mikros/rust
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Point at continue and break that might be in the wrong place

Browse Source 
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 2024-02-26 22:54:34 +00:00
parent 14473adf42
commit 78d29ad8d6
9 changed files with 225 additions and 55 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

163
compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
View File

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

6
tests/ui/liveness/liveness-move-call-arg-2.stderr
View File

@ -16,12 +16,6 @@ LL | fn take(_x: Box<isize>) {}
| ---- ^^^^^^^^^^ this parameter takes ownership of the value
| |
| in this function
help: consider moving the expression out of the loop so it is only moved once
|
LL ~ let mut value = take(x);
LL ~ loop {
LL ~ value;
|
help: consider cloning the value if the performance cost is acceptable
|
LL | take(x.clone());

6
tests/ui/liveness/liveness-move-call-arg.stderr
View File

@ -16,12 +16,6 @@ LL | fn take(_x: Box<isize>) {}
| ---- ^^^^^^^^^^ this parameter takes ownership of the value
| |
| in this function
help: consider moving the expression out of the loop so it is only moved once
|
LL ~ let mut value = take(x);
LL ~ loop {
LL ~ value;
|
help: consider cloning the value if the performance cost is acceptable
|
LL | take(x.clone());

2
tests/ui/moves/borrow-closures-instead-of-move.rs
View File

@ -1,5 +1,5 @@
fn takes_fn(f: impl Fn()) {
loop { //~ HELP consider moving the expression out of the loop so it is only computed once
loop {
takes_fnonce(f);
//~^ ERROR use of moved value
//~| HELP consider borrowing

6
tests/ui/moves/borrow-closures-instead-of-move.stderr
View File

@ -15,12 +15,6 @@ LL | fn takes_fnonce(_: impl FnOnce()) {}
| ------------ ^^^^^^^^^^^^^ this parameter takes ownership of the value
| |
| in this function
help: consider moving the expression out of the loop so it is only moved once
|
LL ~ let mut value = takes_fnonce(f);
LL ~ loop {
LL ~ value;
|
help: consider borrowing `f`
|
LL | takes_fnonce(&f);

26
tests/ui/moves/nested-loop-moved-value-wrong-continue.rs
View File

@ -1,3 +1,27 @@
fn foo() {
let foos = vec![String::new()];
let bars = vec![""];
let mut baz = vec![];
let mut qux = vec![];
for foo in foos { for bar in &bars { if foo == *bar {
//~^ NOTE this reinitialization might get skipped
//~| NOTE move occurs because `foo` has type `String`
//~| NOTE inside of this loop
//~| HELP consider moving the expression out of the loop
//~| NOTE in this expansion of desugaring of `for` loop
baz.push(foo);
//~^ NOTE value moved here
//~| HELP consider cloning the value
continue;
//~^ NOTE verify that your loop breaking logic is correct
//~| NOTE this `continue` advances the loop at $DIR/nested-loop-moved-value-wrong-continue.rs:6:23
} }
qux.push(foo);
//~^ ERROR use of moved value
//~| NOTE value used here
}
}
fn main() {
let foos = vec![String::new()];
let bars = vec![""];
@ -15,6 +39,8 @@ fn main() {
//~^ NOTE value moved here
//~| HELP consider cloning the value
continue;
//~^ NOTE verify that your loop breaking logic is correct
//~| NOTE this `continue` advances the loop at line 33
}
}
qux.push(foo);

52
tests/ui/moves/nested-loop-moved-value-wrong-continue.stderr
View File

@ -1,5 +1,42 @@
error[E0382]: use of moved value: `foo`
--> $DIR/nested-loop-moved-value-wrong-continue.rs:20:18
--> $DIR/nested-loop-moved-value-wrong-continue.rs:19:14
|
LL | for foo in foos { for bar in &bars { if foo == *bar {
| --- ---------------- inside of this loop
| |
| this reinitialization might get skipped
| move occurs because `foo` has type `String`, which does not implement the `Copy` trait
...
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:15:9
|
LL | for foo in foos { for bar in &bars { if foo == *bar {
| --------------- ----------------
...
LL | continue;
| ^^^^^^^^ this `continue` advances the loop at $DIR/nested-loop-moved-value-wrong-continue.rs:6:23: 18:8
help: consider moving the expression out of the loop so it is only moved once
|
LL ~ for foo in foos { let mut value = baz.push(foo);
LL ~ for bar in &bars { if foo == *bar {
LL |
...
LL |
LL ~ value;
|
help: consider cloning the value if the performance cost is acceptable
|
LL | baz.push(foo.clone());
| ++++++++
error[E0382]: use of moved value: `foo`
--> $DIR/nested-loop-moved-value-wrong-continue.rs:46:18
|
LL | for foo in foos {
| ---
@ -16,6 +53,17 @@ LL | baz.push(foo);
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);
@ -30,6 +78,6 @@ help: consider cloning the value if the performance cost is acceptable
LL | baz.push(foo.clone());
| ++++++++
error: aborting due to 1 previous error
error: aborting due to 2 previous errors
For more information about this error, try `rustc --explain E0382`.

2
tests/ui/moves/recreating-value-in-loop-condition.rs
View File

@ -31,6 +31,7 @@ fn qux() {
loop {
if let Some(item) = iter(vec).next() { //~ ERROR use of moved value
println!("{:?}", item);
break;
}
}
}
@ -42,6 +43,7 @@ fn zap() {
loop {
if let Some(item) = iter(vec).next() { //~ ERROR use of moved value
println!("{:?}", item);
break;
}
}
}

17
tests/ui/moves/recreating-value-in-loop-condition.stderr
View File

@ -99,7 +99,7 @@ LL ~ if let Some(item) = value.next() {
|
error[E0382]: use of moved value: `vec`
--> $DIR/recreating-value-in-loop-condition.rs:43:46
--> $DIR/recreating-value-in-loop-condition.rs:44:46
|
LL | let vec = vec!["one", "two", "three"];
| --- move occurs because `vec` has type `Vec<&str>`, which does not implement the `Copy` trait
@ -119,6 +119,21 @@ LL | fn iter<T>(vec: Vec<T>) -> impl Iterator<Item = T> {
| ---- ^^^^^^ this parameter takes ownership of the value
| |
| in this function
note: verify that your loop breaking logic is correct
--> $DIR/recreating-value-in-loop-condition.rs:46:25
|
LL | loop {
| ----
LL | let vec = vec!["one", "two", "three"];
LL | loop {
| ----
LL | loop {
| ----
LL | loop {
| ----
...
LL | break;
| ^^^^^ this `break` exits the loop at line 43
help: consider moving the expression out of the loop so it is only moved once
|
LL ~ let mut value = iter(vec);