Don't allow flattened format_args in const.
Fixes https://github.com/rust-lang/rust/issues/139136
Fixes https://github.com/rust-lang/rust/issues/139621
We allow `format_args!("a")` in const, but don't allow any format_args with arguments in const, such as `format_args!("{}", arg)`.
However, we accidentally allow `format_args!("hello {}", "world")` in const, as it gets flattened to `format_args!("hello world")`.
This also applies to panic in const.
This wasn't supposed to happen. I added protection against this in the format args flattening code, ~~but I accidentally marked a function as const that shouldn't have been const~~ but this was removed in https://github.com/rust-lang/rust/pull/135139.
This is a breaking change. The crater found no breakage, however.
This breaks things like:
```rust
const _: () = if false { panic!("a {}", "a") };
```
and
```rust
const F: std::fmt::Arguments<'static> = format_args!("a {}", "a");
```
Tweak output of const panic diagnostic
### Shorten span of panic failures in const context
Previously, we included a redundant prefix on the panic message and a postfix of the location of the panic. The prefix didn't carry any additional information beyond "something failed", and the location of the panic is redundant with the diagnostic's span, which gets printed out even if its code is not shown.
```
error[E0080]: evaluation of constant value failed
--> $DIR/assert-type-intrinsics.rs:11:9
|
LL | MaybeUninit::<!>::uninit().assume_init();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ panic: aborted execution: attempted to instantiate uninhabited type `!`
```
```
error[E0080]: evaluation of `Fail::<i32>::C` failed
--> $DIR/collect-in-dead-closure.rs:9:19
|
LL | const C: () = panic!();
| ^^^^^^^^ explicit panic
|
= note: this error originates in the macro `$crate::panic::panic_2015` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
```
```
error[E0080]: evaluation of constant value failed
--> $DIR/uninhabited.rs:87:9
|
LL | assert!(false);
| ^^^^^^^^^^^^^^ assertion failed: false
|
= note: this error originates in the macro `assert` (in Nightly builds, run with -Z macro-backtrace for more info)
```
### Remove duplicated span from const eval frame list
When the primary span for a const error is the same as the first frame in the const error report, skip it.
```
error[E0080]: evaluation of constant value failed
--> $DIR/issue-88434-removal-index-should-be-less.rs:3:24
|
LL | const _CONST: &[u8] = &f(&[], |_| {});
| ^^^^^^^^^^^^^^ explicit panic
|
note: inside `f::<{closure@$DIR/issue-88434-removal-index-should-be-less.rs:3:31: 3:34}>`
--> $DIR/issue-88434-removal-index-should-be-less.rs:10:5
|
LL | panic!()
| ^^^^^^^^ the failure occurred here
= note: this error originates in the macro `$crate::panic::panic_2015` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
```
instead of
```
error[E0080]: evaluation of constant value failed
--> $DIR/issue-88434-removal-index-should-be-less.rs:10:5
|
LL | panic!()
| ^^^^^^^^ explicit panic
|
note: inside `f::<{closure@$DIR/issue-88434-removal-index-should-be-less.rs:3:31: 3:34}>`
--> $DIR/issue-88434-removal-index-should-be-less.rs:10:5
|
LL | panic!()
| ^^^^^^^^
note: inside `_CONST`
--> $DIR/issue-88434-removal-index-should-be-less.rs:3:24
|
LL | const _CONST: &[u8] = &f(&[], |_| {});
| ^^^^^^^^^^^^^^
= note: this error originates in the macro `$crate::panic::panic_2015` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
note: erroneous constant encountered
--> $DIR/issue-88434-removal-index-should-be-less.rs:3:23
|
LL | const _CONST: &[u8] = &f(&[], |_| {});
| ^^^^^^^^^^^^^^^
```
r? ``@oli-obk``
Previously, we included a redundant prefix on the panic message and a postfix of the location of the panic. The prefix didn't carry any additional information beyond "something failed", and the location of the panic is redundant with the diagnostic's span, which gets printed out even if its code is not shown.
