Allow null-pointer-optimized enums in FFI if their underlying representation is FFI safe
I'm not sure if this requires an RFC. I attempted to start [a discussion on internals.rust-lang.org](https://internals.rust-lang.org/t/options-ffi-safety-and-guarantees-for-abi-compatibility-with-nonnull-optimizations/9784) and when no one really objected I figured I'd go ahead and try implementing this.
This allows types like `Option<NonZeroU8>` to be used in FFI without triggering the `improper_ctypes` lint. This works by changing the `is_repr_nullable_ptr` function to consider an enum `E` to be FFI-safe if:
- `E` has no explicit `#[repr(...)]`.
- It only has two variants.
- One of those variants is empty (meaning it has no fields).
- The other variant has only one field.
- That field is one of the following:
- `&T`
- `&mut T`
- `extern "C" fn`
- `core::num::NonZero*`
- `core::ptr::NonNull<T>`
- `#[repr(transparent)] struct` wrapper around one of the types in this list.
- The size of `E` and its field are both known and are both the same size (implying `E` is participating in the nonnull optimization).
This logic seems consistent with [the Rust nomicon](https://doc.rust-lang.org/nomicon/repr-rust.html).
This allows types like Option<NonZeroU8> to be used in FFI without triggering the improper_ctypes lint. This works by changing the is_repr_nullable_ptr function to consider an enum E to be FFI-safe if:
- E has no explicit #[repr(...)].
- It only has two variants.
- One of those variants is empty (meaning it has no fields).
- The other variant has only one field.
- That field is one of the following:
- &T
- &mut T
- extern "C" fn
- core::num::NonZero*
- core::ptr::NonNull<T>
- #[repr(transparent)] struct wrapper around one of the types in this list.
- The size of E and its field are both known and are both the same size (implying E is participating in the nonnull optimization).
Ban multi-trait objects via trait aliases
Obviously, multi-trait objects are not normally supported, so they should not be supported via trait aliases.
This has been factored out from the previous PR https://github.com/rust-lang/rust/pull/55994 (see point 1).
r? @Centril
CC @nikomatsakis
------------------
### RELNOTES:
We now allow `dyn Send + fmt::Debug` with equivalent semantics to `dyn fmt::Debug + Send`.
That is, the order of the mentioned traits does not matter wrt. principal/not-principal traits.
This is a small change that might deserve a mention in the blog post because it is a language change but most likely not.
See ce2ee305f9/src/test/ui/traits/wf-trait-object-reverse-order.rs.
// @Centril
Preserve local scopes in generator MIR
Part of #52924, depended upon by the generator layout optimization #60187.
This PR adds `StorageDead` statements in more places in generators, so we can see when non-`Drop` locals have gone out of scope and recover their storage.
The reason this is only done for generators is compiler performance. See https://github.com/rust-lang/rust/pull/60187#issuecomment-485637811 for what happens when we do this for all functions.
For `Drop` locals, we modify the `MaybeStorageLive` analysis to use `drop` to indicate that storage is no longer live for the local. Once `drop` returns or unwinds to our function, we implicitly assume that the local is `StorageDead`.
Instead of using `drop`, it is possible to emit more `StorageDead` statements in the MIR for `Drop` locals so we can handle all locals the same. I am fine with doing it that way, but this was the simplest approach for my purposes. It is also likely to be more performant.
r? @Zoxc (feel free to reassign)
cc @cramertj @eddyb @RalfJung @rust-lang/wg-async-await
Rollup of 10 pull requests
Successful merges:
- #59742 (Move `edition` outside the hygiene lock and avoid accessing it)
- #60581 (convert custom try macro to `?`)
- #60963 (Update boxed::Box docs on memory layout)
- #60973 (Avoid symbol interning in `file_metadata`.)
- #60982 (Do not fail on child without DefId)
- #60991 (LocalDecl push returns Local len)
- #60995 (Add stream_to_parser_with_base_dir)
- #60998 (static_assert: make use of anonymous constants)
- #61003 (Remove impls for `InternedString`/string equality.)
- #61006 (adjust deprecation date of mem::uninitialized)
Failed merges:
r? @ghost
Remove impls for `InternedString`/string equality.
`Symbol` received the same treatment in #60630.
Also, we can derive `PartialEq` for `InternedString`.
r? @petrochenkov
Add stream_to_parser_with_base_dir
This PR adds `stream_to_parser_with_base_dir`, which creates a parser from a token stream and a base directory.
Context: I would like to parse `cfg_if!` macro and get a list of modules defined inside it from rustfmt so that rustfmt can format those modules (cc https://github.com/rust-lang/rustfmt/issues/3253). To do so, I need to create a parser from `TokenStream` and set the directory of `Parser` to the same directory as the parent directory of a file which contains `cfg_if!` invocation. AFAIK there is no way to achieve this, and hence this PR.
