use `#[align]` attribute for `fn_align`
Tracking issue: https://github.com/rust-lang/rust/issues/82232https://github.com/rust-lang/rfcs/pull/3806 decides to add the `#[align]` attribute for alignment of various items. Right now it's used for functions with `fn_align`, in the future it will get more uses (statics, struct fields, etc.)
(the RFC finishes FCP today)
r? `@ghost`
Sized Hierarchy: Part I
This patch implements the non-const parts of rust-lang/rfcs#3729. It introduces two new traits to the standard library, `MetaSized` and `PointeeSized`. See the RFC for the rationale behind these traits and to discuss whether this change makes sense in the abstract.
These traits are unstable (as is their constness), so users cannot refer to them without opting-in to `feature(sized_hierarchy)`. These traits are not behind `cfg`s as this would make implementation unfeasible, there would simply be too many `cfg`s required to add the necessary bounds everywhere. So, like `Sized`, these traits are automatically implemented by the compiler.
RFC 3729 describes changes which are necessary to preserve backwards compatibility given the introduction of these traits, which are implemented and as follows:
- `?Sized` is rewritten as `MetaSized`
- `MetaSized` is added as a default supertrait for all traits w/out an explicit sizedness supertrait already.
There are no edition migrations implemented in this, as these are primarily required for the constness parts of the RFC and prior to stabilisation of this (and so will come in follow-up PRs alongside the const parts). All diagnostic output should remain the same (showing `?Sized` even if the compiler sees `MetaSized`) unless the `sized_hierarchy` feature is enabled.
Due to the use of unstable extern types in the standard library and rustc, some bounds in both projects have had to be relaxed already - this is unfortunate but unavoidable so that these extern types can continue to be used where they were before. Performing these relaxations in the standard library and rustc are desirable longer-term anyway, but some bounds are not as relaxed as they ideally would be due to the inability to relax `Deref::Target` (this will be investigated separately).
It is hoped that this is implemented such that it could be merged and these traits could exist "under the hood" without that being observable to the user (other than in any performance impact this has on the compiler, etc). Some details might leak through due to the standard library relaxations, but this has not been observed in test output.
**Notes:**
- Any commits starting with "upstream:" can be ignored, as these correspond to other upstream PRs that this is based on which have yet to be merged.
- This best reviewed commit-by-commit. I've attempted to make the implementation easy to follow and keep similar changes and test output updates together.
- Each commit has a short description describing its purpose.
- This patch is large but it's primarily in the test suite.
- I've worked on the performance of this patch and a few optimisations are implemented so that the performance impact is neutral-to-minor.
- `PointeeSized` is a different name from the RFC just to make it more obvious that it is different from `std::ptr::Pointee` but all the names are yet to be bikeshed anyway.
- `@nikomatsakis` has confirmed [that this can proceed as an experiment from the t-lang side](https://rust-lang.zulipchat.com/#narrow/channel/435869-project-goals/topic/SVE.20and.20SME.20on.20AArch64.20.28goals.23270.29/near/506196491)
- FCP in https://github.com/rust-lang/rust/pull/137944#issuecomment-2912207485Fixesrust-lang/rust#79409.
r? `@ghost` (I'll discuss this with relevant teams to find a reviewer)
Introduce the `MetaSized` and `PointeeSized` traits as supertraits of
`Sized` and initially implement it on everything that currently
implements `Sized` to isolate any changes that simply adding the
traits introduces.
Unimplement unsized_locals
Implements https://github.com/rust-lang/compiler-team/issues/630
Tracking issue here: https://github.com/rust-lang/rust/issues/111942
Note that this just removes the feature, not the implementation, and does not touch `unsized_fn_params`. This is because it is required to support `Box<dyn FnOnce()>: FnOnce()`.
There may be more that should be removed (possibly in follow up prs)
- the `forget_unsized` function and `forget` intrinsic.
