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Auto merge of rust-lang#118076 - estebank:issue-109429, r=davidtwco
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Tweak `.clone()` suggestion to work in more cases

When going through auto-deref, the `<T as Clone>` impl sometimes needs to be specified for rustc to actually clone the value and not the reference.

```
error[E0507]: cannot move out of dereference of `S`
  --> $DIR/needs-clone-through-deref.rs:15:18
   |
LL |         for _ in self.clone().into_iter() {}
   |                  ^^^^^^^^^^^^ ----------- value moved due to this method call
   |                  |
   |                  move occurs because value has type `Vec<usize>`, which does not implement the `Copy` trait
   |
note: `into_iter` takes ownership of the receiver `self`, which moves value
  --> $SRC_DIR/core/src/iter/traits/collect.rs:LL:COL
help: you can `clone` the value and consume it, but this might not be your desired behavior
   |
LL |         for _ in <Vec<usize> as Clone>::clone(&self.clone()).into_iter() {}
   |                  ++++++++++++++++++++++++++++++            +
```

When encountering a move error, look for implementations of `Clone` for the moved type. If there is one, check if all its obligations are met. If they are, we suggest cloning without caveats. If they aren't, we suggest cloning while mentioning the unmet obligations, potentially suggesting `#[derive(Clone)]` when appropriate.

```
error[E0507]: cannot move out of a shared reference
  --> $DIR/suggest-clone-when-some-obligation-is-unmet.rs:20:28
   |
LL |     let mut copy: Vec<U> = map.clone().into_values().collect();
   |                            ^^^^^^^^^^^ ------------- value moved due to this method call
   |                            |
   |                            move occurs because value has type `HashMap<T, U, Hash128_1>`, which does not implement the `Copy` trait
   |
note: `HashMap::<K, V, S>::into_values` takes ownership of the receiver `self`, which moves value
  --> $SRC_DIR/std/src/collections/hash/map.rs:LL:COL
help: you could `clone` the value and consume it, if the `Hash128_1: Clone` trait bound could be satisfied
   |
LL |     let mut copy: Vec<U> = <HashMap<T, U, Hash128_1> as Clone>::clone(&map.clone()).into_values().collect();
   |                            ++++++++++++++++++++++++++++++++++++++++++++           +
help: consider annotating `Hash128_1` with `#[derive(Clone)]`
   |
LL + #[derive(Clone)]
LL | pub struct Hash128_1;
   |
```

Fix rust-lang#109429.

When encountering multiple mutable borrows, suggest cloning and adding
derive annotations as needed.

```
error[E0596]: cannot borrow `sm.x` as mutable, as it is behind a `&` reference
  --> $DIR/accidentally-cloning-ref-borrow-error.rs:32:9
   |
LL |     foo(&mut sm.x);
   |         ^^^^^^^^^ `sm` is a `&` reference, so the data it refers to cannot be borrowed as mutable
   |
help: `Str` doesn't implement `Clone`, so this call clones the reference `&Str`
  --> $DIR/accidentally-cloning-ref-borrow-error.rs:31:21
   |
LL |     let mut sm = sr.clone();
   |                     ^^^^^^^
help: consider annotating `Str` with `#[derive(Clone)]`
   |
LL + #[derive(Clone)]
LL | struct Str {
   |
help: consider specifying this binding's type
   |
LL |     let mut sm: &mut Str = sr.clone();
   |               ++++++++++
```

Fix rust-lang#34629. Fix rust-lang#76643. Fix rust-lang#91532.
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@bors
bors committed Dec 5, 2023
2 parents 9358642 + a8faa82 commit f67523d
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155 changes: 103 additions & 52 deletions compiler/rustc_borrowck/src/diagnostics/mod.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@ use rustc_hir::def::{CtorKind, Namespace};
use rustc_hir::CoroutineKind;
use rustc_index::IndexSlice;
use rustc_infer::infer::BoundRegionConversionTime;
use rustc_infer::traits::{FulfillmentErrorCode, SelectionError};
use rustc_middle::mir::tcx::PlaceTy;
use rustc_middle::mir::{
AggregateKind, CallSource, ConstOperand, FakeReadCause, Local, LocalInfo, LocalKind, Location,
Expand All @@ -24,10 +25,9 @@ use rustc_mir_dataflow::move_paths::{InitLocation, LookupResult};
use rustc_span::def_id::LocalDefId;
use rustc_span::{symbol::sym, Span, Symbol, DUMMY_SP};
use rustc_target::abi::{FieldIdx, VariantIdx};
use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
use rustc_trait_selection::traits::{
type_known_to_meet_bound_modulo_regions, Obligation, ObligationCause,
};
use rustc_trait_selection::infer::InferCtxtExt;
use rustc_trait_selection::traits::error_reporting::suggestions::TypeErrCtxtExt as _;
use rustc_trait_selection::traits::type_known_to_meet_bound_modulo_regions;

