Add `const Default` impls for `HashSet` and `HashMap` with custom `Hasher`
Follow up to rust-lang/rust#134628. Tracking issue rust-lang/rust#143894.
r? @fmease
cc @fee1-dead @oli-obk
This doesn't allow for `const H: HashSet<()> = Default::default();`, but would allow for it to work with a custom hasher, which would enable the `Fx*` family to work.
remove multiple unhelpful `reason = "..."` values from `#[unstable(...)]` invocations
The vast majority of `#[unstable()]` attributes already has no explicit reason specified. This PR removes the `reason = "..."` value for the following unhelpful or meaningless reasons:
* "recently added"
* "new API"
* "recently redesigned"
* "unstable"
An example of how the message looks with and without a reason:
```rust
fn main() {
Vec::<()>::into_parts;
Vec::<()>::const_make_global;
}
```
```
error[E0658]: use of unstable library feature `box_vec_non_null`: new API
--> src/main.rs:2:5
|
2 | Vec::<()>::into_parts;
| ^^^^^^^^^^^^^^^^^^^^^
|
= note: see issue #130364 <https://github.com/rust-lang/rust/issues/130364> for more information
= help: add `#![feature(box_vec_non_null)]` to the crate attributes to enable
= note: this compiler was built on 2026-01-15; consider upgrading it if it is out of date
error[E0658]: use of unstable library feature `const_heap`
--> src/main.rs:3:5
|
3 | Vec::<()>::const_make_global;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: see issue #79597 <https://github.com/rust-lang/rust/issues/79597> for more information
= help: add `#![feature(const_heap)]` to the crate attributes to enable
= note: this compiler was built on 2026-01-15; consider upgrading it if it is out of date
```
Most of the remaining reasons after this are something similar to "this is an implementation detail for XYZ" or "this is not public". If this PR is approved, I'll look into those next.
The PR also removes the `fd_read` feature gate. It only consists of one attribute applied to an implementation inside a module that is already private and unstable and should not be needed.
fix: WASI threading regression by disabling pthread usage
PR rust-lang/rust#147572 changed WASI to use the Unix threading implementation, but WASI does not support threading. When the Unix code tries to call pthread_create, it fails with EAGAIN, causing libraries like rayon to panic when trying to initialize their global thread pool.
The old wasip1/wasip2 implementations:
- wasip1: Threading conditionally available with atomics (experimental)
- wasip2: Threading unconditionally unsupported
This fix restores that behavior by disabling pthread-based threading for all WASI targets:
1. Guard the pthread-based Thread implementation with #[cfg(not(target_os = "wasi"))]
2. Provide an unsupported stub (Thread(!)) for WASI
3. Return Err(io::Error::UNSUPPORTED_PLATFORM) when Thread::new is called
Fixes the regression where rayon-based code (e.g., lopdf in PDF handling) panicked on WASI after nightly-2025-12-10.
Before fix:
pthread_create returns EAGAIN (error code 6)
ThreadPoolBuildError { kind: IOError(Os { code: 6,
kind: WouldBlock, message: "Resource temporarily unavailable" }) }
After fix:
Thread::new returns Err(io::Error::UNSUPPORTED_PLATFORM)
Libraries can gracefully handle the lack of threading support
r? @alexcrichton
Recent changes made WASI targets use the Unix threading implementation, but
WASI does not support threading. When the Unix code tries to call
pthread_create, it fails with EAGAIN, causing libraries like rayon to
panic when trying to initialize their global thread pool.
This fix adds an early return in Thread::new() that checks for WASI and
returns UNSUPPORTED_PLATFORM. This approach:
- Continues using most of the unix.rs code path (less invasive)
- Only requires a small cfg check at the start of Thread::new()
- Can be easily removed once wasi-sdk is updated with the proper fix
The real fix is being tracked in `WebAssembly/wasi-libc#716` which will
change the error code returned by pthread_create to properly indicate
unsupported operations. Once that propagates to wasi-sdk, this workaround
can be removed.
