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Tweak "object unsafe" errors #78002

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Oct 21, 2020
Merged

Tweak "object unsafe" errors #78002

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ae0e3d0
Tweak "object unsafe" errors
estebank Oct 16, 2020
88f5e11
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estebank Oct 20, 2020
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39 changes: 23 additions & 16 deletions compiler/rustc_infer/src/traits/error_reporting/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,12 +2,12 @@ use super::ObjectSafetyViolation;

use crate::infer::InferCtxt;
use rustc_data_structures::fx::FxHashSet;
use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder};
use rustc_errors::{struct_span_err, DiagnosticBuilder};
use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_middle::ty::TyCtxt;
use rustc_span::symbol::Symbol;
use rustc_span::Span;
use rustc_span::{MultiSpan, Span};
use std::fmt;

impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
Expand Down Expand Up @@ -54,10 +54,11 @@ pub fn report_object_safety_error(
"the trait `{}` cannot be made into an object",
trait_str
);
err.span_label(span, format!("the trait `{}` cannot be made into an object", trait_str));
err.span_label(span, format!("`{}` cannot be made into an object", trait_str));

let mut reported_violations = FxHashSet::default();
let mut had_span_label = false;
let mut multi_span = vec![];
let mut messages = vec![];
for violation in violations {
if let ObjectSafetyViolation::SizedSelf(sp) = &violation {
if !sp.is_empty() {
Expand All @@ -71,31 +72,37 @@ pub fn report_object_safety_error(
let msg = if trait_span.is_none() || spans.is_empty() {
format!("the trait cannot be made into an object because {}", violation.error_msg())
} else {
had_span_label = true;
format!("...because {}", violation.error_msg())
};
if spans.is_empty() {
err.note(&msg);
} else {
for span in spans {
err.span_label(span, &msg);
multi_span.push(span);
messages.push(msg.clone());
}
}
match (trait_span, violation.solution()) {
(Some(_), Some((note, None))) => {
err.help(&note);
}
(Some(_), Some((note, Some((sugg, span))))) => {
err.span_suggestion(span, &note, sugg, Applicability::MachineApplicable);
}
if trait_span.is_some() {
// Only provide the help if its a local trait, otherwise it's not actionable.
_ => {}
violation.solution(&mut err);
}
}
}
if let (Some(trait_span), true) = (trait_span, had_span_label) {
err.span_label(trait_span, "this trait cannot be made into an object...");
let has_multi_span = !multi_span.is_empty();
let mut note_span = MultiSpan::from_spans(multi_span.clone());
if let (Some(trait_span), true) = (trait_span, has_multi_span) {
note_span
.push_span_label(trait_span, "this trait cannot be made into an object...".to_string());
}
for (span, msg) in multi_span.into_iter().zip(messages.into_iter()) {
note_span.push_span_label(span, msg);
}
err.span_note(
note_span,
"for a trait to be \"object safe\" it needs to allow building a vtable to allow the call \
to be resolvable dynamically; for more information visit \
<https://doc.rust-lang.org/reference/items/traits.html#object-safety>",
);

if tcx.sess.trait_methods_not_found.borrow().contains(&span) {
// Avoid emitting error caused by non-existing method (#58734)
Expand Down
76 changes: 55 additions & 21 deletions compiler/rustc_middle/src/traits/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@ use crate::mir::interpret::ErrorHandled;
use crate::ty::subst::SubstsRef;
use crate::ty::{self, AdtKind, Ty, TyCtxt};

use rustc_errors::{Applicability, DiagnosticBuilder};
use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_span::symbol::Symbol;
Expand Down Expand Up @@ -646,13 +647,13 @@ impl ObjectSafetyViolation {
ObjectSafetyViolation::SizedSelf(_) => "it requires `Self: Sized`".into(),
ObjectSafetyViolation::SupertraitSelf(ref spans) => {
if spans.iter().any(|sp| *sp != DUMMY_SP) {
"it uses `Self` as a type parameter in this".into()
"it uses `Self` as a type parameter".into()
} else {
"it cannot use `Self` as a type parameter in a supertrait or `where`-clause"
.into()
}
}
ObjectSafetyViolation::Method(name, MethodViolationCode::StaticMethod(_), _) => {
ObjectSafetyViolation::Method(name, MethodViolationCode::StaticMethod(_, _, _), _) => {
format!("associated function `{}` has no `self` parameter", name).into()
}
ObjectSafetyViolation::Method(
Expand Down Expand Up @@ -686,32 +687,65 @@ impl ObjectSafetyViolation {
}
}

