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Auto merge of rust-lang#124136 - estebank:clone-o-rama-2, r=nnethercote
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Provide more context and suggestions in borrowck errors involving closures

Start pointing to where bindings where declared when they are captured in closures:

```
error[E0597]: `x` does not live long enough
  --> $DIR/suggest-return-closure.rs:23:9
   |
LL |     let x = String::new();
   |         - binding `x` declared here
...
LL |     |c| {
   |     --- value captured here
LL |         x.push(c);
   |         ^ borrowed value does not live long enough
...
LL | }
   | -- borrow later used here
   | |
   | `x` dropped here while still borrowed
```

Suggest cloning in more cases involving closures:

```
error[E0507]: cannot move out of `foo` in pattern guard
  --> $DIR/issue-27282-move-ref-mut-into-guard.rs:11:19
   |
LL |             if { (|| { let mut bar = foo; bar.take() })(); false } => {},
   |                   ^^                 --- move occurs because `foo` has type `&mut Option<&i32>`, which does not implement the `Copy` trait
   |                   |
   |                   `foo` is moved here
   |
   = note: variables bound in patterns cannot be moved from until after the end of the pattern guard
help: consider cloning the value if the performance cost is acceptable
   |
LL |             if { (|| { let mut bar = foo.clone(); bar.take() })(); false } => {},
   |                                         ++++++++
```

Mention when type parameter could be Clone

```
error[E0382]: use of moved value: `t`
  --> $DIR/use_of_moved_value_copy_suggestions.rs:7:9
   |
LL | fn duplicate_t<T>(t: T) -> (T, T) {
   |                   - move occurs because `t` has type `T`, which does not implement the `Copy` trait
...
LL |     (t, t)
   |      -  ^ value used here after move
   |      |
   |      value moved here
   |
help: if `T` implemented `Clone`, you could clone the value
  --> $DIR/use_of_moved_value_copy_suggestions.rs:4:16
   |
LL | fn duplicate_t<T>(t: T) -> (T, T) {
   |                ^ consider constraining this type parameter with `Clone`
...
LL |     (t, t)
   |      - you could clone this value
help: consider restricting type parameter `T`
   |
LL | fn duplicate_t<T: Copy>(t: T) -> (T, T) {
   |                 ++++++
```

The `help` is new. On ADTs, we also extend the output with span labels:

```
error[E0507]: cannot move out of static item `FOO`
  --> $DIR/issue-17718-static-move.rs:6:14
   |
LL |     let _a = FOO;
   |              ^^^ move occurs because `FOO` has type `Foo`, which does not implement the `Copy` trait
   |
note: if `Foo` implemented `Clone`, you could clone the value
  --> $DIR/issue-17718-static-move.rs:1:1
   |
LL | struct Foo;
   | ^^^^^^^^^^ consider implementing `Clone` for this type
...
LL |     let _a = FOO;
   |              --- you could clone this value
help: consider borrowing here
   |
LL |     let _a = &FOO;
   |              +
```

Suggest cloning captured binding in move closure

```
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 1
   |
LL ~         let value = bar.clone();
LL ~         let _h = to_fn_once(move || -> isize { value });
   |
```
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@bors
bors committed Apr 25, 2024
2 parents dfc400e + ad9a5a5 commit cb3752d
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55 changes: 46 additions & 9 deletions compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -347,7 +347,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
mpi: MovePathIndex,
err: &mut Diag<'tcx>,
in_pattern: &mut bool,
move_spans: UseSpans<'_>,
move_spans: UseSpans<'tcx>,
) {
let move_span = match move_spans {
UseSpans::ClosureUse { capture_kind_span, .. } => capture_kind_span,
Expand Down Expand Up @@ -491,11 +491,11 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
..
} = move_spans
{
self.suggest_cloning(err, ty, expr, None);
self.suggest_cloning(err, ty, expr, None, Some(move_spans));
} else if self.suggest_hoisting_call_outside_loop(err, expr) {
// The place where the the type moves would be misleading to suggest clone.
// #121466
self.suggest_cloning(err, ty, expr, None);
self.suggest_cloning(err, ty, expr, None, Some(move_spans));
}
}
if let Some(pat) = finder.pat {
Expand Down Expand Up @@ -1085,6 +1085,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
ty: Ty<'tcx>,
mut expr: &'cx hir::Expr<'cx>,
mut other_expr: Option<&'cx hir::Expr<'cx>>,
use_spans: Option<UseSpans<'tcx>>,
) {
if let hir::ExprKind::Struct(_, _, Some(_)) = expr.kind {
// We have `S { foo: val, ..base }`. In `check_aggregate_rvalue` we have a single
Expand Down Expand Up @@ -1197,14 +1198,50 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
.all(|field| self.implements_clone(field.ty(self.infcx.tcx, args)))
})
{
let ty_span = self.infcx.tcx.def_span(def.did());
let mut span: MultiSpan = ty_span.into();
span.push_span_label(ty_span, "consider implementing `Clone` for this type");
span.push_span_label(expr.span, "you could clone this value");
err.span_note(
self.infcx.tcx.def_span(def.did()),
span,
format!("if `{ty}` implemented `Clone`, you could clone the value"),
);
} else if let ty::Param(param) = ty.kind()
&& let Some(_clone_trait_def) = self.infcx.tcx.lang_items().clone_trait()
&& let generics = self.infcx.tcx.generics_of(self.mir_def_id())
&& let generic_param = generics.type_param(*param, self.infcx.tcx)
&& let param_span = self.infcx.tcx.def_span(generic_param.def_id)
&& if let Some(UseSpans::FnSelfUse { kind, .. }) = use_spans
&& let CallKind::FnCall { fn_trait_id, self_ty } = kind
&& let ty::Param(_) = self_ty.kind()
&& ty == self_ty
&& [
self.infcx.tcx.lang_items().fn_once_trait(),
self.infcx.tcx.lang_items().fn_mut_trait(),
self.infcx.tcx.lang_items().fn_trait(),
]
.contains(&Some(fn_trait_id))
{
// Do not suggest `F: FnOnce() + Clone`.
false
} else {
true
}
{
let mut span: MultiSpan = param_span.into();
span.push_span_label(
param_span,
"consider constraining this type parameter with `Clone`",
);
span.push_span_label(expr.span, "you could clone this value");
err.span_help(
span,
format!("if `{ty}` implemented `Clone`, you could clone the value"),
);
}
}