Fixes the regression where rayon-based code (e.g., lopdf in PDF handling)
panicked on WASI after nightly-2025-12-10.
Before fix:
pthread_create returns EAGAIN (error code 6)
ThreadPoolBuildError { kind: IOError(Os { code: 6,
kind: WouldBlock, message: "Resource temporarily unavailable" }) }
After fix:
Thread::new returns Err(io::Error::UNSUPPORTED_PLATFORM)
Libraries can gracefully handle the lack of threading support
std: Change UEFI env vars to volatile storage
The UEFI variables set by the env vars should be volatile, otherwise they will persist after reboot and use up scarce non-volatile storage.
CC @Ayush1325
std: move `errno` and related functions into `sys::io`
Part of rust-lang/rust#117276.
Currently, `errno` and related functions like `decode_error_kind` are split across `sys::pal` and `sys::pal::os`. This PR moves all of them into a new module inside `sys::io`.
Explicitly export core and std macros
Currently all core and std macros are automatically added to the prelude via #[macro_use]. However a situation arose where we want to add a new macro `assert_matches` but don't want to pull it into the standard prelude for compatibility reasons. By explicitly exporting the macros found in the core and std crates we get to decide on a per macro basis and can later add them via the rust_20xx preludes.
Closes https://github.com/rust-lang/rust/issues/53977
Unlocks https://github.com/rust-lang/rust/pull/137487
Reference PR:
- https://github.com/rust-lang/reference/pull/2077
# Stabilization report lib
Everything N/A or already covered by lang report except, breaking changes: The unstable and never intended for public use `format_args_nl` macro is no longer publicly accessible as requested by @petrochenkov. Affects <10 crates including dependencies.
# Stabilization report lang
## Summary
Explicitly export core and std macros.
This change if merged would change the code injected into user crates to no longer include #[macro_use] on extern crate core and extern crate std. This change is motivated by a near term goal and a longer term goal. The near term goal is to allow a macro to be defined at the std or core crate root but not have it be part of the implicit prelude. Such macros can then be separately promoted to the prelude in a new edition. Specifically this is blocking the stabilization of assert_matches rust-lang/rust#137487. The longer term goal is to gradually deprecate #[macro_use]. By no longer requiring it for standard library usage, this serves as a step towards that goal. For more information see rust-lang/rust#53977.
PR link: https://github.com/rust-lang/rust/pull/139493
Tracking:
- https://github.com/rust-lang/rust/issues/147319
Reference PRs:
- https://github.com/rust-lang/rust/pull/139493
cc @rust-lang/lang @rust-lang/lang-advisors
### What is stabilized
Stabilization:
* `#[macro_use]` is no longer automatically included in the crate root module. This allows the explicit import of macros in the `core` and `std` prelude e.g. `pub use crate::dbg;`.
* `ambiguous_panic_imports` lint. Code that previously passed without warnings, but included the following or equivalent - only pertaining to core vs std panic - will now receive a warning:
```rust
#![no_std]
extern crate std;
use std::prelude::v1::*;
fn xx() {
panic!(); // resolves to core::panic
//~^ WARNING `panic` is ambiguous
//~| WARNING this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
}
```
This lint is tied to a new exception to the name resolution logic in [compiler/rustc_resolve/src/ident.rs](https://github.com/rust-lang/rust/pull/139493/files#diff-c046507afdba3b0705638f53fffa156cbad72ed17aa01d96d7bd1cc10b8d9bce) similar to an exception added for https://github.com/rust-lang/rust/issues/145575. Specifically this only happens if the import of two builtin macros is ambiguous and they are named `sym::panic`. I.e. this can only happen for `core::panic` and `std::panic`. While there are some tiny differences in what syntax is allowed in `std::panic` vs `core::panic` in editions 2015 and 2018, [see](https://github.com/rust-lang/rust/pull/139493#issuecomment-2796481622). The behavior at runtime will always be the same if it compiles, implying minimal risk in what specific macro is resolved. At worst some closed source project not captured by crater will stop compiling because a different panic is resolved than previously and they were using obscure syntax like `panic!(&String::new())`.
