jsonld_compaction/

property.rs

use crate::{
    CompactFragment,
    CompactIndexedFragment,
    Error,
    Options,
    add_value,
    compact_collection_with,
    compact_iri,
    compact_iri_with,
    compact_iri_with_memo,
    iri::{CompactIriMemo, keyword_alias},
    value_value,
};

use jsonld_core::{
    Container,
    ContainerKind,
    Context,
    Id,
    Indexed,
    Loader,
    Node,
    Object,
    Term,
    context::Nest,
    object::{self, List},
};
use jsonld_syntax::{Keyword, native_stack::Recursion};
use rdfx::vocabulary::VocabularyMut;
use std::hash::Hash;

/// Compacts a list object and adds it to `nest_result` under
/// `item_active_property`.
///
/// When the term's container mapping includes `@list` the list becomes a plain
/// array assigned directly to the key. Otherwise it is wrapped back into a list
/// object — a map holding whatever `@list` compacts to, plus `@index` when the
/// list carried one — and added with [`add_value`].
async fn compact_property_list<N, L>(
    vocabulary: &mut N,
    list: &List<N::Iri, N::BlankId>,
    expanded_index: Option<&str>,
    nest_result: &mut jstrict::Object,
    container: Container,
    as_array: bool,
    item_active_property: &str,
    active_context: &Context<N::Iri, N::BlankId>,
    loader: &L,
    options: Options,
) -> Result<(), Error<L::Error>>
where
    N: VocabularyMut,
    N::Iri: Clone + Hash + Eq,
    N::BlankId: Clone + Hash + Eq,
    L: Loader,
{
    // If expanded item is a list object:
    let mut compacted_item = Recursion::new(compact_collection_with(
        vocabulary,
        list.iter(),
        active_context,
        active_context,
        Some(item_active_property),
        loader,
        options,
    ))
    .await?;

    // If compacted item is not an array,
    // then set `compacted_item` to an array containing only `compacted_item`.
    if !compacted_item.is_array() {
        let array = vec![compacted_item];
        compacted_item = jstrict::Value::Array(array);
    }

    // If container does not include @list:
    if container.contains(ContainerKind::List) {
        // Otherwise, set the value of the item active property entry in nest result to compacted item.
        nest_result.insert(item_active_property.into(), compacted_item);
    } else {
        // Convert `compacted_item` to a list object by setting it to
        // a map containing an entry where the key is the result of
        // IRI compacting @list and the value is the original
        // compacted item.
        let key = keyword_alias(vocabulary, active_context, options, Keyword::List);
        let mut compacted_item_list_object = jstrict::Object::default();
        compacted_item_list_object.insert(key.into(), compacted_item);

        // If `expanded_item` contains the entry @index-value,
        // then add an entry to compacted item where the key is
        // the result of IRI compacting @index and value is value.
        if let Some(index) = expanded_index {
            let key = keyword_alias(vocabulary, active_context, options, Keyword::Index);

            compacted_item_list_object.insert(key.into(), jstrict::Value::String(index.into()));
        }

        compacted_item = jstrict::Value::Object(compacted_item_list_object);

        // Use add value to add `compacted_item` to
        // the `item_active_property` entry in `nest_result` using `as_array`.
        add_value(nest_result, item_active_property, compacted_item, as_array);
    }

