Fix ICE when validating transmuting ZST to inhabited enum
MIR validation attempts to determine the number of bytes needed to represent the size of the source type to compute the discriminant for the inhabited target enum. For a ZST source, there is no source data to use as a discriminant so no proper runtime check can be generated.
Since that should never be possible, insert a delayed bug to ensure the problem has been properly reported to the user by the type checker.
Fixesrust-lang/rust#145786
match exhaustiveness diagnostics: show a trailing comma on singleton tuple consructors in witness patterns (and clean up a little)
Constructor patterns of type `(T,)` are written `(pat,)`, not `(pat)`. However, exhaustiveness/usefulness diagnostics would print them as `(pat)` when e.g. providing a witness of non-exhaustiveness and suggesting adding arms to make matches exhaustive; this would result in an error when applied.
rust-analyzer already prints the trailing comma, so it doesn't need changing.
This also includes some cleanup in the second commit, with justification in the commit message.
change HIR typeck region uniquification handling approach
rust-lang/rust#144405 causes structural lookup of opaque types to not work during HIR typeck, so instead avoid uniquifying goals and instead only reprove them if MIR borrowck actually encounters an error.
This doesn't perfectly maintain the property that HIR typeck succeeding implies that MIR typeck succeeds, instead weakening this check to only guarantee that HIR typeck implies that MIR typeck succeeds modulo region uniquification. This means we still get the actually desirable ICEs if we MIR building is broken or we forget to check some property in HIR typeck, without having to deal with the fallout of uniquification in HIR typeck itself.
We report errors using the original obligation sources of HIR typeck so diagnostics aren't that negatively impacted either.
Here's the history of region uniquification while working on the new trait solver:
- rust-lang/rust#107981
- rust-lang/rust#110180
- rust-lang/rust#114117
- rust-lang/rust#130821
- rust-lang/rust#144405
- rust-lang/rust#145706 <- we're here 🎉
r? `@BoxyUwU`
MIR validation attempts to determine the number of bytes needed to
represent the size of the source type to compute the discriminant for
the inhabited target enum. For a ZST source, there is no source data to
use as a discriminant so no proper runtime check can be generated.
Since that should never be possible, insert a delayed bug to ensure the
problem has been properly reported to the user by the type checker.
Revert suggestions for missing methods in tuples
As requested by `@estebank` and as discussed with `@jackh726,` this reverts rust-lang/rust#142034 because of diagnostics ICEs like rust-lang/rust#142488 and its duplicates that have reached stable by now.
We will work on a proper fix to reland this cool work in the near future, but in the meantime, a revert is safer to validate and backport to beta and stable, so here it is.
Experiment: Reborrow trait
Tracking issue: rust-lang/rust#145612
Starting off really small here: just introduce the unstable feature and the feature gate, and one of the two traits that the Reborrow experiment deals with.
### Cliff-notes explanation
The `Reborrow` trait is conceptually a close cousin of `Copy` with the exception that it disables the source (`self`) for the lifetime of the target / result of the reborrow action. It can be viewed as a method of `fn reborrow(self: Self<'a>) -> Self<'a>` with the compiler adding tracking of the resulting `Self<'a>` (or any value derived from it that retains the `'a` lifetime) to keep the `self` disabled for reads and writes.
No method is planned to be surfaced to the user, however, as reborrowing cannot be seen in code (except for method calls [`a.foo()` reborrows `a`] and explicit reborrows [`&*a`]) and thus triggering user-code in it could be viewed as "spooky action at a distance". Furthermore, the added compiler tracking cannot be seen on the method itself, violating the Golden Rule. Note that the userland "reborrow" method is not True Reborrowing, but rather a form of a "Fancy Deref":
```rust
fn reborrow(&'short self: Self<'long>) -> Self<'short>;
```
The lifetime shortening is the issue here: a reborrowed `Self` or any value derived from it is bound to the method that called `reborrow`, since `&'short` is effectively a local variable. True Reborrowing does not shorten the lifetime of the result.
To avoid having to introduce new kinds of references, new kinds of lifetime annotations, or a blessed trait method, no method will be introduced at all. Instead, the `Reborrow` trait is intended to be a derived trait that effectively reborrows each field individually; `Copy` fields end up just copying, while fields that themselves `Reborrow` get disabled in the source, usually leading to the source itself being disabled (some differences may appear with structs that contain multiple reborrowable fields). The goal of the experiment is to determine how the actual implementation here will shape out, and what the "bottom case" for the recursive / deriving `Reborrow` is.
`Reborrow` has a friend trait, `CoerceShared`, which is equivalent to a `&'a mut T -> &'a T` conversion. This is needed as a different trait and different operation due to the different semantics it enforces on the source: a `CoerceShared` operation only disables the source for writes / exclusive access for the lifetime of the result. That trait is not yet introduced in this PR, though there is no particular reason why it could not be introduced.
On E0277, point at type that doesn't implement bound
When encountering an unmet trait bound, point at local type that doesn't implement the trait:
```
error[E0277]: the trait bound `Bar<T>: Foo` is not satisfied
--> $DIR/issue-64855.rs:9:19
|
LL | pub struct Bar<T>(<Self as Foo>::Type) where Self: ;
| ^^^^^^^^^^^^^^^^^^^ unsatisfied trait bound
|
help: the trait `Foo` is not implemented for `Bar<T>`
--> $DIR/issue-64855.rs:9:1
|
LL | pub struct Bar<T>(<Self as Foo>::Type) where Self: ;
| ^^^^^^^^^^^^^^^^^
```
When encountering an unmet trait bound, point at local type that doesn't implement the trait:
```
error[E0277]: the trait bound `Bar<T>: Foo` is not satisfied
--> $DIR/issue-64855.rs:9:19
|
LL | pub struct Bar<T>(<Self as Foo>::Type) where Self: ;
| ^^^^^^^^^^^^^^^^^^^ unsatisfied trait bound
|
help: the trait `Foo` is not implemented for `Bar<T>`
--> $DIR/issue-64855.rs:9:1
|
LL | pub struct Bar<T>(<Self as Foo>::Type) where Self: ;
| ^^^^^^^^^^^^^^^^^
```
Rewrite the new attribute argument parser
Fixes https://github.com/rust-lang/rust/issues/143940
This rewrites the parser, should improve performance and maintainability.
This can be reviewed commit by commit
Gate static closures behind a parser feature
I'd like to gate `static ||` closures behind a feature gate, since we shouldn't allow people to take advantage of this syntax if it's currently unstable. Right now, since it's only rejected after ast lowering, it's accessible to macros.
Let's crater this to see if we can claw it back without breaking anyone's code.
Do not use effective_visibilities query for Adt types of a local trait while proving a where-clause
Partially fixrust-lang/rust#145611, but we should do something make cycle in this situation ICE.
Instead of using a query, call `&tcx.resolutions(()).effective_visibilities`.
r? `````@lcnr`````
cc `````@compiler-errors`````
