Forbid borrows and unsized types from being used as the type of a const generic under `adt_const_params`
Fixes#112219Fixes#112124Fixes#112125
### Motivation
Currently the `adt_const_params` feature allows writing `Foo<const N: [u8]>` this is entirely useless as it is not possible to write an expression which evaluates to a type that is not `Sized`. In order to actually use unsized types in const generics they are typically written as `const N: &[u8]` which *is* possible to provide a value of.
Unfortunately allowing the types of const parameters to contain references is non trivial (#120961) as it introduces a number of difficult questions about how equality of references in the type system should behave. References in the types of const generics is largely only useful for using unsized types in const generics.
This PR introduces a new feature gate `unsized_const_parameters` and moves support for `const N: [u8]` and `const N: &...` from `adt_const_params` into it. The goal here hopefully is to experiment with allowing `const N: [u8]` to work without references and then eventually completely forbid references in const generics.
Splitting this out into a new feature gate means that stabilization of `adt_const_params` does not have to resolve#120961 which is the only remaining "big" blocker for the feature. Remaining issues after this are a few ICEs and naming bikeshed for `ConstParamTy`.
### Implementation
The implementation is slightly subtle here as we would like to ensure that a stabilization of `adt_const_params` is forwards compatible with any outcome of `unsized_const_parameters`. This is inherently tricky as we do not support unstable trait implementations and we determine whether a type is valid as the type of a const parameter via a trait bound.
There are a few constraints here:
- We would like to *allow for the possibility* of adding a `Sized` supertrait to `ConstParamTy` in the event that we wind up opting to not support unsized types and instead requiring people to write the 'sized version', e.g. `const N: [u8; M]` instead of `const N: [u8]`.
- Crates should be able to enable `unsized_const_parameters` and write trait implementations of `ConstParamTy` for `!Sized` types without downstream crates that only enable `adt_const_params` being able to observe this (required for std to be able to `impl<T> ConstParamTy for [T]`
Ultimately the way this is accomplished is via having two traits (sad), `ConstParamTy` and `UnsizedConstParamTy`. Depending on whether `unsized_const_parameters` is enabled or not we change which trait is used to check whether a type is allowed to be a const parameter.
Long term (when stabilizing `UnsizedConstParamTy`) it should be possible to completely merge these traits (and derive macros), only having a single `trait ConstParamTy` and `macro ConstParamTy`.
Under `adt_const_params` it is now illegal to directly refer to `ConstParamTy` it is only used as an internal impl detail by `derive(ConstParamTy)` and checking const parameters are well formed. This is necessary in order to ensure forwards compatibility with all possible future directions for `feature(unsized_const_parameters)`.
Generally the intuition here should be that `ConstParamTy` is the stable trait that everything uses, and `UnsizedConstParamTy` is that plus unstable implementations (well, I suppose `ConstParamTy` isn't stable yet :P).
Use structured suggestions for unconstrained generic parameters on impl blocks
I did not deduplicate with `UnusedGenericParameter`, because in contrast to type declarations, just using a generic parameter in an impl isn't enough, it must be used with the right variance and not just as part of a projection.
`C-cmse-nonsecure-call`: improved error messages
tracking issue: #81391
issue for the error messages (partially implemented by this PR): #81347
related, in that it also deals with CMSE: https://github.com/rust-lang/rust/pull/127766
When using the `C-cmse-nonsecure-call` ABI, both the arguments and return value must be passed via registers. Previously, when violating this constraint, an ugly LLVM error would be shown. Now, the rust compiler itself will print a pretty message and link to more information.
Use more accurate span for `addr_of!` suggestion
Use a multipart suggestion instead of a single whole-span replacement:
```
error[E0796]: creating a shared reference to a mutable static
--> $DIR/reference-to-mut-static-unsafe-fn.rs:10:18
|
LL | let _y = &X;
| ^^ shared reference to mutable static
|
= note: this shared reference has lifetime `'static`, but if the static ever gets mutated, or a mutable reference is created, then any further use of this shared reference is Undefined Behavior
help: use `addr_of!` instead to create a raw pointer
|
LL | let _y = addr_of!(X);
| ~~~~~~~~~ +
```
Use a multipart suggestion instead of a single whole-span replacement:
```
error[E0796]: creating a shared reference to a mutable static
--> $DIR/reference-to-mut-static-unsafe-fn.rs:10:18
|
LL | let _y = &X;
| ^^ shared reference to mutable static
|
= note: this shared reference has lifetime `'static`, but if the static ever gets mutated, or a mutable reference is created, then any further use of this shared reference is Undefined Behavior
help: use `addr_of!` instead to create a raw pointer
|
LL | let _y = addr_of!(X);
| ~~~~~~~~~ +
```
Remove a use of `StructuredDiag`, which is incompatible with automatic error tainting and error translations
fixes#127219
I want to remove all of `StructuredDiag`, but it's a bit more involved as it is also used from the `ItemCtxt`, which doesn't support tainting yet.