- the `unsized_locals` test directory; I've just fixed up the tests for now
- various codegen support for unsized values and allocas
cc ``@JakobDegen`` ``@oli-obk`` ``@Noratrieb`` ``@programmerjake`` ``@bjorn3``
``@rustbot`` label F-unsized_locals
Fixesrust-lang/rust#79409
refactor `AttributeGate` and `rustc_attr!` to emit notes during feature checking
First commit changes the following:
- `AttributeGate ` from an enum with (four) tuple fields to (five) named fields
- adds a `notes` fields that is emitted as notes in the `PostExpansionVisitor` pass
- removes the `this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date` note if the feature gate is `rustc_attrs`.
- various phrasing changes and touchups
- and finally, the reason why I went down this path to begin with: tell people they can use the diagnostic namespace when they hit the rustc_on_unimplemented feature gate 🙈
Second commit removes unused machinery for deprecated attributes
Note the version and PR of removed features when using it
Fixesrust-lang/rust#141619
I added the diagnostic information. Since all the current version information is present, it prints the version information anyway, as shown in tests/ui. And PR will not print if it is None, we can gradually add the PR links.
Split into two commits for easier review.
r? compiler
cc ``@jyn514`` Since you're on vocation in the review list, I can't r? you.
Stabilize keylocker
This PR stabilizes the feature flag `keylocker_x86` (tracking issue rust-lang/rust#134813).
# Public API
The 2 `x86` target features `kl` and `widekl`, and the associated intrinsics in stdarch.
These target features are very specialized, and are only used to signal the presence of the corresponding CPU instruction. They don't have any nontrivial interaction with the ABI (contrary to something like AVX), and serve the only purpose of enabling 11 stdarch intrinsics, all of which have been implemented and propagated to rustc via a stdarch submodule update.
Also, these were added way back in LLVM12, and as the minimum LLVM required for rustc is LLVM19, we are safe in that front too!
# Associated PRs
- rust-lang/rust#134814
- rust-lang/stdarch#1706
- rust-lang/rust#136831 (stdarch submodule update)
- rust-lang/stdarch#1795 (stabilizing the runtime detection and intrinsics)
- rust-lang/rust#141964 (stdarch submodule update for the stabilization of the runtime detection and intrinsics)
As all of the required tasks have been done (adding the target features to rustc, implementing their runtime detection in std_detect and implementing the associated intrinsics in core_arch), these target features can be stabilized now.
cc ````@rust-lang/lang````
cc ````@rust-lang/libs-api```` for the intrinsics and runtime detection
I don't think anyone else worked on this feature, so no one else to ping, maybe cc ````@Amanieu.```` I will send the reference pr soon.
Stabilize `sha512`, `sm3` and `sm4` for x86
This PR stabilizes the feature flag `sha512_sm_x86` (tracking issue rust-lang/rust#126624).
# Public API
The 3 `x86` target features `sha512`, `sm3` and `sm4`, and the associated intrinsics in stdarch.
These target features are very specialized, and are only used to signal the presence of the corresponding CPU instruction. They don't have any nontrivial interaction with the ABI (contrary to something like AVX), and serve the only purpose of enabling 10 stdarch intrinsics, all of which have been implemented and propagated to rustc via a stdarch submodule update.
Also, these were added in LLVM17, and as the minimum LLVM required for rustc is LLVM19, we are safe in that front too!
# Associated PRs
- rust-lang/rust#126704
- rust-lang/stdarch#1592
- rust-lang/stdarch#1790
- rust-lang/rust#140389 (stdarch submodule update)
- rust-lang/stdarch#1796 (stabilizing the runtime detection and intrinsics)
- rust-lang/rust#141964 (stdarch submodule update for the stabilization of the runtime detection and intrinsics)
As all of the required tasks have been done (adding the target features to rustc, implementing their runtime detection in std_detect and implementing the associated intrinsics in core_arch), these target features can be stabilized now.
cc `@rust-lang/lang`
cc `@rust-lang/libs-api` for the intrinsics and runtime detection
I don't think anyone else worked on this feature, so no one else to ping, maybe cc `@Amanieu.` I will send the reference pr soon.
