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Pretty print quantified goals and clauses

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This commit is contained in:
scalexm 2018-10-31 18:55:40 +01:00
parent 64aac8d4c1
commit eacebf24b0
16 changed files with 198 additions and 79 deletions
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149
src/librustc/traits/structural_impls.rs
View file

@ -14,9 +14,11 @@ use traits;
use traits::project::Normalized;
use ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
use ty::{self, Lift, TyCtxt};
use syntax::symbol::InternedString;
use std::fmt;
use std::rc::Rc;
use std::collections::{BTreeSet, BTreeMap};
// structural impls for the structs in traits
@ -479,7 +481,12 @@ impl<'tcx> fmt::Display for traits::DomainGoal<'tcx> {
Holds(wc) => write!(fmt, "{}", wc),
WellFormed(wf) => write!(fmt, "{}", wf),
FromEnv(from_env) => write!(fmt, "{}", from_env),
Normalize(projection) => write!(fmt, "Normalize({})", projection),
Normalize(projection) => write!(
fmt,
"Normalize({} -> {})",
projection.projection_ty,
projection.ty
),
}
}
}
@ -495,6 +502,110 @@ impl fmt::Display for traits::QuantifierKind {
}
}
/// Collect names for regions / types bound by a quantified goal / clause.
/// This collector does not try to do anything clever like in ppaux, it's just used
/// for debug output in tests anyway.
struct BoundNamesCollector {
// Just sort by name because `BoundRegion::BrNamed` does not have a `BoundVar` index anyway.
regions: BTreeSet<InternedString>,
// Sort by `BoundVar` index, so usually this should be equivalent to the order given
// by the list of type parameters.
types: BTreeMap<u32, InternedString>,
binder_index: ty::DebruijnIndex,
}
impl BoundNamesCollector {
fn new() -> Self {
BoundNamesCollector {
regions: BTreeSet::new(),
types: BTreeMap::new(),
binder_index: ty::INNERMOST,
}
}
fn is_empty(&self) -> bool {
self.regions.is_empty() && self.types.is_empty()
}
fn write_names(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
let mut start = true;
for r in &self.regions {
if !start {
write!(fmt, ", ")?;
}
start = false;
write!(fmt, "{}", r)?;
}
for (_, t) in &self.types {
if !start {
write!(fmt, ", ")?;
}
start = false;
write!(fmt, "{}", t)?;
}
Ok(())
}
}
impl<'tcx> TypeVisitor<'tcx> for BoundNamesCollector {
fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> bool {
self.binder_index.shift_in(1);
let result = t.super_visit_with(self);
self.binder_index.shift_out(1);
result
}
fn visit_ty(&mut self, t: ty::Ty<'tcx>) -> bool {
use syntax::symbol::Symbol;
match t.sty {
ty::Bound(bound_ty) if bound_ty.index == self.binder_index => {
self.types.insert(
bound_ty.var.as_u32(),
match bound_ty.kind {
ty::BoundTyKind::Param(name) => name,
ty::BoundTyKind::Anon => Symbol::intern(
&format!("?{}", bound_ty.var.as_u32())
).as_interned_str(),
}
);
}
_ => (),
};
t.super_visit_with(self)
}
fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
use syntax::symbol::Symbol;
match r {
ty::ReLateBound(index, br) if *index == self.binder_index => {
match br {
ty::BoundRegion::BrNamed(_, name) => {
self.regions.insert(*name);
}
ty::BoundRegion::BrAnon(var) => {
self.regions.insert(Symbol::intern(
&format!("?'{}", var)
).as_interned_str());
}
_ => (),
}
}
_ => (),
};
r.super_visit_with(self)
}
}
impl<'tcx> fmt::Display for traits::Goal<'tcx> {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
use traits::GoalKind::*;
@ -514,8 +625,22 @@ impl<'tcx> fmt::Display for traits::Goal<'tcx> {
Not(goal) => write!(fmt, "not {{ {} }}", goal),
DomainGoal(goal) => write!(fmt, "{}", goal),
Quantified(qkind, goal) => {
// FIXME: appropriate binder names
write!(fmt, "{}<> {{ {} }}", qkind, goal.skip_binder())
let mut collector = BoundNamesCollector::new();
goal.skip_binder().visit_with(&mut collector);
if !collector.is_empty() {
write!(fmt, "{}<", qkind)?;
collector.write_names(fmt)?;
write!(fmt, "> {{ ")?;
}
write!(fmt, "{}", goal.skip_binder())?;
if !collector.is_empty() {
write!(fmt, " }}")?;
}
Ok(())
}
CannotProve => write!(fmt, "CannotProve"),
}
@ -546,8 +671,22 @@ impl<'tcx> fmt::Display for traits::Clause<'tcx> {
match self {
Implies(clause) => write!(fmt, "{}", clause),
ForAll(clause) => {
// FIXME: appropriate binder names
write!(fmt, "forall<> {{ {} }}", clause.skip_binder())
let mut collector = BoundNamesCollector::new();
clause.skip_binder().visit_with(&mut collector);
if !collector.is_empty() {
write!(fmt, "forall<")?;
collector.write_names(fmt)?;
write!(fmt, "> {{ ")?;
}
write!(fmt, "{}", clause.skip_binder())?;
if !collector.is_empty() {
write!(fmt, " }}")?;
}
Ok(())
}
}
}

