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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 | LL ~ let value = bar.clone(); LL ~ let _h = to_fn_once(move || -> isize { value }); | ```
This commit is contained in:
parent
d68f2a6b71
commit
ad9a5a5f9f
@ -1241,7 +1241,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
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}
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}
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fn implements_clone(&self, ty: Ty<'tcx>) -> bool {
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pub(crate) fn implements_clone(&self, ty: Ty<'tcx>) -> bool {
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let Some(clone_trait_def) = self.infcx.tcx.lang_items().clone_trait() else { return false };
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self.infcx
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.type_implements_trait(clone_trait_def, [ty], self.param_env)
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@ -2,10 +2,13 @@
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#![allow(rustc::untranslatable_diagnostic)]
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use rustc_errors::{Applicability, Diag};
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use rustc_hir::intravisit::Visitor;
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use rustc_hir::{CaptureBy, ExprKind, HirId, Node};
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use rustc_middle::mir::*;
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use rustc_middle::ty::{self, Ty};
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use rustc_mir_dataflow::move_paths::{LookupResult, MovePathIndex};
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use rustc_span::{BytePos, ExpnKind, MacroKind, Span};
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use rustc_trait_selection::traits::error_reporting::FindExprBySpan;
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use crate::diagnostics::CapturedMessageOpt;
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use crate::diagnostics::{DescribePlaceOpt, UseSpans};
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@ -303,6 +306,121 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
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self.cannot_move_out_of(span, &description)
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}
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fn suggest_clone_of_captured_var_in_move_closure(
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&self,
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err: &mut Diag<'_>,
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upvar_hir_id: HirId,
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upvar_name: &str,
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use_spans: Option<UseSpans<'tcx>>,
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) {
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let tcx = self.infcx.tcx;
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let typeck_results = tcx.typeck(self.mir_def_id());
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let Some(use_spans) = use_spans else { return };
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// We only care about the case where a closure captured a binding.
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let UseSpans::ClosureUse { args_span, .. } = use_spans else { return };
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let Some(body_id) = tcx.hir_node(self.mir_hir_id()).body_id() else { return };
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// Fetch the type of the expression corresponding to the closure-captured binding.
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let Some(captured_ty) = typeck_results.node_type_opt(upvar_hir_id) else { return };
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if !self.implements_clone(captured_ty) {
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// We only suggest cloning the captured binding if the type can actually be cloned.
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return;
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};
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// Find the closure that captured the binding.
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let mut expr_finder = FindExprBySpan::new(args_span, tcx);
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expr_finder.include_closures = true;
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expr_finder.visit_expr(tcx.hir().body(body_id).value);
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let Some(closure_expr) = expr_finder.result else { return };
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let ExprKind::Closure(closure) = closure_expr.kind else { return };
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// We'll only suggest cloning the binding if it's a `move` closure.
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let CaptureBy::Value { .. } = closure.capture_clause else { return };
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// Find the expression within the closure where the binding is consumed.
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let mut suggested = false;
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let use_span = use_spans.var_or_use();
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let mut expr_finder = FindExprBySpan::new(use_span, tcx);
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expr_finder.include_closures = true;
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expr_finder.visit_expr(tcx.hir().body(body_id).value);
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let Some(use_expr) = expr_finder.result else { return };
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let parent = tcx.parent_hir_node(use_expr.hir_id);
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if let Node::Expr(expr) = parent
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&& let ExprKind::Assign(lhs, ..) = expr.kind
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&& lhs.hir_id == use_expr.hir_id
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{
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// Cloning the value being assigned makes no sense:
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//
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// error[E0507]: cannot move out of `var`, a captured variable in an `FnMut` closure
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// --> $DIR/option-content-move2.rs:11:9
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// |
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// LL | let mut var = None;
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// | ------- captured outer variable
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// LL | func(|| {
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// | -- captured by this `FnMut` closure
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// LL | // Shouldn't suggest `move ||.as_ref()` here
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// LL | move || {
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// | ^^^^^^^ `var` is moved here
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// LL |
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// LL | var = Some(NotCopyable);
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// | ---
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// | |
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// | variable moved due to use in closure
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// | move occurs because `var` has type `Option<NotCopyable>`, which does not implement the `Copy` trait
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// |
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return;
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}
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// Search for an appropriate place for the structured `.clone()` suggestion to be applied.
