Tweak output for non-`Clone` values moved into closures #144200

estebank · 2025-07-20T02:27:26Z

When we encounter a non-Clone value being moved into a closure, try to find the corresponding type of the binding being moved, if it is a let-binding or a function parameter. If any of those cases, we point at them with the note explaining that the type is not Copy, instead of giving that label to the place where it is captured. When it is a let-binding with no explicit type, we point at the initializer (if it fits in a single line).

error[E0507]: cannot move out of `foo`, a captured variable in an `Fn` closure
  --> f111.rs:14:25
   |
13 | fn do_stuff(foo: Option<Foo>) {
   |             ---  ----------- move occurs because `foo` has type `Option<Foo>`, which does not implement the `Copy` trait
   |             |
   |             captured outer variable
14 |     require_fn_trait(|| async {
   |                      -- ^^^^^ `foo` is moved here
   |                      |
   |                      captured by this `Fn` closure
15 |         if foo.map_or(false, |f| f.foo()) {
   |            --- variable moved due to use in coroutine

instead of

error[E0507]: cannot move out of `foo`, a captured variable in an `Fn` closure
  --> f111.rs:14:25
   |
13 | fn do_stuff(foo: Option<Foo>) {
   |             --- captured outer variable
14 |     require_fn_trait(|| async {
   |                      -- ^^^^^ `foo` is moved here
   |                      |
   |                      captured by this `Fn` closure
15 |         if foo.map_or(false, |f| f.foo()) {
   |            ---
   |            |
   |            variable moved due to use in coroutine
   |            move occurs because `foo` has type `Option<Foo>`, which does not implement the `Copy` trait

rustbot · 2025-07-20T02:27:30Z

r? @lcnr

rustbot has assigned @lcnr.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

lcnr · 2025-07-21T09:05:58Z

compiler/rustc_borrowck/src/diagnostics/move_errors.rs

+                if let IllegalMoveOriginKind::BorrowedContent { target_place } = &kind
+                    && let ty = target_place.ty(self.body, self.infcx.tcx).ty
+                    && let ty::Closure(def_id, _) = ty.kind()
+                    && def_id.as_local() == Some(self.mir_def_id())


why is this check necessary?

We need to verify that the value is being taking into a closure, but removing the check only triggers for cases of async blocks, which we would also want, so I removed it.

compiler/rustc_borrowck/src/diagnostics/move_errors.rs

tests/ui/span/borrowck-call-is-borrow-issue-12224.stderr

lcnr · 2025-07-21T09:13:20Z

one nit wrt to comments, otherwise r=me

When encountering a non-`Copy` value that is moved into a closure which is coming directly from a fn parameter, point at the parameter's type when mentioning it is not `Copy`. Before: ``` error[E0507]: cannot move out of `foo`, a captured variable in an `Fn` closure --> f111.rs:14:25 | 13 | fn do_stuff(foo: Option<Foo>) { | --- captured outer variable 14 | require_fn_trait(|| async { | -- ^^^^^ `foo` is moved here | | | captured by this `Fn` closure 15 | if foo.map_or(false, |f| f.foo()) { | --- | | | variable moved due to use in coroutine | move occurs because `foo` has type `Option<Foo>`, which does not implement the `Copy` trait ``` After: ``` error[E0507]: cannot move out of `foo`, a captured variable in an `Fn` closure --> f111.rs:14:25 | 13 | fn do_stuff(foo: Option<Foo>) { | --- ----------- move occurs because `foo` has type `Option<Foo>`, which does not implement the `Copy` trait | | | captured outer variable 14 | require_fn_trait(|| async { | -- ^^^^^ `foo` is moved here | | | captured by this `Fn` closure 15 | if foo.map_or(false, |f| f.foo()) { | --- variable moved due to use in coroutine ```