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)
Expand Down Expand Up @@ -1403,7 +1440,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
if let Some(expr) = self.find_expr(borrow_span)
&& let Some(ty) = typeck_results.node_type_opt(expr.hir_id)
{
self.suggest_cloning(&mut err, ty, expr, self.find_expr(span));
self.suggest_cloning(&mut err, ty, expr, self.find_expr(span), Some(move_spans));
}
self.buffer_error(err);
}
Expand Down Expand Up @@ -1964,7 +2001,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
pub(crate) fn find_expr(&self, span: Span) -> Option<&hir::Expr<'_>> {
let tcx = self.infcx.tcx;
let body_id = tcx.hir_node(self.mir_hir_id()).body_id()?;
let mut expr_finder = FindExprBySpan::new(span);
let mut expr_finder = FindExprBySpan::new(span, tcx);
expr_finder.visit_expr(tcx.hir().body(body_id).value);
expr_finder.result
}
Expand Down Expand Up @@ -1998,14 +2035,14 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
};

let mut expr_finder =
FindExprBySpan::new(self.body.local_decls[*index1].source_info.span);
FindExprBySpan::new(self.body.local_decls[*index1].source_info.span, tcx);
expr_finder.visit_expr(hir.body(body_id).value);
let Some(index1) = expr_finder.result else {
note_default_suggestion();
return;
};

expr_finder = FindExprBySpan::new(self.body.local_decls[*index2].source_info.span);
expr_finder = FindExprBySpan::new(self.body.local_decls[*index2].source_info.span, tcx);
expr_finder.visit_expr(hir.body(body_id).value);
let Some(index2) = expr_finder.result else {
note_default_suggestion();
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -76,7 +76,7 @@ impl<'tcx> BorrowExplanation<'tcx> {
&& let Some(body_id) = node.body_id()
{
let body = tcx.hir().body(body_id);
let mut expr_finder = FindExprBySpan::new(span);
let mut expr_finder = FindExprBySpan::new(span, tcx);
expr_finder.visit_expr(body.value);
if let Some(mut expr) = expr_finder.result {
while let hir::ExprKind::AddrOf(_, _, inner)
Expand Down
154 changes: 144 additions & 10 deletions compiler/rustc_borrowck/src/diagnostics/move_errors.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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};
Expand Down Expand Up @@ -303,17 +306,133 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
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>,
deref_target_place: Place<'tcx>,
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));
Expand Down Expand Up @@ -363,8 +482,8 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {

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());

Expand All @@ -380,12 +499,21 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
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);
Expand Down Expand Up @@ -415,7 +543,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
),
(_, _, _) => self.cannot_move_out_of(
span,
&source.describe_for_unnamed_place(self.infcx.tcx),
&source.describe_for_unnamed_place(tcx),
),
}
}
Expand Down Expand Up @@ -447,7 +575,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
};

if let Some(expr) = self.find_expr(span) {
self.suggest_cloning(err, place_ty, expr, self.find_expr(other_span));
self.suggest_cloning(err, place_ty, expr, self.find_expr(other_span), None);
}

err.subdiagnostic(
Expand Down Expand Up @@ -482,7 +610,13 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
};

if let Some(expr) = self.find_expr(use_span) {
self.suggest_cloning(err, place_ty, expr, self.find_expr(span));
self.suggest_cloning(
err,
place_ty,
expr,
self.find_expr(span),
Some(use_spans),
);
}

err.subdiagnostic(
Expand Down Expand Up @@ -595,7 +729,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
let place_desc = &format!("`{}`", self.local_names[*local].unwrap());

if let Some(expr) = self.find_expr(binding_span) {
self.suggest_cloning(err, bind_to.ty, expr, None);
self.suggest_cloning(err, bind_to.ty, expr, None, None);
}

err.subdiagnostic(
Expand Down
20 changes: 18 additions & 2 deletions compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -50,22 +50,38 @@ 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) -> Self {
Self { span, result: None, ty_result: None }
pub fn new(span: Span, tcx: TyCtxt<'hir>) -> Self {
Self { span, result: None, ty_result: None, tcx, include_closures: false }
}
}

impl<'v> Visitor<'v> for FindExprBySpan<'v> {
type NestedFilter = rustc_middle::hir::nested_filter::OnlyBodies;

fn nested_visit_map(&mut self) -> Self::Map {
self.tcx.hir()
}

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);
Expand Down
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