Stabilize `unsafe_attributes`
# Stabilization report
## Summary
This is a tracking issue for the RFC 3325: unsafe attributes
We are stabilizing `#![feature(unsafe_attributes)]`, which makes certain attributes considered 'unsafe', meaning that they must be surrounded by an `unsafe(...)`, as in `#[unsafe(no_mangle)]`.
RFC: rust-lang/rfcs#3325
Tracking issue: #123757
## What is stabilized
### Summary of stabilization
Certain attributes will now be designated as unsafe attributes, namely, `no_mangle`, `export_name`, and `link_section` (stable only), and these attributes will need to be called by surrounding them in `unsafe(...)` syntax. On editions prior to 2024, this is simply an edition lint, but it will become a hard error in 2024. This also works in `cfg_attr`, but `unsafe` is not allowed for any other attributes, including proc-macros ones.
```rust
#[unsafe(no_mangle)]
fn a() {}
#[cfg_attr(any(), unsafe(export_name = "c"))]
fn b() {}
```
For a table showing the attributes that were considered to be included in the list to require unsafe, and subsequent reasoning about why each such attribute was or was not included, see [this comment here](https://github.com/rust-lang/rust/pull/124214#issuecomment-2124753464)
## Tests
The relevant tests are in `tests/ui/rust-2024/unsafe-attributes` and `tests/ui/attributes/unsafe`.
Remove stray println from rustfmt's `rewrite_static`
r? `@calebcartwright` `@ytmimi` -- though anyone should probably r+ this so it gets into nightly sooner than later, since it's obviously wrong.
This can just be fixed in-tree, since I don't think we want to wait until the next sync to fix this.
Fix https://github.com/rust-lang/rustfmt/issues/6210
Fix https://github.com/rust-lang/rust/issues/126887
Implement `use<>` formatting in rustfmt
This PR implements formatting for precise-capturing `use<>` syntax as proposed in https://github.com/rust-lang/rust/pull/126753.
The syntax is implemented as-if the `use<>` bound were a trait bound but with the `use` keyword as its path segment identifier.
I opted to develop this in the rust-lang/rust tree since I'm not certain when the next rustfmt subtree sync is going to be, and I'd rather not block landing nightly support for `use<>` on something I have no control over. If ``@rust-lang/rustfmt`` would rather I move this PR over to that repository, then I would at least like to know when the next rustfmt->rust subtree sync is going to be, since stabilizing `precise_capturing` without formatting will be disruptive.
This implementation is otherwise rather straightforward.
Tracking:
- https://github.com/rust-lang/rust/issues/123432
Rework pattern and expression nonterminal kinds.
Some tweaks to `NonterminalKind` that will assist with #124141. Details in the individual commits.
r? compiler-errors
cc ```@eholk```
Merge `PatParam`/`PatWithOr`, and `Expr`/`Expr2021`, for a few reasons.
- It's conceptually nice, because the two pattern kinds and the two
expression kinds are very similar.
- With expressions in particular, there are several places where both
expression kinds get the same treatment.
- It removes one unreachable match arm.
- Most importantly, for #124141 I will need to introduce a new type
`MetaVarKind` that is very similar to `NonterminalKind`, but records a
couple of extra fields for expression metavars. It's nicer to have a
single `MetaVarKind::Expr` expression variant to hold those extra
fields instead of duplicating them across two variants
`MetaVarKind::{Expr,Expr2021}`. And then it makes sense for patterns
to be treated the same way, and for `NonterminalKind` to also be
treated the same way.
I also clarified the comments, because I have long found them a little
hard to understand.
The `Input::File` and `Input::Text` cases should be very similar.
However, currently the `Input::File` case uses `catch_unwind` because,
until recently (#125815) there was a fallible version of
`new_parser_from_source_str` but only an infallible version of
`new_parser_from_file`. This difference wasn't fundamental, just an
overlooked gap in the API of `rustc_parse`.
Both of those operations are now fallible, so the `Input::File` and
`Input::Text` cases can made more similar, with no need for
`catch_unwind`. This also lets us simplify an `Option<Vec<Diag>>` to
`Vec<Diag>`.
