Point at the `Fn()` or `FnMut()` bound that coerced a closure, which caused a move error by estebank · Pull Request #144558 · rust-lang/rust
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Jul 28, 2025…caused a move error
When encountering a move error involving a closure because the captured value isn't `Copy`, and the obligation comes from a bound on a type parameter that requires `Fn` or `FnMut`, we point at it and explain that an `FnOnce` wouldn't cause the move error.
```
error[E0507]: cannot move out of `foo`, a captured variable in an `Fn` closure
--> f111.rs:15:25
|
14 | fn do_stuff(foo: Option<Foo>) {
| --- ----------- move occurs because `foo` has type `Option<Foo>`, which does not implement the `Copy` trait
| |
| captured outer variable
15 | require_fn_trait(|| async {
| -- ^^^^^ `foo` is moved here
| |
| captured by this `Fn` closure
16 | if foo.map_or(false, |f| f.foo()) {
| --- variable moved due to use in coroutine
|
help: `Fn` and `FnMut` closures require captured values to be able to be consumed multiple times, but an `FnOnce` consume them only once
--> f111.rs:12:53
|
12 | fn require_fn_trait<F: Future<Output = ()>>(_: impl Fn() -> F) {}
| ^^^^^^^^^
help: consider cloning the value if the performance cost is acceptable
|
16 | if foo.clone().map_or(false, |f| f.foo()) {
| ++++++++
```
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Status: Awaiting review from the assignee but also interested parties.labels
Aug 10, 2025samueltardieu added a commit to samueltardieu/rust that referenced this pull request
Aug 10, 2025Point at the `Fn()` or `FnMut()` bound that coerced a closure, which caused a move error
When encountering a move error involving a closure because the captured value isn't `Copy`, and the obligation comes from a bound on a type parameter that requires `Fn` or `FnMut`, we point at it and explain that an `FnOnce` wouldn't cause the move error.
```
error[E0507]: cannot move out of `foo`, a captured variable in an `Fn` closure
--> f111.rs:15:25
|
14 | fn do_stuff(foo: Option<Foo>) {
| --- ----------- move occurs because `foo` has type `Option<Foo>`, which does not implement the `Copy` trait
| |
| captured outer variable
15 | require_fn_trait(|| async {
| -- ^^^^^ `foo` is moved here
| |
| captured by this `Fn` closure
16 | if foo.map_or(false, |f| f.foo()) {
| --- variable moved due to use in coroutine
|
help: `Fn` and `FnMut` closures require captured values to be able to be consumed multiple times, but an `FnOnce` consume them only once
--> f111.rs:12:53
|
12 | fn require_fn_trait<F: Future<Output = ()>>(_: impl Fn() -> F) {}
| ^^^^^^^^^
help: consider cloning the value if the performance cost is acceptable
|
16 | if foo.clone().map_or(false, |f| f.foo()) {
| ++++++++
```
Fix rust-lang#68119, by pointing at `Fn` and `FnMut` bounds involved in move errors.
bors added a commit that referenced this pull request
Aug 10, 2025Rollup of 3 pull requests Successful merges: - #135846 (Detect struct construction with private field in field with default) - #144558 (Point at the `Fn()` or `FnMut()` bound that coerced a closure, which caused a move error) - #145149 (Make config method invoke inside parse use dwn_ctx) r? `@ghost` `@rustbot` modify labels: rollup
Zalathar added a commit to Zalathar/rust that referenced this pull request
Aug 11, 2025Point at the `Fn()` or `FnMut()` bound that coerced a closure, which caused a move error
When encountering a move error involving a closure because the captured value isn't `Copy`, and the obligation comes from a bound on a type parameter that requires `Fn` or `FnMut`, we point at it and explain that an `FnOnce` wouldn't cause the move error.
```
error[E0507]: cannot move out of `foo`, a captured variable in an `Fn` closure
--> f111.rs:15:25
|
14 | fn do_stuff(foo: Option<Foo>) {
| --- ----------- move occurs because `foo` has type `Option<Foo>`, which does not implement the `Copy` trait
| |
| captured outer variable
15 | require_fn_trait(|| async {
| -- ^^^^^ `foo` is moved here
| |
| captured by this `Fn` closure
16 | if foo.map_or(false, |f| f.foo()) {
| --- variable moved due to use in coroutine
|
help: `Fn` and `FnMut` closures require captured values to be able to be consumed multiple times, but an `FnOnce` consume them only once
--> f111.rs:12:53
|
12 | fn require_fn_trait<F: Future<Output = ()>>(_: impl Fn() -> F) {}
| ^^^^^^^^^
help: consider cloning the value if the performance cost is acceptable
|
16 | if foo.clone().map_or(false, |f| f.foo()) {
| ++++++++
```
Fix rust-lang#68119, by pointing at `Fn` and `FnMut` bounds involved in move errors.
bors added a commit that referenced this pull request
Aug 11, 2025Rollup of 7 pull requests Successful merges: - #143949 (Constify remaining traits/impls for `const_ops`) - #144330 (document assumptions about `Clone` and `Eq` traits) - #144350 (std: sys: io: io_slice: Add UEFI types) - #144558 (Point at the `Fn()` or `FnMut()` bound that coerced a closure, which caused a move error) - #145149 (Make config method invoke inside parse use dwn_ctx) - #145227 (Tweak spans providing type context on errors when involving macros) - #145228 (Remove unnecessary parentheses in `assert!`s) r? `@ghost` `@rustbot` modify labels: rollup
rust-timer added a commit that referenced this pull request
Aug 11, 2025Rollup merge of #144558 - estebank:issue-68119, r=lcnr Point at the `Fn()` or `FnMut()` bound that coerced a closure, which caused a move error When encountering a move error involving a closure because the captured value isn't `Copy`, and the obligation comes from a bound on a type parameter that requires `Fn` or `FnMut`, we point at it and explain that an `FnOnce` wouldn't cause the move error. ``` error[E0507]: cannot move out of `foo`, a captured variable in an `Fn` closure --> f111.rs:15:25 | 14 | fn do_stuff(foo: Option<Foo>) { | --- ----------- move occurs because `foo` has type `Option<Foo>`, which does not implement the `Copy` trait | | | captured outer variable 15 | require_fn_trait(|| async { | -- ^^^^^ `foo` is moved here | | | captured by this `Fn` closure 16 | if foo.map_or(false, |f| f.foo()) { | --- variable moved due to use in coroutine | help: `Fn` and `FnMut` closures require captured values to be able to be consumed multiple times, but an `FnOnce` consume them only once --> f111.rs:12:53 | 12 | fn require_fn_trait<F: Future<Output = ()>>(_: impl Fn() -> F) {} | ^^^^^^^^^ help: consider cloning the value if the performance cost is acceptable | 16 | if foo.clone().map_or(false, |f| f.foo()) { | ++++++++ ``` Fix #68119, by pointing at `Fn` and `FnMut` bounds involved in move errors.
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