    Ok(())
}

/// Compacts a graph object and adds it to `nest_result` under
/// `item_active_property`.
///
/// The shape depends on the term's container mapping: `@graph`+`@id` and
/// `@graph`+`@index` turn the key into a map keyed by the graph's `@id` or
/// `@index`; a plain `@graph` container drops the wrapper entirely (collapsing
/// several graph entries into `@included` when they cannot be told apart);
/// anything else rebuilds an explicit graph object with `@graph`, `@id` and
/// `@index` entries.
///
/// Returns [`Error::CollidingEntry`] when a map-shaped container has to be
/// written where an earlier item of the same property already stored a non-map
/// value — a mix the specification defines no output for.
async fn compact_property_graph<N, L>(
    vocabulary: &mut N,
    node: &Node<N::Iri, N::BlankId>,
    expanded_index: Option<&str>,
    nest_result: &mut jstrict::Object,
    container: Container,
    as_array: bool,
    item_active_property: &str,
    active_context: &Context<N::Iri, N::BlankId>,
    loader: &L,
    options: Options,
) -> Result<(), Error<L::Error>>
where
    N: VocabularyMut,
    N::Iri: Clone + Hash + Eq,
    N::BlankId: Clone + Hash + Eq,
    L: Loader,
{
    // If expanded item is a graph object.
    // `compact_property_graph` is only invoked when `node.is_graph()`, so
    // this never actually returns early.
    let Some(graph) = node.graph() else { return Ok(()) };
    let mut compacted_item =
        Recursion::new(graph.compact_fragment_full(vocabulary, active_context, active_context, Some(item_active_property), loader, options)).await?;

    // If `container` includes @graph and @id:
    if container.contains(ContainerKind::Graph) && container.contains(ContainerKind::Id) {
        // Initialize `map_object` to the value of `item_active_property`
        // in `nest_result`, initializing it to a new empty map,
        // if necessary.
        if nest_result.get_unique(item_active_property).is_ok_and(|o| o.is_none()) {
            nest_result.insert(item_active_property.into(), jsonld_syntax::Object::default().into());
        }

        // The entry exists (just inserted above if absent), but may hold a
        // non-map value if an earlier expanded item was routed through the
        // fall-through branch below (e.g. a named graph mixed with simple
        // graphs under the same property); the spec defines no output for
        // that state.
        let Some(map_object) = nest_result
            .get_unique_mut(item_active_property)
            .ok()
            .flatten()
            .and_then(jstrict::Value::as_object_mut)
        else {
            return Err(Error::CollidingEntry);
        };

        // Initialize `map_key` by IRI compacting the value of @id in
        // `expanded_item` or @none if no such value exists
        // with `vocab` set to false if there is an @id entry in
        // `expanded_item`.
        let (id_value, vocab) = match &node.id {
            Some(entry) => (entry.clone().into_term(), false),
            None => (Term::Keyword(Keyword::None), true),
        };

        let Some(map_key) = compact_iri(vocabulary, active_context, &id_value, vocab, false, options)? else {
            return Err(Error::IriConfusedWithPrefix);
        };

        // Use `add_value` to add `compacted_item` to
        // the `map_key` entry in `map_object` using `as_array`.
        add_value(map_object, &map_key, compacted_item, as_array);
    } else if container.contains(ContainerKind::Graph) && container.contains(ContainerKind::Index) && node.is_simple_graph() {
        // Initialize `map_object` to the value of `item_active_property`
        // in `nest_result`, initializing it to a new empty map,
        // if necessary.
        if nest_result.get_unique(item_active_property).is_ok_and(|o| o.is_none()) {
            nest_result.insert(item_active_property.into(), jsonld_syntax::Object::default().into());
        }

        // Same collision case as the `@graph`+`@id` branch above: an earlier
        // named graph routed through the fall-through branch may have stored
        // a non-map value under this key.
        let Some(map_object) = nest_result
            .get_unique_mut(item_active_property)
            .ok()
            .flatten()
            .and_then(jstrict::Value::as_object_mut)
        else {
            return Err(Error::CollidingEntry);
        };

        // Initialize `map_key` the value of @index in `expanded_item`
        // or @none, if no such value exists.
        let map_key = expanded_index.unwrap_or("@none");

        // Use `add_value` to add `compacted_item` to
        // the `map_key` entry in `map_object` using `as_array`.
        add_value(map_object, map_key, compacted_item, as_array);
    } else if container.contains(ContainerKind::Graph) && node.is_simple_graph() {
        // Otherwise, if `container` includes @graph and
        // `expanded_item` is a simple graph object
        // the value cannot be represented as a map object.