pub fn solution(&self) -> Option<(String, Option<(String, Span)>)> {
Some(match *self {
ObjectSafetyViolation::SizedSelf(_) | ObjectSafetyViolation::SupertraitSelf(_) => {
return None;
pub fn solution(&self, err: &mut DiagnosticBuilder<'_>) {
match *self {
ObjectSafetyViolation::SizedSelf(_) | ObjectSafetyViolation::SupertraitSelf(_) => {}
ObjectSafetyViolation::Method(
name,
MethodViolationCode::StaticMethod(sugg, self_span, has_args),
_,
) => {
err.span_suggestion(
self_span,
&format!(
"consider turning `{}` into a method by giving it a `&self` argument",
name
),
format!("&self{}", if has_args { ", " } else { "" }),
Applicability::MaybeIncorrect,
);
match sugg {
Some((sugg, span)) => {
err.span_suggestion(
span,
&format!(
"alternatively, consider constraining `{}` so it does not apply to \
trait objects",
name
),
sugg.to_string(),
Applicability::MaybeIncorrect,
);
}
None => {
err.help(&format!(
"consider turning `{}` into a method by giving it a `&self` \
argument or constraining it so it does not apply to trait objects",
name
));
}
}
}
ObjectSafetyViolation::Method(name, MethodViolationCode::StaticMethod(sugg), _) => (
format!(
"consider turning `{}` into a method by giving it a `&self` argument or \
constraining it so it does not apply to trait objects",
name
),
sugg.map(|(sugg, sp)| (sugg.to_string(), sp)),
),
ObjectSafetyViolation::Method(
name,
MethodViolationCode::UndispatchableReceiver,
span,
) => (
format!("consider changing method `{}`'s `self` parameter to be `&self`", name),
Some(("&Self".to_string(), span)),
),
) => {
err.span_suggestion(
span,
&format!(
"consider changing method `{}`'s `self` parameter to be `&self`",
name
),
"&Self".to_string(),
Applicability::MachineApplicable,
);
}
ObjectSafetyViolation::AssocConst(name, _)
| ObjectSafetyViolation::Method(name, ..) => {
(format!("consider moving `{}` to another trait", name), None)
err.help(&format!("consider moving `{}` to another trait", name));
}
})
}
}

pub fn spans(&self) -> SmallVec<[Span; 1]> {
Expand All @@ -735,7 +769,7 @@ impl ObjectSafetyViolation {
#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)]
pub enum MethodViolationCode {
/// e.g., `fn foo()`
StaticMethod(Option<(&'static str, Span)>),
StaticMethod(Option<(&'static str, Span)>, Span, bool /* has args */),

/// e.g., `fn foo(&self, x: Self)`
ReferencesSelfInput(usize),
Expand Down
111 changes: 63 additions & 48 deletions compiler/rustc_trait_selection/src/traits/object_safety.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,15 +13,15 @@ use super::elaborate_predicates;
use crate::infer::TyCtxtInferExt;
use crate::traits::query::evaluate_obligation::InferCtxtExt;
use crate::traits::{self, Obligation, ObligationCause};
use rustc_errors::{Applicability, FatalError};
use rustc_errors::FatalError;
use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_middle::ty::subst::{GenericArg, InternalSubsts, Subst};
use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable, TypeVisitor, WithConstness};
use rustc_middle::ty::{Predicate, ToPredicate};
use rustc_session::lint::builtin::WHERE_CLAUSES_OBJECT_SAFETY;
use rustc_span::symbol::Symbol;
use rustc_span::Span;
use rustc_span::{MultiSpan, Span};
use smallvec::SmallVec;

use std::array;
Expand Down Expand Up @@ -100,49 +100,7 @@ fn object_safety_violations_for_trait(
span,
) = violation
{
// Using `CRATE_NODE_ID` is wrong, but it's hard to get a more precise id.
// It's also hard to get a use site span, so we use the method definition span.
tcx.struct_span_lint_hir(
WHERE_CLAUSES_OBJECT_SAFETY,
hir::CRATE_HIR_ID,
*span,
|lint| {
let mut err = lint.build(&format!(
"the trait `{}` cannot be made into an object",
tcx.def_path_str(trait_def_id)
));
let node = tcx.hir().get_if_local(trait_def_id);
let msg = if let Some(hir::Node::Item(item)) = node {
err.span_label(
item.ident.span,
"this trait cannot be made into an object...",
);
format!("...because {}", violation.error_msg())
} else {
format!(
"the trait cannot be made into an object because {}",
violation.error_msg()
)
};
err.span_label(*span, &msg);
match (node, violation.solution()) {
(Some(_), Some((note, None))) => {
err.help(&note);
}
(Some(_), Some((note, Some((sugg, span))))) => {
err.span_suggestion(
span,
&note,
sugg,
Applicability::MachineApplicable,
);
}
// Only provide the help if its a local trait, otherwise it's not actionable.
_ => {}
}
err.emit();
},
);
lint_object_unsafe_trait(tcx, *span, trait_def_id, violation);
false
} else {
true
Expand Down Expand Up @@ -180,6 +138,51 @@ fn object_safety_violations_for_trait(
violations
}

