Update books
## rust-embedded/book
1 commits in e88aa4403b4bf2071c8df9509160477e40179099..2463edeb8003c5743918b3739a9f6870b86396f5
2026-03-11 17:49:58 UTC to 2026-03-11 17:49:58 UTC
- Update teaching material duration for bare-metal Rust (rust-embedded/book#409)
## rust-lang/reference
7 commits in c49e89cc8c7c2c43ca625a8d5b7ad9a53a9ce978..7446bf9697c95d155eef33c6a9d91fbd29a5e359
2026-03-18 01:46:01 UTC to 2026-03-10 18:10:22 UTC
- Update `must_use` to use the attribute template (rust-lang/reference#1892)
- Add a rule that enum discriminants may not use generic parameters (rust-lang/reference#2206)
- Actually move out of Box in moving-out-of-Box test (rust-lang/reference#2204)
- Add special cases and links relating to dereferencing boxes (rust-lang/reference#2075)
- Move shebang into its own subchapter (rust-lang/reference#2199)
- Fields of enums and unions should be allowed to overlap (rust-lang/reference#2168)
- [type layout] Clarify size and alignment of pointers to unsized types (rust-lang/reference#2201)
tests/ui/async-await/gat-is-send-across-await.rs: New regression test
The test began passing in `nightly-2025-10-16`. Probably by c50aebba78 (rust-lang/rust#144064) because it fixed two "does not live long enough" errors. The test fails to compile with `nightly-2025-10-15` with such an error:
$ rustc +nightly-2025-10-15 --edition 2018 tests/ui/async-await/gat-is-send-across-await.rs
error: `impl G` does not live long enough
--> tests/ui/async-await/gat-is-send-across-await.rs:16:24
|
16 | let _: &dyn Send = &async move {
| ________________________^
17 | | let _gat = g.as_gat();
18 | | async{}.await
19 | | };
| |_____^
Closesrust-lang/rust#111852 since that's where the test comes from.
const validity checking: do not recurse to references inside MaybeDangling
This arguably should be allowed, but we currently reject it:
```rust
#![feature(maybe_dangling)]
use std::mem::MaybeDangling;
const X: MaybeDangling<&bool> = unsafe { std::mem::transmute(&5u8) };
```
r? @WaffleLapkin
Avoid prematurely choosing a glob import
Fixes rust-lang/rust#153842
Use the following without introducing trait to explain:
```rust
mod a {
pub use crate::x::y as x; // single import #1
}
mod b {
pub mod x {
pub mod y {}
}
}
use a::x; // single import #2
use b::*; // glob import #3
fn main() {}
```
In current implementation, when `#1` is first resolved, `crate::x` is temporarily taken from glob import `#3` as `crate::b::x`. This happens because `single_import_can_define_name` will see that `#2` cannot define `x` (because it depends on `#1` and `#1` is ignored) and then return `false`. Later, during finalization, `crate::x` in `#1` resolves through single import `#2` instead, which no longer matches the initially cached module `crate::b::x` and triggers the ICE.
I think the resolver should keep this unresolved because `#2` may still define `x` to avoid prematurely choosing a glob import.
r? petrochenkov
Remove `ATTRIBUTE_ORDER`
r? @jdonszelmann
There's only a few attributes that use `KeepInnermost` and I think I like the consistency of just making them all `KeepOutermost`
Always check `ConstArgHasType` even when otherwise ignoring
fixes https://github.com/rust-lang/rust/issues/149774
helping @BoxyUwU finish up https://github.com/rust-lang/rust/pull/150322, this is a simple tweak/finishing-up of that PR.
this is a breaking change that crater detected has some issues with in Boxy's PR, and hence needs a t-types FCP. I can go and help fix those crates if/once the break is signed off on.
diagnostics: avoid ICE for undeclared generic parameter in impl
Avoid an ICE for:
struct A;
impl A<B> {}
The compiler no longer panics and can proceed to emit existing diagnostics.
Adds `tests/ui/missing/undeclared-generic-parameter.rs`.
