Don't require method impls for methods with `Self:Sized` bounds for impls for unsized types
Similarly to how #112319 doesn't require specifying associated types with `Self: Sized` bounds on `dyn Trait`, we now don't require assoc items with `Self: Sized` bounds to be in impls of for unsized types.
Additionally we lint assoc items with `Self: Sized` bounds that are in such impls:
```rust
trait Foo {
fn foo() where Self: Sized;
}
impl Foo for () {
fn foo() {}
}
impl Foo for i32 {}
//~^ ERROR: not all trait items implemented, missing: `foo`
impl Foo for dyn std::fmt::Debug {}
#[deny(dead_code)]
impl Foo for dyn std::fmt::Display {
fn foo() {}
//~^ ERROR this item cannot be used as its where bounds are not satisfied
}
```
Note that this works with the same `Self: Sized` specific logic we already have for `dyn Trait`, so no new capabilities like avoiding assoc items with `Self: Copy` bounds on impls for `String` or such are added here. Specifying `where ConcreteType: Sized` in a trait and implementing the trait for `ConcreteType` also does not work, it *must* be exactly `Self: Sized`.
Make `#[used]` work when linking with `ld64`
To make `#[used]` work in static libraries, we use the `symbols.o` trick introduced in https://github.com/rust-lang/rust/pull/95604.
However, the linker shipped with Xcode, ld64, works a bit differently from other linkers; in particular, [it completely ignores undefined symbols by themselves](https://github.com/apple-oss-distributions/ld64/blob/ld64-954.16/src/ld/parsers/macho_relocatable_file.cpp#L2455-L2468), and only consider them if they have relocations (something something atoms something fixups, I don't know the details).
So to make the `symbols.o` file work on ld64, we need to actually insert a relocation. That's kinda cumbersome to do though, since the relocation must be valid, and hence must point to a valid piece of machine code, and is hence very architecture-specific.
Fixes https://github.com/rust-lang/rust/issues/133491, see that for investigation.
---
Another option would be to pass `-u _foo` to the final linker invocation. This has the problem that `-u` causes the linker to not be able to dead-strip the symbol, which is undesirable. (If we did this, we would possibly also want to do it by putting the arguments in a file by itself, and passing that file via ``@`,` e.g. ``@undefined_symbols.txt`,` similar to https://github.com/rust-lang/rust/issues/52699, though that [is only supported since Xcode 12](https://developer.apple.com/documentation/xcode-release-notes/xcode-12-release-notes#Linking), and I'm not sure we wanna bump that).
Various other options that are probably all undesirable as they affect link time performance:
- Pass `-all_load` to the linker.
- Pass `-ObjC` to the linker (the Objective-C support in the linker has different code paths that load more of the binary), and instrument the binaries that contain `#[used]` symbols.
- Pass `-force_load` to libraries that contain `#[used]` symbols.
Failed attempt: Embed `-u _foo` in the object file with `LC_LINKER_OPTION`, akin to https://github.com/rust-lang/rust/issues/121293. Doesn't work, both because `ld64` doesn't read that from archive members unless it already has a reason to load the member (which is what this PR is trying to make it do), and because `ld64` only support the `-l`, `-needed-l`, `-framework` and `-needed_framework` flags in there.
---
TODO:
- [x] Support all Apple architectures.
- [x] Ensure that this works regardless of the actual type of the symbol.
- [x] Write up more docs.
- [x] Wire up a few proper tests.
`@rustbot` label O-apple
Update books
## rust-lang/book
2 commits in d4d2c18cbd20876b2130a546e790446a8444cb32..4a01a9182496f807aaa5f72d93a25ce18bcbe105
2025-02-24 14:48:34 UTC to 2025-02-13 19:29:47 UTC
- Fix typos in chapter 17 (rust-lang/book#4238)
- NoStarch backports (rust-lang/book#4224)
## rust-lang/edition-guide
2 commits in 8dbdda7cae4fa030f09f8f5b63994d4d1dde74b9..daa4b763cd848f986813b5cf8069e1649f7147af
2025-02-22 14:58:51 UTC to 2025-02-21 02:30:17 UTC
- Remove precise capturing features (rust-lang/edition-guide#362)
- use same name as previous example (rust-lang/edition-guide#360)
## rust-lang/nomicon
1 commits in 336f75835a6c0514852cc65aba9a698b699b13c8..8f5c7322b65d079aa5b242eb10d89a98e12471e1
2025-02-19 13:16:47 UTC to 2025-02-19 13:16:47 UTC
- other-reprs: do not make it sound like we are making ABI promises for repr(int) enums (rust-lang/nomicon#461)
## rust-lang/reference
4 commits in 6195dbd70fc6f0980c314b4d23875ac570d8253a..615b4cec60c269cfc105d511c93287620032d5b0
2025-02-18 23:01:53 UTC to 2025-02-13 15:12:49 UTC
- Add rule identifiers to names chapters (rust-lang/reference#1737)
- Switch from AVX to SSE in the example (rust-lang/reference#1735)
- Remove attributes from struct field rest patterns (rust-lang/reference#1736)
- Update reference for target_feature_11. (rust-lang/reference#1720)
Don't immediately panic if dropck fails without returning errors
This span_bug was a little too optimistic. I've decided that matching on the ErrorGuaranteed is a little more sensible than a delay bug that will always be ignored.
closes#137329
r? `@compiler-errors`