Account not only for `fn` parameters when moving non-`Copy` values into closure, but also for let bindings. ``` error[E0507]: cannot move out of `bar`, a captured variable in an `FnMut` closure --> $DIR/borrowck-move-by-capture.rs:9:29 | LL | let bar: Box<_> = Box::new(3); | --- ------ move occurs because `bar` has type `Box<isize>`, which does not implement the `Copy` trait | | | captured outer variable LL | let _g = to_fn_mut(|| { | -- captured by this `FnMut` closure LL | let _h = to_fn_once(move || -> isize { *bar }); | ^^^^^^^^^^^^^^^^ ---- variable moved due to use in closure | | | `bar` is moved here | help: consider cloning the value before moving it into the closure | LL ~ let value = bar.clone(); LL ~ let _h = to_fn_once(move || -> isize { value }); | ``` ``` error[E0507]: cannot move out of `y`, a captured variable in an `Fn` closure --> $DIR/unboxed-closures-move-upvar-from-non-once-ref-closure.rs:12:9 | LL | let y = vec![format!("World")]; | - ---------------------- move occurs because `y` has type `Vec<String>`, which does not implement the `Copy` trait | | | captured outer variable LL | call(|| { | -- captured by this `Fn` closure LL | y.into_iter(); | ^ ----------- `y` moved due to this method call | | | `y` is moved here | note: `into_iter` takes ownership of the receiver `self`, which moves `y` --> $SRC_DIR/core/src/iter/traits/collect.rs:LL:COL help: you can `clone` the value and consume it, but this might not be your desired behavior | LL | <Vec<String> as Clone>::clone(&y).into_iter(); | +++++++++++++++++++++++++++++++ + help: consider cloning the value if the performance cost is acceptable | LL | y.clone().into_iter(); | ++++++++ ```

``` error[E0507]: cannot move out of `f`, a captured variable in an `FnMut` closure --> $DIR/borrowck-call-is-borrow-issue-12224.rs:57:13 | LL | let mut f = move |g: Box<dyn FnMut(isize)>, b: isize| { | ----- captured outer variable ... LL | f(Box::new(|a| { | --- captured by this `FnMut` closure LL | LL | foo(f); | ^ move occurs because `f` has type `{closure@$DIR/borrowck-call-is-borrow-issue-12224.rs:52:17: 52:58}`, which does not implement the `Copy` trait ``` instead of ``` error[E0507]: cannot move out of `f`, a captured variable in an `FnMut` closure --> $DIR/borrowck-call-is-borrow-issue-12224.rs:57:13 | LL | let mut f = move |g: Box<dyn FnMut(isize)>, b: isize| { | _________-----___- | | | | | captured outer variable LL | | let _ = s.len(); LL | | }; | |_____- move occurs because `f` has type `{closure@$DIR/borrowck-call-is-borrow-issue-12224.rs:52:17: 52:58}`, which does not implement the `Copy` trait LL | f(Box::new(|a| { | --- captured by this `FnMut` closure LL | LL | foo(f); | ^ `f` is moved here ```

…ures

estebank · 2025-07-23T17:40:14Z

@bors r=lcnr

bors · 2025-07-23T17:40:17Z

📌 Commit 6237e73 has been approved by lcnr

It is now in the queue for this repository.

…lcnr Tweak output for non-`Clone` values moved into closures When we encounter a non-`Clone` value being moved into a closure, try to find the corresponding type of the binding being moved, if it is a `let`-binding or a function parameter. If any of those cases, we point at them with the note explaining that the type is not `Copy`, instead of giving that label to the place where it is captured. When it is a `let`-binding with no explicit type, we point at the initializer (if it fits in a single line). ``` error[E0507]: cannot move out of `foo`, a captured variable in an `Fn` closure --> f111.rs:14:25 | 13 | fn do_stuff(foo: Option<Foo>) { | --- ----------- move occurs because `foo` has type `Option<Foo>`, which does not implement the `Copy` trait | | | captured outer variable 14 | require_fn_trait(|| async { | -- ^^^^^ `foo` is moved here | | | captured by this `Fn` closure 15 | if foo.map_or(false, |f| f.foo()) { | --- variable moved due to use in coroutine ``` instead of ``` error[E0507]: cannot move out of `foo`, a captured variable in an `Fn` closure --> f111.rs:14:25 | 13 | fn do_stuff(foo: Option<Foo>) { | --- captured outer variable 14 | require_fn_trait(|| async { | -- ^^^^^ `foo` is moved here | | | captured by this `Fn` closure 15 | if foo.map_or(false, |f| f.foo()) { | --- | | | variable moved due to use in coroutine | move occurs because `foo` has type `Option<Foo>`, which does not implement the `Copy` trait ```