Currently we have an awkward mix of fallible and infallible functions:
```
new_parser_from_source_str
maybe_new_parser_from_source_str
new_parser_from_file
(maybe_new_parser_from_file) // missing
(new_parser_from_source_file) // missing
maybe_new_parser_from_source_file
source_str_to_stream
maybe_source_file_to_stream
```
We could add the two missing functions, but instead this commit removes
of all the infallible ones and renames the fallible ones leaving us with
these which are all fallible:
```
new_parser_from_source_str
new_parser_from_file
new_parser_from_source_file
source_str_to_stream
source_file_to_stream
```
This requires making `unwrap_or_emit_fatal` public so callers of
formerly infallible functions can still work.
This does make some of the call sites slightly more verbose, but I think
it's worth it for the simpler API. Also, there are two `catch_unwind`
calls and one `catch_fatal_errors` call in this diff that become
removable thanks this change. (I will do that in a follow-up PR.)
Remove braces when fixing a nested use tree into a single item
[Back in 2019](https://github.com/rust-lang/rust/pull/56645) I added rustfix support for the `unused_imports` lint, to automatically remove them when running `cargo fix`. For the most part this worked great, but when removing all but one childs of a nested use tree it turned `use foo::{Unused, Used}` into `use foo::{Used}`. This is slightly annoying, because it then requires you to run `rustfmt` to get `use foo::Used`.
This PR automatically removes braces and the surrouding whitespace when all but one child of a nested use tree are unused. To get it done I had to add the span of the nested use tree to the AST, and refactor a bit the code I wrote back then.
A thing I noticed is, there doesn't seem to be any `//@ run-rustfix` test for fixing the `unused_imports` lint. I created a test in `tests/suggestions` (is that the right directory?) that for now tests just what I added in the PR. I can followup in a separate PR to add more tests for fixing `unused_lints`.
This PR is best reviewed commit-by-commit.
Add StaticForeignItem and use it on ForeignItemKind
This is in preparation for unsafe extern blocks that adds a safe variant for functions inside extern blocks.
r? `@oli-obk`
cc `@compiler-errors`
Disallow ambiguous attributes on expressions
This implements the suggestion in [#15701](https://github.com/rust-lang/rust/issues/15701#issuecomment-2033124217) to disallow ambiguous outer attributes on expressions. This should resolve one of the concerns blocking the stabilization of `stmt_expr_attributes`.
Implement syntax for `impl Trait` to specify its captures explicitly (`feature(precise_capturing)`)
Implements `impl use<'a, 'b, T, U> Sized` syntax that allows users to explicitly list the captured parameters for an opaque, rather than inferring it from the opaque's bounds (or capturing *all* lifetimes under 2024-edition capture rules). This allows us to exclude some implicit captures, so this syntax may be used as a migration strategy for changes due to #117587.
We represent this list of captured params as `PreciseCapturingArg` in AST and HIR, resolving them between `rustc_resolve` and `resolve_bound_vars`. Later on, we validate that the opaques only capture the parameters in this list.
We artificially limit the feature to *require* mentioning all type and const parameters, since we don't currently have support for non-lifetime bivariant generics. This can be relaxed in the future.
We also may need to limit this to require naming *all* lifetime parameters for RPITIT, since GATs have no variance. I have to investigate this. This can also be relaxed in the future.
r? `@oli-obk`
Tracking issue:
- https://github.com/rust-lang/rust/issues/123432
Cleanup: Rename `ModSep` to `PathSep`
`::` is usually referred to as the *path separator* (citation needed).
The existing name `ModSep` for *module separator* is a bit misleading since it in fact separates the segments of arbitrary path segments, not only ones resolving to modules. Let me just give a shout-out to associated items (`T::Assoc`, `<Ty as Trait>::function`) and enum variants (`Option::None`).
Motivation: Reduce friction for new contributors, prevent potential confusion.
cc `@petrochenkov`
r? nnethercote or compiler
conditionally ignore fatal diagnostic in the SilentEmitter
This change is primarily meant to allow rustfmt to ignore all diagnostics when using the `SilentEmitter`. Back in #121301 the `SilentEmitter` was shared between rustc and rustfmt. This changed rustfmt's behavior from ignoring all diagnostic to emitting fatal diagnostics, which lead to https://github.com/rust-lang/rustfmt/issues/6109.
These changes allow rustfmt to maintain its previous behaviour when using the `SilentEmitter`, while allowing rustc code to still emit fatal diagnostics.