use super::borrow_set::BorrowData;
use super::MirBorrowckCtxt;
Expand Down Expand Up @@ -1043,7 +1043,38 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
}
CallKind::Normal { self_arg, desugaring, method_did, method_args } => {
let self_arg = self_arg.unwrap();
let mut has_sugg = false;
let tcx = self.infcx.tcx;
// Avoid pointing to the same function in multiple different
// error messages.
if span != DUMMY_SP && self.fn_self_span_reported.insert(self_arg.span) {
self.explain_iterator_advancement_in_for_loop_if_applicable(
err,
span,
&move_spans,
);

let func = tcx.def_path_str(method_did);
err.subdiagnostic(CaptureReasonNote::FuncTakeSelf {
func,
place_name: place_name.clone(),
span: self_arg.span,
});
}
let parent_did = tcx.parent(method_did);
let parent_self_ty =
matches!(tcx.def_kind(parent_did), rustc_hir::def::DefKind::Impl { .. })
.then_some(parent_did)
.and_then(|did| match tcx.type_of(did).instantiate_identity().kind() {
ty::Adt(def, ..) => Some(def.did()),
_ => None,
});
let is_option_or_result = parent_self_ty.is_some_and(|def_id| {
matches!(tcx.get_diagnostic_name(def_id), Some(sym::Option | sym::Result))
});
if is_option_or_result && maybe_reinitialized_locations_is_empty {
err.subdiagnostic(CaptureReasonLabel::BorrowContent { var_span });
}
if let Some((CallDesugaringKind::ForLoopIntoIter, _)) = desugaring {
let ty = moved_place.ty(self.body, tcx).ty;
let suggest = match tcx.get_diagnostic_item(sym::IntoIterator) {
Expand Down Expand Up @@ -1108,7 +1139,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
// Erase and shadow everything that could be passed to the new infcx.
let ty = moved_place.ty(self.body, tcx).ty;

if let ty::Adt(def, args) = ty.kind()
if let ty::Adt(def, args) = ty.peel_refs().kind()
&& Some(def.did()) == tcx.lang_items().pin_type()
&& let ty::Ref(_, _, hir::Mutability::Mut) = args.type_at(0).kind()
&& let self_ty = self.infcx.instantiate_binder_with_fresh_vars(
Expand All @@ -1124,56 +1155,76 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
span: move_span.shrink_to_hi(),
},
);
has_sugg = true;
}
if let Some(clone_trait) = tcx.lang_items().clone_trait()
&& let trait_ref = ty::TraitRef::new(tcx, clone_trait, [ty])
&& let o = Obligation::new(
tcx,
ObligationCause::dummy(),
self.param_env,
ty::Binder::dummy(trait_ref),
)
&& self.infcx.predicate_must_hold_modulo_regions(&o)
{
err.span_suggestion_verbose(
move_span.shrink_to_hi(),
"you can `clone` the value and consume it, but this might not be \
your desired behavior",
".clone()".to_string(),
Applicability::MaybeIncorrect,
);
if let Some(clone_trait) = tcx.lang_items().clone_trait() {
let sugg = if moved_place
.iter_projections()
.any(|(_, elem)| matches!(elem, ProjectionElem::Deref))
{
vec![
// We use the fully-qualified path because `.clone()` can
// sometimes choose `<&T as Clone>` instead of `<T as Clone>`
// when going through auto-deref, so this ensures that doesn't
// happen, causing suggestions for `.clone().clone()`.
(move_span.shrink_to_lo(), format!("<{ty} as Clone>::clone(&")),
(move_span.shrink_to_hi(), ")".to_string()),
]
} else {
vec![(move_span.shrink_to_hi(), ".clone()".to_string())]
};
if let Some(errors) =
self.infcx.could_impl_trait(clone_trait, ty, self.param_env)
&& !has_sugg
{
let msg = match &errors[..] {
[] => "you can `clone` the value and consume it, but this \
might not be your desired behavior"
.to_string(),
[error] => {
format!(
"you could `clone` the value and consume it, if \
the `{}` trait bound could be satisfied",
error.obligation.predicate,
)
}
[errors @ .., last] => {
format!(
"you could `clone` the value and consume it, if \
the following trait bounds could be satisfied: {} \
and `{}`",
errors
.iter()
.map(|e| format!("`{}`", e.obligation.predicate))
.collect::<Vec<_>>()
.join(", "),
last.obligation.predicate,
)
}
};
err.multipart_suggestion_verbose(
msg,
sugg.clone(),
Applicability::MaybeIncorrect,
);
for error in errors {
if let FulfillmentErrorCode::CodeSelectionError(
SelectionError::Unimplemented,
) = error.code
&& let ty::PredicateKind::Clause(ty::ClauseKind::Trait(
pred,
)) = error.obligation.predicate.kind().skip_binder()
{
self.infcx.err_ctxt().suggest_derive(
&error.obligation,
err,
error.obligation.predicate.kind().rebind(pred),
);
}
}
}
}
}
// Avoid pointing to the same function in multiple different
// error messages.
if span != DUMMY_SP && self.fn_self_span_reported.insert(self_arg.span) {
self.explain_iterator_advancement_in_for_loop_if_applicable(
err,
span,
&move_spans,
);