Rollup of 16 pull requests Successful merges: - #142569 (Suggest clone in user-write-code instead of inside macro) - #143401 (tests: Don't check for self-printed output in std-backtrace.rs test) - #143424 (clippy fix: rely on autoderef) - #143970 (Update core::mem::copy documentation) - #143979 (Test fixes for Arm64EC Windows) - #144160 (tests: debuginfo: Work around or disable broken tests on powerpc) - #144200 (Tweak output for non-`Clone` values moved into closures) - #144209 (Don't emit two `assume`s in transmutes when one is a subset of the other) - #144225 (Don't special-case llvm.* as nounwind) - #144314 (Hint that choose_pivot returns index in bounds) - #144316 (bootstrap: Move musl-root fallback out of sanity check) - #144364 (Update `dlmalloc` dependency of libstd) - #144368 (resolve: Remove `Scope::CrateRoot`) - #144373 (remove deprecated Error::description in impls) - #144390 (Remove dead code and extend test coverage and diagnostics around it) - #144392 (rustc_public: Remove movability from `RigidTy/AggregateKind::Coroutine`) r? `@ghost` `@rustbot` modify labels: rollup

…lcnr Tweak output for non-`Clone` values moved into closures When we encounter a non-`Clone` value being moved into a closure, try to find the corresponding type of the binding being moved, if it is a `let`-binding or a function parameter. If any of those cases, we point at them with the note explaining that the type is not `Copy`, instead of giving that label to the place where it is captured. When it is a `let`-binding with no explicit type, we point at the initializer (if it fits in a single line). ``` error[E0507]: cannot move out of `foo`, a captured variable in an `Fn` closure --> f111.rs:14:25 | 13 | fn do_stuff(foo: Option<Foo>) { | --- ----------- move occurs because `foo` has type `Option<Foo>`, which does not implement the `Copy` trait | | | captured outer variable 14 | require_fn_trait(|| async { | -- ^^^^^ `foo` is moved here | | | captured by this `Fn` closure 15 | if foo.map_or(false, |f| f.foo()) { | --- variable moved due to use in coroutine ``` instead of ``` error[E0507]: cannot move out of `foo`, a captured variable in an `Fn` closure --> f111.rs:14:25 | 13 | fn do_stuff(foo: Option<Foo>) { | --- captured outer variable 14 | require_fn_trait(|| async { | -- ^^^^^ `foo` is moved here | | | captured by this `Fn` closure 15 | if foo.map_or(false, |f| f.foo()) { | --- | | | variable moved due to use in coroutine | move occurs because `foo` has type `Option<Foo>`, which does not implement the `Copy` trait ```

Rollup of 17 pull requests Successful merges: - #142569 (Suggest clone in user-write-code instead of inside macro) - #143401 (tests: Don't check for self-printed output in std-backtrace.rs test) - #143424 (clippy fix: rely on autoderef) - #143970 (Update core::mem::copy documentation) - #143979 (Test fixes for Arm64EC Windows) - #144160 (tests: debuginfo: Work around or disable broken tests on powerpc) - #144200 (Tweak output for non-`Clone` values moved into closures) - #144209 (Don't emit two `assume`s in transmutes when one is a subset of the other) - #144225 (Don't special-case llvm.* as nounwind) - #144314 (Hint that choose_pivot returns index in bounds) - #144316 (bootstrap: Move musl-root fallback out of sanity check) - #144340 (UI test suite clarity changes: Rename `tests/ui/SUMMARY.md` and update rustc dev guide on `error-pattern`) - #144364 (Update `dlmalloc` dependency of libstd) - #144368 (resolve: Remove `Scope::CrateRoot`) - #144390 (Remove dead code and extend test coverage and diagnostics around it) - #144392 (rustc_public: Remove movability from `RigidTy/AggregateKind::Coroutine`) - #144424 (Allow setting `release-blog-post` label with rustbot) r? `@ghost` `@rustbot` modify labels: rollup

