Remove "visited" set from inhabitedness checking (fix perf regression)
Now that references are no longer recursively checked, this should no longer be necessary, and it's a major performance bottleneck.
This should fix#57028.
r? @varkor
On musl targets assume certain symbols exist (like pipe2 and accept4).
This fixes#56675.
I don't know if this is the best solution, or if I should also add some tests so I'm waiting for some feedback.
Thanks!
When the feature has been added back (#55148) the feature gate has not
been adjusted accordingly. We have it enabled for 1.32.0, currently in
Beta, so adjust it.
Refs: #44431.
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Rework treatment of `$crate` in procedural macros
Important clarification: `$crate` below means "processed `$crate`" or "output `$crate`". In the input of a decl macro `$crate` is just two separate tokens, but in the *output of a decl macro* `$crate` is a single keyword identifier (https://github.com/rust-lang/rust/issues/55640#issuecomment-435692791).
First of all, this PR removes the `eliminate_crate_var` hack.
`$crate::foo` is no longer replaced with `::foo` or `::crate_name::foo` in the input of derive proc macros, it's passed to the macro instead with its precise span and hygiene data, and can be treated as any other path segment keyword (like `crate` or `self`) after that. (Note: `eliminate_crate_var` was never used for non-derive proc macros.)
This creates an annoying problem - derive macros still may stringify their input before processing and expect `$crate` survive that stringification and refer to the same crate (the Rust 1.15-1.29 way of doing things).
Moreover, the input of proc macro attributes and derives (but not fn-like proc macros) also effectively survives stringification before being passed to the macro (also for legacy implementation reasons).
So we kind of resurrect the `eliminate_crate_var` hack in reduced form, but apply it only to AST pretty-printing.
If an AST fragment is pretty-printed, the resulting *text* will have `$crate` replaced with `crate` or `::crate_name`. This should be enough to keep all the legacy cases working.
Closes https://github.com/rust-lang/rust/issues/55640
Closes https://github.com/rust-lang/rust/issues/56622
r? @ghost
also updated some error messages
removed the code manually checking for `receiver_ty: Deref<Target=self_ty>`, in favour of using autoderef but only doing one iteration. This will cause error messages to be more consistent. Before, a "mismatched method receiver" error would be emitted when `receiver_ty` was valid except for a lifetime parameter, but only when `feature(arbitrary_self_types)` was enabled, and without the feature flag the error would be "uncoercible receiver". Now it emits "mismatched method receiver" in both cases.
This lets you write methods using `self: Rc<Self>`, `self: Arc<Self>`, `self: Pin<&mut Self>`, `self: Pin<Box<Self>`, and other combinations involving `Pin` and another stdlib receiver type, without needing the `arbitrary_self_types`. Other user-created receiver types can be used, but they still require the feature flag to use.
This is implemented by introducing a new trait, `Receiver`, which the method receiver's type must implement if the `arbitrary_self_types` feature is not enabled. To keep composed receiver types such as `&Arc<Self>` unstable, the receiver type is also required to implement `Deref<Target=Self>` when the feature flag is not enabled.
This lets you use `self: Rc<Self>` and `self: Arc<Self>` in stable Rust, which was not allowed previously. It was agreed that they would be stabilized in #55786. `self: Pin<&Self>` and other pinned receiver types do not require the `arbitrary_self_types` feature, but they cannot be used on stable because `Pin` still requires the `pin` feature.
trigger unsized coercions keyed on Sized bounds
This PR causes unsized coercions to not be disabled by `$0: Unsize<dyn
Object>` coercion obligations when we have an `$0: Sized` obligation somewhere.
This should be mostly backwards-compatible, because in these cases not doing the unsize coercion should have caused the `$0: Sized` obligation to fail.
Note that `X: Unsize<dyn Object>` obligations can't fail *as obligations* if `X: Sized` holds, so this still maintains some version of monotonicity (I think that an unsized coercion can't be converted to no coercion by unifying type variables).
Fixes#49593 (unblocking never_type).
r? @eddyb
cc @nikomatsakis
