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12 changes: 9 additions & 3 deletions chalk-solve/src/clauses/builtin_traits.rs
Original file line number Diff line number Diff line change
Expand Up @@ -57,11 +57,17 @@ pub fn add_builtin_assoc_program_clauses<I: Interner>(
) -> Result<(), Floundered> {
match well_known {
WellKnownTrait::FnOnce => {
fn_family::add_fn_trait_program_clauses(db, builder, well_known, self_ty)?;
// If `self_ty` contains bound vars, we want to universally quantify them.
// `Generalize` collects them for us.
let generalized = generalize::Generalize::apply(db.interner(), &self_ty);

builder.push_binders(&generalized, |builder, self_ty| {
fn_family::add_fn_trait_program_clauses(db, builder, well_known, self_ty)?;
Ok(())
})
}
_ => {}
_ => Ok(()),
}
Ok(())
}

/// Given a trait ref `T0: Trait` and a list of types `U0..Un`, pushes a clause of the form
Expand Down
5 changes: 0 additions & 5 deletions chalk-solve/src/clauses/builtin_traits/fn_family.rs
Original file line number Diff line number Diff line change
Expand Up @@ -102,11 +102,6 @@ pub fn add_fn_trait_program_clauses<I: Interner>(
let bound = fn_def_datum
.binders
.substitute(builder.interner(), &apply.substitution);
let self_ty = ApplicationTy {
name: apply.name,
substitution: builder.substitution_in_scope(),
}
.intern(interner);
push_clauses_for_apply(
db,
builder,
Expand Down
68 changes: 68 additions & 0 deletions tests/test/fn_def.rs
Original file line number Diff line number Diff line change
Expand Up @@ -96,5 +96,73 @@ fn fn_def_implements_fn_traits() {
} yields {
"Unique"
}

goal {
bar: Fn<(i32,)>
} yields {
"Unique"
}

goal {
Normalize(<bar as FnOnce<(i32,)>>::Output -> ())
} yields {
"Unique"
}

goal {
baz: Fn<(i32,)>
} yields {
"Unique"
}

goal {
Normalize(<baz as FnOnce<(i32,)>>::Output -> u8)
} yields {
"Unique"
}
}
}

#[test]
fn generic_fn_implements_fn_traits() {
test! {
program {
#[lang(fn_once)]
trait FnOnce<Args> {
type Output;
}

#[lang(fn_mut)]
trait FnMut<Args> where Self: FnOnce<Args> { }

#[lang(fn)]
trait Fn<Args> where Self: FnMut<Args> { }

fn foo<T>(t: T) -> T;
}

goal {
exists<T> { foo<T>: Fn<(T,)> }
} yields {
"Unique"
}

goal {
forall<T> { foo<T>: Fn<(T,)> }
} yields {
"Unique"
}

goal {
exists<T> { Normalize(<foo<T> as FnOnce<(T,)>>::Output -> T) }
} yields {
"Unique"
}

goal {
forall<T> { Normalize(<foo<T> as FnOnce<(T,)>>::Output -> T) }
} yields {
"Unique"
}
}
}