bjoernager/rust
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generalize hr alias: avoid unconstrainable infer vars

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This commit is contained in:
lcnr 2024-05-06 21:33:57 +00:00
parent 31110152e2
commit 690d5aa417
7 changed files with 175 additions and 26 deletions
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44
compiler/rustc_infer/src/infer/relate/generalize.rs
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@ -350,7 +350,13 @@ impl<'tcx> Generalizer<'_, 'tcx> {
&mut self,
alias: ty::AliasTy<'tcx>,
) -> Result<Ty<'tcx>, TypeError<'tcx>> {
if self.infcx.next_trait_solver() && !alias.has_escaping_bound_vars() {
// We do not eagerly replace aliases with inference variables if they have
// escaping bound vars, see the method comment for details. However, when we
// are inside of an alias with escaping bound vars replacing nested aliases
// with inference variables can cause incorrect ambiguity.
//
// cc trait-system-refactor-initiative#110
if self.infcx.next_trait_solver() && !alias.has_escaping_bound_vars() && !self.in_alias {
return Ok(self.infcx.next_ty_var_in_universe(
TypeVariableOrigin { param_def_id: None, span: self.span },
self.for_universe,
@ -492,9 +498,30 @@ impl<'tcx> TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
let origin = inner.type_variables().var_origin(vid);
let new_var_id =
inner.type_variables().new_var(self.for_universe, origin);
let u = Ty::new_var(self.tcx(), new_var_id);
debug!("replacing original vid={:?} with new={:?}", vid, u);
Ok(u)
// If we're in the new solver and create a new inference
// variable inside of an alias we eagerly constrain that
// inference variable to prevent unexpected ambiguity errors.
//
// This is incomplete as it pulls down the universe of the
// original inference variable, even though the alias could
// normalize to a type which does not refer to that type at
// all. I don't expect this to cause unexpected errors in
// practice.
//
// We only need to do so for type and const variables, as
// region variables do not impact normalization, and will get
// correctly constrained by `AliasRelate` later on.
//
// cc trait-system-refactor-initiative#108
if self.infcx.next_trait_solver()
&& !self.infcx.intercrate
&& self.in_alias
{
inner.type_variables().equate(vid, new_var_id);
}
debug!("replacing original vid={:?} with new={:?}", vid, new_var_id);
Ok(Ty::new_var(self.tcx(), new_var_id))
}
}
}
@ -614,6 +641,15 @@ impl<'tcx> TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
universe: self.for_universe,
})
.vid;
// See the comment for type inference variables
// for more details.
if self.infcx.next_trait_solver()
&& !self.infcx.intercrate
&& self.in_alias
{
variable_table.union(vid, new_var_id);
}
Ok(ty::Const::new_var(self.tcx(), new_var_id, c.ty()))
}
}