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fix: Function argument type inference with associated type impl trait #16769

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merged 1 commit into from Mar 6, 2024
Merged

fix: Function argument type inference with associated type impl trait #16769

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96 changes: 85 additions & 11 deletions crates/hir-ty/src/lower.rs
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Expand Up @@ -995,12 +995,12 @@ impl<'a> TyLoweringContext<'a> {

pub(crate) fn lower_type_bound(
&'a self,
bound: &'a TypeBound,
bound: &'a Interned<TypeBound>,
self_ty: Ty,
ignore_bindings: bool,
) -> impl Iterator<Item = QuantifiedWhereClause> + 'a {
let mut bindings = None;
let trait_ref = match bound {
let trait_ref = match bound.as_ref() {
TypeBound::Path(path, TraitBoundModifier::None) => {
bindings = self.lower_trait_ref_from_path(path, Some(self_ty));
bindings
Expand Down Expand Up @@ -1055,10 +1055,10 @@ impl<'a> TyLoweringContext<'a> {

fn assoc_type_bindings_from_type_bound(
&'a self,
bound: &'a TypeBound,
bound: &'a Interned<TypeBound>,
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Changed the argument type into Interned for faster equality comparision

trait_ref: TraitRef,
) -> impl Iterator<Item = QuantifiedWhereClause> + 'a {
let last_segment = match bound {
let last_segment = match bound.as_ref() {
TypeBound::Path(path, TraitBoundModifier::None) | TypeBound::ForLifetime(_, path) => {
path.segments().last()
}
Expand Down Expand Up @@ -1121,7 +1121,63 @@ impl<'a> TyLoweringContext<'a> {
);
}
} else {
let ty = self.lower_ty(type_ref);
let ty = 'ty: {
if matches!(
self.impl_trait_mode,
ImplTraitLoweringState::Param(_)
| ImplTraitLoweringState::Variable(_)
) {
// Find the generic index for the target of our `bound`
let target_param_idx = self
.resolver
.where_predicates_in_scope()
.find_map(|p| match p {
WherePredicate::TypeBound {
target: WherePredicateTypeTarget::TypeOrConstParam(idx),
bound: b,
} if b == bound => Some(idx),
_ => None,
});
if let Some(target_param_idx) = target_param_idx {
let mut counter = 0;
for (idx, data) in self.generics().params.type_or_consts.iter()
{
// Count the number of `impl Trait` things that appear before
// the target of our `bound`.
// Our counter within `impl_trait_mode` should be that number
// to properly lower each types within `type_ref`
if data.type_param().is_some_and(|p| {
p.provenance == TypeParamProvenance::ArgumentImplTrait
}) {
counter += 1;
}
if idx == *target_param_idx {
break;
}
}
let mut ext = TyLoweringContext::new_maybe_unowned(
self.db,
self.resolver,
self.owner,
)
.with_type_param_mode(self.type_param_mode);
match &self.impl_trait_mode {
ImplTraitLoweringState::Param(_) => {
ext.impl_trait_mode =
ImplTraitLoweringState::Param(Cell::new(counter));
}
ImplTraitLoweringState::Variable(_) => {
ext.impl_trait_mode = ImplTraitLoweringState::Variable(
Cell::new(counter),
);
}
_ => unreachable!(),
}
break 'ty ext.lower_ty(type_ref);
}
}
self.lower_ty(type_ref)
};
let alias_eq =
AliasEq { alias: AliasTy::Projection(projection_ty.clone()), ty };
predicates.push(crate::wrap_empty_binders(WhereClause::AliasEq(alias_eq)));
Expand Down Expand Up @@ -1403,8 +1459,14 @@ pub(crate) fn generic_predicates_for_param_query(
assoc_name: Option<Name>,
) -> Arc<[Binders<QuantifiedWhereClause>]> {
let resolver = def.resolver(db.upcast());
let ctx = TyLoweringContext::new(db, &resolver, def.into())
.with_type_param_mode(ParamLoweringMode::Variable);
let ctx = if let GenericDefId::FunctionId(_) = def {
TyLoweringContext::new(db, &resolver, def.into())
.with_impl_trait_mode(ImplTraitLoweringMode::Variable)
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impl Traits that appear in the function arguments should be handled as generic parameters with trait implementation predicates. So, we handle impl Trait by the same way with the type parameters.

