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|
//! An iterator over the type substructure.
//! WARNING: this does not keep track of the region depth.
use crate::ty::subst::{GenericArg, GenericArgKind};
use crate::ty::{self, Ty};
use rustc_data_structures::sso::SsoHashSet;
use smallvec::{self, SmallVec};
// The TypeWalker's stack is hot enough that it's worth going to some effort to
// avoid heap allocations.
type TypeWalkerStack<'tcx> = SmallVec<[GenericArg<'tcx>; 8]>;
pub struct TypeWalker<'tcx> {
stack: TypeWalkerStack<'tcx>,
last_subtree: usize,
pub visited: SsoHashSet<GenericArg<'tcx>>,
}
/// 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.
impl<'tcx> TypeWalker<'tcx> {
pub fn new(root: GenericArg<'tcx>) -> 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<'tcx> Iterator for TypeWalker<'tcx> {
type Item = GenericArg<'tcx>;
fn next(&mut self) -> Option<GenericArg<'tcx>> {
debug!("next(): stack={:?}", self.stack);
loop {
let next = self.stack.pop()?;
self.last_subtree = self.stack.len();
if self.visited.insert(next) {
push_inner(&mut self.stack, next);
debug!("next: stack={:?}", self.stack);
return Some(next);
}
}
}
}
impl<'tcx> GenericArg<'tcx> {
/// Iterator that walks `self` and any types reachable from
/// `self`, in depth-first order. Note that just walks the types
/// that appear in `self`, it does not descend into the fields of
/// structs or variants. For example:
///
/// ```text
/// isize => { isize }
/// Foo<Bar<isize>> => { Foo<Bar<isize>>, Bar<isize>, isize }
/// [isize] => { [isize], isize }
/// ```
pub fn walk(self) -> TypeWalker<'tcx> {
TypeWalker::new(self)
}
/// Iterator that walks the immediate children of `self`. Hence
/// `Foo<Bar<i32>, u32>` yields the sequence `[Bar<i32>, u32]`
/// (but not `i32`, like `walk`).
///
/// Iterator only walks items once.
/// It accepts visited set, updates it with all visited types
/// and skips any types that are already there.
pub fn walk_shallow(
self,
visited: &mut SsoHashSet<GenericArg<'tcx>>,
) -> impl Iterator<Item = GenericArg<'tcx>> {
let mut stack = SmallVec::new();
push_inner(&mut stack, self);
stack.retain(|a| visited.insert(*a));
stack.into_iter()
}
}
impl<'tcx> Ty<'tcx> {
/// Iterator that walks `self` and any types reachable from
/// `self`, in depth-first order. Note that just walks the types
/// that appear in `self`, it does not descend into the fields of
/// structs or variants. For example:
///
/// ```text
/// isize => { isize }
/// Foo<Bar<isize>> => { Foo<Bar<isize>>, Bar<isize>, isize }
/// [isize] => { [isize], isize }
/// ```
pub fn walk(self) -> TypeWalker<'tcx> {
TypeWalker::new(self.into())
}
}
impl<'tcx> ty::Const<'tcx> {
/// Iterator that walks `self` and any types reachable from
/// `self`, in depth-first order. Note that just walks the types
/// that appear in `self`, it does not descend into the fields of
/// structs or variants. For example:
///
/// ```text
/// isize => { isize }
/// Foo<Bar<isize>> => { Foo<Bar<isize>>, Bar<isize>, isize }
/// [isize] => { [isize], isize }
/// ```
pub fn walk(self) -> TypeWalker<'tcx> {
TypeWalker::new(self.into())
}
}
/// 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<'tcx>(stack: &mut TypeWalkerStack<'tcx>, parent: GenericArg<'tcx>) {
match parent.unpack() {
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::Array(ty, len) => {
stack.push(len.into());
stack.push(ty.into());
}
ty::Slice(ty) => {
stack.push(ty.into());
}
ty::RawPtr(mt) => {
stack.push(mt.ty.into());
}
ty::Ref(lt, ty, _) => {
stack.push(ty.into());
stack.push(lt.into());
}
ty::Projection(data) => {
stack.extend(data.substs.iter().rev());
}
ty::Dynamic(obj, lt, _) => {
stack.push(lt.into());
stack.extend(obj.iter().rev().flat_map(|predicate| {
let (substs, opt_ty) = match predicate.skip_binder() {
ty::ExistentialPredicate::Trait(tr) => (tr.substs, None),
ty::ExistentialPredicate::Projection(p) => (p.substs, Some(p.term)),
ty::ExistentialPredicate::AutoTrait(_) =>
// Empty iterator
{
(ty::InternalSubsts::empty(), None)
}
};
substs.iter().rev().chain(opt_ty.map(|term| match term.unpack() {
ty::TermKind::Ty(ty) => ty.into(),
ty::TermKind::Const(ct) => ct.into(),
}))
}));
}
ty::Adt(_, substs)
| ty::Opaque(_, substs)
| ty::Closure(_, substs)
| ty::Generator(_, substs, _)
| ty::FnDef(_, substs) => {
stack.extend(substs.iter().rev());
}
ty::Tuple(ts) => stack.extend(ts.as_substs().iter().rev()),
ty::GeneratorWitness(ts) => {
stack.extend(ts.skip_binder().iter().rev().map(|ty| ty.into()));
}
ty::FnPtr(sig) => {
stack.push(sig.skip_binder().output().into());
stack.extend(sig.skip_binder().inputs().iter().copied().rev().map(|ty| ty.into()));
}
},
GenericArgKind::Lifetime(_) => {}
GenericArgKind::Const(parent_ct) => {
stack.push(parent_ct.ty().into());
match parent_ct.kind() {
ty::ConstKind::Infer(_)
| ty::ConstKind::Param(_)
| ty::ConstKind::Placeholder(_)
| ty::ConstKind::Bound(..)
| ty::ConstKind::Value(_)
| ty::ConstKind::Error(_) => {}
ty::ConstKind::Unevaluated(ct) => {
stack.extend(ct.substs.iter().rev());
}
}
}
}
}
|
