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Emit warning when bound is trivially false #100090

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Emit warning when bound is trivially false #100090

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5035049
Emit warning when bound is trivially false
compiler-errors Aug 3, 2022
d7fbaea
Adjust diagnostic
compiler-errors Aug 3, 2022
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90 changes: 67 additions & 23 deletions compiler/rustc_typeck/src/check/wfcheck.rs
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Expand Up @@ -10,7 +10,7 @@ use rustc_hir::ItemKind;
use rustc_infer::infer::outlives::env::{OutlivesEnvironment, RegionBoundPairs};
use rustc_infer::infer::outlives::obligations::TypeOutlives;
use rustc_infer::infer::{self, InferCtxt, TyCtxtInferExt};
use rustc_infer::traits::Normalized;
use rustc_infer::traits::{Normalized, TraitEngine, TraitEngineExt as _};
use rustc_middle::ty::query::Providers;
use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts, Subst};
use rustc_middle::ty::trait_def::TraitSpecializationKind;
Expand All @@ -27,7 +27,8 @@ use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _
use rustc_trait_selection::traits::query::normalize::AtExt;
use rustc_trait_selection::traits::query::NoSolution;
use rustc_trait_selection::traits::{
self, ObligationCause, ObligationCauseCode, ObligationCtxt, WellFormedLoc,
self, FulfillmentContext, ObligationCause, ObligationCauseCode, ObligationCtxt,
SelectionContext, WellFormedLoc,
};

use std::cell::LazyCell;
Expand Down Expand Up @@ -1817,7 +1818,7 @@ impl<'tcx> WfCheckingCtxt<'_, 'tcx> {
/// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
/// aren't true.
fn check_false_global_bounds(&mut self) {
let tcx = self.ocx.infcx.tcx;
let tcx = self.infcx.tcx;
let mut span = self.span;
let empty_env = ty::ParamEnv::empty();

Expand All @@ -1833,33 +1834,76 @@ impl<'tcx> WfCheckingCtxt<'_, 'tcx> {
if let ty::PredicateKind::WellFormed(..) = obligation.predicate.kind().skip_binder() {
continue;
}
let pred = obligation.predicate;
// Match the existing behavior.
if pred.is_global() && !pred.has_late_bound_regions() {
let pred = self.normalize(span, None, pred);
let hir_node = tcx.hir().find(self.body_id);

// only use the span of the predicate clause (#90869)
let pred = obligation.predicate;

if let Some(hir::Generics { predicates, .. }) =
hir_node.and_then(|node| node.generics())
{
let obligation_span = obligation.cause.span();

span = predicates
.iter()
// There seems to be no better way to find out which predicate we are in
.find(|pred| pred.span().contains(obligation_span))
.map(|pred| pred.span())
.unwrap_or(obligation_span);
}
// only use the span of the predicate clause (#90869)
let hir_node = tcx.hir().find(self.body_id);
if let Some(hir::Generics { predicates, .. }) =
hir_node.and_then(|node| node.generics())
{
let obligation_span = obligation.cause.span();
span = predicates
.iter()
// There seems to be no better way to find out which predicate we are in
.find(|pred| pred.span().contains(obligation_span))
.map(|pred| pred.span())
.unwrap_or(obligation_span);
}

// Match the existing behavior.
if pred.is_global() && !pred.has_late_bound_regions() {
let normalized_pred = self.normalize(span, None, pred);
let obligation = traits::Obligation::new(
traits::ObligationCause::new(span, self.body_id, traits::TrivialBound),
empty_env,
pred,
normalized_pred,
);
self.ocx.register_obligation(obligation);
self.register_obligation(obligation);
} else {
self.infcx.probe(|_| {
// Manually normalize because `wfcx.normalize` may report errors
let Normalized { value: normalized_pred, obligations } = traits::normalize(
&mut SelectionContext::new(self.infcx),
self.param_env,
ObligationCause::dummy(),
pred,
);
if normalized_pred.is_global() {
let mut fulfill_cx = FulfillmentContext::new_in_snapshot();
fulfill_cx.register_predicate_obligations(self.infcx, obligations);
fulfill_cx.register_predicate_obligation(
self.infcx,
traits::Obligation::new(
traits::ObligationCause::new(
span,
self.body_id,
traits::TrivialBound,
),
empty_env,
normalized_pred,
),
);
if !fulfill_cx.select_all_or_error(self.infcx).is_empty() {
let mut diag = self.tcx()
.sess
.struct_span_warn(
span,
format!("the where-clause bound `{pred}` is impossible to satisfy"),
);
diag.span_label(
self.span,
"this item cannot be referenced without causing an error",
);
if self.infcx.tcx.sess.opts.unstable_features.is_nightly_build() {
diag.help(
"add `#![feature(trivial_bounds)]` to the crate attributes to allow it",
);
}
diag.emit();
}
}
});
}
}
}
Expand Down
28 changes: 26 additions & 2 deletions src/test/ui/associated-types/bound-lifetime-in-binding-only.ok.stderr
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@@ -1,8 +1,32 @@
warning: the where-clause bound `for<'a> <Parameterized<'a> as Foo>::Item == &'a i32` is impossible to satisfy
--> $DIR/bound-lifetime-in-binding-only.rs:67:19
|
LL | fn ok3<T>() where for<'a> Parameterized<'a>: Foo<Item=&'a i32> {
| _- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
LL | |
LL | |
LL | | }
| |_- this item cannot be referenced without causing an error
|
= help: add `#![feature(trivial_bounds)]` to the crate attributes to allow it