        // If `compacted_item` is an array with more than one value,
        // it cannot be directly represented,
        // as multiple objects would be interpreted as different named graphs.
        // Set `compacted_item` to a new map,
        // containing the key from IRI compacting @included and
        // the original `compacted_item` as the value.
        compacted_item = match compacted_item {
            jstrict::Value::Array(items) if items.len() > 1 => {
                let key = keyword_alias(vocabulary, active_context, options, Keyword::Included);
                let mut map = jstrict::Object::default();
                map.insert(key.into(), jstrict::Value::Array(items));
                jstrict::Value::Object(map)
            }
            item => item,
        };

        // Use `add_value` to add `compacted_item` to the
        // `item_active_property` entry in `nest_result` using `as_array`.
        add_value(nest_result, item_active_property, compacted_item, as_array);
    } else {
        // Otherwise, `container` does not include @graph or
        // otherwise does not match one of the previous cases.

        // Set `compacted_item` to a new map containing the key from
        // IRI compacting @graph using the original `compacted_item` as a value.
        let key = keyword_alias(vocabulary, active_context, options, Keyword::Graph);
        let mut map = jstrict::Object::default();
        map.insert(key.into(), compacted_item);

        // If `expanded_item` contains an @id entry,
        // add an entry in `compacted_item` using the key from
        // IRI compacting @id using the value of
        // IRI compacting the value of @id in `expanded_item` using
        // false for vocab.
        if let Some(id_entry) = &node.id {
            // The key is the literal `"@id"` rather than a `keyword_alias`
            // lookup: this step compacts `@id` with `vocab` set to false, which
            // bypasses the inverse context and so can only ever return `"@id"`.
            let id: Term<N::Iri, N::BlankId> = id_entry.clone().into();
            let value = compact_iri(vocabulary, active_context, &id, false, false, options)?;
            map.insert(
                Keyword::Id.into_str().into(),
                match value {
                    Some(s) => jstrict::Value::String((&*s).into()),
                    None => jstrict::Value::Null,
                },
            );
        }

        // If `expanded_item` contains an @index entry,
        // add an entry in `compacted_item` using the key from
        // IRI compacting @index and the value of @index in `expanded_item`.
        if let Some(index_entry) = expanded_index {
            let key = keyword_alias(vocabulary, active_context, options, Keyword::Index);
            map.insert(key.into(), index_entry.into());
        }

        // Use `add_value` to add `compacted_item` to the
        // `item_active_property` entry in `nest_result` using `as_array`.
        let compacted_item = jstrict::Value::Object(map);
        add_value(nest_result, item_active_property, compacted_item, as_array);
    }

    Ok(())
}

/// Picks the object a compacted property should be written into, and returns it
/// together with the term's container mapping and whether its values must be
/// wrapped in an array.
///
/// A term with a `@nest` entry is written into a nested sub-object of `result`
/// keyed by the nest term, created on demand; every other term is written into
/// `result` itself. `as_array` is true when the container mapping includes
/// `@set`, when the key is `@graph` or `@list`, or when `compact_arrays` is off.
///
/// Returns [`Error::InvalidNestValue`] if `@nest` names something that is not
/// `@nest` or an alias for it, and [`Error::CollidingEntry`] if the nest key
/// already holds a non-map value.
fn select_nest_result<'a, I, B, E>(
    result: &'a mut jstrict::Object,
    active_context: &Context<I, B>,
    item_active_property: &str,
    compact_arrays: bool,
) -> Result<(&'a mut jstrict::Object, Container, bool), Error<E>>
where
    I: Clone + Hash + Eq,
    B: Clone + Hash + Eq,
{
    let (nest_result, container) = match active_context.get(item_active_property) {
        Some(term_definition) => {
            let nest_result = match term_definition.nest() {
                Some(nest_term) => {
                    // If nest term is not @nest,
                    // or a term in the active context that expands to @nest,
                    // an invalid @nest value error has been detected,
                    // and processing is aborted.
                    if *nest_term != Nest::Nest {
                        match active_context.get(nest_term.as_str()) {
                            Some(term_def) if term_def.value() == Some(&Term::Keyword(Keyword::Nest)) => {}
                            _ => return Err(Error::InvalidNestValue),
                        }
                    }

