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Check WF of predicates with defaults only if all params have defaults

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This commit is contained in:
leonardo.yvens 2018-01-22 13:36:51 -02:00
parent addc404d32
commit 75997d85c5
5 changed files with 65 additions and 55 deletions
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7
src/librustc/ty/mod.rs
View file

@ -1040,13 +1040,6 @@ impl<'a, 'gcx, 'tcx> Predicate<'tcx> {
Predicate::ConstEvaluatable(def_id, const_substs.subst(tcx, substs)),
}
}
pub fn as_poly_trait_predicate(&self) -> Option<&PolyTraitPredicate<'tcx>> {
match self {
Predicate::Trait(trait_pred) => Some(trait_pred),
_ => None
}
}
}
#[derive(Clone, Copy, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]

57
src/librustc_typeck/check/wfcheck.rs
View file

@ -392,14 +392,13 @@ impl<'a, 'gcx> CheckTypeWellFormedVisitor<'a, 'gcx> {
// Check that trait predicates are WF when params are substituted by their defaults.
// We don't want to overly constrain the predicates that may be written but we
// want to catch obviously wrong cases such as `struct Foo<T: Copy = String>`
// or cases that may cause backwards incompatibility such as a library going from
// `pub struct Foo<T>` to `pub struct Foo<T, U = i32>` where U: Trait<T>`
// which may break existing uses of Foo<T>.
// Therefore the check we do is: If if all params appearing in the LHS of the predicate
// have defaults then we verify that it is WF with all defaults substituted simultaneously.
// or cases where defaults don't work together such as:
// `struct Foo<T = i32, U = u8> where T: into<U>`
// Therefore we check if a predicate in which all type params are defaulted
// is WF with those defaults simultaneously substituted.
// For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
//
// First, we build the defaulted substitution.
// First we build the defaulted substitution.
let mut defaulted_params = Vec::new();
let substs = ty::subst::Substs::for_item(fcx.tcx, def_id, |def, _| {
// All regions are identity.
@ -414,33 +413,35 @@ impl<'a, 'gcx> CheckTypeWellFormedVisitor<'a, 'gcx> {
fcx.tcx.type_of(def.def_id)
}
});
// In `trait Trait: Super`, checking `Self: Trait` or `Self: Super` is problematic.
// We avoid those by skipping any predicates in trait declarations that contain `Self`,
// which is excessive so we end up checking less than we could.
for pred in predicates.predicates.iter()
.filter_map(ty::Predicate::as_poly_trait_predicate)
.filter(|p| !(is_trait && p.has_self_ty())) {
let is_defaulted_param = |ty: ty::Ty| match ty.sty {
ty::TyParam(p) => defaulted_params.contains(&p.idx),
_ => false
};
// If there is a non-defaulted param in the LHS, don't check the substituted predicate.
// `skip_binder()` is ok, we're only inspecting the type params.
if !pred.skip_binder().self_ty().walk().all(is_defaulted_param) {
let defaulted_params = &defaulted_params;
// Now we build the substituted predicates.
for &pred in predicates.predicates.iter() {
struct HasNonDefaulted<'a> { defaulted_params: &'a Vec<u32> }
impl<'tcx, 'a> ty::fold::TypeVisitor<'tcx> for HasNonDefaulted<'a> {
fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
match t.sty {
ty::TyParam(p) => !self.defaulted_params.contains(&p.idx),
_ => t.super_visit_with(self)
}
}
}
// If there is a non-defaulted param in the predicate, don't check it.
if pred.visit_with(&mut HasNonDefaulted { defaulted_params }) {
continue;
}
let substituted_pred = pred.subst(fcx.tcx, substs);
// `skip_binder()` is ok, we're only inspecting for `has_self_ty()`.
let substituted_lhs = substituted_pred.skip_binder().self_ty();
// In trait defs, don't check `Self: Sized` when `Self` is the default.
let pred_is_sized = Some(pred.def_id()) == fcx.tcx.lang_items().sized_trait();
if is_trait && substituted_lhs.has_self_ty() && pred_is_sized {
continue;
if let ty::Predicate::Trait(trait_pred) = substituted_pred {
// `skip_binder()` is ok, we're only inspecting for `has_self_ty()`.
let lhs_is_self = trait_pred.skip_binder().self_ty().has_self_ty();
let pred_sized = Some(trait_pred.def_id()) == fcx.tcx.lang_items().sized_trait();
if is_trait && lhs_is_self && pred_sized {
continue;
}
}
let pred = ty::Predicate::Trait(pred.subst(fcx.tcx, substs));
// Avoid duplicates.
if !predicates.predicates.contains(&pred) {
substituted_predicates.push(pred);
// Avoid duplication of predicates that contain no parameters, for example.
if !predicates.predicates.contains(&substituted_pred) {
substituted_predicates.push(substituted_pred);
}
}

