kazuyukitanimura commented on code in PR #461:
URL: https://github.com/apache/datafusion-comet/pull/461#discussion_r1613863992


##########
core/src/execution/datafusion/expressions/cast.rs:
##########
@@ -622,14 +590,89 @@ impl Cast {
                     self.eval_mode,
                     from_type,
                     to_type,
-                )?
+                )
+            }
+            _ if Self::is_datafusion_spark_compatible(from_type, to_type) => {
+                // use DataFusion cast only when we know that it is compatible 
with Spark
+                Ok(cast_with_options(&array, to_type, &CAST_OPTIONS)?)
             }
             _ => {
-                // when we have no Spark-specific casting we delegate to 
DataFusion
-                cast_with_options(&array, to_type, &CAST_OPTIONS)?
+                // we should never reach this code because the Scala code 
should be checking
+                // for supported cast operations and falling back to Spark for 
anything that
+                // is not yet supported
+                Err(CometError::Internal(format!(
+                    "Native cast invoked for unsupported cast from 
{from_type:?} to {to_type:?}"
+                )))
             }
         };
-        Ok(spark_cast(cast_result, from_type, to_type))
+        Ok(spark_cast(cast_result?, from_type, to_type))
+    }
+
+    /// Determines if DataFusion supports the given cast in a way that is
+    /// compatible with Spark
+    fn is_datafusion_spark_compatible(from_type: &DataType, to_type: 
&DataType) -> bool {
+        if from_type == to_type {
+            return true;
+        }
+        match from_type {
+            DataType::Boolean => matches!(
+                to_type,
+                DataType::Int8
+                    | DataType::Int16
+                    | DataType::Int32
+                    | DataType::Int64
+                    | DataType::Float32
+                    | DataType::Float64
+                    | DataType::Utf8

Review Comment:
   So right now, there is not `Int8` to `Decimal128` cast supported, looks like?



##########
core/src/execution/datafusion/expressions/cast.rs:
##########
@@ -622,14 +590,89 @@ impl Cast {
                     self.eval_mode,
                     from_type,
                     to_type,
-                )?
+                )
+            }
+            _ if Self::is_datafusion_spark_compatible(from_type, to_type) => {
+                // use DataFusion cast only when we know that it is compatible 
with Spark
+                Ok(cast_with_options(&array, to_type, &CAST_OPTIONS)?)
             }
             _ => {
-                // when we have no Spark-specific casting we delegate to 
DataFusion
-                cast_with_options(&array, to_type, &CAST_OPTIONS)?
+                // we should never reach this code because the Scala code 
should be checking
+                // for supported cast operations and falling back to Spark for 
anything that
+                // is not yet supported
+                Err(CometError::Internal(format!(
+                    "Native cast invoked for unsupported cast from 
{from_type:?} to {to_type:?}"
+                )))
             }
         };
-        Ok(spark_cast(cast_result, from_type, to_type))
+        Ok(spark_cast(cast_result?, from_type, to_type))
+    }
+
+    /// Determines if DataFusion supports the given cast in a way that is
+    /// compatible with Spark
+    fn is_datafusion_spark_compatible(from_type: &DataType, to_type: 
&DataType) -> bool {
+        if from_type == to_type {
+            return true;
+        }
+        match from_type {
+            DataType::Boolean => matches!(
+                to_type,
+                DataType::Int8
+                    | DataType::Int16
+                    | DataType::Int32
+                    | DataType::Int64
+                    | DataType::Float32
+                    | DataType::Float64
+                    | DataType::Utf8
+            ),
+            DataType::Int8 | DataType::Int16 | DataType::Int32 | 
DataType::Int64 => matches!(
+                to_type,
+                DataType::Boolean
+                    | DataType::Int8
+                    | DataType::Int16
+                    | DataType::Int32
+                    | DataType::Int64
+                    | DataType::Float32
+                    | DataType::Float64
+                    | DataType::Decimal128(_, _)
+                    | DataType::Utf8
+            ),
+            DataType::Float32 | DataType::Float64 => matches!(
+                to_type,
+                DataType::Boolean
+                    | DataType::Int8
+                    | DataType::Int16
+                    | DataType::Int32
+                    | DataType::Int64
+                    | DataType::Float32
+                    | DataType::Float64
+            ),
+            DataType::Decimal128(_, _) | DataType::Decimal256(_, _) => 
matches!(
+                to_type,
+                DataType::Int8
+                    | DataType::Int16
+                    | DataType::Int32
+                    | DataType::Int64
+                    | DataType::Float32
+                    | DataType::Float64
+                    | DataType::Decimal128(_, _)
+                    | DataType::Decimal256(_, _)
+            ),
+            DataType::Utf8 => matches!(to_type, DataType::Binary),
+            DataType::Date32 => matches!(to_type, DataType::Utf8),
+            DataType::Timestamp(_, _) => {
+                matches!(
+                    to_type,
+                    DataType::Int64 | DataType::Date32 | DataType::Utf8 | 
DataType::Timestamp(_, _)
+                )
+            }
+            DataType::Binary => {
+                // note that this is not completely Spark compatible because
+                // DataFusion only supports binary data containing valid UTF-8 
strings
+                matches!(to_type, DataType::Utf8)
+            }
+            _ => false,