4
src/librustc_traits/lowering/environment.rs
View file

@ -250,8 +250,8 @@ crate fn environment<'a, 'tcx>(
// In an fn, we assume that the arguments and all their constituents are
// well-formed.
if is_fn {
// `skip_binder` because we move late bound regions to the root binder,
// restored in the return type
// `skip_binder` because we move region parameters to the root binder,
// restored in the return type of this query
let fn_sig = tcx.fn_sig(def_id).skip_binder().subst(tcx, bound_vars);
input_tys.extend(

9
src/librustc_traits/lowering/mod.rs
View file

@ -600,14 +600,7 @@ impl<'a, 'tcx> ClauseDumper<'a, 'tcx> {
let mut strings: Vec<_> = clauses
.iter()
.map(|clause| {
// Skip the top-level binder for a less verbose output
let program_clause = match clause {
Clause::Implies(program_clause) => program_clause,
Clause::ForAll(program_clause) => program_clause.skip_binder(),
};
program_clause.to_string()
})
.map(|clause| clause.to_string())
.collect();
strings.sort();

2
src/test/ui/chalkify/lower_env1.rs
View file

@ -17,7 +17,7 @@ trait Foo { }
trait Bar where Self: Foo { }
#[rustc_dump_env_program_clauses] //~ ERROR program clause dump
fn bar<T: Bar>() {
fn bar<T: Bar + ?Sized>() {
}
fn main() {

13
src/test/ui/chalkify/lower_env1.stderr
View file

@ -4,9 +4,9 @@ error: program clause dump
LL | #[rustc_dump_program_clauses] //~ ERROR program clause dump
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: FromEnv(Self: Foo) :- FromEnv(Self: Bar).
= note: Implemented(Self: Bar) :- FromEnv(Self: Bar).
= note: WellFormed(Self: Bar) :- Implemented(Self: Bar), WellFormed(Self: Foo).
= note: forall<Self> { FromEnv(Self: Foo) :- FromEnv(Self: Bar). }
= note: forall<Self> { Implemented(Self: Bar) :- FromEnv(Self: Bar). }
= note: forall<Self> { WellFormed(Self: Bar) :- Implemented(Self: Bar), WellFormed(Self: Foo). }
error: program clause dump
--> $DIR/lower_env1.rs:19:1
@ -14,10 +14,9 @@ error: program clause dump
LL | #[rustc_dump_env_program_clauses] //~ ERROR program clause dump
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: FromEnv(Self: Foo) :- FromEnv(Self: Bar).
= note: Implemented(Self: Bar) :- FromEnv(Self: Bar).
= note: Implemented(Self: Foo) :- FromEnv(Self: Foo).
= note: Implemented(Self: std::marker::Sized) :- FromEnv(Self: std::marker::Sized).
= note: forall<Self> { FromEnv(Self: Foo) :- FromEnv(Self: Bar). }
= note: forall<Self> { Implemented(Self: Bar) :- FromEnv(Self: Bar). }
= note: forall<Self> { Implemented(Self: Foo) :- FromEnv(Self: Foo). }
error: aborting due to 2 previous errors