## Design
N/A
### Reference
> What updates are needed to the Reference? Link to each PR. If the Reference is missing content needed for describing this feature, discuss that.
- https://github.com/rust-lang/reference/pull/2077
### RFC history
> What RFCs have been accepted for this feature?
N/A
### Answers to unresolved questions
N/A
### Post-RFC changes
> What other user-visible changes have occurred since the RFC was accepted? Describe both changes that the lang team accepted (and link to those decisions) as well as changes that are being presented to the team for the first time in this stabilization report.
N/A
### Key points
> What decisions have been most difficult and what behaviors to be stabilized have proved most contentious? Summarize the major arguments on all sides and link to earlier documents and discussions.
- Nothing was really contentious.
### Nightly extensions
> Are there extensions to this feature that remain unstable? How do we know that we are not accidentally committing to those?
N/A
### Doors closed
> What doors does this stabilization close for later changes to the language? E.g., does this stabilization make any other RFCs, lang experiments, or known in-flight proposals more difficult or impossible to do later?
No known doors are closed.
## Feedback
### Call for testing
> Has a "call for testing" been done? If so, what feedback was received?
No.
### Nightly use
> Do any known nightly users use this feature? Counting instances of `#![feature(FEATURE_NAME)]` on GitHub with grep might be informative.
N/A
## Implementation
### Major parts
> Summarize the major parts of the implementation and provide links into the code and to relevant PRs.
>
> See, e.g., this breakdown of the major parts of async closures:
>
> - <https://rustc-dev-guide.rust-lang.org/coroutine-closures.html>
The key change is [compiler/rustc_builtin_macros/src/standard_library_imports.rs](https://github.com/rust-lang/rust/pull/139493/files#diff-be08752823b8f862bb0c7044ef049b0f4724dbde39306b98dea2adb82ec452b0) removing the macro_use inject and the `v1.rs` preludes now explicitly `pub use`ing the macros https://github.com/rust-lang/rust/pull/139493/files#diff-a6f9f476d41575b19b399c6d236197355556958218fd035549db6d584dbdea1d + https://github.com/rust-lang/rust/pull/139493/files#diff-49849ff961ebc978f98448c8990cf7aae8e94cb03db44f016011aa8400170587.
### Coverage
> Summarize the test coverage of this feature.
>
> Consider what the "edges" of this feature are. We're particularly interested in seeing tests that assure us about exactly what nearby things we're not stabilizing. Tests should of course comprehensively demonstrate that the feature works. Think too about demonstrating the diagnostics seen when common mistakes are made and the feature is used incorrectly.
>
> Within each test, include a comment at the top describing the purpose of the test and what set of invariants it intends to demonstrate. This is a great help to our review.
>
> Describe any known or intentional gaps in test coverage.
>
> Contextualize and link to test folders and individual tests.
A variety of UI tests including edge cases have been added.
### Outstanding bugs
> What outstanding bugs involve this feature? List them. Should any block the stabilization? Discuss why or why not.
An old bug is made more noticeable by this change https://github.com/rust-lang/rust/issues/145577 but it was recommended to not block on it https://github.com/rust-lang/rust/pull/139493#issuecomment-3288311495.
### Outstanding FIXMEs
> What FIXMEs are still in the code for that feature and why is it OK to leave them there?
```
// Turn ambiguity errors for core vs std panic into warnings.
// FIXME: Remove with lang team approval.
```
https://github.com/rust-lang/rust/pull/139493/files#diff-c046507afdba3b0705638f53fffa156cbad72ed17aa01d96d7bd1cc10b8d9bce
### Tool changes
> What changes must be made to our other tools to support this feature. Has this work been done? Link to any relevant PRs and issues.
