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Suggest mutable borrow on read only for-loop that should be mutable

Browse Source 
```
error[E0596]: cannot borrow `*test` as mutable, as it is behind a `&` reference
  --> $DIR/suggest-mut-iterator.rs:22:9
   |
LL |     for test in &tests {
   |                 ------ this iterator yields `&` references
LL |         test.add(2);
   |         ^^^^ `test` is a `&` reference, so the data it refers to cannot be borrowed as mutable
   |
help: use a mutable iterator instead
   |
LL |     for test in &mut tests {
   |                  +++
```

Address #114311.
This commit is contained in:
Esteban Küber 2023-08-23 21:39:16 +00:00
parent fe5f591257
commit c1a7af0f2a
4 changed files with 167 additions and 88 deletions
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179
compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs
View File

@ -225,17 +225,17 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
}
if suggest {
borrow_spans.var_subdiag(
None,
&mut err,
Some(mir::BorrowKind::Mut { kind: mir::MutBorrowKind::Default }),
|_kind, var_span| {
let place = self.describe_any_place(access_place.as_ref());
crate::session_diagnostics::CaptureVarCause::MutableBorrowUsePlaceClosure {
place,
var_span,
}
},
);
None,
&mut err,
Some(mir::BorrowKind::Mut { kind: mir::MutBorrowKind::Default }),
|_kind, var_span| {
let place = self.describe_any_place(access_place.as_ref());
crate::session_diagnostics::CaptureVarCause::MutableBorrowUsePlaceClosure {
place,
var_span,
}
},
);
}
borrow_span
}
@ -262,11 +262,8 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
} => {
err.span_label(span, format!("cannot {act}"));
if let Some(span) = get_mut_span_in_struct_field(
self.infcx.tcx,
Place::ty_from(local, proj_base, self.body, self.infcx.tcx).ty,
*field,
) {
let place = Place::ty_from(local, proj_base, self.body, self.infcx.tcx);
if let Some(span) = get_mut_span_in_struct_field(self.infcx.tcx, place.ty, *field) {
err.span_suggestion_verbose(
span,
"consider changing this to be mutable",
@ -781,83 +778,88 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
// Attempt to search similar mutable associated items for suggestion.
// In the future, attempt in all path but initially for RHS of for_loop
fn suggest_similar_mut_method_for_for_loop(&self, err: &mut Diagnostic) {
fn suggest_similar_mut_method_for_for_loop(&self, err: &mut Diagnostic, span: Span) {
use hir::{
Expr,
ExprKind::{Block, Call, DropTemps, Match, MethodCall},
BorrowKind, Expr,
ExprKind::{AddrOf, Block, Call, MethodCall},
};
let hir_map = self.infcx.tcx.hir();
if let Some(body_id) = hir_map.maybe_body_owned_by(self.mir_def_id()) {
if let Block(
hir::Block {
expr:
Some(Expr {
kind:
DropTemps(Expr {
kind:
Match(
Expr {
kind:
Call(
_,
[
Expr {
kind:
MethodCall(path_segment, _, _, span),
hir_id,
..
},
..,
],
),
..
},
..,
),
..
}),
..
}),
..
},
_,
) = hir_map.body(body_id).value.kind
{
let opt_suggestions = self
.infcx
.tcx
.typeck(path_segment.hir_id.owner.def_id)
.type_dependent_def_id(*hir_id)
.and_then(|def_id| self.infcx.tcx.impl_of_method(def_id))
.map(|def_id| self.infcx.tcx.associated_items(def_id))
.map(|assoc_items| {
assoc_items
.in_definition_order()
.map(|assoc_item_def| assoc_item_def.ident(self.infcx.tcx))
.filter(|&ident| {
let original_method_ident = path_segment.ident;
original_method_ident != ident
&& ident
.as_str()
.starts_with(&original_method_ident.name.to_string())
})
.map(|ident| format!("{ident}()"))
.peekable()
});
struct Finder<'tcx> {
span: Span,
expr: Option<&'tcx Expr<'tcx>>,
}
if let Some(mut suggestions) = opt_suggestions
&& suggestions.peek().is_some()
{
err.span_suggestions(
*span,
"use mutable method",
suggestions,
Applicability::MaybeIncorrect,
);
impl<'tcx> Visitor<'tcx> for Finder<'tcx> {
fn visit_expr(&mut self, e: &'tcx hir::Expr<'tcx>) {
if e.span == self.span && self.expr.is_none() {
self.expr = Some(e);
}
hir::intravisit::walk_expr(self, e);
}
}
if let Some(body_id) = hir_map.maybe_body_owned_by(self.mir_def_id())
&& let Block(block, _) = hir_map.body(body_id).value.kind
{
// `span` corresponds to the expression being iterated, find the `for`-loop desugared
// expression with that span in order to identify potential fixes when encountering a
// read-only iterator that should be mutable.
let mut v = Finder {
span,
expr: None,
};
v.visit_block(block);
if let Some(expr) = v.expr && let Call(_, [expr]) = expr.kind {
match expr.kind {
MethodCall(path_segment, _, _, span) => {
// We have `for _ in iter.read_only_iter()`, try to
// suggest `for _ in iter.mutable_iter()` instead.
let opt_suggestions = self
.infcx
.tcx
.typeck(path_segment.hir_id.owner.def_id)
.type_dependent_def_id(expr.hir_id)
.and_then(|def_id| self.infcx.tcx.impl_of_method(def_id))
.map(|def_id| self.infcx.tcx.associated_items(def_id))
.map(|assoc_items| {
assoc_items
.in_definition_order()
.map(|assoc_item_def| assoc_item_def.ident(self.infcx.tcx))
.filter(|&ident| {
let original_method_ident = path_segment.ident;
original_method_ident != ident
&& ident.as_str().starts_with(
&original_method_ident.name.to_string(),
)
})
.map(|ident| format!("{ident}()"))
.peekable()
});
if let Some(mut suggestions) = opt_suggestions
&& suggestions.peek().is_some()
{
err.span_suggestions(
span,
"use mutable method",
suggestions,
Applicability::MaybeIncorrect,
);
}
}
AddrOf(BorrowKind::Ref, Mutability::Not, expr) => {
// We have `for _ in &i`, suggest `for _ in &mut i`.
err.span_suggestion_verbose(
expr.span.shrink_to_lo(),
"use a mutable iterator instead",
"mut ".to_string(),
Applicability::MachineApplicable,
);
}
_ => {}
}
}
};
}
}
/// Targeted error when encountering an `FnMut` closure where an `Fn` closure was expected.
@ -1003,9 +1005,10 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
match opt_assignment_rhs_span.and_then(|s| s.desugaring_kind()) {
// on for loops, RHS points to the iterator part
Some(DesugaringKind::ForLoop) => {
self.suggest_similar_mut_method_for_for_loop(err);
let span = opt_assignment_rhs_span.unwrap();
self.suggest_similar_mut_method_for_for_loop(err, span);
err.span_label(
opt_assignment_rhs_span.unwrap(),
span,
format!("this iterator yields `{pointer_sigil}` {pointer_desc}s",),
);
None