let func = tcx.def_path_str(method_did);
err.subdiagnostic(CaptureReasonNote::FuncTakeSelf {
func,
place_name,
span: self_arg.span,
});
}
let parent_did = tcx.parent(method_did);
let parent_self_ty =
matches!(tcx.def_kind(parent_did), rustc_hir::def::DefKind::Impl { .. })
.then_some(parent_did)
.and_then(|did| match tcx.type_of(did).instantiate_identity().kind() {
ty::Adt(def, ..) => Some(def.did()),
_ => None,
});
let is_option_or_result = parent_self_ty.is_some_and(|def_id| {
matches!(tcx.get_diagnostic_name(def_id), Some(sym::Option | sym::Result))
});
if is_option_or_result && maybe_reinitialized_locations_is_empty {
err.subdiagnostic(CaptureReasonLabel::BorrowContent { var_span });
}
}
// Other desugarings takes &self, which cannot cause a move
_ => {}
Expand Down
102 changes: 101 additions & 1 deletion compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -3,15 +3,18 @@ use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed
use rustc_hir as hir;
use rustc_hir::intravisit::Visitor;
use rustc_hir::Node;
use rustc_infer::traits;
use rustc_middle::mir::{Mutability, Place, PlaceRef, ProjectionElem};
use rustc_middle::ty::{self, InstanceDef, Ty, TyCtxt};
use rustc_middle::ty::{self, InstanceDef, ToPredicate, Ty, TyCtxt};
use rustc_middle::{
hir::place::PlaceBase,
mir::{self, BindingForm, Local, LocalDecl, LocalInfo, LocalKind, Location},
};
use rustc_span::symbol::{kw, Symbol};
use rustc_span::{sym, BytePos, DesugaringKind, Span};
use rustc_target::abi::FieldIdx;
use rustc_trait_selection::infer::InferCtxtExt;
use rustc_trait_selection::traits::error_reporting::suggestions::TypeErrCtxtExt;

use crate::diagnostics::BorrowedContentSource;
use crate::util::FindAssignments;
Expand Down Expand Up @@ -1212,6 +1215,103 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
if let Some(hir_id) = hir_id
&& let Some(hir::Node::Local(local)) = hir_map.find(hir_id)
{
let tables = self.infcx.tcx.typeck(def_id.as_local().unwrap());
if let Some(clone_trait) = self.infcx.tcx.lang_items().clone_trait()
&& let Some(expr) = local.init
&& let ty = tables.node_type_opt(expr.hir_id)
&& let Some(ty) = ty
&& let ty::Ref(..) = ty.kind()
{
match self
.infcx
.could_impl_trait(clone_trait, ty.peel_refs(), self.param_env)
.as_deref()
{
Some([]) => {
// The type implements Clone.
err.span_help(
expr.span,
format!(
"you can `clone` the `{}` value and consume it, but this \
might not be your desired behavior",
ty.peel_refs(),
),
);
}
None => {
if let hir::ExprKind::MethodCall(segment, _rcvr, [], span) =
expr.kind
&& segment.ident.name == sym::clone
{
err.span_help(
span,
format!(
"`{}` doesn't implement `Clone`, so this call clones \
the reference `{ty}`",
ty.peel_refs(),
),
);
}
// The type doesn't implement Clone.
let trait_ref = ty::Binder::dummy(ty::TraitRef::new(
self.infcx.tcx,
clone_trait,
[ty.peel_refs()],
));
let obligation = traits::Obligation::new(
self.infcx.tcx,
traits::ObligationCause::dummy(),
self.param_env,
trait_ref,
);
self.infcx.err_ctxt().suggest_derive(
&obligation,
err,
trait_ref.to_predicate(self.infcx.tcx),
);
}
Some(errors) => {
if let hir::ExprKind::MethodCall(segment, _rcvr, [], span) =
expr.kind
&& segment.ident.name == sym::clone
{
err.span_help(
span,
format!(
"`{}` doesn't implement `Clone` because its \
implementations trait bounds could not be met, so \
this call clones the reference `{ty}`",
ty.peel_refs(),
),
);
err.note(format!(
"the following trait bounds weren't met: {}",
errors
.iter()
.map(|e| e.obligation.predicate.to_string())
.collect::<Vec<_>>()
.join("\n"),
));
}
// The type doesn't implement Clone because of unmet obligations.
for error in errors {
if let traits::FulfillmentErrorCode::CodeSelectionError(
traits::SelectionError::Unimplemented,
) = error.code
&& let ty::PredicateKind::Clause(ty::ClauseKind::Trait(
pred,
)) = error.obligation.predicate.kind().skip_binder()
{
self.infcx.err_ctxt().suggest_derive(
&error.obligation,
err,
error.obligation.predicate.kind().rebind(pred),
);
}
}
}
}
}
let (changing, span, sugg) = match local.ty {
Some(ty) => ("changing", ty.span, message),
None => {
Expand Down
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