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Object safe for dispatch #57545

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Oct 23, 2019
Merged

Object safe for dispatch #57545

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24 changes: 20 additions & 4 deletions src/librustc/infer/error_reporting/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1146,10 +1146,17 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {

let span = cause.span(self.tcx);

diag.span_label(span, terr.to_string());
if let Some((sp, msg)) = secondary_span {
diag.span_label(sp, msg);
}
// Ignore msg for object safe coercion
// since E0038 message will be printed
match terr {
TypeError::ObjectUnsafeCoercion(_) => {}
_ => {
diag.span_label(span, terr.to_string());
if let Some((sp, msg)) = secondary_span {
diag.span_label(sp, msg);
}
}
};

if let Some((expected, found)) = expected_found {
match (terr, is_simple_error, expected == found) {
Expand All @@ -1169,6 +1176,9 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
&sort_string(values.found),
);
}
(TypeError::ObjectUnsafeCoercion(_), ..) => {
diag.note_unsuccessfull_coercion(found, expected);
}
(_, false, _) => {
if let Some(exp_found) = exp_found {
self.suggest_as_ref_where_appropriate(span, &exp_found, diag);
Expand Down Expand Up @@ -1267,6 +1277,10 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
let span = trace.cause.span(self.tcx);
let failure_code = trace.cause.as_failure_code(terr);
let mut diag = match failure_code {
FailureCode::Error0038(did) => {
let violations = self.tcx.object_safety_violations(did);
self.tcx.report_object_safety_error(span, did, violations)
}
FailureCode::Error0317(failure_str) => {
struct_span_err!(self.tcx.sess, span, E0317, "{}", failure_str)
}
Expand Down Expand Up @@ -1628,6 +1642,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
}

enum FailureCode {
Error0038(DefId),
Error0317(&'static str),
Error0580(&'static str),
Error0308(&'static str),
Expand Down Expand Up @@ -1666,6 +1681,7 @@ impl<'tcx> ObligationCause<'tcx> {
TypeError::IntrinsicCast => {
Error0308("cannot coerce intrinsics to function pointers")
}
TypeError::ObjectUnsafeCoercion(did) => Error0038(did.clone()),
_ => Error0308("mismatched types"),
},
}
Expand Down
32 changes: 15 additions & 17 deletions src/librustc/traits/error_reporting.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -790,15 +790,11 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {

ty::Predicate::ObjectSafe(trait_def_id) => {
let violations = self.tcx.object_safety_violations(trait_def_id);
if let Some(err) = self.tcx.report_object_safety_error(
self.tcx.report_object_safety_error(
span,
trait_def_id,
violations,
) {
err
} else {
return;
}
)
}

ty::Predicate::ClosureKind(closure_def_id, closure_substs, kind) => {
Expand Down Expand Up @@ -934,11 +930,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {

TraitNotObjectSafe(did) => {
let violations = self.tcx.object_safety_violations(did);
if let Some(err) = self.tcx.report_object_safety_error(span, did, violations) {
err
} else {
return;
}
self.tcx.report_object_safety_error(span, did, violations)
}

// already reported in the query
Expand Down Expand Up @@ -1493,11 +1485,7 @@ impl<'tcx> TyCtxt<'tcx> {
span: Span,
trait_def_id: DefId,
violations: Vec<ObjectSafetyViolation>,
) -> Option<DiagnosticBuilder<'tcx>> {
if self.sess.trait_methods_not_found.borrow().contains(&span) {
// Avoid emitting error caused by non-existing method (#58734)
return None;
}
) -> DiagnosticBuilder<'tcx> {
let trait_str = self.def_path_str(trait_def_id);
let span = self.sess.source_map().def_span(span);
let mut err = struct_span_err!(
Expand All @@ -1515,7 +1503,13 @@ impl<'tcx> TyCtxt<'tcx> {
};
}
}
Some(err)

if self.sess.trait_methods_not_found.borrow().contains(&span) {
// Avoid emitting error caused by non-existing method (#58734)
err.cancel();
}

err
}
}

Expand Down Expand Up @@ -1926,6 +1920,10 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
err.note(&format!("required for the cast to the object type `{}`",
self.ty_to_string(object_ty)));
}
ObligationCauseCode::Coercion { source: _, target } => {
err.note(&format!("required by cast to type `{}`",
self.ty_to_string(target)));
}
ObligationCauseCode::RepeatVec => {
err.note("the `Copy` trait is required because the \
repeated element will be copied");
Expand Down
3 changes: 3 additions & 0 deletions src/librustc/traits/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -188,6 +188,9 @@ pub enum ObligationCauseCode<'tcx> {
/// Obligation incurred due to an object cast.
ObjectCastObligation(/* Object type */ Ty<'tcx>),

/// Obligation incurred due to a coercion.
Coercion { source: Ty<'tcx>, target: Ty<'tcx> },

// Various cases where expressions must be sized/copy/etc:
/// L = X implies that L is Sized
AssignmentLhsSized,
Expand Down
8 changes: 7 additions & 1 deletion src/librustc/traits/select.rs
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Expand Up @@ -2246,7 +2246,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
}

if let Some(principal) = data.principal() {
principal.with_self_ty(self.tcx(), self_ty)
if !self.infcx.tcx.features().object_safe_for_dispatch {
principal.with_self_ty(self.tcx(), self_ty)
} else if self.tcx().is_object_safe(principal.def_id()) {
principal.with_self_ty(self.tcx(), self_ty)
} else {
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else if?

return;
}
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Is the check for the feature flag necessary here? It seems like you could check if the trait is object safe anyway, even if the feature is not enabled. Or would that result in duplicate errors?

