Point at continue and break that might be in the wrong place
Sometimes move errors are because of a misplaced `continue`, but we didn't
surface that anywhere. Now when there are more than one set of nested loops
we show them out and point at the `continue` and `break` expressions within
that might need to go elsewhere.
```
error[E0382]: use of moved value: `foo`
--> $DIR/nested-loop-moved-value-wrong-continue.rs:46:18
|
LL | for foo in foos {
| ---
| |
| this reinitialization might get skipped
| move occurs because `foo` has type `String`, which does not implement the `Copy` trait
...
LL | for bar in &bars {
| ---------------- inside of this loop
...
LL | baz.push(foo);
| --- value moved here, in previous iteration of loop
...
LL | qux.push(foo);
| ^^^ value used here after move
|
note: verify that your loop breaking logic is correct
--> $DIR/nested-loop-moved-value-wrong-continue.rs:41:17
|
LL | for foo in foos {
| ---------------
...
LL | for bar in &bars {
| ----------------
...
LL | continue;
| ^^^^^^^^ this `continue` advances the loop at line 33
help: consider moving the expression out of the loop so it is only moved once
|
LL ~ let mut value = baz.push(foo);
LL ~ for bar in &bars {
LL |
...
LL | if foo == *bar {
LL ~ value;
|
help: consider cloning the value if the performance cost is acceptable
|
LL | baz.push(foo.clone());
| ++++++++
```
Fix #92531.
This commit is contained in:
Esteban Küber
parent
14473adf42
commit
78d29ad8d6
9 changed files with 225 additions and 55 deletions
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@ -9,7 +9,7 @@ use rustc_data_structures::fx::FxIndexSet;
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use rustc_errors::{codes::*, struct_span_code_err, Applicability, Diag, MultiSpan};
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use rustc_hir as hir;
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use rustc_hir::def::{DefKind, Res};
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use rustc_hir::intravisit::{walk_block, walk_expr, Visitor};
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use rustc_hir::intravisit::{walk_block, walk_expr, Map, Visitor};
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use rustc_hir::{CoroutineDesugaring, PatField};
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use rustc_hir::{CoroutineKind, CoroutineSource, LangItem};
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use rustc_middle::hir::nested_filter::OnlyBodies;
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@ -799,9 +799,9 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
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let e = match node {
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hir::Node::Expr(e) => e,
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hir::Node::Local(hir::Local { els: Some(els), .. }) => {
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let mut finder = BreakFinder { found_break: false };
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let mut finder = BreakFinder { found_breaks: vec![], found_continues: vec![] };
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finder.visit_block(els);
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if finder.found_break {
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if !finder.found_breaks.is_empty() {
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// Don't suggest clone as it could be will likely end in an infinite
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// loop.
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// let Some(_) = foo(non_copy.clone()) else { break; }
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@ -850,51 +850,148 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
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_ => {}
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}
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}
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let loop_count: usize = tcx
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.hir()
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.parent_iter(expr.hir_id)
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.map(|(_, node)| match node {
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hir::Node::Expr(hir::Expr { kind: hir::ExprKind::Loop(..), .. }) => 1,
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_ => 0,
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})
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.sum();
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/// Look for `break` expressions within any arbitrary expressions. We'll do this to infer
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/// whether this is a case where the moved value would affect the exit of a loop, making it
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/// unsuitable for a `.clone()` suggestion.
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struct BreakFinder {
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found_break: bool,
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found_breaks: Vec<(hir::Destination, Span)>,
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found_continues: Vec<(hir::Destination, Span)>,
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}
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impl<'hir> Visitor<'hir> for BreakFinder {
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fn visit_expr(&mut self, ex: &'hir hir::Expr<'hir>) {
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if let hir::ExprKind::Break(..) = ex.kind {
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self.found_break = true;
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match ex.kind {
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hir::ExprKind::Break(destination, _) => {
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self.found_breaks.push((destination, ex.span));
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}
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hir::ExprKind::Continue(destination) => {
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self.found_continues.push((destination, ex.span));
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}
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_ => {}
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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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if let Some(in_loop) = outer_most_loop
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&& let Some(parent) = parent
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&& let hir::ExprKind::MethodCall(..) | hir::ExprKind::Call(..) = parent.kind
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{
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// FIXME: We could check that the call's *parent* takes `&mut val` to make the
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// suggestion more targeted to the `mk_iter(val).next()` case. Maybe do that only to
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// check for wheter to suggest `let value` or `let mut value`.
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let span = in_loop.span;
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let mut finder = BreakFinder { found_break: false };
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let sm = tcx.sess.source_map();
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if let Some(in_loop) = outer_most_loop {
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let mut finder = BreakFinder { found_breaks: vec![], found_continues: vec![] };
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finder.visit_expr(in_loop);
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let sm = tcx.sess.source_map();
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if (finder.found_break || true)
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&& let Ok(value) = sm.span_to_snippet(parent.span)
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{
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// We know with high certainty that this move would affect the early return of a
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// loop, so we suggest moving the expression with the move out of the loop.