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// If we encounter a statement before the borrow error, we insert a statement there.
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for (_, node) in tcx.hir().parent_iter(closure_expr.hir_id) {
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if let Node::Stmt(stmt) = node {
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let padding = tcx
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.sess
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.source_map()
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.indentation_before(stmt.span)
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.unwrap_or_else(|| " ".to_string());
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err.multipart_suggestion_verbose(
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"clone the value before moving it into the closure",
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vec![
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(
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stmt.span.shrink_to_lo(),
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format!("let value = {upvar_name}.clone();\n{padding}"),
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),
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(use_span, "value".to_string()),
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],
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Applicability::MachineApplicable,
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);
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suggested = true;
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break;
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} else if let Node::Expr(expr) = node
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&& let ExprKind::Closure(_) = expr.kind
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{
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// We want to suggest cloning only on the first closure, not
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// subsequent ones (like `ui/suggestions/option-content-move2.rs`).
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break;
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}
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}
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if !suggested {
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// If we couldn't find a statement for us to insert a new `.clone()` statement before,
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// we have a bare expression, so we suggest the creation of a new block inline to go
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// from `move || val` to `{ let value = val.clone(); move || value }`.
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let padding = tcx
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.sess
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.source_map()
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.indentation_before(closure_expr.span)
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.unwrap_or_else(|| " ".to_string());
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err.multipart_suggestion_verbose(
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"clone the value before moving it into the closure",
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vec![
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(
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closure_expr.span.shrink_to_lo(),
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format!("{{\n{padding}let value = {upvar_name}.clone();\n{padding}"),
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),
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(use_spans.var_or_use(), "value".to_string()),
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(closure_expr.span.shrink_to_hi(), format!("\n{padding}}}")),
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],
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Applicability::MachineApplicable,
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);
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}
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}
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fn report_cannot_move_from_borrowed_content(
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&mut self,
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move_place: Place<'tcx>,
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@ -310,10 +428,11 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
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span: Span,
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use_spans: Option<UseSpans<'tcx>>,
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) -> Diag<'tcx> {
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let tcx = self.infcx.tcx;
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// Inspect the type of the content behind the
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// borrow to provide feedback about why this
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// was a move rather than a copy.
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let ty = deref_target_place.ty(self.body, self.infcx.tcx).ty;
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let ty = deref_target_place.ty(self.body, tcx).ty;
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let upvar_field = self
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.prefixes(move_place.as_ref(), PrefixSet::All)
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.find_map(|p| self.is_upvar_field_projection(p));
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@ -363,8 +482,8 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
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let upvar = &self.upvars[upvar_field.unwrap().index()];
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let upvar_hir_id = upvar.get_root_variable();
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let upvar_name = upvar.to_string(self.infcx.tcx);
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let upvar_span = self.infcx.tcx.hir().span(upvar_hir_id);
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let upvar_name = upvar.to_string(tcx);
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let upvar_span = tcx.hir().span(upvar_hir_id);
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let place_name = self.describe_any_place(move_place.as_ref());
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@ -380,12 +499,21 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
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closure_kind_ty, closure_kind, place_description,
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);
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self.cannot_move_out_of(span, &place_description)
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let closure_span = tcx.def_span(def_id);
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let mut err = self
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.cannot_move_out_of(span, &place_description)
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.with_span_label(upvar_span, "captured outer variable")
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.with_span_label(
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self.infcx.tcx.def_span(def_id),
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closure_span,
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format!("captured by this `{closure_kind}` closure"),
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)
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);
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self.suggest_clone_of_captured_var_in_move_closure(
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&mut err,
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upvar_hir_id,
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&upvar_name,
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use_spans,
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);
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err
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}
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_ => {
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let source = self.borrowed_content_source(deref_base);