In PR 90877 T-lang decided not to remove `intrinsics::pref_align_of`.
However, the intrinsic and its supporting code
1. is a nightly feature, so can be removed at compiler/libs discretion
2. requires considerable effort in the compiler to support, as it
necessarily complicates every single site reasoning about alignment
3. has been justified based on relevance to codegen, but it is only a
requirement for C++ (not C, not Rust) stack frame layout for AIX,
in ways Rust would not consider even with increased C++ interop
4. is only used by rustc to overalign some globals, not correctness
5. can be adequately replaced by other rules for globals, as it mostly
affects alignments for a few types under 16 bytes of alignment
6. has only one clear benefactor: automating C -> Rust translation
for GNU extensions like `__alignof`
7. such code was likely intended to be `alignof` or `_Alignof`,
because the GNU extension is a "false friend" of the C keyword,
which makes the choice to support such a mapping very questionable
8. makes it easy to do incorrect codegen in the compiler by its mere
presence as usual Rust rules of alignment (e.g. `size == align * N`)
do not hold with preferred alignment
The implementation is clearly damaging the code quality of the compiler.
Thus it is within the compiler team's purview to simply rip it out.
If T-lang wishes to have this intrinsic restored for c2rust's benefit,
it would have to use a radically different implementation that somehow
does not cause internal incorrectness.
Until then, remove the intrinsic and its supporting code, as one tool
and an ill-considered GCC extension cannot justify risking correctness.
Because we touch a fair amount of the compiler to change this at all,
and unfortunately the duplication of AbiAndPrefAlign is deep-rooted,
we keep an "AbiAlign" type which we can wean code off later.
Add the AVX10 target features
Parent #138843
Adds the `avx10_target_feature` feature gate, and `avx10.1` and `avx10.2` target features.
It is confirmed that Intel is dropping AVX10/256 (see [this comment](https://github.com/rust-lang/rust/issues/111137#issuecomment-2795442288)), so this should be safe to implement now.
The LLVM fix for llvm/llvm-project#135394 was merged, and has been backported to LLVM20, and the patch has also been propagated to rustc in #140502
`@rustbot` label O-x86_64 O-x86_32 A-target-feature A-SIMD
Implement the internal feature `cfg_target_has_reliable_f16_f128`
Support for `f16` and `f128` is varied across targets, backends, and backend versions. Eventually we would like to reach a point where all backends support these approximately equally, but until then we have to work around some of these nuances of support being observable.
Introduce the `cfg_target_has_reliable_f16_f128` internal feature, which provides the following new configuration gates:
* `cfg(target_has_reliable_f16)`
* `cfg(target_has_reliable_f16_math)`
* `cfg(target_has_reliable_f128)`
* `cfg(target_has_reliable_f128_math)`
`reliable_f16` and `reliable_f128` indicate that basic arithmetic for the type works correctly. The `_math` versions indicate that anything relying on `libm` works correctly, since sometimes this hits a separate class of codegen bugs.
These options match configuration set by the build script at [1]. The logic for LLVM support is duplicated as-is from the same script. There are a few possible updates that will come as a follow up.
The config introduced here is not planned to ever become stable, it is only intended to replace the build scripts for `std` tests and `compiler-builtins` that don't have any way to configure based on the codegen backend.
MCP: https://github.com/rust-lang/compiler-team/issues/866
Closes: https://github.com/rust-lang/compiler-team/issues/866
[1]: 555e1d0386/library/std/build.rs (L84-L186)
---
The second commit makes use of this config to replace `cfg_{f16,f128}{,_math}` in `library/`. I omitted providing a `cfg(bootstrap)` configuration to keep things simpler since the next beta branch is in two weeks.
try-job: aarch64-gnu
try-job: i686-msvc-1
try-job: test-various
try-job: x86_64-gnu
try-job: x86_64-msvc-ext2
Async drop codegen
Async drop implementation using templated coroutine for async drop glue generation.
