Minor: assorted schema handling debug improvements

datafusion/common/src/dfschema.rs

@@ -601,7 +601,7 @@ impl Display for DFSchema {
 ///
 /// Note that this trait is implemented for &[DFSchema] which is
 /// widely used in the DataFusion codebase.
-pub trait ExprSchema {
+pub trait ExprSchema: std::fmt::Debug {
     /// Is this column reference nullable?
     fn nullable(&self, col: &Column) -> Result<bool>;
 
@@ -610,7 +610,7 @@ pub trait ExprSchema {
 }
 
 // Implement `ExprSchema` for `Arc<DFSchema>`
-impl<P: AsRef<DFSchema>> ExprSchema for P {
+impl<P: AsRef<DFSchema> + std::fmt::Debug> ExprSchema for P {
     fn nullable(&self, col: &Column) -> Result<bool> {
         self.as_ref().nullable(col)
     }

datafusion/expr/src/expr_schema.rs

@@ -375,6 +375,7 @@ mod tests {
         );
     }
 
+    #[derive(Debug)]
     struct MockExprSchema {
         nullable: bool,
         data_type: DataType,

datafusion/expr/src/field_util.rs

@@ -51,9 +51,8 @@ pub fn get_indexed_field(data_type: &DataType, key: &ScalarValue) -> Result<Fiel
         (DataType::List(_), _) => Err(DataFusionError::Plan(
             "Only ints are valid as an indexed field in a list".to_string(),
         )),
-        _ => Err(DataFusionError::Plan(
-            "The expression to get an indexed field is only valid for `List` types"
-                .to_string(),
+        (other, _) => Err(DataFusionError::Plan(
+            format!("The expression to get an indexed field is only valid for `List` or `Struct` types, got {other}")
         )),
     }
 }