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Fix an implied bound related to assoc types according to #12 #176

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Merged
merged 1 commit into from
Oct 9, 2018
Merged

Fix an implied bound related to assoc types according to #12 #176

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35 changes: 23 additions & 12 deletions src/rules.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -107,7 +107,7 @@ impl ImplDatum {
/// Given `impl<T: Clone> Clone for Vec<T>`, generate:
///
/// ```notrust
/// forall<T> { (Vec<T>: Clone) :- (T: Clone) }
/// forall<T> { Implemented(Vec<T>: Clone) :- Implemented(T: Clone) }
/// ```
fn to_program_clause(&self) -> ProgramClause {
self.binders
Expand Down Expand Up @@ -137,9 +137,9 @@ impl DefaultImplDatum {
///
/// ```notrust
/// forall<T> {
/// (MyList<T>: Send) :-
/// (T: Send),
/// (Box<Option<MyList<T>>>: Send)
/// Implemented(MyList<T>: Send) :-
/// Implemented(T: Send),
/// Implemented(Box<Option<MyList<T>>>: Send)
/// }
/// ```
fn to_program_clause(&self) -> ProgramClause {
Expand Down Expand Up @@ -179,8 +179,8 @@ impl AssociatedTyValue {
/// ```notrust
/// forall<'a, T> {
/// Normalize(<Vec<T> as Iterable>::IntoIter<'a> -> Iter<'a, T>>) :-
/// (Vec<T>: Iterable), // (1)
/// (Iter<'a, T>: 'a) // (2)
/// Implemented(Vec<T>: Iterable), // (1)
/// Implemented(Iter<'a, T>: 'a) // (2)
/// }
/// ```
///
Expand Down Expand Up @@ -304,7 +304,7 @@ impl StructDatum {
//
// we generate the following clauses:
//
// forall<T> { WF(Foo<T>) :- (T: Eq). }
// forall<T> { WF(Foo<T>) :- Implemented(T: Eq). }
// forall<T> { FromEnv(T: Eq) :- FromEnv(Foo<T>). }
// forall<T> { IsFullyVisible(Foo<T>) :- IsFullyVisible(T) }
//
Expand Down Expand Up @@ -456,7 +456,7 @@ impl TraitDatum {
// we generate the following clause:
//
// forall<Self, T> {
// WF(Self: Ord<T>) :- (Self: Ord<T>), WF(Self: Eq<T>)
// WF(Self: Ord<T>) :- Implemented(Self: Ord<T>), WF(Self: Eq<T>)
// }
//
// and the reverse rules:
Expand Down Expand Up @@ -786,7 +786,7 @@ impl AssociatedTyDatum {
// Well-formedness of projection type.
//
// forall<Self> {
// WellFormed((Foo::Assoc)<Self>) :- Self: Foo, WC.
// WellFormed((Foo::Assoc)<Self>) :- Implemented(Self: Foo), WC.
// }
clauses.push(
Binders {
Expand Down Expand Up @@ -837,12 +837,23 @@ impl AssociatedTyDatum {

// Reverse rule for implied bounds.
//
// forall<T> {
// FromEnv(<T as Foo>::Assoc: Bounds) :- FromEnv(Self: Foo)
// forall<Self> {
// FromEnv(<Self as Foo>::Assoc: Bounds) :- FromEnv(Self: Foo), FromEnv(WC)
// }
clauses.extend(self.bounds_on_self().into_iter().map(|bound| {
// Same as above in case of higher-ranked inline bounds.
let shift = bound.binders.len();
let from_env_trait = iter::once(
FromEnv::Trait(trait_ref.clone()).shifted_in(shift).cast()
);

let where_clauses = self.where_clauses
.iter()
.cloned()
// `wc` may be a higher-ranked where clause
.map(|wc| wc.map(|value| value.into_from_env_goal()))
.casted();

Binders {
binders: bound
.binders
Expand All @@ -852,7 +863,7 @@ impl AssociatedTyDatum {
.collect(),
value: ProgramClauseImplication {
consequence: bound.value.clone().into_from_env_goal(),
conditions: vec![FromEnv::Trait(trait_ref.clone()).shifted_in(shift).cast()],
conditions: from_env_trait.chain(where_clauses).collect(),
},
}.cast()
}));
Expand Down
75 changes: 75 additions & 0 deletions src/rules/wf/test.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -563,3 +563,78 @@ fn higher_ranked_inline_bound_on_gat() {
}
}
}

#[test]
fn assoc_type_recursive_bound() {
lowering_error! {
program {
trait Sized { }
trait Print {
// fn print();
}

trait Foo {
type Item: Sized where <Self as Foo>::Item: Sized;
}

struct i32 { }
struct str { } // not sized

impl Foo for i32 {
// Well-formedness checks require that the following
// goal is true:
// ```
// if (str: Sized) { # if the where clauses hold
// str: Sized # then the bound on the associated type hold
// }
// ```
// which it is :)
type Item = str;
}

struct OnlySized<T> where T: Sized { }
impl<T> Print for OnlySized<T> {
// fn print() {
// println!("{}", std::mem::size_of::<T>());
// }
}

trait Bar {
type Assoc: Print;
}

impl<T> Bar for T where T: Foo {
type Assoc = OnlySized<<T as Foo>::Item>;
}

// Above, we used to incorrectly assume that `OnlySized<<T as Foo>::Item>`
// is well-formed because of the `FromEnv(T: Foo)`, hence making the `T: Bar`
// impl pass the well-formedness check. But the following query will
// (and should) always succeed, as there is no where clauses on `Assoc`:
// ```
// forall<T> { if (T: Bar) { WellFormed(<T as Bar>::Assoc) } }
// ```
//
// This may lead to the following code to compile:

// ```
// fn foo<T: Print>() {
// T::print() // oops, in fact `T = OnlySized<str>` which is ill-formed
// }

// fn bar<T: Bar> {
// // ok, we have `FromEnv(T: Bar)` hence
// // `<T as Bar>::Assoc` is well-formed and
// // `Implemented(<T as Bar>::Assoc: Print)` hold
// foo<<T as Bar>::Assoc>(
// }

// fn main() {
// bar::<i32>() // ok, `Implemented(i32: Bar)` hold
// }
// ```
} error_msg {
"trait impl for \"Bar\" does not meet well-formedness requirements"
}
}
}