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//! Unification and canonicalization logic.
use super::{InferenceContext, Ty, TraitRef, InferTy, HirDatabase};
impl<'a, D: HirDatabase> InferenceContext<'a, D> {
pub(super) fn canonicalizer<'b>(&'b mut self) -> Canonicalizer<'a, 'b, D>
where
'a: 'b,
{
Canonicalizer { ctx: self, free_vars: Vec::new() }
}
}
// TODO improve the interface of this
// TODO move further up?
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub(crate) struct Canonical<T> {
pub value: T,
pub num_vars: usize,
}
pub(super) struct Canonicalizer<'a, 'b, D: HirDatabase>
where
'a: 'b,
{
pub ctx: &'b mut InferenceContext<'a, D>,
pub free_vars: Vec<InferTy>,
}
impl<'a, 'b, D: HirDatabase> Canonicalizer<'a, 'b, D>
where
'a: 'b,
{
fn add(&mut self, free_var: InferTy) -> usize {
self.free_vars.iter().position(|&v| v == free_var).unwrap_or_else(|| {
let next_index = self.free_vars.len();
self.free_vars.push(free_var);
next_index
})
}
pub fn canonicalize_ty(&mut self, ty: Ty) -> Canonical<Ty> {
let value = ty.fold(&mut |ty| match ty {
Ty::Infer(tv) => {
let inner = tv.to_inner();
// TODO prevent infinite loops? => keep var stack
if let Some(known_ty) = self.ctx.var_unification_table.probe_value(inner).known() {
self.canonicalize_ty(known_ty.clone()).value
} else {
let free_var = InferTy::TypeVar(self.ctx.var_unification_table.find(inner));
let position = self.add(free_var);
Ty::Bound(position as u32)
}
}
_ => ty,
});
Canonical { value, num_vars: self.free_vars.len() }
}
pub fn canonicalize_trait_ref(&mut self, trait_ref: TraitRef) -> Canonical<TraitRef> {
let substs = trait_ref
.substs
.iter()
.map(|ty| self.canonicalize_ty(ty.clone()).value)
.collect::<Vec<_>>();
let value = TraitRef { trait_: trait_ref.trait_, substs: substs.into() };
Canonical { value, num_vars: self.free_vars.len() }
}
pub fn apply_solution(&mut self, solution: Canonical<Vec<Ty>>) {
// the solution may contain new variables, which we need to convert to new inference vars
let new_vars =
(0..solution.num_vars).map(|_| self.ctx.new_type_var()).collect::<Vec<_>>().into();
for (i, ty) in solution.value.into_iter().enumerate() {
let var = self.free_vars[i].clone();
self.ctx.unify(&Ty::Infer(var), &ty.subst_bound_vars(&new_vars));
}
}
}
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