                    // If result does not have a nest_term entry,
                    // initialize it to an empty map.
                    if result.get_unique(nest_term.as_str()).is_ok_and(|o| o.is_none()) {
                        result.insert(nest_term.as_str().into(), jstrict::Object::default().into());
                    }

                    // Initialize `nest_result` to the value of `nest_term` in result.
                    // The entry exists (just inserted above if absent), but may hold
                    // a non-map value if another property already compacted to the
                    // same key; the spec defines no output for that state.
                    match result.get_unique_mut(nest_term.as_str()).ok().flatten().and_then(jstrict::Value::as_object_mut) {
                        Some(object) => object,
                        None => return Err(Error::CollidingEntry),
                    }
                }
                None => {
                    // Otherwise, initialize `nest_result` to result.
                    result
                }
            };

            (nest_result, term_definition.container())
        }
        None => (result, Container::None),
    };

    // Initialize container to container mapping for item active property
    // in active context, or to a new empty array,
    // if there is no such container mapping.
    // DONE.

    let as_array = values_as_array(container, item_active_property, compact_arrays);

    Ok((nest_result, container, as_array))
}

/// Checks whether the values of a property are written as an array even when
/// there is only one.
///
/// `item_active_property` is the term the property compacted to and
/// `container` that term's container mapping in the active context, or
/// [`Container::None`] when the term has no definition. Follows the
/// *as array* rule the [compaction algorithm][1] applies to each value of a
/// property: `true` when the container mapping
/// includes `@set`, when the term is `@graph` or `@list`, or when
/// `compact_arrays` is off.
///
/// A term whose container mapping includes `@list` writes a list object's
/// items as an array regardless, and terms with an `@language`, `@index`,
/// `@id` or `@type` container write a map whose entries this flag applies to.
///
/// [1]: https://www.w3.org/TR/json-ld-api/#compaction-algorithm
#[must_use]
pub fn values_as_array(container: Container, item_active_property: &str, compact_arrays: bool) -> bool {
    // Initialize `as_array` to true if `container` includes @set,
    // or if `item_active_property` is @graph or @list,
    // otherwise the negation of `options.compact_arrays`.
    if container.contains(ContainerKind::Set) || item_active_property == "@graph" || item_active_property == "@list" {
        true
    } else {
        !compact_arrays
    }
}

/// Compacts one expanded property and all of its values into `result`.
///
/// Each value is compacted independently, and may select a different term for
/// the same expanded property — a language-tagged string and a node reference
/// can end up under different keys. Values are then routed by the selected
/// term's container mapping: list and graph objects to
/// [`compact_property_list`] and [`compact_property_graph`], and `@language`,
/// `@index`, `@id` and `@type` containers into a map keyed by the corresponding
/// part of the value.
///
/// `inside_reverse` marks the property as coming from an `@reverse` entry, which
/// restricts term selection to terms declared with `@reverse`.
///
/// An empty value array still produces an entry: the property is compacted
/// against an empty node object and assigned an empty array.
pub async fn compact_property<'a, N, L, O, T>(
    vocabulary: &mut N,
    result: &mut jstrict::Object,
    expanded_property: Term<N::Iri, N::BlankId>,
    expanded_value: O,
    active_context: &Context<N::Iri, N::BlankId>,
    loader: &L,
    inside_reverse: bool,
    options: Options,
) -> Result<(), Error<L::Error>>
where
    N: VocabularyMut,
    N::Iri: Clone + Hash + Eq,
    N::BlankId: Clone + Hash + Eq,
    O: IntoIterator<Item = &'a Indexed<T>>,
    T: 'a + object::Any<N::Iri, N::BlankId>,
    L: Loader,
{
    let mut is_empty = true;