- ~~rustfmt~~
- ~~rust-analyzer~~
- ~~rustdoc (both JSON and HTML)~~
- ~~cargo~~
- ~~clippy~~
- ~~rustup~~
- ~~docs.rs~~
No known changes needed or expected.
### Breaking changes
> If this stabilization represents a known breaking change, link to the crater report, the analysis of the crater report, and to all PRs we've made to ecosystem projects affected by this breakage. Discuss any limitations of what we're able to know about or to fix.
Breaking changes:
* It's possible for user code to invoke an ambiguity by defining their own macros with standard library names and glob importing them, e.g. `use nom::*` importing `nom::dbg`. In practice this happens rarely based on crater data. The 3 public crates where this was an issue, have been fixed. The ambiguous panic import is more common and affects a non-trivial amount of the public - and likely private - crate ecosystem. To avoid a breaking change, a new future incompatible lint was added ambiguous_panic_imports see https://github.com/rust-lang/rust/issues/147319. This allows current code to continue compiling, albeit with a new warning. Future editions of Rust make this an error and future versions of Rust can choose to make this error. Technically this is a breaking change, but crater gives us the confidence that the impact will be at worst a new warning for 99+% of public and private crates.
```rust
#![no_std]
extern crate std;
use std::prelude::v1::*;
fn xx() {
panic!(); // resolves to core::panic
//~^ WARNING `panic` is ambiguous
//~| WARNING this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
}
```
* Code using `#![no_implicit_prelude]` *and* Rust edition 2015 will no longer automatically have access to the prelude macros. The following works on nightly but would stop working with this change:
```rust
#![no_implicit_prelude]
// Uncomment to fix error.
// use std::vec;
fn main() {
let _ = vec![3, 6];
}
```
Inversely with this change the `panic` and `unreachable` macro will always be in the prelude even if `#![no_implicit_prelude]` is specified.
Error matrix when using `#![no_implicit_prelude]`, ✅ means compiler passes 🚫 means compiler error:
Configuration | Rust 2015 | Rust 2018+
--------------|-----------|-----------
Nightly (panic\|unreachable) macro | ✅ | 🚫
PR (panic\|unreachable) macro | ✅ | ✅
Nightly (column\|concat\|file\|line\|module_path\|stringify) macro | ✅ | ✅
PR (column\|concat\|file\|line\|module_path\|stringify) macro | ✅ | ✅
Nightly remaining macros | ✅ | 🚫
PR remaining macros | 🚫 | 🚫
Addressing this issue is deemed expensive.
Crater found no instance of this pattern in use. Affected code can fix the issue by directly importing the macros. The new behavior matches the behavior of `#![no_implicit_prelude]` in Rust editions 2018 and beyond and it's intuitive meaning.
Crater report:
- https://crater-reports.s3.amazonaws.com/pr-139493-2/index.html (latest run, but partial run)
- https://crater-reports.s3.amazonaws.com/pr-139493-1/index.html (previous full run, one fix missing)
Crater analysis:
- Discussed in breaking changes.
PRs to affected crates:
- https://github.com/Michael-F-Bryan/gcode-rs/pull/57
- https://github.com/stbuehler/rust-ipcrypt/pull/1
- https://github.com/jcreekmore/dmidecode/pull/55
## Type system, opsem
### Compile-time checks
> What compilation-time checks are done that are needed to prevent undefined behavior?
>
> Link to tests demonstrating that these checks are being done.
N/A
### Type system rules
> What type system rules are enforced for this feature and what is the purpose of each?
N/A
### Sound by default?
> Does the feature's implementation need specific checks to prevent UB, or is it sound by default and need specific opt-in to perform the dangerous/unsafe operations? If it is not sound by default, what is the rationale?
N/A
### Breaks the AM?
> Can users use this feature to introduce undefined behavior, or use this feature to break the abstraction of Rust and expose the underlying assembly-level implementation? Describe this if so.
