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Suggest cloning captured binding in move closure

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```
error[E0507]: cannot move out of `bar`, a captured variable in an `FnMut` closure
  --> $DIR/borrowck-move-by-capture.rs:9:29
   |
LL |     let bar: Box<_> = Box::new(3);
   |         --- captured outer variable
LL |     let _g = to_fn_mut(|| {
   |                        -- captured by this `FnMut` closure
LL |         let _h = to_fn_once(move || -> isize { *bar });
   |                             ^^^^^^^^^^^^^^^^   ----
   |                             |                  |
   |                             |                  variable moved due to use in closure
   |                             |                  move occurs because `bar` has type `Box<isize>`, which does not implement the `Copy` trait
   |                             `bar` is moved here
   |
help: clone the value before moving it into the closure
   |
LL ~         let value = bar.clone();
LL ~         let _h = to_fn_once(move || -> isize { value });
   |
```
This commit is contained in:
Esteban Küber 2024-04-19 04:26:42 +00:00
parent d68f2a6b71
commit ad9a5a5f9f
8 changed files with 267 additions and 22 deletions
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2
compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
View file

@ -1241,7 +1241,7 @@ pub(crate) fn suggest_cloning(
}
}
fn implements_clone(&self, ty: Ty<'tcx>) -> bool {
pub(crate) fn implements_clone(&self, ty: Ty<'tcx>) -> bool {
let Some(clone_trait_def) = self.infcx.tcx.lang_items().clone_trait() else { return false };
self.infcx
.type_implements_trait(clone_trait_def, [ty], self.param_env)

142
compiler/rustc_borrowck/src/diagnostics/move_errors.rs
View file

@ -2,10 +2,13 @@
#![allow(rustc::untranslatable_diagnostic)]
use rustc_errors::{Applicability, Diag};
use rustc_hir::intravisit::Visitor;
use rustc_hir::{CaptureBy, ExprKind, HirId, Node};
use rustc_middle::mir::*;
use rustc_middle::ty::{self, Ty};
use rustc_mir_dataflow::move_paths::{LookupResult, MovePathIndex};
use rustc_span::{BytePos, ExpnKind, MacroKind, Span};
use rustc_trait_selection::traits::error_reporting::FindExprBySpan;
use crate::diagnostics::CapturedMessageOpt;
use crate::diagnostics::{DescribePlaceOpt, UseSpans};
@ -303,6 +306,121 @@ fn report_cannot_move_from_static(&mut self, place: Place<'tcx>, span: Span) ->
self.cannot_move_out_of(span, &description)
}
fn suggest_clone_of_captured_var_in_move_closure(
&self,
err: &mut Diag<'_>,
upvar_hir_id: HirId,
upvar_name: &str,
use_spans: Option<UseSpans<'tcx>>,
) {
let tcx = self.infcx.tcx;
let typeck_results = tcx.typeck(self.mir_def_id());
let Some(use_spans) = use_spans else { return };
// We only care about the case where a closure captured a binding.
let UseSpans::ClosureUse { args_span, .. } = use_spans else { return };
let Some(body_id) = tcx.hir_node(self.mir_hir_id()).body_id() else { return };
// Fetch the type of the expression corresponding to the closure-captured binding.
let Some(captured_ty) = typeck_results.node_type_opt(upvar_hir_id) else { return };
if !self.implements_clone(captured_ty) {
// We only suggest cloning the captured binding if the type can actually be cloned.
return;
};
// Find the closure that captured the binding.
let mut expr_finder = FindExprBySpan::new(args_span, tcx);
expr_finder.include_closures = true;
expr_finder.visit_expr(tcx.hir().body(body_id).value);
let Some(closure_expr) = expr_finder.result else { return };
let ExprKind::Closure(closure) = closure_expr.kind else { return };
// We'll only suggest cloning the binding if it's a `move` closure.
let CaptureBy::Value { .. } = closure.capture_clause else { return };
// Find the expression within the closure where the binding is consumed.