30
tests/ui/borrowck/suggest-mut-iterator.fixed Normal file
View File

@ -0,0 +1,30 @@
// run-rustfix
struct Test {
a: u32
}
impl Test {
pub fn add(&mut self, value: u32) {
self.a += value;
}
pub fn print_value(&self) {
println!("Value of a is: {}", self.a);
}
}
fn main() {
let mut tests = Vec::new();
for i in 0..=10 {
tests.push(Test {a: i});
}
for test in &mut tests {
test.add(2); //~ ERROR cannot borrow `*test` as mutable, as it is behind a `&` reference
}
for test in &mut tests {
test.add(2);
}
for test in &tests {
test.print_value();
}
}

30
tests/ui/borrowck/suggest-mut-iterator.rs Normal file
View File

@ -0,0 +1,30 @@
// run-rustfix
struct Test {
a: u32
}
impl Test {
pub fn add(&mut self, value: u32) {
self.a += value;
}
pub fn print_value(&self) {
println!("Value of a is: {}", self.a);
}
}
fn main() {
let mut tests = Vec::new();
for i in 0..=10 {
tests.push(Test {a: i});
}
for test in &tests {
test.add(2); //~ ERROR cannot borrow `*test` as mutable, as it is behind a `&` reference
}
for test in &mut tests {
test.add(2);
}
for test in &tests {
test.print_value();
}
}

16
tests/ui/borrowck/suggest-mut-iterator.stderr Normal file
View File

@ -0,0 +1,16 @@
error[E0596]: cannot borrow `*test` as mutable, as it is behind a `&` reference
--> $DIR/suggest-mut-iterator.rs:22:9
|
LL | for test in &tests {
| ------ this iterator yields `&` references
LL | test.add(2);
| ^^^^ `test` is a `&` reference, so the data it refers to cannot be borrowed as mutable
|
help: use a mutable iterator instead
|
LL | for test in &mut tests {
| +++
error: aborting due to previous error
For more information about this error, try `rustc --explain E0596`.