Sketch how the converters will be used in UnsafeGeneratedAggregate

sql/core/src/main/scala/org/apache/spark/sql/execution/UnsafeGeneratedAggregate.scala

@@ -35,10 +35,10 @@ import org.apache.spark.unsafe.memory.MemoryAllocator
  */
 @DeveloperApi
 case class UnsafeGeneratedAggregate(
-  partial: Boolean,
-  groupingExpressions: Seq[Expression],
-  aggregateExpressions: Seq[NamedExpression],
-  child: SparkPlan)
+    partial: Boolean,
+    groupingExpressions: Seq[Expression],
+    aggregateExpressions: Seq[NamedExpression],
+    child: SparkPlan)
   extends UnaryNode {
 
   override def requiredChildDistribution: Seq[Distribution] =
@@ -267,17 +267,25 @@ case class UnsafeGeneratedAggregate(
         // We're going to need to allocate a lot of empty aggregation buffers, so let's do it
         // once and keep a copy of the serialized buffer and copy it into the hash map when we see
         // new keys:
-        val javaAggregationBuffer: MutableRow =
-          newAggregationBuffer(EmptyRow).asInstanceOf[MutableRow]
-        val numberOfFieldsInAggregationBuffer: Int = javaAggregationBuffer.schema.fields.length
-        val aggregationBufferSchema: StructType = javaAggregationBuffer.schema
-        // TODO perform that conversion to an UnsafeRow
-        // Allocate some scratch space for holding the keys that we use to index into the hash map.
-        val unsafeRowBuffer: Array[Long] = new Array[Long](1024)
+        val (emptyAggregationBuffer: Array[Long], numberOfColumnsInAggBuffer: Int) = {
+          val javaBuffer: MutableRow = newAggregationBuffer(EmptyRow).asInstanceOf[MutableRow]
+          val converter = new UnsafeRowConverter(javaBuffer.schema.fields.map(_.dataType))
+          val buffer = new Array[Long](converter.getSizeRequirement(javaBuffer))
+          converter.writeRow(javaBuffer, buffer, PlatformDependent.LONG_ARRAY_OFFSET)
+          (buffer, javaBuffer.schema.fields.length)
+        }
 
         // TODO: there's got got to be an actual way of obtaining this up front.
         var groupProjectionSchema: StructType = null
 
+        val keyToUnsafeRowConverter: UnsafeRowConverter = {
+          new UnsafeRowConverter(groupProjectionSchema.fields.map(_.dataType))
+        }
+
+        // Allocate some scratch space for holding the keys that we use to index into the hash map.
+        // 16 MB ought to be enough for anyone (TODO)
+        val unsafeRowBuffer: Array[Long] = new Array[Long](1024 * 16 / 8)
+
         while (iter.hasNext) {
           // Zero out the buffer that's used to hold the current row. This is necessary in order
           // to ensure that rows hash properly, since garbage data from the previous row could
@@ -291,7 +299,13 @@ case class UnsafeGeneratedAggregate(
           val currentGroup: Row = groupProjection(currentJavaRow)
           // Convert the current group into an UnsafeRow so that we can use it as a key for our
           // aggregation hash map
-          // --- TODO ---
+          val groupProjectionSize = keyToUnsafeRowConverter.getSizeRequirement(currentGroup)
+          if (groupProjectionSize > unsafeRowBuffer.length) {
+            throw new IllegalStateException("Group projection does not fit into buffer")
+          }
+          keyToUnsafeRowConverter.writeRow(
+            currentGroup, unsafeRowBuffer, PlatformDependent.LONG_ARRAY_OFFSET)
+
           val keyLengthInBytes: Int = 0
           val loc: BytesToBytesMap#Location =
             buffers.lookup(unsafeRowBuffer, PlatformDependent.LONG_ARRAY_OFFSET, keyLengthInBytes)
@@ -308,18 +322,18 @@ case class UnsafeGeneratedAggregate(
               unsafeRowBuffer,
               PlatformDependent.LONG_ARRAY_OFFSET,
               keyLengthInBytes,
-              null, // empty agg buffer
+              emptyAggregationBuffer,
               PlatformDependent.LONG_ARRAY_OFFSET,
-              0 // length of the aggregation buffer
+              emptyAggregationBuffer.length
             )
           }
           // Reset our pointer to point to the buffer stored in the hash map
           val address = loc.getValueAddress
           currentBuffer.set(
             address.getBaseObject,
             address.getBaseOffset,
-            numberOfFieldsInAggregationBuffer,
-            javaAggregationBuffer.schema
+            numberOfColumnsInAggBuffer,
+            null
           )
           // Target the projection at the current aggregation buffer and then project the updated
           // values.
@@ -346,8 +360,8 @@ case class UnsafeGeneratedAggregate(
             value.set(
               valueAddress.getBaseObject,
               valueAddress.getBaseOffset,
-              aggregationBufferSchema.fields.length,
-              aggregationBufferSchema
+              numberOfColumnsInAggBuffer,
+              null
             )
             // TODO: once the iterator has been fully consumed, we need to free the map so that
             // its off-heap memory is reclaimed.  This may mean that we'll have to perform an extra