[breaking-change]
The `mut` in slices is now redundant. Mutability is 'inferred' from position. This means that if mutability is only obvious from the type, you will need to use explicit calls to the slicing methods.
closes#19141closes#20193closes#20228
---
Currently whenever we encounter `let f = || {/* */}`, we *always* type check the RHS as a *boxed* closure. This is wrong when the RHS is `move || {/* */}` (because boxed closures can't capture by value) and generates all sort of badness during trans (see issues above). What we *should* do is always type check `move || {/* */}` as an *unboxed* closure, but ~~I *think* (haven't tried)~~ (2) this is not feasible right now because we have a limited form of kind (`Fn` vs `FnMut` vs `FnOnce`) inference that only works when there is an expected type (1).
In this PR, I've chosen to generate a type error whenever `let f = move || {/* */}` is encountered. The error asks the user to annotate the kind of the unboxed closure (e.g. `move |:| {/* */}`). Once annotated, the compiler will type check the RHS as an unboxed closure which is what the user wants.
r? @nikomatsakis
(1) AIUI it only triggers in this scenario:
``` rust
fn is_uc<F>(_: F) where F: FnOnce() {}
fn main() {
is_uc(|| {}); // type checked as unboxed closure with kind `FnOnce`
}
```
(2) I checked, and it's not possible because `check_unboxed_closure` expects a `kind` argument, but we can't supply that argument in this case (i.e. `let f = || {}`, what's the kind?). We could force the `FnOnce` kind in that case, but that's ad hoc. We should try to infer the kind depending on how the closure is used afterwards, but there is no inference mechanism to do that (at least, not right now).
More work on opt-in built in traits. `Send` and `Sync` are not opt-in, `OwnedPtr` renamed to `UniquePtr` and the `Send` and `Sync` traits are now unsafe.
NOTE: This likely needs to be rebased on top of the yet-to-land snapshot.
r? @nikomatsakis
cc #13231
`check::autoderef()` returns a `ty_err` when it fails to infer the type. `probe::probe()` should respect this failure and fail together to prevent further corruption.
Fixes#19692.
Fixes#19583.
Fixes#19297.
RFC 248? I think you meant RFC 438.
There ain’t an RFC 248, while 438 looks to be what is being referred to:
https://github.com/rust-lang/rfcs/blob/master/text/0438-precedence-of-plus.md
--------------
Chis Morgan has a pretty important documentation fix in #19385 and he hasn't responded in a while to that pull request so I rebased it for him
Closes#19385
check::autoderef() returns a ty_err when it fails to infer the type.
probe::probe() should respect this failure and fail together to prevent
further corruption.
Call stack: check::check_method_call() -> method::lookup() ->
probe::probe() + confirm::confirm()
Fixes#19692.
Fixes#19583.
Fixes#19297.