Fixesrust-lang/rust#154165 and introduced by rust-lang/rust#152913
allow `incomplete_features` in most UI tests
This PR allows the `incomplete_features` lint for all UI tests except for the three directories with the largest number of tests (`traits`, `specialization` and `const-generics`) triggering this lint to keep the size of this PR manageable. The remaining three directories will be handled in followup PRs.
Part of https://github.com/rust-lang/rust/issues/154168.
ui/lto: move and rename two tests from issues/
Move:
- `tests/ui/issues/issue-44056.rs` -> `tests/ui/lto/lto-avx-target-feature.rs`
- The first test enables both AVX target features and LTO but does not exercise AVX-specific behavior. The test primarily checks that LTO builds successfully with these flags; place it under `ui/lto` for consistency.
- `tests/ui/issues/issue-51947.rs` -> `tests/ui/lto/lto-weak-merge-functions.rs`
- The second test exercises weak linkage interacting with LTO (merge-functions), so it should belong in `ui/lto`.
I have also added a commented line at the top of each test file indicating the issue it originated from.
Improve inline assembly error messages
by
- using `DiagSymbolList` to get nicely formatted lists
- mentioning the `modifier` when an invalid modifier is used. This is useful in case the span cannot be resolved (which I ran into).
diagnostics: avoid ICE in confusable_method_name for associated functions
Avoid unconditionally slicing `inputs()[1..]`, which assumes a `self` parameter. Use `is_method()` to conditionally skip the receiver, preventing out-of-bounds access and fixing suggestions for associated functions.
On E0277 tweak help when single type impls traits
When encountering an unmet predicate, when we point at the trait impls that do exist, if they are all for the same self type, tweak the wording to make it less verbose.
refactor RangeFromIter overflow-checks impl
Crates with different overflow-checks settings accessing the same RangeFromIter resulted in incorrect values being yielded
Fixesrust-lang/rust#154124
r? @tgross35
[BPF] add target feature allows-misaligned-mem-access
This PR adds the allows-misaligned-mem-access target feature to the BPF target. The feature can enable misaligned memory access support in the LLVM backend, aligning Rust’s BPF target behavior with the corresponding LLVM update introduced in [llvm/llvm-project#167013](https://github.com/llvm/llvm-project/pull/167013) (included in LLVM 22).
by
- using `DiagSymbolList` to get nicely formatted lists
- mentioning the `modifier` when an invalid modifier is used. This is useful in case the span cannot be resolved (which I ran into).
Avoid unconditionally slicing `inputs()[1..]`, which assumes a `self`
parameter. Use `is_method()` to conditionally skip the receiver,
preventing out-of-bounds access and fixing suggestions for associated
functions.
Signed-off-by: Usman Akinyemi <usmanakinyemi202@gmail.com>
Avoid an ICE for:
struct A;
impl A<B> {}
The compiler no longer panics and can proceed to emit existing diagnostics.
Adds `tests/ui/missing/undeclared-generic-parameter.rs`.
Signed-off-by: Usman Akinyemi <usmanakinyemi202@gmail.com>
The test began passing in `nightly-2025-10-16`. Probably by c50aebba78
because it fixed two "does not live long enough" errors. The test fails
to compile with `nightly-2025-10-15` with such an error:
$ rustc +nightly-2025-10-15 --edition 2018 tests/ui/async-await/gat-is-send-across-await.rs
error: `impl G` does not live long enough
--> tests/ui/async-await/gat-is-send-across-await.rs:16:24
|
16 | let _: &dyn Send = &async move {
| ________________________^
17 | | let _gat = g.as_gat();
18 | | async{}.await
19 | | };
| |_____^
When encountering an unmet predicate, when we point at the trait impls that do exist, if they are all for the same self type, tweak the wording to make it less verbose.
don't suggest non-deriveable traits for unions
Fixesrust-lang/rust#137587
Before, the compiler suggested adding `#[derive(Debug)]` (other traits too) for unions,
which is misleading because some traits can't be automatically derived.
Only traits that are still suggested are Copy and Clone.
