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Suggest move in nested closure when appropriate

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Fix #64008.
This commit is contained in:
Esteban Küber 2023-01-07 22:17:00 +00:00
parent 97872b792c
commit e6b84eb797
5 changed files with 98 additions and 21 deletions
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28
compiler/rustc_borrowck/src/diagnostics/region_errors.rs
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@ -583,10 +583,12 @@ fn report_fnmut_error(
let err = FnMutError {
span: *span,
ty_err: match output_ty.kind() {
ty::Closure(_, _) => FnMutReturnTypeErr::ReturnClosure { span: *span },
ty::Generator(def, ..) if self.infcx.tcx.generator_is_async(*def) => {
FnMutReturnTypeErr::ReturnAsyncBlock { span: *span }
}
_ if output_ty.contains_closure() => {
FnMutReturnTypeErr::ReturnClosure { span: *span }
}
_ => FnMutReturnTypeErr::ReturnRef { span: *span },
},
};
@ -997,7 +999,7 @@ fn suggest_adding_lifetime_params(
fn suggest_move_on_borrowing_closure(&self, diag: &mut Diagnostic) {
let map = self.infcx.tcx.hir();
let body_id = map.body_owned_by(self.mir_def_id());
let expr = &map.body(body_id).value;
let expr = &map.body(body_id).value.peel_blocks();
let mut closure_span = None::<rustc_span::Span>;
match expr.kind {
hir::ExprKind::MethodCall(.., args, _) => {
@ -1012,20 +1014,14 @@ fn suggest_move_on_borrowing_closure(&self, diag: &mut Diagnostic) {
}
}
}
hir::ExprKind::Block(blk, _) => {
if let Some(expr) = blk.expr {
// only when the block is a closure
if let hir::ExprKind::Closure(hir::Closure {
capture_clause: hir::CaptureBy::Ref,
body,
..
}) = expr.kind
{
let body = map.body(*body);
if !matches!(body.generator_kind, Some(hir::GeneratorKind::Async(..))) {
closure_span = Some(expr.span.shrink_to_lo());
}
}
hir::ExprKind::Closure(hir::Closure {
capture_clause: hir::CaptureBy::Ref,
body,
..
}) => {
let body = map.body(*body);
if !matches!(body.generator_kind, Some(hir::GeneratorKind::Async(..))) {
closure_span = Some(expr.span.shrink_to_lo());
}
}
_ => {}

22
compiler/rustc_middle/src/ty/sty.rs
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@ -2043,6 +2043,28 @@ fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
cf.is_break()
}
/// Checks whether a type recursively contains any closure
///
/// Example: `Option<[closure@file.rs:4:20]>` returns true
pub fn contains_closure(self) -> bool {
struct ContainsClosureVisitor;
impl<'tcx> TypeVisitor<'tcx> for ContainsClosureVisitor {
type BreakTy = ();
fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
if let ty::Closure(_, _) = t.kind() {
ControlFlow::Break(())
} else {
t.super_visit_with(self)
}
}
}
let cf = self.visit_with(&mut ContainsClosureVisitor);
cf.is_break()
}
/// Returns the type and mutability of `*ty`.
///
/// The parameter `explicit` indicates if this is an *explicit* dereference.

26
tests/ui/borrowck/issue-95079-missing-move-in-nested-closure.fixed Normal file
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@ -0,0 +1,26 @@
// run-rustfix
#![allow(dead_code, path_statements)]
fn foo1(s: &str) -> impl Iterator<Item = String> + '_ {
None.into_iter()
.flat_map(move |()| s.chars().map(move |c| format!("{}{}", c, s)))
//~^ ERROR captured variable cannot escape `FnMut` closure body
//~| HELP consider adding 'move' keyword before the nested closure
}
fn foo2(s: &str) -> impl Sized + '_ {
move |()| s.chars().map(move |c| format!("{}{}", c, s))
//~^ ERROR lifetime may not live long enough
//~| HELP consider adding 'move' keyword before the nested closure
}
pub struct X;
pub fn foo3<'a>(
bar: &'a X,
) -> impl Iterator<Item = ()> + 'a {
Some(()).iter().flat_map(move |()| {
Some(()).iter().map(move |()| { bar; }) //~ ERROR captured variable cannot escape
//~^ HELP consider adding 'move' keyword before the nested closure
})
}
fn main() {}