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@bovinebuddha bovinebuddha Mar 11, 2019 •
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I believe this is the code which adds the automatic 'impl Trait for dyn Trait' predicate to trait objects. Maybe the branches should be clarified and a comment added. Like:

// If we should add the automatic 'impl Trait for dyn Trait' or not
let object_impl_trait = !self.infcx.tcx.features().object_safe_for_dispatch ||
                        self.tcx().is_object_safe(principal.def_id());
 
if (object_impl_trait) {
  principal.with_self_ty(self.tcx(), self_ty)
} else {
 return;
}

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At minimum, a comment would be good here -- I think I vaguely prefer the if object_impl_trait { .. } version as well.

But a comment like this would be great:

// Prior to RFC 2027, dyn Foo: Foo was always true. But RFC 2027 makes that only true if Foo is object safe.

} else {
// Only auto-trait bounds exist.
return;
Expand Down
4 changes: 4 additions & 0 deletions src/librustc/traits/structural_impls.rs
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Expand Up @@ -481,6 +481,10 @@ impl<'a, 'tcx> Lift<'tcx> for traits::ObligationCauseCode<'a> {
.and_then(|r| Some(super::ObjectTypeBound(ty, r)))
),
super::ObjectCastObligation(ty) => tcx.lift(&ty).map(super::ObjectCastObligation),
super::Coercion { source, target } => Some(super::Coercion {
source: tcx.lift(&source)?,
target: tcx.lift(&target)?,
}),
super::AssignmentLhsSized => Some(super::AssignmentLhsSized),
super::TupleInitializerSized => Some(super::TupleInitializerSized),
super::StructInitializerSized => Some(super::StructInitializerSized),
Expand Down
3 changes: 2 additions & 1 deletion src/librustc/ty/error.rs
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Expand Up @@ -45,7 +45,7 @@ pub enum TypeError<'tcx> {
ProjectionMismatched(ExpectedFound<DefId>),
ProjectionBoundsLength(ExpectedFound<usize>),
ExistentialMismatch(ExpectedFound<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>),

ObjectUnsafeCoercion(DefId),
ConstMismatch(ExpectedFound<&'tcx ty::Const<'tcx>>),

IntrinsicCast,
Expand Down Expand Up @@ -179,6 +179,7 @@ impl<'tcx> fmt::Display for TypeError<'tcx> {
IntrinsicCast => {
write!(f, "cannot coerce intrinsics to function pointers")
}
ObjectUnsafeCoercion(_) => write!(f, "coercion to object-unsafe trait object"),
}
}
}
Expand Down
2 changes: 2 additions & 0 deletions src/librustc/ty/structural_impls.rs
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Expand Up @@ -749,6 +749,7 @@ impl<'a, 'tcx> Lift<'tcx> for ty::error::TypeError<'a> {
ExistentialMismatch(ref x) => return tcx.lift(x).map(ExistentialMismatch),
ConstMismatch(ref x) => return tcx.lift(x).map(ConstMismatch),
IntrinsicCast => IntrinsicCast,
ObjectUnsafeCoercion(ref x) => return tcx.lift(x).map(ObjectUnsafeCoercion),
})
}
}
Expand Down Expand Up @@ -1356,6 +1357,7 @@ EnumTypeFoldableImpl! {
(ty::error::TypeError::ExistentialMismatch)(x),
(ty::error::TypeError::ConstMismatch)(x),
(ty::error::TypeError::IntrinsicCast),
(ty::error::TypeError::ObjectUnsafeCoercion)(x),
}
}

Expand Down
25 changes: 15 additions & 10 deletions src/librustc/ty/wf.rs
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Expand Up @@ -380,16 +380,21 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
// obligations that don't refer to Self and
// checking those

let cause = self.cause(traits::MiscObligation);
let component_traits =
data.auto_traits().chain(data.principal_def_id());
self.out.extend(
component_traits.map(|did| traits::Obligation::new(
cause.clone(),
param_env,
ty::Predicate::ObjectSafe(did)
))
);
let defer_to_coercion =
self.infcx.tcx.features().object_safe_for_dispatch;

if !defer_to_coercion {
let cause = self.cause(traits::MiscObligation);
let component_traits =
data.auto_traits().chain(data.principal_def_id());
self.out.extend(
component_traits.map(|did| traits::Obligation::new(
cause.clone(),
param_env,
ty::Predicate::ObjectSafe(did)
))
);
}
}

