[ARROW-11077] [Rust] ParquetFileArrowReader panicks when trying to read nested list

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Invalid
• Fix Version/s: 5.0.0
• Component/s: Rust
• External issue URL: https://github.com/apache/arrow/issues/26989
• Assignee: Neville Dipale
• Reporter: Ben Sully
• Created: 30/Dec/20 16:37
• Updated: 11/Jan/23 08:17
• Resolved: 26/Apr/21 12:44

Description

I think this is documented in the code, but I can't be 100% sure.

When trying to execute a DataFusion query over a Parquet file where one field is a struct with a nested list, the thread panicks due to unwrapping on an `Option::None` at this point ..] This `None` is returned by `visit_primitive`, but I can't quite make sense of why it returns a `None` rather than an error?

I added a couple of dbg! calls to see what the item_type and list_type are:

[/home/ben/repos/rust/arrow/rust/parquet/src/arrow/array_reader.rs:1339] &item_type = PrimitiveType {
    basic_info: BasicTypeInfo {
        name: "item",
        repetition: Some(
            OPTIONAL,
        ),
        logical_type: UTF8,
        id: None,
    },
    physical_type: BYTE_ARRAY,
    type_length: -1,
    scale: -1,
    precision: -1,
}
[/home/ben/repos/rust/arrow/rust/parquet/src/arrow/array_reader.rs:1340] &list_type = GroupType {
    basic_info: BasicTypeInfo {
        name: "tags",
        repetition: Some(
            OPTIONAL,
        ),
        logical_type: LIST,
        id: None,
    },
    fields: [
        GroupType {
            basic_info: BasicTypeInfo {
                name: "list",
                repetition: Some(
                    REPEATED,
                ),
                logical_type: NONE,
                id: None,
            },
            fields: [
                PrimitiveType {
                    basic_info: BasicTypeInfo {
                        name: "item",
                        repetition: Some(
                            OPTIONAL,
                        ),
                        logical_type: UTF8,
                        id: None,
                    },
                    physical_type: BYTE_ARRAY,
                    type_length: -1,
                    scale: -1,
                    precision: -1,
                },
            ],
        },
    ],
}

I guess we should at least use `.expect` here instead of `.unwrap` so it's more clear why this is happening!