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Commit fde4556

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Properly check constrainedness of gen params in the presence of weak alias types
1 parent 8677d64 commit fde4556

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9 files changed

+105
-17
lines changed

9 files changed

+105
-17
lines changed

‎compiler/rustc_hir_analysis/src/collect/predicates_of.rs‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -307,7 +307,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
307307
tcx,
308308
&mut predicates,
309309
trait_ref,
310-
&mut cgp::parameters_for_impl(self_ty, trait_ref),
310+
&mut cgp::parameters_for_impl(tcx,self_ty, trait_ref),
311311
);
312312
}
313313

‎compiler/rustc_hir_analysis/src/constrained_generic_params.rs‎

Lines changed: 33 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,5 @@
11
use rustc_data_structures::fx::FxHashSet;
2+
use rustc_data_structures::stack::ensure_sufficient_stack;
23
use rustc_middle::ty::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitor};
34
use rustc_middle::ty::{self, Ty, TyCtxt};
45
use rustc_span::Span;
@@ -27,12 +28,13 @@ impl From<ty::ParamConst> for Parameter {
2728

2829
/// Returns the set of parameters constrained by the impl header.
2930
pub fn parameters_for_impl<'tcx>(
31+
tcx: TyCtxt<'tcx>,
3032
impl_self_ty: Ty<'tcx>,
3133
impl_trait_ref: Option<ty::TraitRef<'tcx>>,
3234
) -> FxHashSet<Parameter> {
3335
let vec = match impl_trait_ref {
34-
Some(tr) => parameters_for(&tr, false),
35-
None => parameters_for(&impl_self_ty, false),
36+
Some(tr) => parameters_for(tcx,&tr, false),
37+
None => parameters_for(tcx,&impl_self_ty, false),
3638
};
3739
vec.into_iter().collect()
3840
}
@@ -43,26 +45,47 @@ pub fn parameters_for_impl<'tcx>(
4345
/// of parameters whose values are needed in order to constrain `ty` - these
4446
/// differ, with the latter being a superset, in the presence of projections.
4547
pub fn parameters_for<'tcx>(
48+
tcx: TyCtxt<'tcx>,
4649
t: &impl TypeVisitable<TyCtxt<'tcx>>,
4750
include_nonconstraining: bool,
4851
) -> Vec<Parameter> {
49-
let mut collector = ParameterCollector { parameters: vec![], include_nonconstraining };
52+
let mut collector =
53+
ParameterCollector { tcx, parameters: vec![], include_nonconstraining, depth: 0 };
5054
t.visit_with(&mut collector);
5155
collector.parameters
5256
}
5357

54-
struct ParameterCollector {
58+
struct ParameterCollector<'tcx> {
59+
tcx: TyCtxt<'tcx>,
5560
parameters: Vec<Parameter>,
5661
include_nonconstraining: bool,
62+
depth: usize,
5763
}
5864

59-
impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ParameterCollector {
65+
impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ParameterCollector<'tcx> {
6066
fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
6167
match *t.kind() {
62-
ty::Alias(..) if !self.include_nonconstraining => {
63-
// projections are not injective
68+
ty::Alias(ty::Projection | ty::Inherent | ty::Opaque, _)
69+
if !self.include_nonconstraining =>
70+
{
71+
// Projections are not injective in general.
6472
return ControlFlow::Continue(());
6573
}
74+
ty::Alias(ty::Weak, alias) if !self.include_nonconstraining => {
75+
if !self.tcx.recursion_limit().value_within_limit(self.depth) {
76+
// Other constituent types may still constrain some generic params, consider
77+
// `<T> (Overflow, T)` for example. Therefore we want to continue instead of
78+
// breaking. Only affects diagnostics.
79+
return ControlFlow::Continue(());
80+
}
81+
self.depth += 1;
82+
return ensure_sufficient_stack(|| {
83+
self.tcx
84+
.type_of(alias.def_id)
85+
.instantiate(self.tcx, alias.args)
86+
.visit_with(self)
87+
});
88+
}
6689
ty::Param(data) => {
6790
self.parameters.push(Parameter::from(data));
6891
}
@@ -82,7 +105,7 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ParameterCollector {
82105
fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
83106
match c.kind() {
84107
ty::ConstKind::Unevaluated(..) if !self.include_nonconstraining => {
85-
// Constant expressions are not injective
108+
// Constant expressions are not injective in general.
86109
return c.ty().visit_with(self);
87110
}
88111
ty::ConstKind::Param(data) => {
@@ -201,12 +224,12 @@ pub fn setup_constraining_predicates<'tcx>(
201224
// `<<T as Bar>::Baz as Iterator>::Output = <U as Iterator>::Output`
202225
// Then the projection only applies if `T` is known, but it still
203226
// does not determine `U`.
204-
let inputs = parameters_for(&projection.projection_ty, true);
227+
let inputs = parameters_for(tcx,&projection.projection_ty, true);
205228
let relies_only_on_inputs = inputs.iter().all(|p| input_parameters.contains(p));
206229
if !relies_only_on_inputs {
207230
continue;
208231
}
209-
input_parameters.extend(parameters_for(&projection.term, false));
232+
input_parameters.extend(parameters_for(tcx,&projection.term, false));
210233
} else {
211234
continue;
212235
}