Scopes changes to generate `async_drop_in_place()` awaits, when async droppable objects are out-of-scope in async context.
Implementation details:
https://github.com/azhogin/posts/blob/main/async-drop-impl.md
New fields in Drop terminator (drop & async_fut). Processing in codegen/miri must validate that those fields are empty (in full version async Drop terminator will be expanded at StateTransform pass or reverted to sync version). Changes in terminator visiting to consider possible new successor (drop field).
ResumedAfterDrop messages for panic when coroutine is resumed after it is started to be async drop'ed.
Lang item for generated coroutine for async function async_drop_in_place. `async fn async_drop_in_place<T>()::{{closure0}}`.
Scopes processing for generate async drop preparations. Async drop is a hidden Yield, so potentially async drops require the same dropline preparation as for Yield terminators.
Processing in StateTransform: async drops are expanded into yield-point. Generation of async drop of coroutine itself added.
Shims for AsyncDropGlueCtorShim, AsyncDropGlue and FutureDropPoll.
```rust
#[lang = "async_drop"]
pub trait AsyncDrop {
#[allow(async_fn_in_trait)]
async fn drop(self: Pin<&mut Self>);
}
impl Drop for Foo {
fn drop(&mut self) {
println!("Foo::drop({})", self.my_resource_handle);
}
}
impl AsyncDrop for Foo {
async fn drop(self: Pin<&mut Self>) {
println!("Foo::async drop({})", self.my_resource_handle);
}
}
```
First async drop glue implementation re-worked to use the same drop elaboration code as for sync drop.
`async_drop_in_place` changed to be `async fn`. So both `async_drop_in_place` ctor and produced coroutine have their lang items (`AsyncDropInPlace`/`AsyncDropInPlacePoll`) and shim instances (`AsyncDropGlueCtorShim`/`AsyncDropGlue`).
```
pub async unsafe fn async_drop_in_place<T: ?Sized>(_to_drop: *mut T) {
}
```
AsyncDropGlue shim generation uses `elaborate_drops::elaborate_drop` to produce drop ladder (in the similar way as for sync drop glue) and then `coroutine::StateTransform` to convert function into coroutine poll.
AsyncDropGlue coroutine's layout can't be calculated for generic T, it requires known final dropee type to be generated (in StateTransform). So, `templated coroutine` was introduced here (`templated_coroutine_layout(...)` etc).
Such approach overrides the first implementation using mixing language-level futures in https://github.com/rust-lang/rust/pull/121801.
Implement a lint for implicit autoref of raw pointer dereference - take 2
*[t-lang nomination comment](https://github.com/rust-lang/rust/pull/123239#issuecomment-2727551097)*
This PR aims at implementing a lint for implicit autoref of raw pointer dereference, it is based on #103735 with suggestion and improvements from https://github.com/rust-lang/rust/pull/103735#issuecomment-1370420305.
The goal is to catch cases like this, where the user probably doesn't realise it just created a reference.
```rust
pub struct Test {
data: [u8],
}
pub fn test_len(t: *const Test) -> usize {
unsafe { (*t).data.len() } // this calls <[T]>::len(&self)
}
```
Since #103735 already went 2 times through T-lang, where they T-lang ended-up asking for a more restricted version (which is what this PR does), I would prefer this PR to be reviewed first before re-nominating it for T-lang.
----
Compared to the PR it is as based on, this PR adds 3 restrictions on the outer most expression, which must either be:
1. A deref followed by any non-deref place projection (that intermediate deref will typically be auto-inserted)
2. A method call annotated with `#[rustc_no_implicit_refs]`.
3. A deref followed by a `addr_of!` or `addr_of_mut!`. See bottom of post for details.
There are several points that are not 100% clear to me when implementing the modifications:
- ~~"4. Any number of automatically inserted deref/derefmut calls." I as never able to trigger this. Am I missing something?~~ Fixed
- Are "index" and "field" enough?