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@ -415,7 +543,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
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),
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(_, _, _) => self.cannot_move_out_of(
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span,
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&source.describe_for_unnamed_place(self.infcx.tcx),
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&source.describe_for_unnamed_place(tcx),
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),
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}
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}
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@ -50,12 +50,13 @@ pub struct FindExprBySpan<'hir> {
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pub span: Span,
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pub result: Option<&'hir hir::Expr<'hir>>,
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pub ty_result: Option<&'hir hir::Ty<'hir>>,
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pub include_closures: bool,
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pub tcx: TyCtxt<'hir>,
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}
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impl<'hir> FindExprBySpan<'hir> {
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pub fn new(span: Span, tcx: TyCtxt<'hir>) -> Self {
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Self { span, result: None, ty_result: None, tcx }
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Self { span, result: None, ty_result: None, tcx, include_closures: false }
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}
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}
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@ -70,9 +71,17 @@ impl<'v> Visitor<'v> for FindExprBySpan<'v> {
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if self.span == ex.span {
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self.result = Some(ex);
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} else {
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if let hir::ExprKind::Closure(..) = ex.kind
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&& self.include_closures
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&& let closure_header_sp = self.span.with_hi(ex.span.hi())
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&& closure_header_sp == ex.span
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{
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self.result = Some(ex);
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}
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hir::intravisit::walk_expr(self, ex);
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}
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}
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fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
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if self.span == ty.span {
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self.ty_result = Some(ty);
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@ -11,6 +11,12 @@ LL | let _h = to_fn_once(move || -> isize { *bar });
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| | variable moved due to use in closure
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| | move occurs because `bar` has type `Box<isize>`, which does not implement the `Copy` trait
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| `bar` is moved here
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help: clone the value before moving it into the closure
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LL ~ let value = bar.clone();
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LL ~ let _h = to_fn_once(move || -> isize { value });
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error: aborting due to 1 previous error
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@ -1,8 +1,10 @@
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struct NotCopyable;
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#[derive(Clone)]
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struct NotCopyableButCloneable;
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fn func<F: FnMut() -> H, H: FnMut()>(_: F) {}
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fn parse() {
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fn foo() {
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let mut var = None;
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func(|| {
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// Shouldn't suggest `move ||.as_ref()` here
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@ -12,5 +14,15 @@ fn parse() {
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}
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});
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}
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fn bar() {
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let mut var = None;
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func(|| {
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// Shouldn't suggest `move ||.as_ref()` nor to `clone()` here
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move || {
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//~^ ERROR: cannot move out of `var`
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var = Some(NotCopyableButCloneable);
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}
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});
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}
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fn main() {}
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@ -1,5 +1,5 @@
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error[E0507]: cannot move out of `var`, a captured variable in an `FnMut` closure
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--> $DIR/option-content-move2.rs:9:9
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--> $DIR/option-content-move2.rs:11:9
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LL | let mut var = None;
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| ------- captured outer variable
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@ -15,6 +15,23 @@ LL | var = Some(NotCopyable);
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| variable moved due to use in closure
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| move occurs because `var` has type `Option<NotCopyable>`, which does not implement the `Copy` trait
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error: aborting due to 1 previous error
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error[E0507]: cannot move out of `var`, a captured variable in an `FnMut` closure
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--> $DIR/option-content-move2.rs:21:9
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|
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LL | let mut var = None;
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| ------- captured outer variable
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LL | func(|| {
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| -- captured by this `FnMut` closure
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LL | // Shouldn't suggest `move ||.as_ref()` nor to `clone()` here
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LL | move || {
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| ^^^^^^^ `var` is moved here
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LL |
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LL | var = Some(NotCopyableButCloneable);
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| ---
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| |
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| variable moved due to use in closure
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| move occurs because `var` has type `Option<NotCopyableButCloneable>`, which does not implement the `Copy` trait
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error: aborting due to 2 previous errors
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For more information about this error, try `rustc --explain E0507`.
