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Add shorter and more direct error for dyn AsyncFn
Fix #132713
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@@ -0,0 +1,31 @@ | ||
The `Async{Fn, FnMut, FnOnce}` traits are not yet `dyn`-compatible. | ||
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Erroneous code example: | ||
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```compile_fail,E0802 | ||
async fn call_async_fn_twice(some_fn: &dyn AsyncFn()) { | ||
some_fn().await; | ||
some_fn().await; | ||
} | ||
``` | ||
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One workaround to this issue is to use `impl Async...` instead: | ||
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``` | ||
async fn call_async_fn_twice(some_fn: &impl AsyncFn()) { | ||
some_fn().await; | ||
some_fn().await; | ||
} | ||
``` | ||
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This error indicates that you attempted to use `dyn AsyncFn`, | ||
`dyn AsyncFnMut`, or `dyn AsyncFnOnce`. | ||
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This is not yet possible because the `Async...` traits internally return | ||
a concrete `Future` associated type. For dynamic callsites, it is impossible | ||
to know the size of the returned `Future` object since different | ||
`Async...` implementations may return differently-sized `Future` objects. | ||
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This is analogous to the more general issue of creating a `dyn` type without | ||
specifying associated types, e.g. `dyn Iterator` as opposed to | ||
`dyn Iterator<Item = SomeItemType>`. |
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@@ -541,6 +541,7 @@ E0798: 0798, | |
E0799: 0799, | ||
E0800: 0800, | ||
E0801: 0801, | ||
E0802: 0802, | ||
); | ||
) | ||
} | ||
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// Test the diagnostic output (error descriptions) resulting from `dyn AsyncFn{,Mut,Once}`. | ||
//@ edition:2018 | ||
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#![feature(async_closure)] | ||
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use core::ops::{AsyncFn, AsyncFnMut, AsyncFnOnce}; | ||
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// --- Explicit `dyn` --- | ||
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fn takes_async_fn(_: &dyn AsyncFn()) {} | ||
//~^ ERROR the trait `AsyncFn` is not yet `dyn`-compatible | ||
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fn takes_async_fn_mut(_: &mut dyn AsyncFnMut()) {} | ||
//~^ ERROR the trait `AsyncFnMut` is not yet `dyn`-compatible | ||
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fn takes_async_fn_once(_: Box<dyn AsyncFnOnce()>) {} | ||
//~^ ERROR the trait `AsyncFnOnce` is not yet `dyn`-compatible | ||
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// --- Non-explicit `dyn` --- | ||
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#[allow(bare_trait_objects)] | ||
fn takes_async_fn_implicit_dyn(_: &AsyncFn()) {} | ||
//~^ ERROR the trait `AsyncFn` is not yet `dyn`-compatible | ||
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#[allow(bare_trait_objects)] | ||
fn takes_async_fn_mut_implicit_dyn(_: &mut AsyncFnMut()) {} | ||
//~^ ERROR the trait `AsyncFnMut` is not yet `dyn`-compatible | ||
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#[allow(bare_trait_objects)] | ||
fn takes_async_fn_once_implicit_dyn(_: Box<AsyncFnOnce()>) {} | ||
//~^ ERROR the trait `AsyncFnOnce` is not yet `dyn`-compatible | ||
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// --- Supertrait --- | ||
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trait SubAsyncFn: AsyncFn() {} | ||
fn takes_sub_async_fn(_: &dyn SubAsyncFn) {} | ||
//~^ ERROR the trait `SubAsyncFn` cannot be made into an object | ||
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fn main() {} |
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