----
cc `@JakobDegen` `@WaffleLapkin`
r? `@RalfJung`
try-job: dist-various-1
try-job: dist-various-2
Support for `f16` and `f128` is varied across targets, backends, and
backend versions. Eventually we would like to reach a point where all
backends support these approximately equally, but until then we have to
work around some of these nuances of support being observable.
Introduce the `cfg_target_has_reliable_f16_f128` internal feature, which
provides the following new configuration gates:
* `cfg(target_has_reliable_f16)`
* `cfg(target_has_reliable_f16_math)`
* `cfg(target_has_reliable_f128)`
* `cfg(target_has_reliable_f128_math)`
`reliable_f16` and `reliable_f128` indicate that basic arithmetic for
the type works correctly. The `_math` versions indicate that anything
relying on `libm` works correctly, since sometimes this hits a separate
class of codegen bugs.
These options match configuration set by the build script at [1]. The
logic for LLVM support is duplicated as-is from the same script. There
are a few possible updates that will come as a follow up.
The config introduced here is not planned to ever become stable, it is
only intended to replace the build scripts for `std` tests and
`compiler-builtins` that don't have any way to configure based on the
codegen backend.
MCP: https://github.com/rust-lang/compiler-team/issues/866
Closes: https://github.com/rust-lang/compiler-team/issues/866
[1]: 555e1d0386/library/std/build.rs (L84-L186)
Stabilize `naked_functions`
tracking issue: https://github.com/rust-lang/rust/issues/90957
request for stabilization on tracking issue: https://github.com/rust-lang/rust/issues/90957#issuecomment-2539270352
reference PR: https://github.com/rust-lang/reference/pull/1689
# Request for Stabilization
Two years later, we're ready to try this again. Even though this issue is already marked as having passed FCP, given the amount of time that has passed and the changes in implementation strategy, we should follow the process again.
## Summary
The `naked_functions` feature has two main parts: the `#[naked]` function attribute, and the `naked_asm!` macro.
An example of a naked function:
```rust
const THREE: usize = 3;
#[naked]
pub extern "sysv64" fn add_n(number: usize) -> usize {
// SAFETY: the validity of the used registers
// is guaranteed according to the "sysv64" ABI
unsafe {
core::arch::naked_asm!(
"add rdi, {}",
"mov rax, rdi",
"ret",
const THREE,
)
}
}
```
When the `#[naked]` attribute is applied to a function, the compiler won't emit a [function prologue](https://en.wikipedia.org/wiki/Function_prologue_and_epilogue) or epilogue when generating code for this function. This attribute is analogous to [`__attribute__((naked))`](https://developer.arm.com/documentation/100067/0608/Compiler-specific-Function--Variable--and-Type-Attributes/--attribute----naked---function-attribute) in C. The use of this feature allows the programmer to have precise control over the assembly that is generated for a given function.
The body of a naked function must consist of a single `naked_asm!` invocation, a heavily restricted variant of the `asm!` macro: the only legal operands are `const` and `sym`, and the only legal options are `raw` and `att_syntax`. In lieu of specifying operands, the `naked_asm!` within a naked function relies on the function's calling convention to determine the validity of registers.
## Documentation
The Rust Reference: https://github.com/rust-lang/reference/pull/1689
(Previous PR: https://github.com/rust-lang/reference/pull/1153)
## Tests
* [tests/run-make/naked-symbol-visiblity](https://github.com/rust-lang/rust/tree/master/tests/codegen/naked-fn) verifies that `pub`, `#[no_mangle]` and `#[linkage = "..."]` work correctly for naked functions
* [tests/codegen/naked-fn](https://github.com/rust-lang/rust/tree/master/tests/codegen/naked-fn) has tests for function alignment, use of generics, and validates the exact assembly output on linux, macos, windows and thumb
* [tests/ui/asm/naked-*](https://github.com/rust-lang/rust/tree/master/tests/ui/asm) tests for incompatible attributes, generating errors around incorrect use of `naked_asm!`, etc
## Interaction with other (unstable) features
### [fn_align](https://github.com/rust-lang/rust/issues/82232)
Combining `#[naked]` with `#[repr(align(N))]` works well, and is tested e.g. here
- https://github.com/rust-lang/rust/blob/master/tests/codegen/naked-fn/aligned.rs
- https://github.com/rust-lang/rust/blob/master/tests/codegen/naked-fn/min-function-alignment.rs
It's tested extensively because we do need to explicitly support the `repr(align)` attribute (and make sure we e.g. don't mistake powers of two for number of bytes).