4
src/test/ui/chalkify/lower_env2.rs
View file

@ -14,12 +14,12 @@
trait Foo { }
#[rustc_dump_program_clauses] //~ ERROR program clause dump
struct S<'a, T> where T: Foo {
struct S<'a, T: ?Sized> where T: Foo {
data: &'a T,
}
#[rustc_dump_env_program_clauses] //~ ERROR program clause dump
fn bar<'a, T: Foo>(x: S<T>) {
fn bar<T: Foo>(_x: S<'_, T>) { // note that we have an implicit `T: Sized` bound
}
fn main() {

16
src/test/ui/chalkify/lower_env2.stderr
View file

@ -4,10 +4,9 @@ error: program clause dump
LL | #[rustc_dump_program_clauses] //~ ERROR program clause dump
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: FromEnv(T: Foo) :- FromEnv(S<'a, T>).
= note: FromEnv(T: std::marker::Sized) :- FromEnv(S<'a, T>).
= note: TypeOutlives(T : 'a) :- FromEnv(S<'a, T>).
= note: WellFormed(S<'a, T>) :- Implemented(T: std::marker::Sized), Implemented(T: Foo), TypeOutlives(T : 'a).
= note: forall<'a, T> { FromEnv(T: Foo) :- FromEnv(S<'a, T>). }
= note: forall<'a, T> { TypeOutlives(T : 'a) :- FromEnv(S<'a, T>). }
= note: forall<'a, T> { WellFormed(S<'a, T>) :- Implemented(T: Foo), TypeOutlives(T : 'a). }
error: program clause dump
--> $DIR/lower_env2.rs:21:1
@ -15,11 +14,10 @@ error: program clause dump
LL | #[rustc_dump_env_program_clauses] //~ ERROR program clause dump
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: FromEnv(T: Foo) :- FromEnv(S<'a, T>).
= note: FromEnv(T: std::marker::Sized) :- FromEnv(S<'a, T>).
= note: Implemented(Self: Foo) :- FromEnv(Self: Foo).
= note: Implemented(Self: std::marker::Sized) :- FromEnv(Self: std::marker::Sized).
= note: TypeOutlives(T : 'a) :- FromEnv(S<'a, T>).
= note: forall<'a, T> { FromEnv(T: Foo) :- FromEnv(S<'a, T>). }
= note: forall<'a, T> { TypeOutlives(T : 'a) :- FromEnv(S<'a, T>). }
= note: forall<Self> { Implemented(Self: Foo) :- FromEnv(Self: Foo). }
= note: forall<Self> { Implemented(Self: std::marker::Sized) :- FromEnv(Self: std::marker::Sized). }
error: aborting due to 2 previous errors

8
src/test/ui/chalkify/lower_env3.stderr
View file

@ -4,7 +4,7 @@ error: program clause dump
LL | #[rustc_dump_env_program_clauses] //~ ERROR program clause dump
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: Implemented(Self: Foo) :- FromEnv(Self: Foo).
= note: forall<Self> { Implemented(Self: Foo) :- FromEnv(Self: Foo). }
error: program clause dump
--> $DIR/lower_env3.rs:20:5
@ -12,9 +12,9 @@ error: program clause dump
LL | #[rustc_dump_env_program_clauses] //~ ERROR program clause dump
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: FromEnv(Self: std::marker::Sized) :- FromEnv(Self: std::clone::Clone).
= note: Implemented(Self: std::clone::Clone) :- FromEnv(Self: std::clone::Clone).
= note: Implemented(Self: std::marker::Sized) :- FromEnv(Self: std::marker::Sized).
= note: forall<Self> { FromEnv(Self: std::marker::Sized) :- FromEnv(Self: std::clone::Clone). }
= note: forall<Self> { Implemented(Self: std::clone::Clone) :- FromEnv(Self: std::clone::Clone). }
= note: forall<Self> { Implemented(Self: std::marker::Sized) :- FromEnv(Self: std::marker::Sized). }
error: aborting due to 2 previous errors

