Function preprocess

prqlc/prqlc/src/sql/pq/preprocess.rs:22–38

Converts RQ AST into SqlRQ AST and applies a few preprocessing operations. Note that some SQL translation mechanisms depend on behavior of some of these functions (i.e. reorder).

(
    pipeline: Vec<Transform>,
    ctx: &mut Context,
)

/// Note that some SQL translation mechanisms depend on behavior of some of these
/// functions (i.e. reorder).
pub(in crate::sql) fn preprocess(
    pipeline: Vec<Transform>,
    ctx: &mut Context,
) -> Result<Vec<SqlTransform>> {
    Ok(pipeline)
        .and_then(normalize)
        .and_then(|p| wrap(p, ctx))
        .and_then(|p| prune_inputs(p, ctx))
        .and_then(|p| distinct(p, ctx))
        .and_then(|p| union(p, ctx))
        .and_then(|p| except(p, ctx))
        .and_then(|p| intersect(p, ctx))
        .map(reorder)
        .inspect(|p| {
            debug::log_entry(|| debug::DebugEntryKind::ReprPqEarly(p.clone()));
        })
}

// This function was disabled because it changes semantics of the pipeline in some cases.
// /// Pushes all [Transform::Select]s to the back of the pipeline.