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Simplify the collecting of ? Trait bounds in where clause #87338

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Jul 24, 2021
Merged

Simplify the collecting of ? Trait bounds in where clause #87338

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7af840f
Simplify the collecting of `? Trait` bounds in where clause
Jul 21, 2021
0f5bfc2
Correct fmt
Jul 21, 2021
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50 changes: 17 additions & 33 deletions compiler/rustc_ast_lowering/src/item.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1373,50 +1373,34 @@ impl<'hir> LoweringContext<'_, 'hir> {
itctx: ImplTraitContext<'_, 'hir>,
) -> GenericsCtor<'hir> {
// Collect `?Trait` bounds in where clause and move them to parameter definitions.
// FIXME: this could probably be done with less rightward drift. It also looks like two
// control paths where `report_error` is called are the only paths that advance to after the
// match statement, so the error reporting could probably just be moved there.
let mut add_bounds: NodeMap<Vec<_>> = Default::default();
for pred in &generics.where_clause.predicates {
if let WherePredicate::BoundPredicate(ref bound_pred) = *pred {
'next_bound: for bound in &bound_pred.bounds {
if let GenericBound::Trait(_, TraitBoundModifier::Maybe) = *bound {
let report_error = |this: &mut Self| {
this.diagnostic().span_err(
bound_pred.bounded_ty.span,
"`?Trait` bounds are only permitted at the \
point where a type parameter is declared",
);
};
// Check if the where clause type is a plain type parameter.
match bound_pred.bounded_ty.kind {
TyKind::Path(None, ref path)
if path.segments.len() == 1
&& bound_pred.bound_generic_params.is_empty() =>
match self
.resolver
.get_partial_res(bound_pred.bounded_ty.id)
.map(|d| (d.base_res(), d.unresolved_segments()))
{
Some((Res::Def(DefKind::TyParam, def_id), 0))
if bound_pred.bound_generic_params.is_empty() =>
{
if let Some(Res::Def(DefKind::TyParam, def_id)) = self
.resolver
.get_partial_res(bound_pred.bounded_ty.id)
.map(|d| d.base_res())
{
if let Some(def_id) = def_id.as_local() {
for param in &generics.params {
if let GenericParamKind::Type { .. } = param.kind {
if def_id == self.resolver.local_def_id(param.id) {
add_bounds
.entry(param.id)
.or_default()
.push(bound.clone());
continue 'next_bound;
}
}
}
for param in &generics.params {
if def_id == self.resolver.local_def_id(param.id).to_def_id() {
add_bounds.entry(param.id).or_default().push(bound.clone());
continue 'next_bound;
}
}
report_error(self)
}
_ => report_error(self),
_ => {}
}
self.diagnostic().span_err(
bound_pred.bounded_ty.span,
"`?Trait` bounds are only permitted at the \
point where a type parameter is declared",
);
}
}
}
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