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Fix completion with a partially unknown type

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To test whether the receiver type matches for the impl, we unify the given self
type (in this case `HashSet<{unknown}>`) with the self type of the
impl (`HashSet<?0>`), but if the given self type contains Unknowns, they won't
be unified with the variables in those places. So we got a receiver type that
was different from the expected one, and concluded the impl doesn't match.

The fix is slightly hacky; if after the unification, our variables are still
there, we make them fall back to Unknown. This does make some sense though,
since we don't want to 'leak' the variables.

Fixes #3547.
This commit is contained in:
Florian Diebold 2020-03-10 20:56:26 +01:00
parent e5df8c4028
commit adc7b8ea2d
2 changed files with 56 additions and 3 deletions
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28
crates/ra_hir_ty/src/method_resolution.rs
View file

@ -516,9 +516,31 @@ pub(crate) fn inherent_impl_substs(
let self_ty_with_vars =
Canonical { num_vars: vars.len() + self_ty.num_vars, value: self_ty_with_vars };
let substs = super::infer::unify(&self_ty_with_vars, self_ty);
// we only want the substs for the vars we added, not the ones from self_ty
let result = substs.map(|s| s.suffix(vars.len()));
result
// We only want the substs for the vars we added, not the ones from self_ty.
// Also, if any of the vars we added are still in there, we replace them by
// Unknown. I think this can only really happen if self_ty contained
// Unknown, and in that case we want the result to contain Unknown in those
// places again.
substs.map(|s| fallback_bound_vars(s.suffix(vars.len()), self_ty.num_vars))
}
/// This replaces any 'free' Bound vars in `s` (i.e. those with indices past
/// num_vars_to_keep) by `Ty::Unknown`.
fn fallback_bound_vars(s: Substs, num_vars_to_keep: usize) -> Substs {
s.fold_binders(
&mut |ty, binders| {
if let Ty::Bound(idx) = &ty {
if *idx >= binders as u32 {
Ty::Unknown
} else {
ty
}
} else {
ty
}
},
num_vars_to_keep,
)
}
fn transform_receiver_ty(