batch-impl 0.7.0

//! `Ty` traversal: parallel expansion ([`Expand`]) and the single child-map
//! home ([`Ty::map_children`]). Split from `types.rs` so node definitions and
//! traversal stay under the per-file budget.

use crate::apply::check_expand_limit;
use crate::ast::types::{
    Ty, TyArray, TyFn, TyGeneric, TyGroup, TyKind, TyParams, TyPrimitiveArray,
    TyTuple, TyTypeParam, TyWithAttr, TyWithCode, TyWithPrefix, TyWithTrait,
    TyWithType, TyWithWhere,
};

pub(crate) enum Expand {
    Leaf(Ty),
    Many(Vec<Ty>),
}

/// Splat consumption: flatten a splat element (or any container / generator)
/// into its element list, hoisting fresh declarations out. Returns the flat
/// elements plus the merged declaration (if any generator was flattened — the
/// caller wraps the enclosing container in `WithType(decl, ...)`).
///
/// Shared by the parse layer (container element collection) and the apply
/// layer (right-splat argument appending / left-splat distribution).
pub(crate) fn splat_expand(ty: Ty) -> (Vec<Ty>, Option<TyTypeParam>) {
    match ty.kind {
        TyKind::Splat(s) => fold_splat_elems(s.elems().to_vec()),
        TyKind::Array(a) => fold_splat_elems(a.0),
        // Splat expands ONE layer: tuples are types, so they stay as single
        // elements — `*((a,b),)` = `(a,b)` (one tuple impl), and a tuple
        // inside a splat (`*(a,(b,c))`) keeps `(b,c)` intact. Only lists
        // (arrays, nested splats) and generators flatten.
        TyKind::Tuple(t) => {
            (vec![Ty { span: ty.span, kind: TyKind::Tuple(t) }], None)
        }
        TyKind::Group(g) => splat_expand(*g.0),
        // Generator: its inner container is a *param list* (the fresh tuple),
        // not a type — flatten it even though bare tuples stay single
        // elements (`(*(()^3))` = `(P0,P1,P2)`, not `((P0,P1,P2),)`).
        TyKind::WithType(wt) => {
            let TyWithType(params, inner) = wt;
            let (elems, _) = match inner.kind {
                TyKind::Tuple(t) => fold_splat_elems(t.0),
                _ => splat_expand(*inner),
            };
            (elems, Some(params))
        }
        // Anything else (primitive / generic / nested containers that belong
        // to the element itself, e.g. `Vec<()^2>`) stays a single element.
        other => (vec![Ty { span: ty.span, kind: other }], None),
    }
}

fn fold_splat_elems(elems: Vec<Ty>) -> (Vec<Ty>, Option<TyTypeParam>) {
    let mut flat = vec![];
    let mut decl = None;
    for e in elems {
        let (mut es, d) = splat_expand(e);
        flat.append(&mut es);
        decl = merge_decls(decl, d);
    }
    (flat, decl)
}

/// Flatten top-level splat params (`T<*(A,B)>` → `T<A,B>`) and hoist
/// generator declarations (`T<()^2>` = `<A,B>T<(A,B)>`) without recursing
/// into ordinary names; returns flat params + any hoisted declaration.
/// Shared by `expand_tp` (structure level, recurses afterwards) and
/// `extract_impl_parts` (trait args, rendered to tokens).
pub(crate) fn flat_splat_params(params: TyParams) -> (TyParams, Option<TyTypeParam>) {
    let mut flat = vec![];
    let mut decl = None;
    for (name, bound) in params {
        match name.kind {
            // `*(A,B)` param → its flat elements
            TyKind::Splat(_) => {
                let (es, d) = splat_expand(*name);
                decl = merge_decls(decl, d);
                flat.extend(es.into_iter().map(|e| (Box::new(e), None)));
            }
            // generator param (`()^N`) → hoist the fresh declaration; the
            // inner tuple stays the arg (`T<()^2>` = `<A,B>T<(A,B)>`), but a
            // splat re-wrap (`*()^N` → `<A,B>T<A,B>`) flattens further.
            TyKind::WithType(wt) => {
                decl = merge_decls(decl, Some(wt.0));
                let inner = *wt.1;
                match inner.kind {
                    TyKind::Splat(_) => {
                        let (es, d) = splat_expand(inner);
                        decl = merge_decls(decl, d);
                        flat.extend(es.into_iter().map(|e| (Box::new(e), None)));
                    }
                    _ => flat.push((Box::new(inner), bound)),
                }
            }
            _ => flat.push((name, bound)),
        }
    }
    (flat, decl)
}

/// Merge two optional fresh declarations (`TyTypeParam::extend` semantics).
pub(crate) fn merge_decls(
    a: Option<TyTypeParam>, b: Option<TyTypeParam>,
) -> Option<TyTypeParam> {
    match (a, b) {
        (None, b) => b,
        (a, None) => a,
        (Some(mut a), Some(b)) => {
            a.extend(b);
            Some(a)
        }
    }
}