warning: the where-clause bound `for<'a> Parameterized<'a>: Foo` is impossible to satisfy
--> $DIR/bound-lifetime-in-binding-only.rs:67:19
|
LL | fn ok3<T>() where for<'a> Parameterized<'a>: Foo<Item=&'a i32> {
| _- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
LL | |
LL | |
LL | | }
| |_- this item cannot be referenced without causing an error
|
= help: add `#![feature(trivial_bounds)]` to the crate attributes to allow it

error: fatal error triggered by #[rustc_error]
--> $DIR/bound-lifetime-in-binding-only.rs:71:1
--> $DIR/bound-lifetime-in-binding-only.rs:73:1
|
LL | fn main() { }
| ^^^^^^^^^

error: aborting due to previous error
error: aborting due to previous error; 2 warnings emitted

2 changes: 2 additions & 0 deletions src/test/ui/associated-types/bound-lifetime-in-binding-only.rs
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Expand Up @@ -65,6 +65,8 @@ fn ok2<T: for<'a,'b> Fn<(&'b Parameterized<'a>,), Output=&'a i32>>() {

#[cfg(ok)]
fn ok3<T>() where for<'a> Parameterized<'a>: Foo<Item=&'a i32> {
//[ok]~^ WARNING the where-clause bound
//[ok]~| WARNING the where-clause bound
}

#[rustc_error]
Expand Down
2 changes: 1 addition & 1 deletion src/test/ui/associated-types/issue-59324.rs
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Expand Up @@ -12,7 +12,7 @@ pub trait ThriftService<Bug: NotFoo>:
//~^ ERROR the trait bound `Bug: Foo` is not satisfied
//~| ERROR the trait bound `Bug: Foo` is not satisfied
Service<AssocType = <Bug as Foo>::OnlyFoo>
{
{
fn get_service(
//~^ ERROR the trait bound `Bug: Foo` is not satisfied
&self,
Expand Down
1 change: 1 addition & 0 deletions src/test/ui/associated-types/issue-69398.rs
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Expand Up @@ -12,6 +12,7 @@ pub trait Broken {
impl<T> Broken for T {
type Assoc = ();
fn broken(&self) where Self::Assoc: Foo {
//~^ WARNING the where-clause bound
let _x: <Self::Assoc as Foo>::Bar;
}
}
Expand Down
14 changes: 14 additions & 0 deletions src/test/ui/associated-types/issue-69398.stderr
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@@ -0,0 +1,14 @@
warning: the where-clause bound `<T as Broken>::Assoc: Foo` is impossible to satisfy
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It's a bit unfortunate that the bound we say is not the bound that's written.

--> $DIR/issue-69398.rs:14:28
|
LL | fn broken(&self) where Self::Assoc: Foo {
| _____- ^^^^^^^^^^^^^^^^
LL | |
LL | | let _x: <Self::Assoc as Foo>::Bar;
LL | | }
| |_____- this item cannot be referenced without causing an error
|
= help: add `#![feature(trivial_bounds)]` to the crate attributes to allow it

warning: 1 warning emitted

3 changes: 3 additions & 0 deletions src/test/ui/consts/issue-67696-const-prop-ice.rs
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Expand Up @@ -11,6 +11,9 @@ trait A {

impl A for [fn(&())] {
fn foo(&self) -> Self where Self: Copy { *(&[] as &[_]) }
//~^ WARNING the where-clause bound
//~| WARNING the where-clause bound
//~| WARNING the where-clause bound
}

impl A for i32 {
Expand Down
26 changes: 26 additions & 0 deletions src/test/ui/consts/issue-67696-const-prop-ice.stderr
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@@ -0,0 +1,26 @@
warning: the where-clause bound `[for<'r> fn(&'r ())]: Copy` is impossible to satisfy
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This is certainly not great.