10
src/test/run-pass/defaults-well-formedness.rs
View file

@ -11,11 +11,13 @@
trait Trait<T> {}
struct Foo<U, V=i32>(U, V) where U: Trait<V>;
trait Trait2 {}
trait Marker {}
struct TwoParams<T, U>(T, U);
impl Trait2 for TwoParams<i32, i32> {}
impl Marker for TwoParams<i32, i32> {}
// Check that defaults are substituted simultaneously.
struct IndividuallyBogus<T = i32, U = i32>(TwoParams<T, U>) where TwoParams<T, U>: Trait2;
struct IndividuallyBogus<T = i32, U = i32>(TwoParams<T, U>) where TwoParams<T, U>: Marker;
// Clauses with non-defaulted params are not checked.
struct NonDefaultedInClause<T, U = i32>(TwoParams<T, U>) where TwoParams<T, U>: Trait2;
struct NonDefaultedInClause<T, U = i32>(TwoParams<T, U>) where TwoParams<T, U>: Marker;
struct DefaultedLhs<U, V=i32>(U, V) where V: Trait<U>;
fn main() {}

15
src/test/ui/type-check-defaults.rs
View file

@ -37,11 +37,14 @@ trait Super<T: Copy> { }
trait Base<T = String>: Super<T> { }
//~^ error: the trait bound `T: std::marker::Copy` is not satisfied [E0277]
trait Trait<T> {}
struct DefaultedLhs<U, V=i32>(U, V) where V: Trait<U>;
//~^ error: the trait bound `i32: Trait<U>` is not satisfied [E0277]
trait ProjectionPred<T:Iterator = IntoIter<i32>> where T::Item : Add<u8> {}
//~^ error: the trait bound `i32: std::ops::Add<u8>` is not satisfied [E0277]
// Defaults must work together.
struct TwoParams<T = u32, U = i32>(T, U) where T: Bar<U>;
//~^ the trait bound `u32: Bar<i32>` is not satisfied [E0277]
trait Bar<V> {}
impl Bar<String> for u32 { }
impl Bar<i32> for String { }
// FIXME: Deal with projection predicates
// trait ProjectionPred<T:Iterator = IntoIter<i32>> where T::Item : Add<u8> {}
// ~^ error: the trait bound `i32: std::ops::Add<u8>` is not satisfied [E0277]
fn main() { }

31
src/test/ui/type-check-defaults.stderr
View file

@ -79,17 +79,28 @@ note: required by `Super`
36 | trait Super<T: Copy> { }
| ^^^^^^^^^^^^^^^^^^^^
error[E0277]: the trait bound `i32: Trait<U>` is not satisfied
--> $DIR/type-check-defaults.rs:41:1
|
41 | struct DefaultedLhs<U, V=i32>(U, V) where V: Trait<U>;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Trait<U>` is not implemented for `i32`
|
note: required by `Trait`
error[E0277]: the trait bound `i32: std::ops::Add<u8>` is not satisfied
--> $DIR/type-check-defaults.rs:40:1
|
40 | trait Trait<T> {}
| ^^^^^^^^^^^^^^
40 | trait ProjectionPred<T:Iterator = IntoIter<i32>> where T::Item : Add<u8> {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ no implementation for `i32 + u8`
|
= help: the trait `std::ops::Add<u8>` is not implemented for `i32`
= note: required by `std::ops::Add`
error: aborting due to 9 previous errors
error[E0277]: the trait bound `u32: Bar<i32>` is not satisfied
--> $DIR/type-check-defaults.rs:44:1
|
44 | struct TwoParams<T = u32, U = i32>(T, U) where T: Bar<U>;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Bar<i32>` is not implemented for `u32`
|
= help: the following implementations were found:
<u32 as Bar<std::string::String>>
note: required by `Bar`
--> $DIR/type-check-defaults.rs:46:1
|
46 | trait Bar<V> {}
| ^^^^^^^^^^^^
error: aborting due to 10 previous errors