/// Shared "recurse inner and rewrap" logic for wrapper variants: `make` rebuilds
/// the wrapper from the inner; when `inner` is `None` (bare wrapper), `make(None)`
/// returns it as-is (a leaf). Reused by the WithCode/WithWhere/WithAttr/WithPrefix arms.
fn expand_wrapped<F>(make: F, inner: Option<Box<Ty>>) -> Expand
where
    F: Fn(Option<Box<Ty>>) -> Ty,
{
    match inner {
        Some(i) => match i.expand() {
            Expand::Many(v) => {
                Expand::Many(v.into_iter().map(|e| make(Some(e.into()))).collect())
            }
            Expand::Leaf(l) => Expand::Leaf(make(Some(l.into()))),
        },
        None => Expand::Leaf(make(None)),
    }
}

/// Like [`expand_wrapped`], but the inner always exists (`WithType`/`WithTrait`
/// boxes are non-`Option`).
fn expand_rebuild<F>(make: F, inner: Ty) -> Expand
where
    F: Fn(Box<Ty>) -> Ty,
{
    match inner.expand() {
        Expand::Many(v) => {
            Expand::Many(v.into_iter().map(|e| make(e.into())).collect())
        }
        Expand::Leaf(l) => Expand::Leaf(make(l.into())),
    }
}

impl Ty {
    /// Maps every child `Ty` node (recursing into lists/optionals), rebuilding
    /// the node with its span preserved. Single exhaustive home for the
    /// "recurse into children" pattern — `hoist_type_params` and future
    /// rebuild-style traversals compose on top of it instead of re-matching
    /// all 18 variants.
    #[allow(clippy::redundant_closure)] // `&mut FnMut` cannot be moved into `.map(f)`
    pub(crate) fn map_children(self, f: &mut impl FnMut(Ty) -> Ty) -> Ty {
        let span = self.span;
        match self.kind {
            TyKind::Array(a) => TyArray(a.0.into_iter().map(|e| f(e)).collect())
                .to_ty()
                .with_span(span),
            TyKind::Tuple(t) => TyTuple(t.0.into_iter().map(|e| f(e)).collect())
                .to_ty()
                .with_span(span),
            TyKind::Group(g) => TyGroup(f(*g.0).into()).to_ty().with_span(span),
            TyKind::PrimitiveArray(pa) => {
                TyPrimitiveArray(pa.0.map(|e| f(*e).into()), pa.1)
                    .to_ty()
                    .with_span(span)
            }
            TyKind::Generic(g) => {
                TyGeneric(f(*g.0).into(), g.1).to_ty().with_span(span)
            }
            TyKind::WithPrefix(wp) => {
                TyWithPrefix(wp.0, wp.1.map(|e| f(*e).into())).to_ty().with_span(span)
            }
            TyKind::WithTrait(wt) => {
                TyWithTrait(wt.0, f(*wt.1).into()).to_ty().with_span(span)
            }
            TyKind::WithCode(wc) => {
                TyWithCode(wc.0.map(|e| f(*e).into()), wc.1).to_ty().with_span(span)
            }
            TyKind::WithWhere(ww) => {
                TyWithWhere(ww.0.map(|e| f(*e).into()), ww.1).to_ty().with_span(span)
            }
            TyKind::WithType(wt) => {
                TyWithType(wt.0, f(*wt.1).into()).to_ty().with_span(span)
            }
            TyKind::WithAttr(wa) => {
                TyWithAttr(wa.0, wa.1.map(|e| f(*e).into())).to_ty().with_span(span)
            }
            TyKind::Fn(fn_) => TyFn(
                fn_.0.map(|params| params.into_iter().map(|p| f(p)).collect()),
                fn_.1.map(|r| f(*r).into()),
                fn_.2,
            )
            .to_ty()
            .with_span(span),
            // No children: keep as-is.
            other => Ty { span, kind: other },
        }
    }

