bjoernager/rust
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Provide more suggestions for cloning immutable bindings

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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();
   |               ++++++++++
```

```
error[E0596]: cannot borrow `*inner` as mutable, as it is behind a `&` reference
  --> $DIR/issue-91206.rs:14:5
   |
LL |     inner.clear();
   |     ^^^^^ `inner` is a `&` reference, so the data it refers to cannot be borrowed as mutable
   |
help: you can `clone` the `Vec<usize>` value and consume it, but this might not be your desired behavior
  --> $DIR/issue-91206.rs:11:17
   |
LL |     let inner = client.get_inner_ref();
   |                 ^^^^^^^^^^^^^^^^^^^^^^
help: consider specifying this binding's type
   |
LL |     let inner: &mut Vec<usize> = client.get_inner_ref();
   |              +++++++++++++++++
```
This commit is contained in:
Esteban Küber 2023-11-21 23:41:50 +00:00
parent 210a672005
commit cc80106cb5
9 changed files with 196 additions and 10 deletions
Download patch file Download diff file Expand all files Collapse all files

102
compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs
View file

@ -3,8 +3,9 @@ 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},
@ -12,6 +13,8 @@ use rustc_middle::{
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;
@ -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 => {