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let indent = if let Some(indent) = sm.indentation_before(span) {
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format!("\n{indent}")
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} else {
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" ".to_string()
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// All of the spans for `break` and `continue` expressions.
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let spans = finder
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.found_breaks
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.iter()
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.chain(finder.found_continues.iter())
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.map(|(_, span)| *span)
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.filter(|span| {
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!matches!(
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span.desugaring_kind(),
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Some(DesugaringKind::ForLoop | DesugaringKind::WhileLoop)
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)
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})
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.collect::<Vec<Span>>();
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// All of the spans for the loops above the expression with the move error.
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let loop_spans: Vec<_> = tcx
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.hir()
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.parent_iter(expr.hir_id)
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.filter_map(|(_, node)| match node {
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hir::Node::Expr(hir::Expr { span, kind: hir::ExprKind::Loop(..), .. }) => {
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Some(*span)
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}
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_ => None,
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})
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.collect();
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// It is possible that a user written `break` or `continue` is in the wrong place. We
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// point them out at the user for them to make a determination. (#92531)
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if !spans.is_empty() && loop_count > 1 {
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// Getting fancy: if the spans of the loops *do not* overlap, we only use the line
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// number when referring to them. If there *are* overlaps (multiple loops on the
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// same line) then we use the more verbose span output (`file.rs:col:ll`).
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let mut lines: Vec<_> =
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loop_spans.iter().map(|sp| sm.lookup_char_pos(sp.lo()).line).collect();
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lines.sort();
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lines.dedup();
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let fmt_span = |span: Span| {
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if lines.len() == loop_spans.len() {
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format!("line {}", sm.lookup_char_pos(span.lo()).line)
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} else {
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sm.span_to_diagnostic_string(span)
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}
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};
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err.multipart_suggestion(
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"consider moving the expression out of the loop so it is only moved once",
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vec![
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(parent.span, "value".to_string()),
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(span.shrink_to_lo(), format!("let mut value = {value};{indent}")),
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],
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Applicability::MaybeIncorrect,
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);
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let mut spans: MultiSpan = spans.clone().into();
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// Point at all the `continue`s and explicit `break`s in the relevant loops.
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for (desc, elements) in [
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("`break` exits", &finder.found_breaks),
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("`continue` advances", &finder.found_continues),
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] {
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for (destination, sp) in elements {
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if let Ok(hir_id) = destination.target_id
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&& let hir::Node::Expr(expr) = tcx.hir().hir_node(hir_id)
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&& !matches!(
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sp.desugaring_kind(),
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Some(DesugaringKind::ForLoop | DesugaringKind::WhileLoop)
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)
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{
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spans.push_span_label(
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*sp,
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format!("this {desc} the loop at {}", fmt_span(expr.span)),
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);
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}
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}
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}
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// Point at all the loops that are between this move and the parent item.
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for span in loop_spans {
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spans.push_span_label(sm.guess_head_span(span), "");
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}
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// note: verify that your loop breaking logic is correct
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// --> $DIR/nested-loop-moved-value-wrong-continue.rs:41:17
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// |
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// 28 | for foo in foos {
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// | ---------------
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// ...
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// 33 | for bar in &bars {
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// | ----------------
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// ...
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// 41 | continue;
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// | ^^^^^^^^ this `continue` advances the loop at line 33
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err.span_note(spans, "verify that your loop breaking logic is correct");
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}
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if let Some(parent) = parent
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&& let hir::ExprKind::MethodCall(..) | hir::ExprKind::Call(..) = parent.kind
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{
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// FIXME: We could check that the call's *parent* takes `&mut val` to make the
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// suggestion more targeted to the `mk_iter(val).next()` case. Maybe do that only to
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// check for wheter to suggest `let value` or `let mut value`.
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let span = in_loop.span;
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if !finder.found_breaks.is_empty()
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&& let Ok(value) = sm.span_to_snippet(parent.span)
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{
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// We know with high certainty that this move would affect the early return of a
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// loop, so we suggest moving the expression with the move out of the loop.
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let indent = if let Some(indent) = sm.indentation_before(span) {
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format!("\n{indent}")
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} else {
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" ".to_string()
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};
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err.multipart_suggestion(
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"consider moving the expression out of the loop so it is only moved once",
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vec![
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(parent.span, "value".to_string()),
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(span.shrink_to_lo(), format!("let mut value = {value};{indent}")),
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],
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Applicability::MaybeIncorrect,
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);
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}
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}
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}
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can_suggest_clone
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