    /// Expands parallel-list nodes: `Array` unwraps directly, wrappers (With*) recurse.
    ///
    /// [`Expand::Leaf`] = non-expandable leaf returned as-is (collected as one impl);
    /// [`Expand::Many`] = expands into multiple nodes. Wrappers pass arrays through
    /// transparently: `<T>[A,B]` becomes `<T>A, <T>B` (generic declarations are not
    /// repeated into a single impl); WithAttr/WithPrefix passthrough is defensive
    /// (array dispatch already happens in apply; uniform passthrough prevents regressions).
    pub(crate) fn expand(self) -> Expand {
        let Ty { span, kind } = self;
        match kind {
            TyKind::Array(ty) => Expand::Many(ty.0),
            // Top-level splat: consume (flatten containers/generators) and
            // distribute like a list. Fresh declarations from flattened
            // generators wrap each distributed element.
            TyKind::Splat(s) => {
                let (elems, decl) = splat_expand(s.to_ty().with_span(span));
                Expand::Many(
                    elems
                        .into_iter()
                        .map(|e| match &decl {
                            Some(d) => TyWithType(d.clone(), e.into())
                                .to_ty()
                                .with_span(span),
                            None => e,
                        })
                        .collect(),
                )
            }
            TyKind::Tuple(t) => {
                // List distribution: an array element (a dispatch list) makes
                // the tuple expand by Cartesian product — `(X, [A, B])` →
                // `(X, A)`, `(X, B)`. Combos that still contain arrays
                // re-expand through the driver work queue (recursive
                // distribution, which also covers pow_cartesian outputs
                // nested in outer tuples). Pure tuples stay a Leaf.
                if t.0.iter().any(|e| matches!(e.kind, TyKind::Array(_))) {
                    let mut combos: Vec<Vec<Ty>> = vec![vec![]];
                    for e in &t.0 {
                        let candidates = match &e.kind {
                            TyKind::Array(a) => a.0.clone(),
                            _ => vec![e.clone()],
                        };
                        let mut next =
                            Vec::with_capacity(combos.len() * candidates.len());
                        for ex in &combos {
                            for c in &candidates {
                                let mut combo = ex.clone();
                                combo.push(c.clone());
                                next.push(combo);
                            }
                        }
                        combos = next;
                    }
                    if let Some(e) =
                        check_expand_limit("tuple list distribution", combos.len())
                    {
                        return e.expand();
                    }
                    Expand::Many(
                        combos
                            .into_iter()
                            .map(|combo| TyTuple(combo).to_ty().with_span(span))
                            .collect(),
                    )
                } else {
                    Expand::Leaf(t.to_ty().with_span(span))
                }
            }
            TyKind::WithCode(wc) => {
                let TyWithCode(inner, payload) = wc;
                expand_wrapped(
                    move |i| TyWithCode(i, payload.clone()).to_ty().with_span(span),
                    inner,
                )
            }
            TyKind::WithWhere(ww) => {
                let TyWithWhere(inner, payload) = ww;
                expand_wrapped(
                    move |i| TyWithWhere(i, payload.clone()).to_ty().with_span(span),
                    inner,
                )
            }
            TyKind::WithType(wt) => {
                let TyWithType(params, inner) = wt;
                expand_rebuild(
                    move |e| TyWithType(params.clone(), e).to_ty().with_span(span),
                    *inner,
                )
            }
            TyKind::WithTrait(wt) => {
                let TyWithTrait(t, inner) = wt;
                expand_rebuild(
                    move |e| TyWithTrait(t.clone(), e).to_ty().with_span(span),
                    *inner,
                )
            }
            TyKind::WithAttr(wa) => {
                let TyWithAttr(attr, inner) = wa;
                expand_wrapped(
                    move |i| TyWithAttr(attr.clone(), i).to_ty().with_span(span),
                    inner,
                )
            }
            TyKind::WithPrefix(wp) => {
                let TyWithPrefix(prefix, inner) = wp;
                expand_wrapped(
                    move |i| TyWithPrefix(prefix, i).to_ty().with_span(span),
                    inner,
                )
            }
            TyKind::Group(g) => (*g.0).expand(),
            TyKind::Generic(g) => {
                // Array args distribute like a list — `T<[A,B]>` → `[T<A>, T<B>]`
                // (Cartesian across multiple arrays). This is the single
                // authority for array-arg distribution: literal `[A,B]`, the
                // `[u8,...]` from a `@u*` constant, and the `TyArray` produced
                // by splat powers (`*(*@u*)^2` → `[*(u8,u8), ...]`) all reach
                // params as a `TyArray` and distribute here.
                if g.1.params.iter().any(|(n, _)| matches!(n.kind, TyKind::Array(_)))
                {
                    let mut combos: Vec<TyParams> = vec![vec![]];
                    for (name, bound) in &g.1.params {
                        let candidates: TyParams = match &name.kind {
                            TyKind::Array(a) => {
                                a.0.iter()
                                    .map(|e| (Box::new(e.clone()), bound.clone()))
                                    .collect()
                            }
                            _ => vec![(name.clone(), bound.clone())],
                        };
                        let mut next =
                            Vec::with_capacity(combos.len() * candidates.len());
                        for ex in &combos {
                            for c in &candidates {
                                let mut combo = ex.clone();
                                combo.push(c.clone());
                                next.push(combo);
                            }
                        }
                        combos = next;
                    }
                    if let Some(e) =
                        check_expand_limit("generic array distribution", combos.len())
                    {
                        return e.expand();
                    }
                    Expand::Many(
                        combos
                            .into_iter()
                            .map(|params| {
                                TyGeneric(
                                    g.0.clone(),
                                    TyTypeParam {
                                        params,
                                        bindings: g.1.bindings.clone(),
                                    },
                                )
                                .to_ty()
                                .with_span(span)
                            })
                            .collect(),
                    )
                } else {
                    Expand::Leaf(Ty { span, kind: TyKind::Generic(g) })
                }
            }
            other => Expand::Leaf(Ty { span, kind: other }),
        }
    }
}