/// Lint object-unsafe trait.
fn lint_object_unsafe_trait(
tcx: TyCtxt<'_>,
span: Span,
trait_def_id: DefId,
violation: &ObjectSafetyViolation,
) {
// Using `CRATE_NODE_ID` is wrong, but it's hard to get a more precise id.
// It's also hard to get a use site span, so we use the method definition span.
tcx.struct_span_lint_hir(WHERE_CLAUSES_OBJECT_SAFETY, hir::CRATE_HIR_ID, span, |lint| {
let mut err = lint.build(&format!(
"the trait `{}` cannot be made into an object",
tcx.def_path_str(trait_def_id)
));
let node = tcx.hir().get_if_local(trait_def_id);
let mut spans = MultiSpan::from_span(span);
if let Some(hir::Node::Item(item)) = node {
spans.push_span_label(
item.ident.span,
"this trait cannot be made into an object...".into(),
);
spans.push_span_label(span, format!("...because {}", violation.error_msg()));
} else {
spans.push_span_label(
span,
format!(
"the trait cannot be made into an object because {}",
violation.error_msg()
),
);
};
err.span_note(
spans,
"for a trait to be \"object safe\" it needs to allow building a vtable to allow the \
call to be resolvable dynamically; for more information visit \
<https://doc.rust-lang.org/reference/items/traits.html#object-safety>",
);
if node.is_some() {
// Only provide the help if its a local trait, otherwise it's not
violation.solution(&mut err);
}
err.emit();
});
}

fn sized_trait_bound_spans<'tcx>(
tcx: TyCtxt<'tcx>,
bounds: hir::GenericBounds<'tcx>,
Expand Down Expand Up @@ -385,6 +388,8 @@ fn virtual_call_violation_for_method<'tcx>(
trait_def_id: DefId,
method: &ty::AssocItem,
) -> Option<MethodViolationCode> {
let sig = tcx.fn_sig(method.def_id);

// The method's first parameter must be named `self`
if !method.fn_has_self_parameter {
// We'll attempt to provide a structured suggestion for `Self: Sized`.
Expand All @@ -395,11 +400,21 @@ fn virtual_call_violation_for_method<'tcx>(
[.., pred] => (", Self: Sized", pred.span().shrink_to_hi()),
},
);
return Some(MethodViolationCode::StaticMethod(sugg));
// Get the span pointing at where the `self` receiver should be.
let sm = tcx.sess.source_map();
let self_span = method.ident.span.to(tcx
.hir()
.span_if_local(method.def_id)
.unwrap_or_else(|| sm.next_point(method.ident.span))
.shrink_to_hi());
let self_span = sm.span_through_char(self_span, '(').shrink_to_hi();
return Some(MethodViolationCode::StaticMethod(
sugg,
self_span,
!sig.inputs().skip_binder().is_empty(),
));
}

let sig = tcx.fn_sig(method.def_id);

for (i, input_ty) in sig.skip_binder().inputs()[1..].iter().enumerate() {
if contains_illegal_self_type_reference(tcx, trait_def_id, input_ty) {
return Some(MethodViolationCode::ReferencesSelfInput(i));
Expand Down
14 changes: 8 additions & 6 deletions src/test/ui/associated-consts/associated-const-in-trait.stderr
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@@ -1,15 +1,17 @@
error[E0038]: the trait `Trait` cannot be made into an object
--> $DIR/associated-const-in-trait.rs:9:6
|
LL | trait Trait {
| ----- this trait cannot be made into an object...
LL | const N: usize;
| - ...because it contains this associated `const`
...
LL | impl dyn Trait {
| ^^^^^^^^^ the trait `Trait` cannot be made into an object
| ^^^^^^^^^ `Trait` cannot be made into an object
|
= help: consider moving `N` to another trait
note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
--> $DIR/associated-const-in-trait.rs:6:11
|
LL | trait Trait {
| ----- this trait cannot be made into an object...
LL | const N: usize;
| ^ ...because it contains this associated `const`

error: aborting due to previous error

Expand Down
14 changes: 8 additions & 6 deletions src/test/ui/associated-item/issue-48027.stderr
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@@ -1,15 +1,17 @@
error[E0038]: the trait `Bar` cannot be made into an object
--> $DIR/issue-48027.rs:6:6
|
LL | trait Bar {
| --- this trait cannot be made into an object...
LL | const X: usize;
| - ...because it contains this associated `const`
...
LL | impl dyn Bar {}
| ^^^^^^^ the trait `Bar` cannot be made into an object
| ^^^^^^^ `Bar` cannot be made into an object
|
= help: consider moving `X` to another trait
note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
--> $DIR/issue-48027.rs:2:11
|
LL | trait Bar {
| --- this trait cannot be made into an object...
LL | const X: usize;
| ^ ...because it contains this associated `const`

error[E0283]: type annotations needed
--> $DIR/issue-48027.rs:3:32
Expand Down
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