Make `Ty::boxed_ty` return an `Option`
Looks like a good place to use Rust's type system.
---
Most of 4ac7bcbaad/compiler/rustc_middle/src/ty/sty.rs (L971-L1963) looks like it could be moved to `TyKind` (then I guess `Ty` should be made to deref to `TyKind`).
Check WF of source type's signature on fn pointer cast
This PR patches the implied bounds holes slightly for #129005, #25860.
Like most implied bounds related unsoundness fixes, this isn't complete w.r.t. higher-ranked function signatures, but I believe it implements a pretty good heuristic for now.
### What does this do?
This PR makes a partial patch for a soundness hole in a `FnDef` -> `FnPtr` "reifying" pointer cast where we were never checking that the signature we are casting *from* is actually well-formed. Because of this, and because `FnDef` doesn't require its signature to be well-formed (just its predicates must hold), we are essentially allowed to "cast away" implied bounds that are assumed within the body of the `FnDef`:
```
fn foo<'a, 'b, T>(_: &'a &'b (), v: &'b T) -> &'a T { v }
fn bad<'short, T>(x: &'short T) -> &'static T {
let f: fn(_, &'short T) -> &'static T = foo;
f(&&(), x)
}
```
In this example, subtyping ends up casting the `_` type (which should be `&'static &'short ()`) to some other type that no longer serves as a "witness" to the lifetime relationship `'short: 'static` which would otherwise be required for this call to be WF. This happens regardless of if `foo`'s lifetimes are early- or late-bound.
This PR implements two checks:
1. We check that the signature of the `FnDef` is well-formed *before* casting it. This ensures that there is at least one point in the MIR where we ensure that the `FnDef`'s implied bounds are actually satisfied by the caller.
2. Implements a special case where if we're casting from a higher-ranked `FnDef` to a non-higher-ranked, we instantiate the binder of the `FnDef` with *infer vars* and ensure that it is a supertype of the target of the cast.
The (2.) is necessary to validate that these pointer casts are valid for higher-ranked `FnDef`. Otherwise, the example above would still pass even if `help`'s `'a` lifetime were late-bound.
### Further work
The WF checks for function calls are scattered all over the MIR. We check the WF of args in call terminators, we check the WF of `FnDef` when we create a `const` operand referencing it, and we check the WF of the return type in #115538, to name a few.
One way to make this a bit cleaner is to simply extend #115538 to always check that the signature is WF for `FnDef` types. I may do this as a follow-up, but I wanted to keep this simple since this leads to some pretty bad NLL diagnostics regressions, and AFAICT this solution is *complete enough*.
### Crater triage
Done here: https://github.com/rust-lang/rust/pull/129021#issuecomment-2297702647
r? lcnr
Remove `#[macro_use] extern crate tracing`, round 4
Because explicit importing of macros via use items is nicer (more standard and readable) than implicit importing via #[macro_use]. Continuing the work from #124511, #124914, and #125434. After this PR no `rustc_*` crates use `#[macro_use] extern crate tracing` except for `rustc_codegen_gcc` which is a special case and I will do separately.
r? ```@jieyouxu```
Remove Duplicate E0381 Label
Aims to resolve https://github.com/rust-lang/rust/issues/129274, and adds a test for the case.
Essentially, we are duplicating this span for some reason. For now, I'm just using a set to collect the spans rather than the vec. I imagine there's probably no real reason to inspect duplicates in this area, but if I'm wrong I can adjust to collect "seen spans" in just the point where this label is applied.
I'm not sure why it's producing duplicate spans. Looks like this has been this way for a while? I think it gives the duplicate label on 1.75.0 for example.
Add `#[warn(unreachable_pub)]` to a bunch of compiler crates
By default `unreachable_pub` identifies things that need not be `pub` and tells you to make them `pub(crate)`. But sometimes those things don't need any kind of visibility. So they way I did these was to remove the visibility entirely for each thing the lint identifies, and then add `pub(crate)` back in everywhere the compiler said it was necessary. (Or occasionally `pub(super)` when context suggested that was appropriate.) Tedious, but results in more `pub` removal.
There are plenty more crates to do but this seems like enough for a first PR.
r? `@compiler-errors`
Record the correct target type when coercing fn items/closures to pointers
Self-explanatory. We were previously not recording the *target* type of a coercion as the output of an adjustment. This should remedy that.
We must also modify the function pointer casts in MIR typeck to use subtyping, since those broke since #118247.
r? lcnr
Shrink `TyKind::FnPtr`.
By splitting the `FnSig` within `TyKind::FnPtr` into `FnSigTys` and `FnHeader`, which can be packed more efficiently. This reduces the size of the hot `TyKind` type from 32 bytes to 24 bytes on 64-bit platforms. This reduces peak memory usage by a few percent on some benchmarks. It also reduces cache misses and page faults similarly, though this doesn't translate to clear cycles or wall-time improvements on CI.
r? `@compiler-errors`
Normalize struct tail properly for `dyn` ptr-to-ptr casting in new solver
Realized that the new solver didn't handle ptr-to-ptr casting correctly.
r? lcnr
Built on #128694
Use more slice patterns inside the compiler
Nothing super noteworthy. Just replacing the common 'fragile' pattern of "length check followed by indexing or unwrap" with slice patterns for legibility and 'robustness'.
r? ghost
By splitting the `FnSig` within `TyKind::FnPtr` into `FnSigTys` and
`FnHeader`, which can be packed more efficiently. This reduces the size
of the hot `TyKind` type from 32 bytes to 24 bytes on 64-bit platforms.
This reduces peak memory usage by a few percent on some benchmarks. It
also reduces cache misses and page faults similarly, though this doesn't
translate to clear cycles or wall-time improvements on CI.
Peel off explicit (or implicit) deref before suggesting clone on move error in borrowck, remove some hacks
Also remove a heck of a lot of weird hacks in `suggest_cloning` that I don't think we should have around.
I know this regresses tests, but I don't believe most of these suggestions were accurate, b/c:
1. They either produced type errors (e.g. turning `&x` into `x.clone()`)
2. They don't fix the issue
3. They fix the issue ostensibly, but introduce logic errors (e.g. cloning a `&mut Option<T>` to then `Option::take` out...)
Most of the suggestions are still wrong, but they're not particularly *less* wrong IMO.
Stacked on top of #128241, which is an "obviously worth landing" subset of this PR.
r? estebank
Remove logic to suggest clone of function output
I can't exactly tell, but I believe that this suggestion is operating off of a heuristic that the lifetime of a function's input is correlated with the lifetime of a function's output in such a way that cloning would fix an error. I don't think that actually manages to hit the bar of "actually provides useful suggestions" most of the time.
Specifically, I've hit false-positives due to this suggestion *twice* when fixing ICEs in the compiler, so I don't think it's worthwhile having this logic around. Neither of the two affected UI tests are actually fixed by the suggestion.
Reword E0626 to mention static coroutine, add structured suggestion for adding `static`
Not certain how to make the example feel less artificial. 🤷
My main point though is that we should probably emphasize that the first solution to making a coroutine allow a borrow across an await is making it `static`.
Also adds a structured suggestion.
Matthias Krüger