash can be used on Maptype") {
+  test(s"SPARK-27619: When ${SQLConf.LEGACY_ALLOW_HASH_ON_MAPTYPE.key} is true, hash can be " +
+    "used on Maptype") {
     Seq("hash", "xxhash64").foreach {
       case hashExpression =>
-        withSQLConf(SQLConf.LEGACY_USE_HASH_ON_MAPTYPE.key -> "true") {
+        withSQLConf(SQLConf.LEGACY_ALLOW_HASH_ON_MAPTYPE.key -> "true") {
           val df = spark.createDataset(Map() :: Nil)
           checkAnswer(df.selectExpr(s"$hashExpression(*)"), sql(s"SELECT $hashExpression(map())"))
         }