I noticed the error label changed after removing the suggestion. I hope this isn't a big deal, but let me know if that's an issue.
original example:
```rs
union Union {
member: usize,
}
impl PartialEq<u8> for Union {
fn eq(&self, rhs: &u8) -> bool {
unsafe { self.member == (*rhs).into() }
}
}
fn main() {
assert_eq!(Union { member: 0 }, 0);
}
```
before:
```
error[E0277]: `Union` doesn't implement `Debug`
--> src\main.rs:13:5
|
13 | assert_eq!(Union { member: 0 }, 0);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Debug` is not implemented for `Union`
|
= note: add `#[derive(Debug)]` to `Union` or manually `impl Debug for Union`
= note: this error originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider annotating `Union` with `#[derive(Debug)]`
|
2 + #[derive(Debug)]
3 | union Union {
|
```
after (the message doesn't suggest adding #[derive(Debug)] to unions)
```
error[E0277]: `Union` doesn't implement `Debug`
--> src\main.rs:13:5
|
13 | assert_eq!(Union { member: 0 }, 0);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unsatisfied trait bound
|
help: the trait `Debug` is not implemented for `Union`
--> src\main.rs:2:1
|
2 | union Union {
| ^^^^^^^^^^^
= note: manually `impl Debug for Union`
```
Allow passing `expr` metavariable as `cfg` predicate
This PR allows expanding `expr` metavariables inside the configuration predicates of `cfg` and `cfg_attr` invocations.
For example, the following code will now compile:
```rust
macro_rules! mac {
($e:expr) => {
#[cfg_attr($e, inline)]
#[cfg($e)]
fn func() {}
#[cfg(not($e))]
fn func() {
panic!()
}
}
}
mac!(any(unix, feature = "foo"));
```
There is currently no `macro_rules` fragment specifier that can represent all valid `cfg` predicates. `meta` comes closest, but excludes `true` and `false`. By fixing that, this change makes it easier to write declarative macros that parse `cfg` or `cfg_attr` invocations, for example https://github.com/rust-lang/rust/pull/146281/.
@rustbot label T-lang needs-fcp A-attributes A-cfg A-macros
tests/ui/async-await/drop-option-future.rs: New regression test
The test began compiling with `nightly-2022-11-25`. I bisected it further, and the commit that made it compile was 9f36f988ad (rust-lang/rust#104321). The test fails to compile with `nightly-2022-11-24`:
$ rustc +nightly-2022-11-24 --edition 2018 tests/ui/async-await/drop-option-future.rs
error[E0597]: `value` does not live long enough
--> tests/ui/async-await/drop-option-future.rs:12:22
|
12 | f = Some(async { value });
| --^^^^^--
| | |
| | borrowed value does not live long enough
| value captured here by generator
13 | core::mem::drop(f);
14 | }
| -
| |
| `value` dropped here while still borrowed
| borrow might be used here, when `f` is dropped and runs the destructor for type `Option<impl Future<Output = i32>>`
The fix 9f36f988ad does not appear to affect or include a regression test for the rust-lang/rust#98077 case, so let's add that test.
Closesrust-lang/rust#98077 since we add the test from that issue.
Emit fewer errors for incorrect rtn and `=` -> `:` typos in bindings
Make all existing `:` -> `=` typo suggestions verbose and tweak the suggested code.
Stash parse errors when pasing rtn that doesn't use `(..)`.
Emit single error on `Foo::bar(qux)` that looks like rtn in incorrect position and suggest `Foo::bar(..)`.
```
error: return type notation not allowed in this position yet
--> $DIR/let-binding-init-expr-as-ty.rs:18:10
|
LL | struct K(S::new(()));
| ^^^^^^^^^^
|
help: furthermore, argument types not allowed with return type notation
|
LL - struct K(S::new(()));
LL + struct K(S::new(..));
|
```
On incorrect rtn in let binding type for an existing inherent associated function, suggest `:` -> `=` to turn the "type" into a call expression. (Fixrust-lang/rust#134087)
```
error: expected type, found associated function call
--> $DIR/let-binding-init-expr-as-ty.rs:29:12
|
LL | let x: S::new(());
| ^^^^^^^^^^
|
help: use `=` if you meant to assign
|
LL - let x: S::new(());
LL + let x = S::new(());
|
```
Jacob Pratt