N/A
## Common interactions
### Temporaries
> Does this feature introduce new expressions that can produce temporaries? What are the scopes of those temporaries?
N/A
### Drop order
> Does this feature raise questions about the order in which we should drop values? Talk about the decisions made here and how they're consistent with our earlier decisions.
N/A
### Pre-expansion / post-expansion
> Does this feature raise questions about what should be accepted pre-expansion (e.g. in code covered by `#[cfg(false)]`) versus what should be accepted post-expansion? What decisions were made about this?
N/A
### Edition hygiene
> If this feature is gated on an edition, how do we decide, in the context of the edition hygiene of tokens, whether to accept or reject code. E.g., what token do we use to decide?
N/A
### SemVer implications
> Does this feature create any new ways in which library authors must take care to prevent breaking downstreams when making minor-version releases? Describe these. Are these new hazards "major" or "minor" according to [RFC 1105](https://rust-lang.github.io/rfcs/1105-api-evolution.html)?
No.
### Exposing other features
> Are there any other unstable features whose behavior may be exposed by this feature in any way? What features present the highest risk of that?
No.
## History
> List issues and PRs that are important for understanding how we got here.
- This change was asked for here https://github.com/rust-lang/rust/pull/137487#issuecomment-2770801974
## Acknowledgments
> Summarize contributors to the feature by name for recognition and so that those people are notified about the stabilization. Does anyone who worked on this *not* think it should be stabilized right now? We'd like to hear about that if so.
More or less solo developed by @Voultapher with some help from @petrochenkov.
## Open items
> List any known items that have not yet been completed and that should be before this is stabilized.
None.
Currently all core and std macros are automatically added to the prelude
via #[macro_use]. However a situation arose where we want to add a new macro
`assert_matches` but don't want to pull it into the standard prelude for
compatibility reasons. By explicitly exporting the macros found in the core and
std crates we get to decide on a per macro basis and can later add them via
the rust_20xx preludes.
std: Fix size returned by UEFI tcp4 read operations
The read and read_vectored methods were returning the length of the input buffer, rather than the number of bytes actually read. Fix by changing read_inner to return the correct value, and have both read and read_vectored return that.
The read and read_vectored methods were returning the length of the
input buffer, rather than the number of bytes actually read. Fix by
changing read_inner to return the correct value, and have both read and
read_vectored return that.
std: sys: fs: uefi: Implement copy
- Using the implementation from sys::fs::common since ther is no built-in copy implementation in UEFI.
- Tested with OVMF on QEMU.
@rustbot label +O-UEFI
std: sys: fs: uefi: Implement File::flush
- Also forward fsync and datasync to flush. UEFI does not have anything separate for metadata sync.
@rustbot label +O-UEFI
Fix the connect_error test on FreeBSD 15+
On FreeBSD 15, the error code returned in this situation changed. It's now ENETUNREACH. I think that error code is reasonable, and it's documented for connect(2), so we should expect that it might be returned.
- Using the implementation from sys::fs::common since ther is no
built-in copy implementation in UEFI.
- Tested with OVMF on QEMU.
Signed-off-by: Ayush Singh <ayush@beagleboard.org>
Remove std_detect_file_io and std_detect_dlsym_getauxval features
They were introduced back when std_detect was a standalone crate published to crates.io. The [motivation](https://github.com/rust-lang/stdarch/issues/655) for `std_detect_dlsym_getauxval` was to allow using `getauxval` without `dlopen` when statically linking musl, which we now unconditionally do for musl. And for `std_detect_file_io` to allow `no_std` usage, which std_detect now supports even with that feature enabled as it directly uses libc. This also prevents accidentally disabling runtime feature detection when using `cargo build -Zbuild-std -Zbuild-std-features=`
Implement create_dir_all() to operate iteratively instead of recursively
The current implementation of `create_dir_all(...)` in std::fs operates recursively. As mentioned in rust-lang/rust#124309, this could run into a stack overflow with big paths. To avoid this stack overflow issue, this PR implements the method in an iterative manner, preserving the documented behavior of:
```
Recursively create a directory and all of its parent components if they are missing.
