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//! An iterator over the type substructure.
//! WARNING: this does not keep track of the region depth.
use smallvec::{SmallVec, smallvec};
use tracing::debug;
use crate::data_structures::SsoHashSet;
use crate::inherent::*;
use crate::{self as ty, Interner};
// The TypeWalker's stack is hot enough that it's worth going to some effort to
// avoid heap allocations.
type TypeWalkerStack<I> = SmallVec<[<I as Interner>::GenericArg; 8]>;
/// An iterator for walking the type tree.
///
/// It's very easy to produce a deeply
/// nested type tree with a lot of
/// identical subtrees. In order to work efficiently
/// in this situation walker only visits each type once.
/// It maintains a set of visited types and
/// skips any types that are already there.
pub struct TypeWalker<I: Interner> {
stack: TypeWalkerStack<I>,
last_subtree: usize,
pub visited: SsoHashSet<I::GenericArg>,
}
impl<I: Interner> TypeWalker<I> {
pub fn new(root: I::GenericArg) -> Self {
Self { stack: smallvec![root], last_subtree: 1, visited: SsoHashSet::new() }
}
/// Skips the subtree corresponding to the last type
/// returned by `next()`.
///
/// Example: Imagine you are walking `Foo<Bar<i32>, usize>`.
///
/// ```ignore (illustrative)
/// let mut iter: TypeWalker = ...;
/// iter.next(); // yields Foo
/// iter.next(); // yields Bar<i32>
/// iter.skip_current_subtree(); // skips i32
/// iter.next(); // yields usize
/// ```
pub fn skip_current_subtree(&mut self) {
self.stack.truncate(self.last_subtree);
}
}
impl<I: Interner> Iterator for TypeWalker<I> {
type Item = I::GenericArg;
fn next(&mut self) -> Option<I::GenericArg> {
debug!("next(): stack={:?}", self.stack);
loop {
let next = self.stack.pop()?;
self.last_subtree = self.stack.len();
if self.visited.insert(next) {
push_inner::<I>(&mut self.stack, next);
debug!("next: stack={:?}", self.stack);
return Some(next);
}
}
}
}
/// We push `GenericArg`s on the stack in reverse order so as to
/// maintain a pre-order traversal. As of the time of this
/// writing, the fact that the traversal is pre-order is not
/// known to be significant to any code, but it seems like the
/// natural order one would expect (basically, the order of the
/// types as they are written).
fn push_inner<I: Interner>(stack: &mut TypeWalkerStack<I>, parent: I::GenericArg) {
match parent.kind() {
ty::GenericArgKind::Type(parent_ty) => match parent_ty.kind() {
ty::Bool
| ty::Char
| ty::Int(_)
| ty::Uint(_)
| ty::Float(_)
| ty::Str
| ty::Infer(_)
| ty::Param(_)
| ty::Never
| ty::Error(_)
| ty::Placeholder(..)
| ty::Bound(..)
| ty::Foreign(..) => {}
ty::Pat(ty, pat) => {
push_ty_pat::<I>(stack, pat);
stack.push(ty.into());
}
ty::Array(ty, len) => {
stack.push(len.into());
stack.push(ty.into());
}
ty::Slice(ty) => {
stack.push(ty.into());
}
ty::RawPtr(ty, _) => {
stack.push(ty.into());
}
ty::Ref(lt, ty, _) => {
stack.push(ty.into());
stack.push(lt.into());
}
ty::Alias(alias) => {
stack.extend(alias.args.iter().rev());
}
ty::Dynamic(obj, lt) => {
stack.push(lt.into());
stack.extend(
obj.iter()
.rev()
.filter_map(|predicate| {
let (args, opt_ty) = match predicate.skip_binder() {
ty::ExistentialPredicate::Trait(tr) => (tr.args, None),
ty::ExistentialPredicate::Projection(p) => (p.args, Some(p.term)),
ty::ExistentialPredicate::AutoTrait(_) => {
return None;
}
};
Some(args.iter().rev().chain(opt_ty.map(|term| match term.kind() {
ty::TermKind::Ty(ty) => ty.into(),
ty::TermKind::Const(ct) => ct.into(),
})))
})
.flatten(),
);
}
ty::Adt(_, args)
| ty::Closure(_, args)
| ty::CoroutineClosure(_, args)
| ty::Coroutine(_, args)
| ty::CoroutineWitness(_, args)
| ty::FnDef(_, args) => {
stack.extend(args.iter().rev());
}
ty::Tuple(ts) => stack.extend(ts.iter().rev().map(|ty| ty.into())),
ty::FnPtr(sig_tys, _hdr) => {
stack.extend(
sig_tys.skip_binder().inputs_and_output.iter().rev().map(|ty| ty.into()),
);
}
ty::UnsafeBinder(bound_ty) => {
stack.push(bound_ty.skip_binder().into());
}
},
ty::GenericArgKind::Lifetime(_) => {}
ty::GenericArgKind::Const(parent_ct) => match parent_ct.kind() {
ty::ConstKind::Infer(_)
| ty::ConstKind::Param(_)
| ty::ConstKind::Placeholder(_)
| ty::ConstKind::Bound(..)
| ty::ConstKind::Error(_) => {}
ty::ConstKind::Value(cv) => stack.push(cv.ty().into()),
ty::ConstKind::Expr(expr) => stack.extend(expr.args().iter().rev()),
ty::ConstKind::Unevaluated(ct) => {
stack.extend(ct.args.iter().rev());
}
},
}
}
fn push_ty_pat<I: Interner>(stack: &mut TypeWalkerStack<I>, pat: I::Pat) {
match pat.kind() {
ty::PatternKind::Range { start, end } => {
stack.push(end.into());
stack.push(start.into());
}
ty::PatternKind::Or(pats) => {
for pat in pats.iter() {
push_ty_pat::<I>(stack, pat)
}
}
ty::PatternKind::NotNull => {}
}
}