Ban associated type bounds in bad positions
We should not try to lower associated type bounds into TAITs in positions where `impl Trait` is not allowed (except for in `where` clauses, like `where T: Trait<Assoc: Bound>`).
This is achieved by using the same `rustc_ast_lowering` machinery as impl-trait does to characterize positions as universal/existential/disallowed.
Fixes#106077
Split out the first commit into #108066, since it's not really related.
rework min_choice algorithm of member constraints
See [this comment](https://github.com/rust-lang/rust/pull/105300#issuecomment-1384312743) for the description of the new algorithm.
Fixes#63033Fixes#104639
This uses a more general algorithm than #89056 that doesn't treat `'static` as a special case. It thus accepts more code. For example:
```rust
async fn test2<'s>(_: &'s u8, _: &'_ &'s u8, _: &'_ &'s u8) {}
```
I claim it's more correct as well because it fixes#104639.
cc ``@nikomatsakis`` ``@lqd`` ``@tmandry`` ``@eholk`` ``@chenyukang`` ``@oli-obk``
r? types
Considering the following code
```rust
fn foo() -> u8 {
async fn async_fn() -> u8 { 22 }
async_fn()
}
fn main() {}
```
the error generated before this commit from the compiler is
```
➜ rust git:(macros/async_fn_suggestion) ✗ rustc test.rs --edition 2021
error[E0308]: mismatched types
--> test.rs:4:5
|
1 | fn foo() -> u8 {
| -- expected `u8` because of return type
...
4 | async_fn()
| ^^^^^^^^^^ expected `u8`, found opaque type
|
= note: expected type `u8`
found opaque type `impl Future<Output = u8>`
help: consider `await`ing on the `Future`
|
4 | async_fn().await
| ++++++
error: aborting due to previous error
```
In this case the error is nor perfect, and can confuse the user
that do not know that the opaque type is the future.
So this commit will propose (and conclude the work start in
https://github.com/rust-lang/rust/issues/80658)
to change the string `opaque type` to `future` when applicable
and also remove the Expected vs Received note by adding a more
specific one regarding the async function that return a future type.
So the new error emitted by the compiler is
```
error[E0308]: mismatched types
--> test.rs:4:5
|
1 | fn foo() -> u8 {
| -- expected `u8` because of return type
...
4 | async_fn()
| ^^^^^^^^^^ expected `u8`, found future
|
note: calling an async function returns a future
--> test.rs:4:5
|
4 | async_fn()
| ^^^^^^^^^^
help: consider `await`ing on the `Future`
|
4 | async_fn().await
| ++++++
error: aborting due to previous error
```
Signed-off-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>
This adds one more test that should track improvements to generator
layout, like #62958 and #62575.
In particular, this test highlights suboptimal layout, as the storage
for the argument future is not being reused across its usage as `upvar`,
`local` and `awaitee` (being polled to completion).
Especially when trying to diagnose runaway future sizes, it might be
more intuitive to sort the variants according to the control flow
(aka their yield points) rather than the size of the variants.
Don't cause a cycle when formatting query description that references a FnDef
When a function returns `-> _`, we use typeck to compute what the resulting type of the body _should_ be. If we call another query inside of typeck and hit a cycle error, we attempt to report the cycle error which requires us to compute all of the query descriptions for the stack.
However, if one of the queries in that cycle has a query description that references this function as a FnDef type, we'll cause a *second* cycle error from within the cycle error reporting code, since rendering a FnDef requires us to compute its signature. This causes an unwrap to ICE, since during the *second* cycle reporting code, we try to look for a job that isn't in the active jobs list.
We can avoid this by using `with_no_queries!` when computing these query descriptions.
Fixes#107089
The only drawback is that the rendering of opaque types in cycles regresses a bit :| I'm open to alternate suggestions about how we may handle this...
Remove confusing 'while checking' note from opaque future type mismatches
Maybe I'm just misinterpreting the wording of the note. The only value I can see in this note is that it points out where the async's opaque future is coming from, but the way it's doing it is misleading IMO.
For example:
```rust
note: while checking the return type of the `async fn`
--> $DIR/dont-suggest-missing-await.rs:7:24
|
LL | async fn make_u32() -> u32 {
| ^^^ checked the `Output` of this `async fn`, found opaque type
```
We point at the type `u32` in the HIR, but then say "found opaque type". We also say "while checking"... but we're typechecking a totally different function when we get this type mismatch!
r? ``@estebank`` but feel free to reassign and/or take your time reviewing this. I'd be inclined to also discuss reworking the presentation of this type mismatch to restore some of these labels in a way that makes it more clear what it's trying to point out.
Suggest using a lock for `*Cell: Sync` bounds
I mostly did this for `OnceCell<T>` at first because users will be confused to see that the `OnceCell<T>` in `std` isn't `Sync` but then extended it to `Cell<T>` and `RefCell<T>` as well.
[drop tracking] Visit break expressions
This fixes https://github.com/rust-lang/rust/issues/102383 by remembering to visit the expression in `break expr` when building the drop tracking CFG. Missing this step was causing an off-by-one error which meant after a number of awaits we'd be
looking for dropped values at the wrong point in the code.
Additionally, this changes the order of traversal for assignment expressions to visit the rhs and then the lhs. This matches what is done elsewhere.
Finally, this improves some of the debugging output (for example, the CFG visualizer) to make it easier to figure out these sorts of issues.