Rollup of 16 pull requests
Successful merges:
- #123374 (DOC: Add FFI example for slice::from_raw_parts())
- #124514 (Recommend to never display zero disambiguators when demangling v0 symbols)
- #125978 (Cleanup: HIR ty lowering: Consolidate the places that do assoc item probing & access checking)
- #125980 (Nvptx remove direct passmode)
- #126187 (For E0277 suggest adding `Result` return type for function when using QuestionMark `?` in the body.)
- #126210 (docs(core): make more const_ptr doctests assert instead of printing)
- #126249 (Simplify `[T; N]::try_map` signature)
- #126256 (Add {{target}} substitution to compiletest)
- #126263 (Make issue-122805.rs big endian compatible)
- #126281 (set_env: State the conclusion upfront)
- #126286 (Make `storage-live.rs` robust against rustc internal changes.)
- #126287 (Update a cranelift patch file for formatting changes.)
- #126301 (Use `tidy` to sort crate attributes for all compiler crates.)
- #126305 (Make PathBuf less Ok with adding UTF-16 then `into_string`)
- #126310 (Migrate run make prefer rlib)
- #126314 (fix RELEASES: we do not support upcasting to auto traits)
r? `@ghost`
`@rustbot` modify labels: rollup
Cleanup: Replace item names referencing GitHub issues or error codes with something more meaningful
**lcnr** in https://github.com/rust-lang/rust/pull/117164#pullrequestreview-1969935387:
> […] while I know that there's precendent to name things `Issue69420`, I really dislike this as it requires looking up the issue to figure out the purpose of such a variant. Actually referring to the underlying issue, e.g. `AliasMayNormToUncovered` or whatever and then linking to the issue in a doc comment feels a lot more desirable to me. We should ideally rename all the functions and enums which currently use issue numbers.
I've grepped through `compiler/` like crazy and think that I've found all instances of this pattern.
However, I haven't renamed `compute_2229_migrations_*`. Should I?
The first commit introduces an abhorrent and super long name for an item because naming is hard but also scary looking / unwelcoming names are good for things related to temporary-ish backcompat hacks. I'll let you discover it by yourself.
Contains a bit of drive-by cleanup and a diag migration bc that was the simplest option.
r? lcnr or compiler
Reject overly generic assoc const binding types
Split off from #119385 to make #119385 easier to review.
---
In the *instantiated* type of assoc const bindings
1. reject **early-bound generic params**
* Provide a rich error message instead of ICE'ing ([#108271](https://github.com/rust-lang/rust/issues/108271)).
* This is a temporary and semi-artificial restriction until the arrival of *generic const generics*.
* It's quite possible that rustc could already perfectly support this subset of generic const generics if we just removed some checks (some `.no_bound_vars().expect(…)`) but even if that was the case, I'd rather gate it behind a new feature flag. Reporting an error instead of ICE'ing is a good first step towards an eventual feature gate error.
2. reject **escaping late-bound generic params**
* They lead to ICEs before & I'm pretty sure that they remain incorrect even in a world with *generic const generics*
---
Together with #118668 & #119385, this supersedes #118360.
Fixes#108271.
Split refining_impl_trait lint into _reachable, _internal variants
As discussed in https://github.com/rust-lang/rust/issues/119535#issuecomment-1909352040:
> We discussed this today in triage and developed a consensus to:
>
> * Add a separate lint against impls that refine a return type defined with RPITIT even when the trait is not crate public.
> * Place that in a lint group along with the analogous crate public lint.
> * Create an issue to solicit feedback on these lints (or perhaps two separate ones).
> * Have the warnings displayed with each lint reference this issue in a similar manner to how we do that today with the required `Self: '0'` bound on GATs.
> * Make a note to review this feedback on 2-3 release cycles.
This points users to https://github.com/rust-lang/rust/issues/121718 to leave feedback.
Add help to `hir_analysis_unrecognized_intrinsic_function`
To help remind forgetful people like me what step they forgot.
(If this just ICE'd, https://github.com/rust-lang/compiler-team/issues/620 style, the stack trace would point me here, but since there's a "nice" error that information is lost.)