--> $DIR/issue-67696-const-prop-ice.rs:13:33
|
LL | fn foo(&self) -> Self where Self: Copy { *(&[] as &[_]) }
| ----------------------------^^^^^^^^^^------------------- this item cannot be referenced without causing an error
|
= help: add `#![feature(trivial_bounds)]` to the crate attributes to allow it

warning: the where-clause bound `[for<'r> fn(&'r ())]: Clone` is impossible to satisfy
--> $DIR/issue-67696-const-prop-ice.rs:13:33
|
LL | fn foo(&self) -> Self where Self: Copy { *(&[] as &[_]) }
| ----------------------------^^^^^^^^^^------------------- this item cannot be referenced without causing an error
|
= help: add `#![feature(trivial_bounds)]` to the crate attributes to allow it

warning: the where-clause bound `[for<'r> fn(&'r ())]: Sized` is impossible to satisfy
--> $DIR/issue-67696-const-prop-ice.rs:13:33
|
LL | fn foo(&self) -> Self where Self: Copy { *(&[] as &[_]) }
| ----------------------------^^^^^^^^^^------------------- this item cannot be referenced without causing an error
|
= help: add `#![feature(trivial_bounds)]` to the crate attributes to allow it

warning: 3 warnings emitted

1 change: 1 addition & 0 deletions src/test/ui/feature-gates/feature-gate-trivial_bounds.rs
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Expand Up @@ -63,6 +63,7 @@ fn return_str() -> str where str: Sized { //~ ERROR
// This is currently accepted because the function pointer isn't
// considered global.
fn global_hr(x: fn(&())) where fn(&()): Foo { // OK
//~^ WARNING the where-clause bound
x.test();
}

Expand Down
14 changes: 13 additions & 1 deletion src/test/ui/feature-gates/feature-gate-trivial_bounds.stderr
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Expand Up @@ -113,6 +113,18 @@ LL | fn return_str() -> str where str: Sized {
= help: see issue #48214
= help: add `#![feature(trivial_bounds)]` to the crate attributes to enable

error: aborting due to 11 previous errors
warning: the where-clause bound `for<'r> fn(&'r ()): Foo` is impossible to satisfy
--> $DIR/feature-gate-trivial_bounds.rs:65:32
|
LL | fn global_hr(x: fn(&())) where fn(&()): Foo { // OK
| _- ^^^^^^^^^^^^
LL | |
LL | | x.test();
LL | | }
| |_- this item cannot be referenced without causing an error
|
= help: add `#![feature(trivial_bounds)]` to the crate attributes to allow it

error: aborting due to 11 previous errors; 1 warning emitted

For more information about this error, try `rustc --explain E0277`.
2 changes: 2 additions & 0 deletions src/test/ui/higher-rank-trait-bounds/normalize-under-binder/issue-89118.rs
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Expand Up @@ -7,6 +7,7 @@ impl<B: BufferMut, C> BufferUdpStateContext<B> for C {}
trait StackContext
where
Ctx<()>: for<'a> BufferUdpStateContext<&'a ()>,
//~^ WARNING the where-clause bound
{
type Dispatcher;
}
Expand All @@ -26,6 +27,7 @@ where
struct EthernetWorker<C>(C)
where
Ctx<()>: for<'a> BufferUdpStateContext<&'a ()>;
//~^ WARNING the where-clause bound
impl<C> EthernetWorker<C> {}
//~^ ERROR: is not satisfied [E0277]