4
src/test/ui/chalkify/lower_impl.stderr
View file

@ -4,7 +4,7 @@ error: program clause dump
LL | #[rustc_dump_program_clauses] //~ ERROR program clause dump
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: Implemented(T: Foo) :- ProjectionEq(<T as std::iter::Iterator>::Item == i32), TypeOutlives(T : 'static), Implemented(T: std::iter::Iterator), Implemented(T: std::marker::Sized).
= note: forall<T> { Implemented(T: Foo) :- ProjectionEq(<T as std::iter::Iterator>::Item == i32), TypeOutlives(T : 'static), Implemented(T: std::iter::Iterator), Implemented(T: std::marker::Sized). }
error: program clause dump
--> $DIR/lower_impl.rs:23:5
@ -12,7 +12,7 @@ error: program clause dump
LL | #[rustc_dump_program_clauses] //~ ERROR program clause dump
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: Normalize(<T as Bar>::Assoc == std::vec::Vec<T>) :- Implemented(T: Bar).
= note: forall<T> { Normalize(<T as Bar>::Assoc -> std::vec::Vec<T>) :- Implemented(T: Bar). }
error: aborting due to 2 previous errors

4
src/test/ui/chalkify/lower_struct.rs
View file

@ -11,8 +11,8 @@
#![feature(rustc_attrs)]
#[rustc_dump_program_clauses] //~ ERROR program clause dump
struct Foo<T> where Box<T>: Clone {
_x: std::marker::PhantomData<T>,
struct Foo<'a, T> where Box<T>: Clone {
_x: std::marker::PhantomData<&'a T>,
}
fn main() { }

7
src/test/ui/chalkify/lower_struct.stderr
View file

@ -4,9 +4,10 @@ error: program clause dump
LL | #[rustc_dump_program_clauses] //~ ERROR program clause dump
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: FromEnv(T: std::marker::Sized) :- FromEnv(Foo<T>).
= note: FromEnv(std::boxed::Box<T>: std::clone::Clone) :- FromEnv(Foo<T>).
= note: WellFormed(Foo<T>) :- Implemented(T: std::marker::Sized), Implemented(std::boxed::Box<T>: std::clone::Clone).
= note: forall<'a, T> { FromEnv(T: std::marker::Sized) :- FromEnv(Foo<'a, T>). }
= note: forall<'a, T> { FromEnv(std::boxed::Box<T>: std::clone::Clone) :- FromEnv(Foo<'a, T>). }
= note: forall<'a, T> { TypeOutlives(T : 'a) :- FromEnv(Foo<'a, T>). }
= note: forall<'a, T> { WellFormed(Foo<'a, T>) :- Implemented(T: std::marker::Sized), Implemented(std::boxed::Box<T>: std::clone::Clone), TypeOutlives(T : 'a). }
error: aborting due to previous error