let mut suggested = false;
let use_span = use_spans.var_or_use();
let mut expr_finder = FindExprBySpan::new(use_span, tcx);
expr_finder.include_closures = true;
expr_finder.visit_expr(tcx.hir().body(body_id).value);
let Some(use_expr) = expr_finder.result else { return };
let parent = tcx.parent_hir_node(use_expr.hir_id);
if let Node::Expr(expr) = parent
&& let ExprKind::Assign(lhs, ..) = expr.kind
&& lhs.hir_id == use_expr.hir_id
{
// Cloning the value being assigned makes no sense:
//
// error[E0507]: cannot move out of `var`, a captured variable in an `FnMut` closure
// --> $DIR/option-content-move2.rs:11:9
// |
// LL | let mut var = None;
// | ------- captured outer variable
// LL | func(|| {
// | -- captured by this `FnMut` closure
// LL | // Shouldn't suggest `move ||.as_ref()` here
// LL | move || {
// | ^^^^^^^ `var` is moved here
// LL |
// LL | var = Some(NotCopyable);
// | ---
// | |
// | variable moved due to use in closure
// | move occurs because `var` has type `Option<NotCopyable>`, which does not implement the `Copy` trait
// |
return;
}
// Search for an appropriate place for the structured `.clone()` suggestion to be applied.
// If we encounter a statement before the borrow error, we insert a statement there.
for (_, node) in tcx.hir().parent_iter(closure_expr.hir_id) {
if let Node::Stmt(stmt) = node {
let padding = tcx
.sess
.source_map()
.indentation_before(stmt.span)
.unwrap_or_else(|| " ".to_string());
err.multipart_suggestion_verbose(
"clone the value before moving it into the closure",
vec![
(
stmt.span.shrink_to_lo(),
format!("let value = {upvar_name}.clone();\n{padding}"),
),
(use_span, "value".to_string()),
],
Applicability::MachineApplicable,
);
suggested = true;
break;
} else if let Node::Expr(expr) = node
&& let ExprKind::Closure(_) = expr.kind
{
// We want to suggest cloning only on the first closure, not
// subsequent ones (like `ui/suggestions/option-content-move2.rs`).
break;
}
}
if !suggested {
// If we couldn't find a statement for us to insert a new `.clone()` statement before,
// we have a bare expression, so we suggest the creation of a new block inline to go
// from `move || val` to `{ let value = val.clone(); move || value }`.
let padding = tcx
.sess
.source_map()
.indentation_before(closure_expr.span)
.unwrap_or_else(|| " ".to_string());
err.multipart_suggestion_verbose(
"clone the value before moving it into the closure",
vec![
(
closure_expr.span.shrink_to_lo(),
format!("{{\n{padding}let value = {upvar_name}.clone();\n{padding}"),
),
(use_spans.var_or_use(), "value".to_string()),
(closure_expr.span.shrink_to_hi(), format!("\n{padding}}}")),
],
Applicability::MachineApplicable,
);
}
}
fn report_cannot_move_from_borrowed_content(
&mut self,
move_place: Place<'tcx>,
@ -310,10 +428,11 @@ fn report_cannot_move_from_borrowed_content(
span: Span,
use_spans: Option<UseSpans<'tcx>>,
) -> Diag<'tcx> {
let tcx = self.infcx.tcx;
// Inspect the type of the content behind the
// borrow to provide feedback about why this
// was a move rather than a copy.
