luaur-analysis 0.1.3

Luau type checker and type inference (Rust).
Documentation 
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use crate::enums::relation::Relation;
use crate::enums::table_state::TableState;
use crate::functions::flip::flip;
use crate::functions::relate_simplify::relate;
use crate::functions::relate_table_to_prop::relate_table_to_prop;
use crate::records::table_type::TableType;
use crate::type_aliases::simplifier_seen_set::SimplifierSeenSet;
use luaur_common::macros::luau_assert::LUAU_ASSERT;

pub fn relate_tables(
    left_table: &TableType,
    right_table: &TableType,
    seen: &mut SimplifierSeenSet,
) -> Relation {
    // FIXME CLI-189216: As noted in the body this is not complete.
    if left_table.state != TableState::Sealed || right_table.state != TableState::Sealed {
        return Relation::Intersects;
    }

    if right_table.props.len() == 1 && right_table.indexer.is_none() {
        let (name, prop) = right_table.props.iter().next().unwrap();
        let res = relate_table_to_prop(left_table, name, prop, seen);
        // If the single property is coincident with the member in the left table, then
        // by width subtyping the left table is a subset.
        if res == Relation::Coincident {
            return Relation::Subset;
        }
        return res;
    }

    if left_table.props.len() == 1 && left_table.indexer.is_none() {
        let (name, prop) = left_table.props.iter().next().unwrap();
        let res = flip(relate_table_to_prop(right_table, name, prop, seen));
        // If the single property is coincident with the member in the right table, then
        // by width subtyping the right table is a subset (so we return superset).
        if res == Relation::Coincident {
            return Relation::Superset;
        }
        return res;
    }

    // This can potentially not account for something like
    //
    //  { x: number, y: number } & { x: number, y: number, z: number }
    //
    // ... where we _ought_ to say superset.
    if left_table.props.len() != right_table.props.len()
        || left_table.indexer.is_some() != right_table.indexer.is_some()
    {
        return Relation::Intersects;
    }

    let mut has_subset = false;

    for (right_name, right_prop) in &right_table.props {
        match relate_table_to_prop(left_table, right_name, right_prop, seen) {
            Relation::Disjoint => return Relation::Disjoint,
            // We're being _very_ conservative here. We could update this in the future to
            // account for a case like:
            //
            //  (T & { x: number }) & (T & { read x: number? })
            //
            // ... by running this loop twice.
            Relation::Superset | Relation::Intersects => return Relation::Intersects,
            Relation::Subset => {
                has_subset = true;
            }
            Relation::Coincident => {}
        }
    }

    if left_table.indexer.is_none() {
        LUAU_ASSERT!(right_table.indexer.is_none());
        return if has_subset {
            Relation::Subset
        } else {
            Relation::Coincident
        };
    }

    let left_indexer = left_table.indexer.as_ref().unwrap();
    let right_indexer = right_table.indexer.as_ref().unwrap();

    if relate(left_indexer.index_type, right_indexer.index_type, seen) != Relation::Coincident {
        return Relation::Intersects;
    }

    if relate(left_indexer.index_type, right_indexer.index_type, seen) != Relation::Coincident {
        return Relation::Intersects;
    }

    if has_subset {
        Relation::Subset
    } else {
        Relation::Coincident
    }
}