## History
This feature was originally proposed in [RFC 1201](https://github.com/rust-lang/rfcs/pull/1201), filed on 2015-07-10 and accepted on 2016-03-21. Support for this feature was added in [#32410](https://github.com/rust-lang/rust/pull/32410), landing on 2016-03-23. Development languished for several years as it was realized that the semantics given in RFC 1201 were insufficiently specific. To address this, a minimal subset of naked functions was specified by [RFC 2972](https://github.com/rust-lang/rfcs/pull/2972), filed on 2020-08-07 and accepted on 2021-11-16. Prior to the acceptance of RFC 2972, all of the stricter behavior specified by RFC 2972 was implemented as a series of warn-by-default lints that would trigger on existing uses of the `naked` attribute; these lints became hard errors in [#93153](https://github.com/rust-lang/rust/pull/93153) on 2022-01-22. As a result, today RFC 2972 has completely superseded RFC 1201 in describing the semantics of the `naked` attribute.
More recently, the `naked_asm!` macro was added to replace the earlier use of a heavily restricted `asm!` invocation. The `naked_asm!` name is clearer in error messages, and provides a place for documenting the specific requirements of inline assembly in naked functions.
The implementation strategy was changed to emitting a global assembly block. In effect, an extern function
```rust
extern "C" fn foo() {
core::arch::naked_asm!("ret")
}
```
is emitted as something similar to
```rust
core::arch::global_asm!(
"foo:",
"ret"
);
extern "C" {
fn foo();
}
```
The codegen approach was chosen over the llvm naked function attribute because:
- the rust compiler can guarantee the behavior (no sneaky additional instructions, no inlining, etc.)
- behavior is the same on all backends (llvm, cranelift, gcc, etc)
Finally, there is now an allow list of compatible attributes on naked functions, so that e.g. `#[inline]` is rejected with an error. The `#[target_feature]` attribute on naked functions was later made separately unstable, because implementing it is complex and we did not want to block naked functions themselves on how target features work on them. See also https://github.com/rust-lang/rust/issues/138568.
relevant PRs for these recent changes
- https://github.com/rust-lang/rust/pull/127853
- https://github.com/rust-lang/rust/pull/128651
- https://github.com/rust-lang/rust/pull/128004
- https://github.com/rust-lang/rust/pull/138570
-
### Various historical notes
#### `noreturn`
[RFC 2972](https://github.com/rust-lang/rfcs/blob/master/text/2972-constrained-naked.md) mentions that naked functions
> must have a body which contains only a single asm!() statement which:
> iii. must contain the noreturn option.
Instead of `asm!`, the current implementation mandates that the body contain a single `naked_asm!` statement. The `naked_asm!` macro is a heavily restricted version of the `asm!` macro, making it easier to talk about and document the rules of assembly in naked functions and give dedicated error messages.
For `naked_asm!`, the behavior of the `asm!`'s `noreturn` option is implicit. The `noreturn` option means that it is UB for control flow to fall through the end of the assembly block. With `asm!`, this option is usually used for blocks that diverge (and thus have no return and can be typed as `!`). With `naked_asm!`, the intent is different: usually naked funtions do return, but they must do so from within the assembly block. The `noreturn` option was used so that the compiler would not itself also insert a `ret` instruction at the very end.