Review Comment:
   Casting to narrower type like `Int64` to `Int32` cases are not supported 
when `self.eval_mode == EvalMode::Try`?



##########
core/src/execution/datafusion/expressions/cast.rs:
##########
@@ -622,14 +590,89 @@ impl Cast {
                     self.eval_mode,
                     from_type,
                     to_type,
-                )?
+                )
+            }
+            _ if Self::is_datafusion_spark_compatible(from_type, to_type) => {
+                // use DataFusion cast only when we know that it is compatible 
with Spark
+                Ok(cast_with_options(&array, to_type, &CAST_OPTIONS)?)
             }
             _ => {
-                // when we have no Spark-specific casting we delegate to 
DataFusion
-                cast_with_options(&array, to_type, &CAST_OPTIONS)?
+                // we should never reach this code because the Scala code 
should be checking
+                // for supported cast operations and falling back to Spark for 
anything that
+                // is not yet supported
+                Err(CometError::Internal(format!(
+                    "Native cast invoked for unsupported cast from 
{from_type:?} to {to_type:?}"
+                )))
             }
         };
-        Ok(spark_cast(cast_result, from_type, to_type))
+        Ok(spark_cast(cast_result?, from_type, to_type))
+    }
+
+    /// Determines if DataFusion supports the given cast in a way that is
+    /// compatible with Spark
+    fn is_datafusion_spark_compatible(from_type: &DataType, to_type: 
&DataType) -> bool {
+        if from_type == to_type {
+            return true;
+        }
+        match from_type {
+            DataType::Boolean => matches!(
+                to_type,
+                DataType::Int8
+                    | DataType::Int16
+                    | DataType::Int32
+                    | DataType::Int64
+                    | DataType::Float32
+                    | DataType::Float64
+                    | DataType::Utf8
+            ),
+            DataType::Int8 | DataType::Int16 | DataType::Int32 | 
DataType::Int64 => matches!(
+                to_type,
+                DataType::Boolean
+                    | DataType::Int8
+                    | DataType::Int16
+                    | DataType::Int32
+                    | DataType::Int64
+                    | DataType::Float32
+                    | DataType::Float64
+                    | DataType::Decimal128(_, _)
+                    | DataType::Utf8
+            ),
+            DataType::Float32 | DataType::Float64 => matches!(
+                to_type,
+                DataType::Boolean
+                    | DataType::Int8
+                    | DataType::Int16
+                    | DataType::Int32
+                    | DataType::Int64
+                    | DataType::Float32
+                    | DataType::Float64

Review Comment:
   For `Float32/64` to `Int8/16/32/64`, I saw 
`spark_cast_nonintegral_numeric_to_integral` covers them above.
   Is this for the case `self.eval_mode == EvalMode::Try`?



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