vbarua commented on code in PR #15854:
URL: https://github.com/apache/datafusion/pull/15854#discussion_r2067003785
##########
datafusion/substrait/src/logical_plan/producer.rs:
##########
@@ -1590,6 +1590,21 @@ pub fn from_cast(
schema: &DFSchemaRef,
) -> Result<Expression> {
let Cast { expr, data_type } = cast;
+ // since substrait Null must be typed, so if we see a cast(null, dt), we
make it a typed null
+ if let Expr::Literal(lit) = expr.as_ref() {
+ if lit.is_null() {
Review Comment:
The one thing I'm not sure about is the usage of `is_null()` here. I think
the logic inside that works for non-compound types here:
```rust
pub fn is_null(&self) -> bool {
match self {
ScalarValue::Boolean(v) => v.is_none(),
ScalarValue::Null => true,
ScalarValue::Float16(v) => v.is_none(),
```
But for compound types I'm not sure if it does the right thing for the fold
you're introducing:
```rust
ScalarValue::List(arr) => arr.len() == arr.null_count(),
ScalarValue::LargeList(arr) => arr.len() == arr.null_count(),
ScalarValue::FixedSizeList(arr) => arr.len() == arr.null_count(),
ScalarValue::Struct(arr) => arr.len() == arr.null_count(),
ScalarValue::Map(arr) => arr.len() == arr.null_count(),
```
because I don't think that it make sense to flatten empty compound types. If
I understand how this would work, something like
```
Cast(List[], List<Int32>)
```
would get flattened into a null literal of type `List<i32>` which is subtly
wrong, because it should be a empty `List<i32>`.
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