12
tests/ui/borrowck/issue-95079-missing-move-in-nested-closure.rs
View File

@ -1,3 +1,5 @@
// run-rustfix
#![allow(dead_code, path_statements)]
fn foo1(s: &str) -> impl Iterator<Item = String> + '_ {
None.into_iter()
.flat_map(move |()| s.chars().map(|c| format!("{}{}", c, s)))
@ -11,4 +13,14 @@ fn foo2(s: &str) -> impl Sized + '_ {
//~| HELP consider adding 'move' keyword before the nested closure
}
pub struct X;
pub fn foo3<'a>(
bar: &'a X,
) -> impl Iterator<Item = ()> + 'a {
Some(()).iter().flat_map(move |()| {
Some(()).iter().map(|()| { bar; }) //~ ERROR captured variable cannot escape
//~^ HELP consider adding 'move' keyword before the nested closure
})
}
fn main() {}

31
tests/ui/borrowck/issue-95079-missing-move-in-nested-closure.stderr
View File

@ -1,5 +1,5 @@
error: captured variable cannot escape `FnMut` closure body
--> $DIR/issue-95079-missing-move-in-nested-closure.rs:3:29
--> $DIR/issue-95079-missing-move-in-nested-closure.rs:5:29
|
LL | fn foo1(s: &str) -> impl Iterator<Item = String> + '_ {
| - variable defined here
@ -7,7 +7,7 @@ LL | None.into_iter()
LL | .flat_map(move |()| s.chars().map(|c| format!("{}{}", c, s)))
| - -^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| | |
| | returns a reference to a captured variable which escapes the closure body
| | returns a closure that contains a reference to a captured variable, which then escapes the closure body
| | variable captured here
| inferred to be a `FnMut` closure
|
@ -19,12 +19,12 @@ LL | .flat_map(move |()| s.chars().map(move |c| format!("{}{}", c, s)))
| ++++
error: lifetime may not live long enough
--> $DIR/issue-95079-missing-move-in-nested-closure.rs:9:15
--> $DIR/issue-95079-missing-move-in-nested-closure.rs:11:15
|
LL | move |()| s.chars().map(|c| format!("{}{}", c, s))
| --------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ returning this value requires that `'1` must outlive `'2`
| | |
| | return type of closure `Map<Chars<'_>, [closure@$DIR/issue-95079-missing-move-in-nested-closure.rs:9:29: 9:32]>` contains a lifetime `'2`
| | return type of closure `Map<Chars<'_>, [closure@$DIR/issue-95079-missing-move-in-nested-closure.rs:11:29: 11:32]>` contains a lifetime `'2`
| lifetime `'1` represents this closure's body
|
= note: closure implements `Fn`, so references to captured variables can't escape the closure
@ -33,5 +33,26 @@ help: consider adding 'move' keyword before the nested closure
LL | move |()| s.chars().map(move |c| format!("{}{}", c, s))
| ++++
error: aborting due to 2 previous errors
error: captured variable cannot escape `FnMut` closure body
--> $DIR/issue-95079-missing-move-in-nested-closure.rs:21:9
|
LL | bar: &'a X,
| --- variable defined here
LL | ) -> impl Iterator<Item = ()> + 'a {
LL | Some(()).iter().flat_map(move |()| {
| - inferred to be a `FnMut` closure
LL | Some(()).iter().map(|()| { bar; })
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^---^^^^
| | |
| | variable captured here
| returns a closure that contains a reference to a captured variable, which then escapes the closure body
|
= note: `FnMut` closures only have access to their captured variables while they are executing...
= note: ...therefore, they cannot allow references to captured variables to escape
help: consider adding 'move' keyword before the nested closure
|
LL | Some(()).iter().map(move |()| { bar; })
| ++++
error: aborting due to 3 previous errors