This function is not atomic. If it returns an error, any parent components it was able to create will remain.
If the empty path is passed to this function, it always succeeds without creating any directories.
```
Fix std::fs::copy on WASI by setting proper OpenOptions flags
When PR rust-lang/rust#147572 switched WASI to use Unix-style filesystem APIs, the open_to_and_set_permissions function for WASI was implemented to call OpenOptions::new().open() without setting any access mode flags.
This causes std::fs::copy to fail with the error:
"must specify at least one of read, write, or append access"
The fix is to explicitly set .write(true), .create(true), and .truncate(true) on the OpenOptions, matching the behavior of the non-WASI Unix implementation but without the permission handling that WASI doesn't support.
Minimal reproduction:
```rs
fn main() {
std::fs::write("/src.txt", b"test").unwrap();
match std::fs::copy("/src.txt", "/dst.txt") {
Ok(_) => println!("PASS: fs::copy works!"),
Err(e) => println!("FAIL: {}", e),
}
}
```
# Compile and run:
rustc +nightly --target wasm32-wasip2 test.rs -o test.wasm
wasmtime -S cli --dir . test.wasm
# Before fix: FAIL: must specify at least one of read, write, or append access
# After fix: PASS: fs::copy works!
Note: The existing test library/std/src/fs/tests.rs::copy_file_ok would have caught this regression if the std test suite ran on WASI targets. Currently std tests don't compile for wasm32-wasip2 due to Unix-specific test code in library/std/src/sys/fd/unix/tests.rs.
Fixes the regression introduced in nightly-2025-12-10.
r? @alexcrichton
- Make flush a noop since it is only for buffered writers.
- Also forward fsync to datasync. UEFI does not have anything
separate for metadata sync.
Signed-off-by: Ayush Singh <ayush@beagleboard.org>
When PR #147572 switched WASI to use Unix-style filesystem APIs, the
open_to_and_set_permissions function for WASI was implemented to call
OpenOptions::new().open() without setting any access mode flags.
This causes std::fs::copy to fail with the error:
"must specify at least one of read, write, or append access"
The fix is to explicitly set .write(true), .create(true), and
.truncate(true) on the OpenOptions, matching the behavior of the
non-WASI Unix implementation but without the permission handling
that WASI doesn't support.
Minimal reproduction:
fn main() {
std::fs::write("/src.txt", b"test").unwrap();
match std::fs::copy("/src.txt", "/dst.txt") {
Ok(_) => println!("PASS: fs::copy works!"),
Err(e) => println!("FAIL: {}", e),
}
}
# Compile and run:
rustc +nightly --target wasm32-wasip2 test.rs -o test.wasm
wasmtime -S cli --dir . test.wasm
# Before fix: FAIL: must specify at least one of read, write, or append access
# After fix: PASS: fs::copy works!
Note: The existing test library/std/src/fs/tests.rs::copy_file_ok
would have caught this regression if the std test suite ran on WASI
targets. Currently std tests don't compile for wasm32-wasip2 due to
Unix-specific test code in library/std/src/sys/fd/unix/tests.rs.
Fixes the regression introduced in nightly-2025-12-10.
Finish transition from `semitransparent` to `semiopaque` for `rustc_macro_transparency`
Since it's a bit annoying to have different names for the same thing.
My understanding is that this is just internal stuff that is not part of any public API even tough rust-analyzer knows about it.
Continuation of
- https://github.com/rust-lang/rust/pull/139084.
Discovered while investigating
- https://github.com/rust-lang/rust/issues/150514
std: sys: fs: uefi: Implement remove_dir_all
- Using the implementation from sys::fs::common since UEFI does not have a built-in for this functionality.
@rustbot label +O-UEFI