    // A property's values are near-always alike — an array of value objects, or
    // of node references — and IRI compaction reads the value only through a
    // handful of features. Remembering the last one lets a run of them share a
    // single term selection. Valid only because every other argument below is
    // fixed for this call.
    let mut memo = CompactIriMemo::new();

    // For each item `expanded_item` in `expanded value`
    for expanded_item in expanded_value {
        is_empty = false;
        // Initialize `item_active_property` by IRI compacting `expanded_property`
        // using `expanded_item` for value and `inside_reverse` for `reverse`.
        let item_active_property = compact_iri_with_memo(
            vocabulary,
            active_context,
            &expanded_property,
            expanded_item,
            true,
            inside_reverse,
            options,
            &mut memo,
        )?;

        // If the term definition for `item_active_property` in the active context
        // has a nest value entry (nest term)
        if let Some(item_active_property) = item_active_property {
            let (nest_result, container, as_array) = select_nest_result(result, active_context, &item_active_property, options.compact_arrays)?;

            // Initialize `compacted_item` to the result of using this algorithm
            // recursively, passing `active_context`, `item_active_property` for
            // `active_property`, `expanded_item` for `element`, along with the
            // `compact_arrays` and `ordered_flags`.
            // If `expanded_item` is a list object or a graph object,
            // use the value of the @list or @graph entries, respectively,
            // for `element` instead of `expanded_item`.
            match expanded_item.inner().as_ref() {
                object::Ref::List(list) => {
                    compact_property_list(
                        vocabulary,
                        list,
                        expanded_item.index(),
                        nest_result,
                        container,
                        as_array,
                        &item_active_property,
                        active_context,
                        loader,
                        options,
                    )
                    .await?;
                }
                object::Ref::Node(node) if node.is_graph() => {
                    compact_property_graph(
                        vocabulary,
                        node,
                        expanded_item.index(),
                        nest_result,
                        container,
                        as_array,
                        &item_active_property,
                        active_context,
                        loader,
                        options,
                    )
                    .await?;
                }
                _ => {
                    let mut compacted_item = Recursion::new(expanded_item.compact_fragment_full(
                        vocabulary,
                        active_context,
                        active_context,
                        Some(&item_active_property),
                        loader,
                        options,
                    ))
                    .await?;

                    // if container includes @language, @index, @id,
                    // or @type and container does not include @graph:
                    if !container.contains(ContainerKind::Graph)
                        && (container.contains(ContainerKind::Language)
                            || container.contains(ContainerKind::Index)
                            || container.contains(ContainerKind::Id)
                            || container.contains(ContainerKind::Type))
                    {
                        // Initialize `map_object` to the value of
                        // `item_active_property` in `nest_result`,
                        // initializing it to a new empty map, if necessary.
                        if nest_result.get_unique(&*item_active_property).is_ok_and(|o| o.is_none()) {
                            nest_result.insert((&*item_active_property).into(), jstrict::Object::default().into());
                        }

                        // The entry exists (just inserted above if absent), but may
                        // hold a non-map value if another property already compacted
                        // to the same key with a different container shape; the spec
                        // defines no output for that state.
                        let Some(map_object) = nest_result
                            .get_unique_mut(&*item_active_property)
                            .ok()
                            .flatten()
                            .and_then(jstrict::Value::as_object_mut)
                        else {
                            return Err(Error::CollidingEntry);
                        };

