Description
The 2024 migration for actix-web-lab@0.23.0 failed to detect a situation where an impl trait needs some kind of capture. The following error occurs after updating to 2024:
error[E0515]: cannot return value referencing local data `this`
--> examples/from_fn.rs:100:26
|
100 | async move { Self::mw_cb(&this, req, next).await }
| ^^^^^^^^^^^^-----^^^^^^^^^^^^^^^^^^
| | |
| | `this` is borrowed here
| returns a value referencing data owned by the current function
|
note: this call may capture more lifetimes than intended, because Rust 2024 has adjusted the `impl Trait` lifetime capture rules
--> examples/from_fn.rs:100:26
|
100 | async move { Self::mw_cb(&this, req, next).await }
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: add a precise capturing bound to avoid overcapturing
|
72 | ) -> Result<ServiceResponse<impl MessageBody + use<impl MessageBody + 'static>>, Error> {
|
I would expect impl_trait_overcaptures to migrate this, or if migration isn't possible to at least generate a warning.
Additionally, the suggestion provided in this error message is not valid syntax. use<> cannot have impl MessageBody.
I believe this is an example of APIT migration. That is, the following change I think is a suggestion it could provide:
--- a/examples/from_fn.rs
+++ b/examples/from_fn.rs
@@ -65,11 +65,11 @@ async fn timeout_10secs(
struct MyMw(bool);
impl MyMw {
- async fn mw_cb(
+ async fn mw_cb<T: MessageBody + 'static>(
&self,
req: ServiceRequest,
- next: Next<impl MessageBody + 'static>,
- ) -> Result<ServiceResponse<impl MessageBody>, Error> {
+ next: Next<T>,
+ ) -> Result<ServiceResponse<impl MessageBody + use<T>>, Error> {
let mut res = match self.0 {
true => req.into_response("short-circuited").map_into_right_body(),
false => next.call(req).await?.map_into_left_body(),Here the impl trait gets lifted to have a named type parameter which can then be used in the use<> bound.
Or...There might be other suggestions, I don't know. The offending code involves some tricky async-block stuff.
Meta
rustc --version --verbose:
rustc 1.84.0-nightly (59cec72a5 2024-11-08)
binary: rustc
commit-hash: 59cec72a57af178767a7b8e7f624b06cc50f1087
commit-date: 2024-11-08
host: aarch64-unknown-linux-gnu
release: 1.84.0-nightly
LLVM version: 19.1.3