#### padding / `ud2`
A `naked_asm!` block that violates the safety assumption that control flow must not fall through the end of the assembly block is UB. Because no return instruction is emitted, whatever bytes follow the naked function will be executed, resulting in truly undefined behavior. There has been discussion whether rustc should emit an invalid instruction (e.g. `ud2` on x86) after the `naked_asm!` block to at least fail early in the case of an invalid `naked_asm!`. It was however decided that it is more useful to guarantee that `#[naked]` functions NEVER contain any instructions besides those in the `naked_asm!` block.
# unresolved questions
None
r? ``@Amanieu``
I've validated the tests on x86_64 and aarch64
Rollup of 9 pull requests
Successful merges:
- #135340 (Add `explicit_extern_abis` Feature and Enforce Explicit ABIs)
- #139440 (rustc_target: RISC-V: feature addition batch 2)
- #139667 (cfi: Remove #[no_sanitize(cfi)] for extern weak functions)
- #139828 (Don't require rigid alias's trait to hold)
- #139854 (Improve parse errors for stray lifetimes in type position)
- #139889 (Clean UI tests 3 of n)
- #139894 (Fix `opt-dist` CLI flag and make it work without LLD)
- #139900 (stepping into impls for normalization is unproductive)
- #139915 (replace some #[rustc_intrinsic] usage with use of the libcore declarations)
r? `@ghost`
`@rustbot` modify labels: rollup
Stabilize `cfg_boolean_literals`
Closes#131204
`@rustbot` labels +T-lang +I-lang-nominated
This will end up conflicting with the test in #138293 so whichever doesn't land first will need updating
--
# Stabilization Report
## General design
### What is the RFC for this feature and what changes have occurred to the user-facing design since the RFC was finalized?
[RFC 3695](https://github.com/rust-lang/rfcs/pull/3695), none.
### What behavior are we committing to that has been controversial? Summarize the major arguments pro/con.
None
### Are there extensions to this feature that remain unstable? How do we know that we are not accidentally committing to those?
None
## Has a call-for-testing period been conducted? If so, what feedback was received?
Yes; only positive feedback was received.
## Implementation quality
### Summarize the major parts of the implementation and provide links into the code (or to PRs)
Implemented in [#131034](https://github.com/rust-lang/rust/pull/131034).
### Summarize existing test coverage of this feature
- [Basic usage, including `#[cfg()]`, `cfg!()` and `#[cfg_attr()]`](6d71251cf9/tests/ui/cfg/true-false.rs)
- [`--cfg=true/false` on the command line being accessible via `r#true/r#false`](6d71251cf9/tests/ui/cfg/raw-true-false.rs)
- [Interaction with the unstable `#[doc(cfg(..))]` feature](https://github.com/rust-lang/rust/tree/6d71251/tests/rustdoc-ui/cfg-boolean-literal.rs)
- [Denying `--check-cfg=cfg(true/false)`](https://github.com/rust-lang/rust/tree/6d71251/tests/ui/check-cfg/invalid-arguments.rs)
- Ensuring `--cfg false` on the command line doesn't change the meaning of `cfg(false)`: `tests/ui/cfg/cmdline-false.rs`
- Ensuring both `cfg(true)` and `cfg(false)` on the same item result in it being disabled: `tests/ui/cfg/both-true-false.rs`
### What outstanding bugs in the issue tracker involve this feature? Are they stabilization-blocking?
The above mentioned issue; it should not block as it interacts with another unstable feature.
### What FIXMEs are still in the code for that feature and why is it ok to leave them there?
None
### Summarize contributors to the feature by name for recognition and assuredness that people involved in the feature agree with stabilization
- `@clubby789` (RFC)
- `@Urgau` (Implementation in rustc)
### Which tools need to be adjusted to support this feature. Has this work been done?
`rustdoc`'s unstable`#[doc(cfg(..)]` has been updated to respect it. `cargo` has been updated with a forward compatibility lint to enable supporting it in cargo once stabilized.
## Type system and execution rules
### What updates are needed to the reference/specification? (link to PRs when they exist)
A few lines to be added to the reference for configuration predicates, specified in the RFC.