// Inference variables are the complicated case, since we don't
Expand Down
26 changes: 26 additions & 0 deletions src/librustc_errors/diagnostic.rs
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Expand Up @@ -152,6 +152,32 @@ impl Diagnostic {
self.note_expected_found_extra(label, expected, found, &"", &"")
}

pub fn note_unsuccessfull_coercion(&mut self,
expected: DiagnosticStyledString,
found: DiagnosticStyledString)
-> &mut Self
{
let mut msg: Vec<_> =
vec![(format!("required when trying to coerce from type `"),
Style::NoStyle)];
msg.extend(expected.0.iter()
.map(|x| match *x {
StringPart::Normal(ref s) => (s.to_owned(), Style::NoStyle),
StringPart::Highlighted(ref s) => (s.to_owned(), Style::Highlight),
}));
msg.push((format!("` to type '"), Style::NoStyle));
msg.extend(found.0.iter()
.map(|x| match *x {
StringPart::Normal(ref s) => (s.to_owned(), Style::NoStyle),
StringPart::Highlighted(ref s) => (s.to_owned(), Style::Highlight),
}));
msg.push((format!("`"), Style::NoStyle));

// For now, just attach these as notes
self.highlighted_note(msg);
self
}

pub fn note_expected_found_extra(&mut self,
label: &dyn fmt::Display,
expected: DiagnosticStyledString,
Expand Down
5 changes: 5 additions & 0 deletions src/librustc_errors/diagnostic_builder.rs
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Expand Up @@ -209,6 +209,11 @@ impl<'a> DiagnosticBuilder<'a> {
found_extra: &dyn fmt::Display,
) -> &mut Self);

forward!(pub fn note_unsuccessfull_coercion(&mut self,
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Nit: I think it is spelled unsuccessful (with one l), at least in American English.

expected: DiagnosticStyledString,
found: DiagnosticStyledString,
) -> &mut Self);

forward!(pub fn note(&mut self, msg: &str) -> &mut Self);
forward!(pub fn span_note<S: Into<MultiSpan>>(&mut self,
sp: S,
Expand Down
3 changes: 1 addition & 2 deletions src/librustc_typeck/astconv.rs
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Expand Up @@ -1275,8 +1275,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
span,
item.trait_ref().def_id(),
object_safety_violations
)
.map(|mut err| err.emit());
).emit();
return tcx.types.err;
}
}
Expand Down
43 changes: 32 additions & 11 deletions src/librustc_typeck/check/cast.rs
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Expand Up @@ -428,21 +428,36 @@ impl<'a, 'tcx> CastCheck<'tcx> {
self.report_cast_to_unsized_type(fcx);
} else if self.expr_ty.references_error() || self.cast_ty.references_error() {
// No sense in giving duplicate error messages
} else if self.try_coercion_cast(fcx) {
self.trivial_cast_lint(fcx);
debug!(" -> CoercionCast");
fcx.tables.borrow_mut().set_coercion_cast(self.expr.hir_id.local_id);

} else {
match self.do_check(fcx) {
Ok(k) => {
debug!(" -> {:?}", k);
match self.try_coercion_cast(fcx) {
Ok(()) => {
self.trivial_cast_lint(fcx);
debug!(" -> CoercionCast");
fcx.tables.borrow_mut()
.set_coercion_cast(self.expr.hir_id.local_id);
}
Err(ty::error::TypeError::ObjectUnsafeCoercion(did)) => {
self.report_object_unsafe_cast(&fcx, did);
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I think these changes would fall out from the approach I highlighted, and then changing the trait error handling code.

}
Err(_) => {
match self.do_check(fcx) {
Ok(k) => {
debug!(" -> {:?}", k);
}
Err(e) => self.report_cast_error(fcx, e),
};
}
Err(e) => self.report_cast_error(fcx, e),
};
}
}

fn report_object_unsafe_cast(&self, fcx: &FnCtxt<'a, 'tcx>, did: DefId) {
let violations = fcx.tcx.object_safety_violations(did);
let mut err = fcx.tcx.report_object_safety_error(self.cast_span, did, violations);
err.note(&format!("required by cast to type '{}'", fcx.ty_to_string(self.cast_ty)));
err.emit();
}

/// Checks a cast, and report an error if one exists. In some cases, this
/// can return Ok and create type errors in the fcx rather than returning
/// directly. coercion-cast is handled in check instead of here.
Expand Down Expand Up @@ -646,8 +661,14 @@ impl<'a, 'tcx> CastCheck<'tcx> {
}
}

fn try_coercion_cast(&self, fcx: &FnCtxt<'a, 'tcx>) -> bool {
fcx.try_coerce(self.expr, self.expr_ty, self.cast_ty, AllowTwoPhase::No).is_ok()
fn try_coercion_cast(
&self,
fcx: &FnCtxt<'a, 'tcx>,
) -> Result<(), ty::error::TypeError<'_>> {
match fcx.try_coerce(self.expr, self.expr_ty, self.cast_ty, AllowTwoPhase::No) {
Ok(_) => Ok(()),
Err(err) => Err(err),
}
}
}

Expand Down
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