14
src/test/ui/chalkify/lower_trait.stderr
View file

@ -4,10 +4,10 @@ error: program clause dump
LL | #[rustc_dump_program_clauses] //~ ERROR program clause dump
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: FromEnv(<Self as Foo<S, T>>::Assoc: Bar) :- FromEnv(Self: Foo<S, T>).
= note: FromEnv(S: std::marker::Sized) :- FromEnv(Self: Foo<S, T>).
= note: Implemented(Self: Foo<S, T>) :- FromEnv(Self: Foo<S, T>).
= note: WellFormed(Self: Foo<S, T>) :- Implemented(Self: Foo<S, T>), WellFormed(S: std::marker::Sized), WellFormed(<Self as Foo<S, T>>::Assoc: Bar).
= note: forall<Self, S, T> { FromEnv(<Self as Foo<S, T>>::Assoc: Bar) :- FromEnv(Self: Foo<S, T>). }
= note: forall<Self, S, T> { FromEnv(S: std::marker::Sized) :- FromEnv(Self: Foo<S, T>). }
= note: forall<Self, S, T> { Implemented(Self: Foo<S, T>) :- FromEnv(Self: Foo<S, T>). }
= note: forall<Self, S, T> { WellFormed(Self: Foo<S, T>) :- Implemented(Self: Foo<S, T>), WellFormed(S: std::marker::Sized), WellFormed(<Self as Foo<S, T>>::Assoc: Bar). }
error: program clause dump
--> $DIR/lower_trait.rs:17:5
@ -15,9 +15,9 @@ error: program clause dump
LL | #[rustc_dump_program_clauses] //~ ERROR program clause dump
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: FromEnv(Self: Foo<S, T>) :- FromEnv(Unnormalized(<Self as Foo<S, T>>::Assoc)).
= note: ProjectionEq(<Self as Foo<S, T>>::Assoc == Unnormalized(<Self as Foo<S, T>>::Assoc)).
= note: WellFormed(Unnormalized(<Self as Foo<S, T>>::Assoc)) :- Implemented(Self: Foo<S, T>).
= note: forall<Self, S, T> { FromEnv(Self: Foo<S, T>) :- FromEnv(Unnormalized(<Self as Foo<S, T>>::Assoc)). }
= note: forall<Self, S, T> { ProjectionEq(<Self as Foo<S, T>>::Assoc == Unnormalized(<Self as Foo<S, T>>::Assoc)). }
= note: forall<Self, S, T> { WellFormed(Unnormalized(<Self as Foo<S, T>>::Assoc)) :- Implemented(Self: Foo<S, T>). }
error: aborting due to 2 previous errors

3
src/test/ui/chalkify/lower_trait_higher_rank.rs
View file

@ -11,9 +11,8 @@
#![feature(rustc_attrs)]
#[rustc_dump_program_clauses] //~ ERROR program clause dump
trait Foo<F> where for<'a> F: Fn(&'a (u8, u16)) -> &'a u8
trait Foo<F: ?Sized> where for<'a> F: Fn(&'a (u8, u16)) -> &'a u8
{
fn s(_: F) -> F;
}
fn main() {

9
src/test/ui/chalkify/lower_trait_higher_rank.stderr
View file

@ -4,11 +4,10 @@ error: program clause dump
LL | #[rustc_dump_program_clauses] //~ ERROR program clause dump
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: FromEnv(F: std::marker::Sized) :- FromEnv(Self: Foo<F>).
= note: FromEnv(F: std::ops::Fn<(&'a (u8, u16),)>) :- FromEnv(Self: Foo<F>).
= note: Implemented(Self: Foo<F>) :- FromEnv(Self: Foo<F>).
= note: ProjectionEq(<F as std::ops::FnOnce<(&'a (u8, u16),)>>::Output == &'a u8) :- FromEnv(Self: Foo<F>).
= note: WellFormed(Self: Foo<F>) :- Implemented(Self: Foo<F>), WellFormed(F: std::marker::Sized), forall<> { WellFormed(F: std::ops::Fn<(&'a (u8, u16),)>) }, forall<> { ProjectionEq(<F as std::ops::FnOnce<(&'a (u8, u16),)>>::Output == &'a u8) }.
= note: forall<'a, Self, F> { FromEnv(F: std::ops::Fn<(&'a (u8, u16),)>) :- FromEnv(Self: Foo<F>). }
= note: forall<'a, Self, F> { ProjectionEq(<F as std::ops::FnOnce<(&'a (u8, u16),)>>::Output == &'a u8) :- FromEnv(Self: Foo<F>). }
= note: forall<Self, F> { Implemented(Self: Foo<F>) :- FromEnv(Self: Foo<F>). }
= note: forall<Self, F> { WellFormed(Self: Foo<F>) :- Implemented(Self: Foo<F>), forall<'a> { WellFormed(F: std::ops::Fn<(&'a (u8, u16),)>) }, forall<'a> { ProjectionEq(<F as std::ops::FnOnce<(&'a (u8, u16),)>>::Output == &'a u8) }. }
error: aborting due to previous error

