Function test_expr_placeholder

datafusion/expr/src/expr_schema.rs:1098–1146

()

    #[test]
    fn test_expr_placeholder() {
        let schema = MockExprSchema::new();

        let mut placeholder_meta = HashMap::new();
        placeholder_meta.insert("bar".to_string(), "buzz".to_string());
        let placeholder_meta = FieldMetadata::from(placeholder_meta);

        let expr = Expr::Placeholder(Placeholder::new_with_field(
            "".to_string(),
            Some(
                Field::new("", DataType::Utf8, true)
                    .with_metadata(placeholder_meta.to_hashmap())
                    .into(),
            ),
        ));

        let field = expr.to_field(&schema).unwrap().1;
        assert_eq!(
            (field.data_type(), field.is_nullable()),
            (&DataType::Utf8, true)
        );
        assert_eq!(placeholder_meta, expr.metadata(&schema).unwrap());

        let expr_alias = expr.alias("a placeholder by any other name");
        let expr_alias_field = expr_alias.to_field(&schema).unwrap().1;
        assert_eq!(
            (expr_alias_field.data_type(), expr_alias_field.is_nullable()),
            (&DataType::Utf8, true)
        );
        assert_eq!(placeholder_meta, expr_alias.metadata(&schema).unwrap());

        // Non-nullable placeholder field should remain non-nullable
        let expr = Expr::Placeholder(Placeholder::new_with_field(
            "".to_string(),
            Some(Field::new("", DataType::Utf8, false).into()),
        ));
        let expr_field = expr.to_field(&schema).unwrap().1;
        assert_eq!(
            (expr_field.data_type(), expr_field.is_nullable()),
            (&DataType::Utf8, false)
        );

        let expr_alias = expr.alias("a placeholder by any other name");
        let expr_alias_field = expr_alias.to_field(&schema).unwrap().1;
        assert_eq!(
            (expr_alias_field.data_type(), expr_alias_field.is_nullable()),
            (&DataType::Utf8, false)
        );
    }

    #[derive(Debug)]
    struct MockExprSchema {