Alternatively, I could change the visibility of `Parser.directory` from `crate` to `pub` so that the value can be modified after initializing a parser. I don't have a preference over either approach (or others, as long as it works).
Avoid symbol interning in `file_metadata`.
This commit changes `created_files` so it uses strings directly as keys,
rather than symbols derived from the strings. This avoids the cost of
having to do the hash table lookups to produce the symbols from the
strings.
The commit also uses `entry` to avoid doing a repeated hash table lookup
(`get` + `insert`).
Note that PR #60467 improved this code somewhat; this is a further
improvement.
r? @davidtwco
Update boxed::Box docs on memory layout
The existing docs for the `Box` type state that "the way `Box` allocates and releases memory is unspecified", and that therefore the only valid pointer to pass to `Box::from_raw` is one obtained from `Box::into_raw`. This is inconsistent with the module-level docs which specify,
> It is valid to convert both ways between a Box and a raw pointer allocated with the Global allocator, given that the Layout used with the allocator is correct for the type. More precisely, a value: *mut T that has been allocated with the Global allocator with Layout::for_value(&*value) may be converted into a box using Box::<T>::from_raw(value). Conversely, the memory backing a value: *mut T obtained from Box::<T>::into_raw may be deallocated using the Global allocator with Layout::for_value(&*value).
This pull request updates the docs for `Box` to make them consistent with the module-level docs and adds some examples of how to use the global allocator in conjunction with `Box::from_raw` and `Box::into_raw`.
debuginfo: Revert to old/more verbose behavior for -Cdebuginfo=1
https://github.com/rust-lang/rust/commit/cff075009 made LLVM emit less debuginfo when compiling with "line-tables-only". The change was essentially correct but the reduced amount of debuginfo broke
a number of tools.
This commit reverts the change so we get back the old behavior, until we figure out how to do this properly and give external tools to adapt to the new format.
See https://github.com/rust-lang/rust/issues/60020 for more info.
r? @cuviper
cc @jrmuizel & @froydnj
https://github.com/rust-lang/rust/commit/cff075009 made LLVM emit
less debuginfo when compiling with "line-tables-only". The change
was essentially correct but the reduced amount of debuginfo broke
a number of tools.
This commit reverts the change so we get back the old behavior,
until we figure out how to do this properly and give external
tools to adapt to the new format.
See https://github.com/rust-lang/rust/issues/60020 for more info.
Move gensym operations from `Symbol` to `Ident`
Gensyms are always at the `Ident` level, and long-term we probably want to record gensym-ness in hygiene data.
r? @petrochenkov
Set -funwind-tables and -fno-exceptions unconditionally for LLVM's libunwind
These are required otherwise libunwind will end up with undefined
references to __gxx_personality_v0 which is provided by C++ ABI
library and that's undesirable.
remove confusing remarks about mixed volatile and non-volatile accesses
These comments were originally added by @ecstatic-morse in 911d35f0bf and then later edited by me. The intention, I think, was to make sure people do both their reads and writes with these methods if the affected memory really is used for communication with external devices.
However, [people read this as saying that mixed volatile/non-volatile accesses are UB](https://github.com/rust-lang/rust/issues/58599#issuecomment-493791130), which -- to my knowledge -- they are not. So better remove this.
Cc @rkruppe @rust-lang/wg-unsafe-code-guidelines
rustc: Improve type size assertions
Now they
- Tell what the new size is, when it changes
- Do not require passing an identifier
```
::: src\libsyntax\parse\token.rs:223:1
|
223 | static_assert_size!(Token, 123);
| -------------------------------- in this macro invocation
|
= note: expected type `[(); 123]`
found type `[(); 16]`
```
Document BinaryHeap time complexity
I went into some detail on the time complexity of `push` because it is relevant for using BinaryHeap efficiently -- specifically that you should avoid pushing many elements in ascending order when possible.
r? @Amanieu
Closes#47976. Closes#59698.
stable hashing: Remove unused field and add documentation.
This PR removes the `bytes_hashed` field from `StableHasher` which in the past has been used for collecting some statistics but has gone unused for quite a while (months at least) now.
The PR also tries to document some requirements for `HashStable` implementations that haven't been written down explicitly anywhere.
Fix intra-doc link resolution failure on re-exporting libstd
Currently, re-exporting libstd items as below will [occur a lot of failures](https://gist.github.com/taiki-e/e33e0e8631ef47f65a74a3b69f456366).
```rust
pub use std::*;
```
Until the underlying issue (#56922) fixed, we can fix that so they don't propagate to downstream crates.
Related: https://github.com/rust-lang/rust/pull/56941 (That PR fixed failures that occur when re-exporting from libcore to libstd.)
r? @QuietMisdreavus
Fix search sidebar width when no crate select is present
Fixes#60480.
I also fixed the box-shadow that seemed to have been kind of removed?
r? @QuietMisdreavus
These are required otherwise libunwind will end up with undefined
references to __gxx_personality_v0 which is provided by C++ ABI
library and that's undesirable.