14
src/test/ui/chalkify/lower_trait_where_clause.rs
View file

@ -10,22 +10,16 @@
#![feature(rustc_attrs)]
use std::fmt::{Debug, Display};
use std::borrow::Borrow;
#[rustc_dump_program_clauses] //~ ERROR program clause dump
trait Foo<'a, 'b, S, T, U>
trait Foo<'a, 'b, T, U>
where
S: Debug,
T: Borrow<U>,
U: ?Sized,
T: Borrow<U> + ?Sized,
U: ?Sized + 'b,
'a: 'b,
U: 'b,
Vec<T>:, // NOTE(#53696) this checks an empty list of bounds.
Box<T>:, // NOTE(#53696) this checks an empty list of bounds.
{
fn s(_: S) -> S;
fn t(_: T) -> T;
fn u(_: U) -> U;
}
fn main() {

17
src/test/ui/chalkify/lower_trait_where_clause.stderr
View file

@ -1,18 +1,15 @@
error: program clause dump
--> $DIR/lower_trait_where_clause.rs:16:1
--> $DIR/lower_trait_where_clause.rs:15:1
|
LL | #[rustc_dump_program_clauses] //~ ERROR program clause dump
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: FromEnv(S: std::fmt::Debug) :- FromEnv(Self: Foo<'a, 'b, S, T, U>).
= note: FromEnv(S: std::marker::Sized) :- FromEnv(Self: Foo<'a, 'b, S, T, U>).
= note: FromEnv(T: std::borrow::Borrow<U>) :- FromEnv(Self: Foo<'a, 'b, S, T, U>).
= note: FromEnv(T: std::marker::Sized) :- FromEnv(Self: Foo<'a, 'b, S, T, U>).
= note: Implemented(Self: Foo<'a, 'b, S, T, U>) :- FromEnv(Self: Foo<'a, 'b, S, T, U>).
= note: RegionOutlives('a : 'b) :- FromEnv(Self: Foo<'a, 'b, S, T, U>).
= note: TypeOutlives(U : 'b) :- FromEnv(Self: Foo<'a, 'b, S, T, U>).
= note: WellFormed(Self: Foo<'a, 'b, S, T, U>) :- Implemented(Self: Foo<'a, 'b, S, T, U>), WellFormed(S: std::marker::Sized), WellFormed(T: std::marker::Sized), WellFormed(S: std::fmt::Debug), WellFormed(T: std::borrow::Borrow<U>), RegionOutlives('a : 'b), TypeOutlives(U : 'b), WellFormed(std::vec::Vec<T>).
= note: WellFormed(std::vec::Vec<T>) :- FromEnv(Self: Foo<'a, 'b, S, T, U>).
= note: forall<'a, 'b, Self, T, U> { FromEnv(T: std::borrow::Borrow<U>) :- FromEnv(Self: Foo<'a, 'b, T, U>). }
= note: forall<'a, 'b, Self, T, U> { Implemented(Self: Foo<'a, 'b, T, U>) :- FromEnv(Self: Foo<'a, 'b, T, U>). }
= note: forall<'a, 'b, Self, T, U> { RegionOutlives('a : 'b) :- FromEnv(Self: Foo<'a, 'b, T, U>). }
= note: forall<'a, 'b, Self, T, U> { TypeOutlives(U : 'b) :- FromEnv(Self: Foo<'a, 'b, T, U>). }
= note: forall<'a, 'b, Self, T, U> { WellFormed(Self: Foo<'a, 'b, T, U>) :- Implemented(Self: Foo<'a, 'b, T, U>), WellFormed(T: std::borrow::Borrow<U>), TypeOutlives(U : 'b), RegionOutlives('a : 'b), WellFormed(std::boxed::Box<T>). }
= note: forall<'a, 'b, Self, T, U> { WellFormed(std::boxed::Box<T>) :- FromEnv(Self: Foo<'a, 'b, T, U>). }
error: aborting due to previous error