Function hash_union_array

datafusion/common/src/hash_utils.rs:713–732

(
    array: &UnionArray,
    random_state: &RandomState,
    hashes_buffer: &mut [u64],
)

#[cfg(not(feature = "force_hash_collisions"))]
fn hash_union_array(
    array: &UnionArray,
    random_state: &RandomState,
    hashes_buffer: &mut [u64],
) -> Result<()> {
    let DataType::Union(union_fields, _mode) = array.data_type() else {
        unreachable!()
    };

    if array.is_dense() {
        // Dense union: children only contain values of their type, so they're already compact.
        // Use the default hashing approach which is efficient for dense unions.
        hash_union_array_default(array, union_fields, random_state, hashes_buffer)
    } else {
        // Sparse union: each child has the same length as the union array.
        // Optimization: only hash the elements that are actually referenced by type_ids,
        // instead of hashing all K*N elements (where K = num types, N = array length).
        hash_sparse_union_array(array, union_fields, random_state, hashes_buffer)
    }
}

/// Default hashing for union arrays - hashes all elements of each child array fully.
///