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I wonder if we should just require the modes to specified in the new constructor. Feels like an easy to cause bug by relying on a default.

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That would be better. Actually, I've been considering giving a shot for #16584 while writing this PR and that would require some changes to lower.rs. It would be good to apply your suggestions while making that changes

.with_type_param_mode(ParamLoweringMode::Variable)
} else {
TyLoweringContext::new(db, &resolver, def.into())
.with_type_param_mode(ParamLoweringMode::Variable)
};
let generics = generics(db.upcast(), def);

// we have to filter out all other predicates *first*, before attempting to lower them
Expand Down Expand Up @@ -1490,8 +1552,14 @@ pub(crate) fn trait_environment_query(
def: GenericDefId,
) -> Arc<TraitEnvironment> {
let resolver = def.resolver(db.upcast());
let ctx = TyLoweringContext::new(db, &resolver, def.into())
.with_type_param_mode(ParamLoweringMode::Placeholder);
let ctx = if let GenericDefId::FunctionId(_) = def {
TyLoweringContext::new(db, &resolver, def.into())
.with_impl_trait_mode(ImplTraitLoweringMode::Param)
.with_type_param_mode(ParamLoweringMode::Placeholder)
} else {
TyLoweringContext::new(db, &resolver, def.into())
.with_type_param_mode(ParamLoweringMode::Placeholder)
};
let mut traits_in_scope = Vec::new();
let mut clauses = Vec::new();
for pred in resolver.where_predicates_in_scope() {
Expand Down Expand Up @@ -1549,8 +1617,14 @@ pub(crate) fn generic_predicates_query(
def: GenericDefId,
) -> Arc<[Binders<QuantifiedWhereClause>]> {
let resolver = def.resolver(db.upcast());
let ctx = TyLoweringContext::new(db, &resolver, def.into())
.with_type_param_mode(ParamLoweringMode::Variable);
let ctx = if let GenericDefId::FunctionId(_) = def {
TyLoweringContext::new(db, &resolver, def.into())
.with_impl_trait_mode(ImplTraitLoweringMode::Variable)
.with_type_param_mode(ParamLoweringMode::Variable)
} else {
TyLoweringContext::new(db, &resolver, def.into())
.with_type_param_mode(ParamLoweringMode::Variable)
};
let generics = generics(db.upcast(), def);

let mut predicates = resolver
Expand Down
47 changes: 47 additions & 0 deletions crates/hir-ty/src/tests/traits.rs
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Expand Up @@ -1231,6 +1231,53 @@ fn test(x: impl Trait<u64>, y: &impl Trait<u64>) {
);
}

#[test]
fn argument_impl_trait_with_projection() {
check_infer(
r#"
trait X {
type Item;
}

impl<T> X for [T; 2] {
type Item = T;
}

trait Y {}

impl<T> Y for T {}

enum R<T, U> {
A(T),
B(U),
}

fn foo<T>(x: impl X<Item = R<impl Y, T>>) -> T { loop {} }

fn bar() {
let a = foo([R::A(()), R::B(7)]);
}
"#,
expect![[r#"
153..154 'x': impl X<Item = R<impl Y + ?Sized, T>> + ?Sized
190..201 '{ loop {} }': T
192..199 'loop {}': !
197..199 '{}': ()
212..253 '{ ...)]); }': ()
222..223 'a': i32
226..229 'foo': fn foo<i32>([R<(), i32>; 2]) -> i32
226..250 'foo([R...B(7)])': i32
230..249 '[R::A(...:B(7)]': [R<(), i32>; 2]
231..235 'R::A': extern "rust-call" A<(), i32>(()) -> R<(), i32>
231..239 'R::A(())': R<(), i32>
236..238 '()': ()
241..245 'R::B': extern "rust-call" B<(), i32>(i32) -> R<(), i32>
241..248 'R::B(7)': R<(), i32>
246..247 '7': i32
"#]],
);
}

#[test]
fn simple_return_pos_impl_trait() {
cov_mark::check!(lower_rpit);
Expand Down