let ty = deref_target_place.ty(self.body, self.infcx.tcx).ty;
let ty = deref_target_place.ty(self.body, tcx).ty;
let upvar_field = self
.prefixes(move_place.as_ref(), PrefixSet::All)
.find_map(|p| self.is_upvar_field_projection(p));
@ -363,8 +482,8 @@ fn report_cannot_move_from_borrowed_content(
let upvar = &self.upvars[upvar_field.unwrap().index()];
let upvar_hir_id = upvar.get_root_variable();
let upvar_name = upvar.to_string(self.infcx.tcx);
let upvar_span = self.infcx.tcx.hir().span(upvar_hir_id);
let upvar_name = upvar.to_string(tcx);
let upvar_span = tcx.hir().span(upvar_hir_id);
let place_name = self.describe_any_place(move_place.as_ref());
@ -380,12 +499,21 @@ fn report_cannot_move_from_borrowed_content(
closure_kind_ty, closure_kind, place_description,
);
self.cannot_move_out_of(span, &place_description)
let closure_span = tcx.def_span(def_id);
let mut err = self
.cannot_move_out_of(span, &place_description)
.with_span_label(upvar_span, "captured outer variable")
.with_span_label(
self.infcx.tcx.def_span(def_id),
closure_span,
format!("captured by this `{closure_kind}` closure"),
)
);
self.suggest_clone_of_captured_var_in_move_closure(
&mut err,
upvar_hir_id,
&upvar_name,
use_spans,
);
err
}
_ => {
let source = self.borrowed_content_source(deref_base);
@ -415,7 +543,7 @@ fn report_cannot_move_from_borrowed_content(
),
(_, _, _) => self.cannot_move_out_of(
span,
&source.describe_for_unnamed_place(self.infcx.tcx),
&source.describe_for_unnamed_place(tcx),
),
}
}

11
compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
View file

@ -50,12 +50,13 @@ pub struct FindExprBySpan<'hir> {
pub span: Span,
pub result: Option<&'hir hir::Expr<'hir>>,
pub ty_result: Option<&'hir hir::Ty<'hir>>,
pub include_closures: bool,
pub tcx: TyCtxt<'hir>,
}
impl<'hir> FindExprBySpan<'hir> {
pub fn new(span: Span, tcx: TyCtxt<'hir>) -> Self {
Self { span, result: None, ty_result: None, tcx }
Self { span, result: None, ty_result: None, tcx, include_closures: false }
}
}
@ -70,9 +71,17 @@ fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
if self.span == ex.span {
self.result = Some(ex);
} else {
if let hir::ExprKind::Closure(..) = ex.kind
&& self.include_closures
&& let closure_header_sp = self.span.with_hi(ex.span.hi())
&& closure_header_sp == ex.span
{
self.result = Some(ex);
}
hir::intravisit::walk_expr(self, ex);
}
}
fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
if self.span == ty.span {
self.ty_result = Some(ty);

6
tests/ui/borrowck/borrowck-move-by-capture.stderr
View file

@ -11,6 +11,12 @@ LL | let _h = to_fn_once(move || -> isize { *bar });
| | variable moved due to use in closure
| | move occurs because `bar` has type `Box<isize>`, which does not implement the `Copy` trait
| `bar` is moved here
|
help: clone the value before moving it into the closure
|
LL ~ let value = bar.clone();
LL ~ let _h = to_fn_once(move || -> isize { value });
|
error: aborting due to 1 previous error

14
tests/ui/suggestions/option-content-move2.rs
View file

@ -1,8 +1,10 @@
struct NotCopyable;
#[derive(Clone)]
struct NotCopyableButCloneable;
fn func<F: FnMut() -> H, H: FnMut()>(_: F) {}
fn parse() {
fn foo() {
let mut var = None;
func(|| {
// Shouldn't suggest `move ||.as_ref()` here
@ -12,5 +14,15 @@ fn parse() {
}
});
}
fn bar() {
let mut var = None;
func(|| {
// Shouldn't suggest `move ||.as_ref()` nor to `clone()` here
move || {
//~^ ERROR: cannot move out of `var`
var = Some(NotCopyableButCloneable);
}
});
}
fn main() {}

21
tests/ui/suggestions/option-content-move2.stderr
View file

@ -1,5 +1,5 @@
error[E0507]: cannot move out of `var`, a captured variable in an `FnMut` closure
--> $DIR/option-content-move2.rs:9:9
--> $DIR/option-content-move2.rs:11:9
|
LL | let mut var = None;
| ------- captured outer variable
@ -15,6 +15,23 @@ LL | var = Some(NotCopyable);
| variable moved due to use in closure
| move occurs because `var` has type `Option<NotCopyable>`, which does not implement the `Copy` trait
error: aborting due to 1 previous error
error[E0507]: cannot move out of `var`, a captured variable in an `FnMut` closure
--> $DIR/option-content-move2.rs:21:9
|
LL | let mut var = None;
| ------- captured outer variable
LL | func(|| {
| -- captured by this `FnMut` closure
LL | // Shouldn't suggest `move ||.as_ref()` nor to `clone()` here
LL | move || {
| ^^^^^^^ `var` is moved here
LL |
LL | var = Some(NotCopyableButCloneable);
| ---
| |
| variable moved due to use in closure
| move occurs because `var` has type `Option<NotCopyableButCloneable>`, which does not implement the `Copy` trait
error: aborting due to 2 previous errors
For more information about this error, try `rustc --explain E0507`.