                        // Initialize container key by IRI compacting either
                        // @language, @index, @id, or @type based on the contents of container.
                        let container_type = if container.contains(ContainerKind::Language) {
                            ContainerKind::Language
                        } else if container.contains(ContainerKind::Index) {
                            ContainerKind::Index
                        } else if container.contains(ContainerKind::Id) {
                            ContainerKind::Id
                        } else {
                            ContainerKind::Type
                        };

                        let mut container_key: String = keyword_alias(vocabulary, active_context, options, container_type.into()).to_string();

                        // Initialize `index_key` to the value of index mapping in
                        // the term definition associated with `item_active_property`
                        // in active context, or @index (None in our case), if no such value exists.
                        let index_key = match active_context.get(&*item_active_property) {
                            Some(def) if def.index().is_some() => def.index(),
                            _ => None,
                        };

                        // If `container` includes @language and `expanded_item`
                        // contains a @value entry, then set `compacted_item` to
                        // the value associated with its @value entry.
                        // Set `map_key` to the value of @language in `expanded_item`,
                        // if any.
                        let map_key = if container_type == ContainerKind::Language && expanded_item.is_value() {
                            if let object::Ref::Value(value) = expanded_item.inner().as_ref() {
                                compacted_item = value_value(value);
                            }

                            expanded_item.language().map(std::string::ToString::to_string)
                        } else if container_type == ContainerKind::Index {
                            match index_key {
                                Some(index_key) => {
                                    // Otherwise, if `container` includes @index and
                                    // `index_key` is not @index:

                                    // Reinitialize `container_key` by
                                    // IRI compacting `index_key`.
                                    container_key =
                                        match compact_iri(vocabulary, active_context, &Term::Id(Id::Invalid(index_key.to_string())), true, false, options)? {
                                            Some(arc) => arc.to_string(),
                                            None => return Err(Error::IriConfusedWithPrefix),
                                        };

                                    // Set `map_key` to the first value of
                                    // `container_key` in `compacted_item`, if any.
                                    let (map_key, remaining_values) = match &mut compacted_item {
                                        jstrict::Value::Object(map) => match map.remove_unique(container_key.as_str()).ok().flatten() {
                                            Some(entry) => match entry.value {
                                                jstrict::Value::String(s) => (Some(s.to_string()), Vec::new()),
                                                jstrict::Value::Array(values) => {
                                                    let mut values = values.into_iter();
                                                    match values.next() {
                                                        Some(first_value) => (first_value.as_str().map(std::string::ToString::to_string), values.collect()),
                                                        None => (None, values.collect()),
                                                    }
                                                }
                                                other => (None, vec![other]),
                                            },
                                            None => (None, Vec::new()),
                                        },
                                        _ => (None, Vec::new()),
                                    };

                                    // If there are remaining values in `compacted_item`
                                    // for container key, use `add_value` to add
                                    // those remaining values to the `container_key`
                                    // in `compacted_item`.
                                    // Otherwise, remove that entry from compacted item.
                                    if !remaining_values.is_empty()
                                        && let Some(map) = compacted_item.as_object_mut()
                                    {
                                        for value in remaining_values {
                                            add_value(map, container_key.as_str(), value, false);
                                        }
                                    }

                                    map_key
                                }
                                None => {
                                    // Otherwise, if `container` includes @index and
                                    // `index_key` is @index, set `map_key` to the value of
                                    // @index in `expanded_item`, if any.
                                    expanded_item.index().map(ToOwned::to_owned)
                                }
                            }
                        } else if container_type == ContainerKind::Id {
                            // Otherwise, if `container` includes @id,
                            // set `map_key` to the value of `container_key` in
                            // `compacted_item` and remove `container_key` from
                            // `compacted_item`.
                            compacted_item
                                .as_object_mut()
                                .and_then(|map| {
                                    map.remove_unique(container_key.as_str())
                                        .ok()
                                        .flatten()
                                        .map(|entry| entry.value.as_str().map(ToOwned::to_owned))
                                })
                                .flatten()
                        } else {
                            // Otherwise, if container includes @type:

                            // Set `map_key` to the first value of `container_key` in
                            // `compacted_item`, if any.
                            let (map_key, remaining_values) = match compacted_item.as_object_mut() {
                                Some(map) => match map.remove_unique(container_key.as_str()).ok().flatten() {
                                    Some(entry) => match entry.value {
                                        jstrict::Value::String(s) => (Some((*s).to_string()), Vec::new()),
                                        jstrict::Value::Array(values) => {
                                            let mut values = values.into_iter();
                                            match values.next() {
                                                Some(first_value) => (first_value.as_str().map(ToOwned::to_owned), values.collect()),
                                                None => (None, values.collect()),
                                            }
                                        }
                                        other => (None, vec![other]),
                                    },
                                    None => (None, Vec::new()),
                                },
                                _ => (None, Vec::new()),
                            };

                            // If there are remaining values in `compacted_item` for
                            // `container_key`, use `add_value` to add those
                            // remaining values to the `container_key` in
                            // `compacted_item`.
                            // Otherwise, remove that entry from compacted item.
                            if !remaining_values.is_empty()
                                && let Some(map) = compacted_item.as_object_mut()
                            {
                                for value in remaining_values {
                                    add_value(map, container_key.as_str(), value, false);
                                }
                            }

                            // If `compacted_item` contains a single entry with a key
                            // expanding to @id, set `compacted_item` to the result of
                            // using this algorithm recursively,
                            // passing `active_context`, `item_active_property` for
                            // `active_property`, and a map composed of the single
                            // entry for @id from `expanded_item` for `element`.
                            if let Some(map) = compacted_item.as_object()
                                && map.len() == 1
                                && map.get_unique("@id").ok().flatten().is_some()
                                // An `@id`-only map implies the expanded item has an
                                // `id`, so this last condition always holds here.
                                && let Some(id) = expanded_item.id()
                            {
                                let obj = Object::node(Node::with_id(id.clone()));
                                compacted_item = Recursion::new(obj.compact_indexed_fragment(
                                    vocabulary,
                                    None,
                                    active_context,
                                    active_context,
                                    Some(&item_active_property),
                                    loader,
                                    options,
                                ))
                                .await?;
                            }

                            map_key
                        };

                        // If `map_key` is null, set it to the result of
                        // IRI compacting @none.
                        let map_key = match map_key {
                            Some(key) => key,
                            None => keyword_alias(vocabulary, active_context, options, Keyword::None).to_string(),
                        };

                        // Use `add_value` to add `compacted_item` to
                        // the `map_key` entry in `map_object` using `as_array`.
                        add_value(map_object, &map_key, compacted_item, as_array);
                    } else {
                        // Otherwise, use `add_value` to add `compacted_item` to the
                        // `item_active_property` entry in `nest_result` using `as_array`.
                        add_value(nest_result, &item_active_property, compacted_item, as_array);
                    }
                }
            }
        }
    }

    // If expanded value is an empty array:
    if is_empty {
        // Initialize `item_active_property` by IRI compacting
        // `expanded_property` using `expanded_value` for `value` and
        // `inside_reverse` for `reverse`.
        let item_active_property = compact_iri_with(
            vocabulary,
            active_context,
            &expanded_property,
            &Indexed::new(Object::node(Node::new()), None),
            true,
            inside_reverse,
            options,
        )?;

        // If the term definition for `item_active_property` in the active context
        // has a nest value entry (nest term):
        if let Some(item_active_property) = item_active_property {
            let (nest_result, _, _) = select_nest_result(result, active_context, &item_active_property, options.compact_arrays)?;

            // Use `add_value` to add an empty array to the `item_active_property` entry in
            // `nest_result` using true for `as_array`.
            add_value(nest_result, &item_active_property, Vec::new().into(), true);
        }
    }

    Ok(())
}