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Explain method-call move errors in loops
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PR #73708 added a more detailed explanation of move errors that occur
due to a call to a method that takes `self`. This PR extends that logic
to work when a move error occurs due to a method call in the previous
iteration of a loop.
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@Aaron1011
Aaron1011 committed Jan 8, 2021
1 parent ddf2cc7 commit de90afc
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Showing 4 changed files with 90 additions and 76 deletions.
142 changes: 68 additions & 74 deletions compiler/rustc_mir/src/borrow_check/diagnostics/conflict_errors.rs
View file
Expand Up @@ -151,95 +151,88 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {

let move_msg = if move_spans.for_closure() { " into closure" } else { "" };

let loop_message = if location == move_out.source || move_site.traversed_back_edge {
", in previous iteration of loop"
} else {
""
};

if location == move_out.source {
err.span_label(
span,
format!(
"value {}moved{} here, in previous iteration of loop",
partially_str, move_msg
),
);
is_loop_move = true;
} else if move_site.traversed_back_edge {
err.span_label(
move_span,
format!(
"value {}moved{} here, in previous iteration of loop",
partially_str, move_msg
),
);
} else {
if let UseSpans::FnSelfUse { var_span, fn_call_span, fn_span, kind } =
move_spans
{
let place_name = self
.describe_place(moved_place.as_ref())
.map(|n| format!("`{}`", n))
.unwrap_or_else(|| "value".to_owned());
match kind {
FnSelfUseKind::FnOnceCall => {
}

if let UseSpans::FnSelfUse { var_span, fn_call_span, fn_span, kind } = move_spans {
let place_name = self
.describe_place(moved_place.as_ref())
.map(|n| format!("`{}`", n))
.unwrap_or_else(|| "value".to_owned());
match kind {
FnSelfUseKind::FnOnceCall => {
err.span_label(
fn_call_span,
&format!(
"{} {}moved due to this call{}",
place_name, partially_str, loop_message
),
);
err.span_note(
var_span,
"this value implements `FnOnce`, which causes it to be moved when called",
);
}
FnSelfUseKind::Operator { self_arg } => {
err.span_label(
fn_call_span,
&format!(
"{} {}moved due to usage in operator{}",
place_name, partially_str, loop_message
),
);
if self.fn_self_span_reported.insert(fn_span) {
err.span_note(
self_arg.span,
"calling this operator moves the left-hand side",
);
}
}
FnSelfUseKind::Normal { self_arg, implicit_into_iter } => {
if implicit_into_iter {
err.span_label(
fn_call_span,
&format!(
"{} {}moved due to this call",
place_name, partially_str
"{} {}moved due to this implicit call to `.into_iter()`{}",
place_name, partially_str, loop_message
),
);
err.span_note(
var_span,
"this value implements `FnOnce`, which causes it to be moved when called",
);
}
FnSelfUseKind::Operator { self_arg } => {
} else {
err.span_label(
fn_call_span,
&format!(
"{} {}moved due to usage in operator",
place_name, partially_str
"{} {}moved due to this method call{}",
place_name, partially_str, loop_message
),
);
if self.fn_self_span_reported.insert(fn_span) {
err.span_note(
self_arg.span,
"calling this operator moves the left-hand side",
);
}
}
FnSelfUseKind::Normal { self_arg, implicit_into_iter } => {
if implicit_into_iter {
err.span_label(
fn_call_span,
&format!(
"{} {}moved due to this implicit call to `.into_iter()`",
place_name, partially_str
),
);
} else {
err.span_label(
fn_call_span,
&format!(
"{} {}moved due to this method call",
place_name, partially_str
),
);
}
// Avoid pointing to the same function in multiple different
// error messages
if self.fn_self_span_reported.insert(self_arg.span) {
err.span_note(
self_arg.span,
&format!("this function consumes the receiver `self` by taking ownership of it, which moves {}", place_name)
);
}
// Avoid pointing to the same function in multiple different
// error messages
if self.fn_self_span_reported.insert(self_arg.span) {
err.span_note(
self_arg.span,
&format!("this function consumes the receiver `self` by taking ownership of it, which moves {}", place_name)
);
}
// Deref::deref takes &self, which cannot cause a move
FnSelfUseKind::DerefCoercion { .. } => unreachable!(),
}
} else {
err.span_label(
move_span,
format!("value {}moved{} here", partially_str, move_msg),
);
// Deref::deref takes &self, which cannot cause a move
FnSelfUseKind::DerefCoercion { .. } => unreachable!(),
}
} else {
err.span_label(
move_span,
format!("value {}moved{} here{}", partially_str, move_msg, loop_message),
);
// If the move error occurs due to a loop, don't show
// another message for the same span
if loop_message.is_empty() {
move_spans.var_span_label(
&mut err,
format!(
Expand All @@ -250,6 +243,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
);
}
}

if let UseSpans::PatUse(span) = move_spans {
err.span_suggestion_verbose(
span.shrink_to_lo(),
Expand Down
5 changes: 5 additions & 0 deletions src/test/ui/moves/move-fn-self-receiver.rs
View file
Expand Up @@ -69,6 +69,11 @@ fn move_out(val: Container) {
let container = Container(vec![]);
for _val in container.custom_into_iter() {}
container; //~ ERROR use of moved

let foo2 = Foo;
loop {
foo2.use_self(); //~ ERROR use of moved
}
}

fn main() {}
11 changes: 10 additions & 1 deletion src/test/ui/moves/move-fn-self-receiver.stderr
View file
Expand Up @@ -152,7 +152,16 @@ note: this function consumes the receiver `self` by taking ownership of it, whic
LL | fn custom_into_iter(self) -> impl Iterator<Item = bool> {
| ^^^^

error: aborting due to 11 previous errors
error[E0382]: use of moved value: `foo2`
--> $DIR/move-fn-self-receiver.rs:75:9
|
LL | let foo2 = Foo;
| ---- move occurs because `foo2` has type `Foo`, which does not implement the `Copy` trait
LL | loop {
LL | foo2.use_self();
| ^^^^ ---------- `foo2` moved due to this method call, in previous iteration of loop

error: aborting due to 12 previous errors

Some errors have detailed explanations: E0382, E0505.
For more information about an error, try `rustc --explain E0382`.
8 changes: 7 additions & 1 deletion src/test/ui/suggestions/borrow-for-loop-head.stderr
View file
Expand Up @@ -15,8 +15,14 @@ LL | for i in &a {
LL | for j in a {
| ^
| |
| value moved here, in previous iteration of loop
| `a` moved due to this implicit call to `.into_iter()`, in previous iteration of loop
| help: consider borrowing to avoid moving into the for loop: `&a`
|
note: this function consumes the receiver `self` by taking ownership of it, which moves `a`
--> $SRC_DIR/core/src/iter/traits/collect.rs:LL:COL
|
LL | fn into_iter(self) -> Self::IntoIter;
| ^^^^

error: aborting due to 2 previous errors

Expand Down

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