…lcnr Tweak output for non-`Clone` values moved into closures When we encounter a non-`Clone` value being moved into a closure, try to find the corresponding type of the binding being moved, if it is a `let`-binding or a function parameter. If any of those cases, we point at them with the note explaining that the type is not `Copy`, instead of giving that label to the place where it is captured. When it is a `let`-binding with no explicit type, we point at the initializer (if it fits in a single line). ``` error[E0507]: cannot move out of `foo`, a captured variable in an `Fn` closure --> f111.rs:14:25 | 13 | fn do_stuff(foo: Option<Foo>) { | --- ----------- move occurs because `foo` has type `Option<Foo>`, which does not implement the `Copy` trait | | | captured outer variable 14 | require_fn_trait(|| async { | -- ^^^^^ `foo` is moved here | | | captured by this `Fn` closure 15 | if foo.map_or(false, |f| f.foo()) { | --- variable moved due to use in coroutine ``` instead of ``` error[E0507]: cannot move out of `foo`, a captured variable in an `Fn` closure --> f111.rs:14:25 | 13 | fn do_stuff(foo: Option<Foo>) { | --- captured outer variable 14 | require_fn_trait(|| async { | -- ^^^^^ `foo` is moved here | | | captured by this `Fn` closure 15 | if foo.map_or(false, |f| f.foo()) { | --- | | | variable moved due to use in coroutine | move occurs because `foo` has type `Option<Foo>`, which does not implement the `Copy` trait ```

Rollup of 16 pull requests Successful merges: - #142569 (Suggest clone in user-write-code instead of inside macro) - #143401 (tests: Don't check for self-printed output in std-backtrace.rs test) - #143424 (clippy fix: rely on autoderef) - #143970 (Update core::mem::copy documentation) - #143979 (Test fixes for Arm64EC Windows) - #144160 (tests: debuginfo: Work around or disable broken tests on powerpc) - #144200 (Tweak output for non-`Clone` values moved into closures) - #144209 (Don't emit two `assume`s in transmutes when one is a subset of the other) - #144314 (Hint that choose_pivot returns index in bounds) - #144316 (bootstrap: Move musl-root fallback out of sanity check) - #144340 (UI test suite clarity changes: Rename `tests/ui/SUMMARY.md` and update rustc dev guide on `error-pattern`) - #144364 (Update `dlmalloc` dependency of libstd) - #144368 (resolve: Remove `Scope::CrateRoot`) - #144390 (Remove dead code and extend test coverage and diagnostics around it) - #144392 (rustc_public: Remove movability from `RigidTy/AggregateKind::Coroutine`) - #144424 (Allow setting `release-blog-post` label with rustbot) r? `@ghost` `@rustbot` modify labels: rollup

Rollup of 12 pull requests Successful merges: - #142569 (Suggest clone in user-write-code instead of inside macro) - #143401 (tests: Don't check for self-printed output in std-backtrace.rs test) - #143424 (clippy fix: rely on autoderef) - #143970 (Update core::mem::copy documentation) - #143979 (Test fixes for Arm64EC Windows) - #144200 (Tweak output for non-`Clone` values moved into closures) - #144209 (Don't emit two `assume`s in transmutes when one is a subset of the other) - #144314 (Hint that choose_pivot returns index in bounds) - #144340 (UI test suite clarity changes: Rename `tests/ui/SUMMARY.md` and update rustc dev guide on `error-pattern`) - #144368 (resolve: Remove `Scope::CrateRoot`) - #144390 (Remove dead code and extend test coverage and diagnostics around it) - #144392 (rustc_public: Remove movability from `RigidTy/AggregateKind::Coroutine`) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #144200 - estebank:dont-point-at-closure, r=lcnr Tweak output for non-`Clone` values moved into closures When we encounter a non-`Clone` value being moved into a closure, try to find the corresponding type of the binding being moved, if it is a `let`-binding or a function parameter. If any of those cases, we point at them with the note explaining that the type is not `Copy`, instead of giving that label to the place where it is captured. When it is a `let`-binding with no explicit type, we point at the initializer (if it fits in a single line). ``` error[E0507]: cannot move out of `foo`, a captured variable in an `Fn` closure --> f111.rs:14:25 | 13 | fn do_stuff(foo: Option<Foo>) { | --- ----------- move occurs because `foo` has type `Option<Foo>`, which does not implement the `Copy` trait | | | captured outer variable 14 | require_fn_trait(|| async { | -- ^^^^^ `foo` is moved here | | | captured by this `Fn` closure 15 | if foo.map_or(false, |f| f.foo()) { | --- variable moved due to use in coroutine ``` instead of ``` error[E0507]: cannot move out of `foo`, a captured variable in an `Fn` closure --> f111.rs:14:25 | 13 | fn do_stuff(foo: Option<Foo>) { | --- captured outer variable 14 | require_fn_trait(|| async { | -- ^^^^^ `foo` is moved here | | | captured by this `Fn` closure 15 | if foo.map_or(false, |f| f.foo()) { | --- | | | variable moved due to use in coroutine | move occurs because `foo` has type `Option<Foo>`, which does not implement the `Copy` trait ```