‎compiler/rustc_hir_analysis/src/impl_wf_check.rs‎

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -94,7 +94,7 @@ fn enforce_impl_params_are_constrained(
9494
let impl_predicates = tcx.predicates_of(impl_def_id);
9595
let impl_trait_ref = tcx.impl_trait_ref(impl_def_id).map(ty::EarlyBinder::instantiate_identity);
9696

97-
let mut input_parameters = cgp::parameters_for_impl(impl_self_ty, impl_trait_ref);
97+
let mut input_parameters = cgp::parameters_for_impl(tcx,impl_self_ty, impl_trait_ref);
9898
cgp::identify_constrained_generic_params(
9999
tcx,
100100
impl_predicates,
@@ -111,7 +111,7 @@ fn enforce_impl_params_are_constrained(
111111
match item.kind {
112112
ty::AssocKind::Type => {
113113
if item.defaultness(tcx).has_value() {
114-
cgp::parameters_for(&tcx.type_of(def_id).instantiate_identity(), true)
114+
cgp::parameters_for(tcx,&tcx.type_of(def_id).instantiate_identity(), true)
115115
} else {
116116
vec![]
117117
}

‎compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs‎

Lines changed: 4 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -266,15 +266,15 @@ fn unconstrained_parent_impl_args<'tcx>(
266266
continue;
267267
}
268268

269-
unconstrained_parameters.extend(cgp::parameters_for(&projection_ty, true));
269+
unconstrained_parameters.extend(cgp::parameters_for(tcx,&projection_ty, true));
270270

271-
for param in cgp::parameters_for(&projected_ty, false) {
271+
for param in cgp::parameters_for(tcx,&projected_ty, false) {
272272
if !unconstrained_parameters.contains(&param) {
273273
constrained_params.insert(param.0);
274274
}
275275
}
276276

277-
unconstrained_parameters.extend(cgp::parameters_for(&projected_ty, true));
277+
unconstrained_parameters.extend(cgp::parameters_for(tcx,&projected_ty, true));
278278
}
279279
}
280280

@@ -312,7 +312,7 @@ fn check_duplicate_params<'tcx>(
312312
parent_args: &Vec<GenericArg<'tcx>>,
313313
span: Span,
314314
) -> Result<(), ErrorGuaranteed> {
315-
let mut base_params = cgp::parameters_for(parent_args, true);
315+
let mut base_params = cgp::parameters_for(tcx,parent_args, true);
316316
base_params.sort_by_key(|param| param.0);
317317
if let (_, [duplicate, ..]) = base_params.partition_dedup() {
318318
let param = impl1_args[duplicate.0 as usize];
Lines changed: 27 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,27 @@
1+
//@ check-pass
2+
3+
#![feature(lazy_type_alias)]
4+
#![allow(incomplete_features)]
5+
6+
type Injective<T> = Local<T>;
7+
struct Local<T>(T);
8+
9+
impl<T> Injective<T> {
10+
fn take(_: T) {}
11+
}
12+
13+
trait Trait {
14+
type Out;
15+
fn produce() -> Self::Out;
16+
}
17+
18+
impl<T: Default> Trait for Injective<T> {
19+
type Out = T;
20+
fn produce() -> Self::Out { T::default() }
21+
}
22+
23+
fn main() {
24+
Injective::take(0);
25+
let _: String = Injective::produce();
26+
let _: bool = Local::produce();
27+
}
Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,8 @@
1+
#![feature(lazy_type_alias)]
2+
#![allow(incomplete_features)]
3+
4+
impl<T> Loop<T> {} //~ ERROR the type parameter `T` is not constrained
5+
6+
type Loop<T> = Loop<T>;
7+
8+
fn main() {}
Lines changed: 9 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,9 @@
1+
error[E0207]: the type parameter `T` is not constrained by the impl trait, self type, or predicates
2+
--> $DIR/unconstrained-param-due-to-overflow.rs:4:6
3+
|
4+
LL | impl<T> Loop<T> {}
5+
| ^ unconstrained type parameter
6+
7+
error: aborting due to 1 previous error
8+
9+
For more information about this error, try `rustc --explain E0207`.
Lines changed: 12 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,12 @@
1+
#![feature(lazy_type_alias)]
2+
#![allow(incomplete_features)]
3+
4+
impl<T> NotInjective<T> {} //~ ERROR the type parameter `T` is not constrained
5+
6+
type NotInjective<T: ?Sized> = Local<<T as Discard>::Out>;
7+
struct Local<T>(T);
8+
9+
trait Discard { type Out; }
10+
impl<T: ?Sized> Discard for T { type Out = (); }
11+
12+
fn main() {}
Lines changed: 9 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,9 @@
1+
error[E0207]: the type parameter `T` is not constrained by the impl trait, self type, or predicates
2+
--> $DIR/unconstrained-params.rs:4:6
3+
|
4+
LL | impl<T> NotInjective<T> {}
5+
| ^ unconstrained type parameter
6+
7+
error: aborting due to 1 previous error
8+
9+
For more information about this error, try `rustc --explain E0207`.

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