Expand Down
35 changes: 30 additions & 5 deletions src/test/ui/higher-rank-trait-bounds/normalize-under-binder/issue-89118.stderr
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@@ -1,5 +1,20 @@
warning: the where-clause bound `for<'a> Ctx<()>: BufferUdpStateContext<&'a ()>` is impossible to satisfy
--> $DIR/issue-89118.rs:9:5
|
LL | / trait StackContext
LL | | where
LL | | Ctx<()>: for<'a> BufferUdpStateContext<&'a ()>,
| | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
LL | |
LL | | {
LL | | type Dispatcher;
LL | | }
| |_- this item cannot be referenced without causing an error
|
= help: add `#![feature(trivial_bounds)]` to the crate attributes to allow it

error[E0277]: the trait bound `for<'a> &'a (): BufferMut` is not satisfied
--> $DIR/issue-89118.rs:19:8
--> $DIR/issue-89118.rs:20:8
|
LL | C: StackContext,
| ^^^^^^^^^^^^ the trait `for<'a> BufferMut` is not implemented for `&'a ()`
Expand All @@ -18,8 +33,18 @@ LL | where
LL | Ctx<()>: for<'a> BufferUdpStateContext<&'a ()>,
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `StackContext`

warning: the where-clause bound `for<'a> Ctx<()>: BufferUdpStateContext<&'a ()>` is impossible to satisfy
--> $DIR/issue-89118.rs:29:5
|
LL | / struct EthernetWorker<C>(C)
LL | | where
LL | | Ctx<()>: for<'a> BufferUdpStateContext<&'a ()>;
| |_____^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^- this item cannot be referenced without causing an error
|
= help: add `#![feature(trivial_bounds)]` to the crate attributes to allow it

error[E0277]: the trait bound `for<'a> &'a (): BufferMut` is not satisfied
--> $DIR/issue-89118.rs:29:9
--> $DIR/issue-89118.rs:31:9
|
LL | impl<C> EthernetWorker<C> {}
| ^^^^^^^^^^^^^^^^^ the trait `for<'a> BufferMut` is not implemented for `&'a ()`
Expand All @@ -30,7 +55,7 @@ note: required because of the requirements on the impl of `for<'a> BufferUdpStat
LL | impl<B: BufferMut, C> BufferUdpStateContext<B> for C {}
| ^^^^^^^^^^^^^^^^^^^^^^^^ ^
note: required by a bound in `EthernetWorker`
--> $DIR/issue-89118.rs:28:14
--> $DIR/issue-89118.rs:29:14
|
LL | struct EthernetWorker<C>(C)
| -------------- required by a bound in this
Expand All @@ -39,7 +64,7 @@ LL | Ctx<()>: for<'a> BufferUdpStateContext<&'a ()>;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `EthernetWorker`

error[E0277]: the trait bound `for<'a> &'a (): BufferMut` is not satisfied
--> $DIR/issue-89118.rs:22:20
--> $DIR/issue-89118.rs:23:20
|
LL | type Handler = Ctx<C::Dispatcher>;
| ^^^^^^^^^^^^^^^^^^ the trait `for<'a> BufferMut` is not implemented for `&'a ()`
Expand All @@ -58,6 +83,6 @@ LL | where
LL | Ctx<()>: for<'a> BufferUdpStateContext<&'a ()>,
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `StackContext`

error: aborting due to 3 previous errors
error: aborting due to 3 previous errors; 2 warnings emitted

For more information about this error, try `rustc --explain E0277`.
1 change: 1 addition & 0 deletions src/test/ui/issues/issue-36839.rs
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Expand Up @@ -12,6 +12,7 @@ pub trait Broken {
impl<T> Broken for T {
type Assoc = ();
fn broken(&self) where Self::Assoc: Foo {
//~^ WARNING the where-clause bound
let _x: <Self::Assoc as Foo>::Bar;
}
}
Expand Down
14 changes: 14 additions & 0 deletions src/test/ui/issues/issue-36839.stderr
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@@ -0,0 +1,14 @@
warning: the where-clause bound `<T as Broken>::Assoc: Foo` is impossible to satisfy
--> $DIR/issue-36839.rs:14:28
|
LL | fn broken(&self) where Self::Assoc: Foo {
| _____- ^^^^^^^^^^^^^^^^
LL | |
LL | | let _x: <Self::Assoc as Foo>::Bar;
LL | | }
| |_____- this item cannot be referenced without causing an error
|
= help: add `#![feature(trivial_bounds)]` to the crate attributes to allow it

warning: 1 warning emitted

1 change: 1 addition & 0 deletions src/test/ui/issues/issue-39970.rs
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Expand Up @@ -13,6 +13,7 @@ impl<'a> Array<'a> for () {
impl Visit for () where
//(): for<'a> Array<'a, Element=&'a ()>, // No ICE
(): for<'a> Array<'a, Element=()>, // ICE
//~^ WARNING the where-clause bound
{}

fn main() {
Expand Down