pepijnve commented on code in PR #19321:
URL: https://github.com/apache/datafusion/pull/19321#discussion_r2623296165
##########
datafusion/expr/src/expr.rs:
##########
@@ -2701,6 +2785,20 @@ fn rewrite_placeholder(expr: &mut Expr, other: &Expr,
schema: &DFSchema) -> Resu
Ok(())
}
+/// Sets the [`DataType`] of a [`Placeholder`] expression if it is currently
`None`.
+///
+/// This is used during placeholder type inference to assign a specific data
type
+/// to untyped placeholders based on context (e.g., the expected type from a
function signature).
+fn rewrite_placeholder_type(expr: &mut Expr, dt: &DataType) -> Result<()> {
+ if let Expr::Placeholder(Placeholder { id: _, field }) = expr
+ && field.is_none()
+ && !dt.is_null()
+ {
+ *field = Some(Arc::new(Field::new("", dt.clone(), true)));
Review Comment:
Using the empty string here as the name of the field is appropriate, but we
do get a subtle difference in behaviour compared to `rewrite_placeholder`.
There the result of `Expr::to_field` is used verbatim, which may result in e.g.
the name of column popping up in the placeholder. Would it be preferable to
either always use the empty string of the id of the placeholder as field name
in `rewrite_placeholder` as well?
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