19
tests/ui/suggestions/option-content-move3.rs
View file

@ -1,10 +1,23 @@
#[derive(Debug, Clone)]
#[derive(Debug)]
struct NotCopyable;
#[derive(Debug, Clone)]
struct NotCopyableButCloneable;
fn func<F: FnMut() -> H, H: FnMut()>(_: F) {}
fn parse() {
let mut var = NotCopyable;
fn foo() {
let var = NotCopyable;
func(|| {
// Shouldn't suggest `move ||.as_ref()` here
move || { //~ ERROR cannot move out of `var`
let x = var; //~ ERROR cannot move out of `var`
println!("{x:?}");
}
});
}
fn bar() {
let var = NotCopyableButCloneable;
func(|| {
// Shouldn't suggest `move ||.as_ref()` here
move || { //~ ERROR cannot move out of `var`

74
tests/ui/suggestions/option-content-move3.stderr
View file

@ -1,24 +1,32 @@
error[E0507]: cannot move out of `var`, a captured variable in an `FnMut` closure
--> $DIR/option-content-move3.rs:11:21
--> $DIR/option-content-move3.rs:13:21
|
LL | let mut var = NotCopyable;
| ------- captured outer variable
LL | let var = NotCopyable;
| --- captured outer variable
...
LL | move || {
| ------- captured by this `FnMut` closure
LL | let x = var;
| ^^^ move occurs because `var` has type `NotCopyable`, which does not implement the `Copy` trait
|
note: if `NotCopyable` implemented `Clone`, you could clone the value
--> $DIR/option-content-move3.rs:2:1
|
LL | struct NotCopyable;
| ^^^^^^^^^^^^^^^^^^ consider implementing `Clone` for this type
...
LL | let x = var;
| --- you could clone this value
help: consider borrowing here
|
LL | let x = &var;
| +
error[E0507]: cannot move out of `var`, a captured variable in an `FnMut` closure
--> $DIR/option-content-move3.rs:10:9
--> $DIR/option-content-move3.rs:12:9
|
LL | let mut var = NotCopyable;
| ------- captured outer variable
LL | let var = NotCopyable;
| --- captured outer variable
LL | func(|| {
| -- captured by this `FnMut` closure
LL | // Shouldn't suggest `move ||.as_ref()` here
@ -29,7 +37,59 @@ LL | let x = var;
| |
| variable moved due to use in closure
| move occurs because `var` has type `NotCopyable`, which does not implement the `Copy` trait
|
note: if `NotCopyable` implemented `Clone`, you could clone the value
--> $DIR/option-content-move3.rs:2:1
|
LL | struct NotCopyable;
| ^^^^^^^^^^^^^^^^^^ consider implementing `Clone` for this type
...
LL | let x = var;
| --- you could clone this value
error: aborting due to 2 previous errors
error[E0507]: cannot move out of `var`, a captured variable in an `FnMut` closure
--> $DIR/option-content-move3.rs:24:21
|
LL | let var = NotCopyableButCloneable;
| --- captured outer variable
...
LL | move || {
| ------- captured by this `FnMut` closure
LL | let x = var;
| ^^^ move occurs because `var` has type `NotCopyableButCloneable`, which does not implement the `Copy` trait
|
help: consider borrowing here
|
LL | let x = &var;
| +
error[E0507]: cannot move out of `var`, a captured variable in an `FnMut` closure
--> $DIR/option-content-move3.rs:23:9
|
LL | let var = NotCopyableButCloneable;
| --- captured outer variable
LL | func(|| {
| -- captured by this `FnMut` closure
LL | // Shouldn't suggest `move ||.as_ref()` here
LL | move || {
| ^^^^^^^ `var` is moved here
LL | let x = var;
| ---
| |
| variable moved due to use in closure
| move occurs because `var` has type `NotCopyableButCloneable`, which does not implement the `Copy` trait
|
help: clone the value before moving it into the closure
|
LL ~ {
LL + let value = var.clone();
LL ~ move || {
LL ~ let x = value;
LL | println!("{x:?}");
LL ~ }
LL + }
|
error: aborting due to 4 previous errors
For more information about this error, try `rustc --explain E0507`.