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@ -1,10 +1,23 @@
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#[derive(Debug, Clone)]
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#[derive(Debug)]
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struct NotCopyable;
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#[derive(Debug, Clone)]
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struct NotCopyableButCloneable;
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fn func<F: FnMut() -> H, H: FnMut()>(_: F) {}
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fn parse() {
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let mut var = NotCopyable;
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fn foo() {
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let var = NotCopyable;
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func(|| {
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// Shouldn't suggest `move ||.as_ref()` here
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move || { //~ ERROR cannot move out of `var`
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let x = var; //~ ERROR cannot move out of `var`
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println!("{x:?}");
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}
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});
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}
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fn bar() {
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let var = NotCopyableButCloneable;
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func(|| {
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// Shouldn't suggest `move ||.as_ref()` here
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move || { //~ ERROR cannot move out of `var`
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@ -1,24 +1,32 @@
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error[E0507]: cannot move out of `var`, a captured variable in an `FnMut` closure
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--> $DIR/option-content-move3.rs:11:21
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--> $DIR/option-content-move3.rs:13:21
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|
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LL | let mut var = NotCopyable;
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| ------- captured outer variable
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LL | let var = NotCopyable;
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| --- captured outer variable
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...
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LL | move || {
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| ------- captured by this `FnMut` closure
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LL | let x = var;
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| ^^^ move occurs because `var` has type `NotCopyable`, which does not implement the `Copy` trait
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|
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note: if `NotCopyable` implemented `Clone`, you could clone the value
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--> $DIR/option-content-move3.rs:2:1
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|
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LL | struct NotCopyable;
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| ^^^^^^^^^^^^^^^^^^ consider implementing `Clone` for this type
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...
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LL | let x = var;
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| --- you could clone this value
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help: consider borrowing here
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|
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LL | let x = &var;
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| +
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error[E0507]: cannot move out of `var`, a captured variable in an `FnMut` closure
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--> $DIR/option-content-move3.rs:10:9
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--> $DIR/option-content-move3.rs:12:9
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|
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LL | let mut var = NotCopyable;
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| ------- captured outer variable
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LL | let var = NotCopyable;
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| --- captured outer variable
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LL | func(|| {
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| -- captured by this `FnMut` closure
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LL | // Shouldn't suggest `move ||.as_ref()` here
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@ -29,7 +37,59 @@ LL | let x = var;
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| |
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| variable moved due to use in closure
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| move occurs because `var` has type `NotCopyable`, which does not implement the `Copy` trait
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|
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note: if `NotCopyable` implemented `Clone`, you could clone the value
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--> $DIR/option-content-move3.rs:2:1
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|
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LL | struct NotCopyable;
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| ^^^^^^^^^^^^^^^^^^ consider implementing `Clone` for this type
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...
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LL | let x = var;
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| --- you could clone this value
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error: aborting due to 2 previous errors
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error[E0507]: cannot move out of `var`, a captured variable in an `FnMut` closure
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--> $DIR/option-content-move3.rs:24:21
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|
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LL | let var = NotCopyableButCloneable;
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| --- captured outer variable
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...
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LL | move || {
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| ------- captured by this `FnMut` closure
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LL | let x = var;
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| ^^^ move occurs because `var` has type `NotCopyableButCloneable`, which does not implement the `Copy` trait
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|
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help: consider borrowing here
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|
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LL | let x = &var;
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| +
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error[E0507]: cannot move out of `var`, a captured variable in an `FnMut` closure
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--> $DIR/option-content-move3.rs:23:9
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|
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LL | let var = NotCopyableButCloneable;
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| --- captured outer variable
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LL | func(|| {
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| -- captured by this `FnMut` closure
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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`.
|
||||
|
Loading…
Reference in New Issue
Block a user