Rollup of 12 pull requests Successful merges: - rust-lang/rust#142569 (Suggest clone in user-write-code instead of inside macro) - rust-lang/rust#143401 (tests: Don't check for self-printed output in std-backtrace.rs test) - rust-lang/rust#143424 (clippy fix: rely on autoderef) - rust-lang/rust#143970 (Update core::mem::copy documentation) - rust-lang/rust#143979 (Test fixes for Arm64EC Windows) - rust-lang/rust#144200 (Tweak output for non-`Clone` values moved into closures) - rust-lang/rust#144209 (Don't emit two `assume`s in transmutes when one is a subset of the other) - rust-lang/rust#144314 (Hint that choose_pivot returns index in bounds) - rust-lang/rust#144340 (UI test suite clarity changes: Rename `tests/ui/SUMMARY.md` and update rustc dev guide on `error-pattern`) - rust-lang/rust#144368 (resolve: Remove `Scope::CrateRoot`) - rust-lang/rust#144390 (Remove dead code and extend test coverage and diagnostics around it) - rust-lang/rust#144392 (rustc_public: Remove movability from `RigidTy/AggregateKind::Coroutine`) r? `@ghost` `@rustbot` modify labels: rollup

rustbot assigned lcnr Jul 20, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jul 20, 2025

lcnr reviewed Jul 21, 2025

View reviewed changes

compiler/rustc_borrowck/src/diagnostics/move_errors.rs Outdated Show resolved Hide resolved

lcnr reviewed Jul 21, 2025

View reviewed changes

tests/ui/span/borrowck-call-is-borrow-issue-12224.stderr Outdated Show resolved Hide resolved

estebank added 4 commits July 21, 2025 16:21

Reduce comment verbosity

dafc9f9

estebank force-pushed the dont-point-at-closure branch from 2c06936 to 493700f Compare July 21, 2025 16:53

This comment has been minimized.

Sign in to view

Point at the type that doesn't impl Clone in more cases beyond clos…

6237e73

…ures

estebank force-pushed the dont-point-at-closure branch from 493700f to 6237e73 Compare July 23, 2025 16:04

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 23, 2025

fmease mentioned this pull request Jul 24, 2025

Rollup of 16 pull requests #144418

Closed

fmease mentioned this pull request Jul 25, 2025

Rollup of 17 pull requests #144428

Closed

This was referenced Jul 25, 2025

Rollup of 16 pull requests #144436

Closed

Rollup of 12 pull requests #144440

Merged

bors merged commit 33a9e4f into rust-lang:master Jul 25, 2025
11 checks passed

rustbot added this to the 1.90.0 milestone Jul 25, 2025

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Tweak output for non-`Clone` values moved into closures #144200

Tweak output for non-`Clone` values moved into closures #144200

Uh oh!

estebank commented Jul 20, 2025

Uh oh!

rustbot commented Jul 20, 2025

Uh oh!

lcnr Jul 21, 2025

Uh oh!

estebank Jul 21, 2025

Uh oh!

Uh oh!

Uh oh!

lcnr commented Jul 21, 2025

Uh oh!

This comment has been minimized.

estebank commented Jul 23, 2025

Uh oh!

bors commented Jul 23, 2025

Uh oh!

Uh oh!

Uh oh!

Tweak output for non-Clone values moved into closures #144200

Tweak output for non-Clone values moved into closures #144200

Uh oh!

Conversation

estebank commented Jul 20, 2025

Uh oh!

rustbot commented Jul 20, 2025

Uh oh!

lcnr Jul 21, 2025

Choose a reason for hiding this comment

Uh oh!

estebank Jul 21, 2025

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

lcnr commented Jul 21, 2025

Uh oh!

This comment has been minimized.

estebank commented Jul 23, 2025

Uh oh!

bors commented Jul 23, 2025

Uh oh!

Uh oh!

Uh oh!

Tweak output for non-`Clone` values moved into closures #144200

Tweak output for non-`Clone` values moved into closures #144200