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Correct Fixes for Options and Results in Certain Contexts #96537

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Correct Fixes for Options and Results in Certain Contexts #96537

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28f8485
Simplify code, change applicability
George-lewis Apr 28, 2022
355dafa
Tidy
George-lewis Apr 28, 2022
aee411f
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George-lewis Apr 28, 2022
58443e7
Delete dead code
George-lewis Apr 28, 2022
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20 changes: 16 additions & 4 deletions compiler/rustc_borrowck/src/diagnostics/move_errors.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@ use rustc_middle::ty;
use rustc_mir_dataflow::move_paths::{
IllegalMoveOrigin, IllegalMoveOriginKind, LookupResult, MoveError, MovePathIndex,
};
use rustc_span::{sym, Span};
use rustc_span::{sym, BytePos, Span};

use crate::diagnostics::UseSpans;
use crate::prefixes::PrefixSet;
Expand Down Expand Up @@ -414,11 +414,23 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
&& use_spans.map_or(true, |v| !v.for_closure())
&& !has_complex_bindings
{
err.span_suggestion_verbose(
let span = match use_spans {
Some(UseSpans::FnSelfUse { var_span, fn_call_span, .. }) => {
// `fn_call_span` is the span of `unwrap()`
// This gets the 'variable' span excluding the unwrap
let span = var_span.until(fn_call_span);

// Unfortunately the new span has a "." on the end which makes
// the suggestion format strangely, so we adjust the hi bound manually
span.with_hi(span.hi() - BytePos(1))
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If it has . on the end, then maybe we should suggest as_ref(). instead of .as_ref().

Span arithmetic is dangerous because macros can set spans arbitrarily and span - BytePos(1) can potentially underflow or point into the middle of a unicode character producing an ICE.

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@George-lewis George-lewis Apr 29, 2022 •
edited
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Sounds good to me, I'll remove the span arithmetic. This + the previous suggestion gives the following output for issue-96438.rs:

error[E0507]: cannot move out of dereference of `RefMut<'_, Option<Vec<()>>>`
 --> ./src/test/ui/borrowck/issue-96438.rs:4:5
  |
4 |     cell.borrow_mut().unwrap().pop().unwrap();
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^ move occurs because value has type `Option<Vec<()>>`, which does not implement the `Copy` trait
  |
help: consider borrowing the `Option`'s content
  |
4 |     cell.borrow_mut().as_ref().unwrap().pop().unwrap();
  |                       +++++++++
help: consider borrowing the `Option`'s content
  |
4 |     cell.borrow_mut().as_mut().unwrap().pop().unwrap();
  |                       +++++++++

error: aborting due to previous error

For more information about this error, try `rustc --explain E0507`.

Which is alright, however it doesn't seem to fix the double application in option-content-move.stderr unfortunately.

}
_ => span,
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I suspect that this case may never happen (as an Option or Result must always be unwraped, or expected, etc) but am not confident enough to make this a panic or some such. Can change at reviewer discretion

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I'm not sure, let's keep it as is.
(And set applicability to MaybeIncorrect for this case.)

};
err.span_suggestions(
span.shrink_to_hi(),
&format!("consider borrowing the `{}`'s content", diag_name.unwrap()),
".as_ref()".to_string(),
Applicability::MaybeIncorrect,
vec![".as_ref()".to_string(), ".as_mut()".to_string()].into_iter(),
Applicability::MachineApplicable,
);
} else if let Some(use_spans) = use_spans {
self.explain_captures(
Expand Down
13 changes: 13 additions & 0 deletions src/test/ui/borrowck/issue-96438.rs
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@@ -0,0 +1,13 @@
use std::cell::RefCell;

fn foo(cell: &RefCell<Option<Vec<()>>>) {
cell.borrow_mut().unwrap().pop().unwrap();
//~^ ERROR cannot move out of dereference of `RefMut<'_, Option<Vec<()>>>` [E0507]
//~| NOTE move occurs because value has type `Option<Vec<()>>`, which does not implement the `Copy` trait
//~| HELP consider borrowing the `Option`'s content
}

fn main() {
let cell = RefCell::new(None);
foo(&cell);
}
16 changes: 16 additions & 0 deletions src/test/ui/borrowck/issue-96438.stderr
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@@ -0,0 +1,16 @@
error[E0507]: cannot move out of dereference of `RefMut<'_, Option<Vec<()>>>`
--> $DIR/issue-96438.rs:4:5
|
LL | cell.borrow_mut().unwrap().pop().unwrap();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ move occurs because value has type `Option<Vec<()>>`, which does not implement the `Copy` trait
|
help: consider borrowing the `Option`'s content
|
LL | cell.borrow_mut().as_mut().unwrap().pop().unwrap();
| +++++++++
LL | cell.borrow_mut().as_ref().unwrap().pop().unwrap();
| +++++++++

error: aborting due to previous error

For more information about this error, try `rustc --explain E0507`.
4 changes: 2 additions & 2 deletions src/test/ui/suggestions/option-content-move.fixed
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Expand Up @@ -8,7 +8,7 @@ impl LipogramCorpora {
pub fn validate_all(&mut self) -> Result<(), char> {
for selection in &self.selections {
if selection.1.is_some() {
if selection.1.as_ref().unwrap().contains(selection.0) {
if selection.1.as_ref().as_mut().unwrap().contains(selection.0) {
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@George-lewis George-lewis Apr 29, 2022 •
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I'm not sure how to stop it from doing this (applying both suggestions)

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What happens if you use span_suggestion_verbose twice instead of one span_suggestions?

//~^ ERROR cannot move out of `selection.1`
return Err(selection.0);
}
Expand All @@ -26,7 +26,7 @@ impl LipogramCorpora2 {
pub fn validate_all(&mut self) -> Result<(), char> {
for selection in &self.selections {
if selection.1.is_ok() {
if selection.1.as_ref().unwrap().contains(selection.0) {
if selection.1.as_ref().as_mut().unwrap().contains(selection.0) {
//~^ ERROR cannot move out of `selection.1`
return Err(selection.0);
}
Expand Down
4 changes: 4 additions & 0 deletions src/test/ui/suggestions/option-content-move.stderr
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Expand Up @@ -6,6 +6,8 @@ LL | if selection.1.unwrap().contains(selection.0) {
|
help: consider borrowing the `Option`'s content
|
LL | if selection.1.as_mut().unwrap().contains(selection.0) {
| +++++++++
LL | if selection.1.as_ref().unwrap().contains(selection.0) {
| +++++++++

Expand All @@ -17,6 +19,8 @@ LL | if selection.1.unwrap().contains(selection.0) {
|
help: consider borrowing the `Result`'s content
|
LL | if selection.1.as_mut().unwrap().contains(selection.0) {
| +++++++++
LL | if selection.1.as_ref().unwrap().contains(selection.0) {
| +++++++++

Expand Down