Function anchor_split

prqlc/prqlc/src/sql/pq/anchor.rs:228–304

Applies adjustments to second part of a pipeline when it's split: - append Select to preceding pipeline - prepend From to atomic pipeline - redefine columns materialized in atomic pipeline - redirect all references to original columns to the new ones

(
    ctx: &mut AnchorContext,
    preceding: Vec<SqlTransform>,
    atomic: Vec<SqlTransform>,
)

/// - redefine columns materialized in atomic pipeline
/// - redirect all references to original columns to the new ones
pub(super) fn anchor_split(
    ctx: &mut AnchorContext,
    preceding: Vec<SqlTransform>,
    atomic: Vec<SqlTransform>,
) -> Vec<SqlTransform> {
    let new_tid = ctx.tid.gen();

    let preceding_select = &preceding.last().unwrap().as_super().unwrap();
    let cols_at_split = preceding_select.as_select().unwrap();

    log::debug!("split pipeline, first pipeline output: {cols_at_split:?}");

    // redefine columns of the atomic pipeline
    let mut cid_redirects = HashMap::<CId, CId>::new();
    let mut new_columns = Vec::new();
    let mut used_new_names = HashSet::new();
    for old_cid in cols_at_split {
        let new_cid = ctx.cid.gen();

        let old_name = ctx.ensure_column_name(*old_cid).cloned();

        let mut new_name = old_name;
        if let Some(new) = &mut new_name {
            if used_new_names.contains(new) {
                *new = ctx.col_name.gen();
                ctx.column_names.insert(*old_cid, new.clone());
            }

            used_new_names.insert(new.clone());
            ctx.column_names.insert(new_cid, new.clone());
        }

        let old_def = ctx.column_decls.get(old_cid).unwrap();

        let col = match old_def {
            ColumnDecl::RelationColumn(_, _, RelationColumn::Wildcard) => RelationColumn::Wildcard,
            _ => RelationColumn::Single(new_name),
        };

        new_columns.push((col, new_cid));
        cid_redirects.insert(*old_cid, new_cid);
    }

    // define a new table
    let columns = cols_at_split
        .iter()
        .map(|_| RelationColumn::Single(None))
        .collect_vec();
    ctx.table_decls.insert(
        new_tid,
        SqlTableDecl {
            id: new_tid,
            name: None,
            relation: RelationStatus::NotYetDefined(RelationAdapter::Preprocessed(
                preceding, columns,
            )),
            redirect_to: None,
        },