```
error[E0080]: evaluation of constant value failed
--> $DIR/assert-type-intrinsics.rs:11:9
|
LL | MaybeUninit::<!>::uninit().assume_init();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation panicked: aborted execution: attempted to instantiate uninhabited type `!`
```
```
error[E0080]: evaluation of `Fail::<i32>::C` failed
--> $DIR/collect-in-dead-closure.rs:9:19
|
LL | const C: () = panic!();
| ^^^^^^^^ evaluation panicked: explicit panic
|
= note: this error originates in the macro
`$crate::panic::panic_2015` which comes from the expansion of the macro
`panic` (in Nightly builds, run with -Z macro-backtrace for more info)
```
```
error[E0080]: evaluation of constant value failed
--> $DIR/uninhabited.rs:41:9
|
LL | assert!(false);
| ^^^^^^^^^^^^^^ evaluation panicked: assertion failed: false
|
= note: this error originates in the macro `assert` (in Nightly builds, run with -Z macro-backtrace for more info)
```
---
When the primary span for a const error is the same as the first frame in the const error report, skip it.
```
error[E0080]: evaluation of constant value failed
--> $DIR/issue-88434-removal-index-should-be-less.rs:3:24
|
LL | const _CONST: &[u8] = &f(&[], |_| {});
| ^^^^^^^^^^^^^^ evaluation panicked: explicit panic
|
note: inside `f::<{closure@$DIR/issue-88434-removal-index-should-be-less.rs:3:31: 3:34}>`
--> $DIR/issue-88434-removal-index-should-be-less.rs:10:5
|
LL | panic!()
| ^^^^^^^^ the failure occurred here
= note: this error originates in the macro `$crate::panic::panic_2015` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
```
instead of
```
error[E0080]: evaluation of constant value failed
--> $DIR/issue-88434-removal-index-should-be-less.rs:10:5
|
LL | panic!()
| ^^^^^^^^ explicit panic
|
note: inside `f::<{closure@$DIR/issue-88434-removal-index-should-be-less.rs:3:31: 3:34}>`
--> $DIR/issue-88434-removal-index-should-be-less.rs:10:5
|
LL | panic!()
| ^^^^^^^^
note: inside `_CONST`
--> $DIR/issue-88434-removal-index-should-be-less.rs:3:24
|
LL | const _CONST: &[u8] = &f(&[], |_| {});
| ^^^^^^^^^^^^^^
= note: this error originates in the macro `$crate::panic::panic_2015` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
```
---
Revert order of constant evaluation errors
Point at the code the user wrote first and std functions last.
```
error[E0080]: evaluation of constant value failed
--> $DIR/const-errs-dont-conflict-103369.rs:5:25
|
LL | impl ConstGenericTrait<{my_fn(1)}> for () {}
| ^^^^^^^^ evaluation panicked: Some error occurred
|
note: called from `my_fn`
--> $DIR/const-errs-dont-conflict-103369.rs:10:5
|
LL | panic!("Some error occurred");
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= note: this error originates in the macro `$crate::panic::panic_2015` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
```
instead of
```
error[E0080]: evaluation of constant value failed
--> $DIR/const-errs-dont-conflict-103369.rs:10:5
|
LL | panic!("Some error occurred");
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Some error occurred
|
note: called from `<() as ConstGenericTrait<{my_fn(1)}>>::{constant#0}`
--> $DIR/const-errs-dont-conflict-103369.rs:5:25
|
LL | impl ConstGenericTrait<{my_fn(1)}> for () {}
| ^^^^^^^^
= note: this error originates in the macro `$crate::panic::panic_2015` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
```
Implement `int_from_ascii` (#134821)
Provides unstable `T::from_ascii()` and `T::from_ascii_radix()` for integer types `T`, as drafted in tracking issue #134821.
To deduplicate documentation without additional macros, implementations of `isize` and `usize` no longer delegate to equivalent integer types. After #132870 they are inlined anyway.
Provides unstable `T::from_ascii()` and `T::from_ascii_radix()` for integer
types `T`, as drafted in tracking issue #134821.
To deduplicate documentation without additional macros, implementations of
`isize` and `usize` no longer delegate to equivalent integer types.
After #132870 they are inlined anyway.
Consider comments and bare delimiters the same as an "empty line" for purposes of hiding rendered code output of long multispans. This results in more aggressive shortening of rendered output without losing too much context, specially in `*.stderr` tests that have "hidden" comments.
Centralize emitting an error in `const_to_pat` so that all errors from that evaluating a `const` in a pattern can add addditional information. With this, now point at the `const` item's definition:
```
error[E0158]: constant pattern depends on a generic parameter
--> $DIR/associated-const-type-parameter-pattern.rs:20:9
|
LL | pub trait Foo {
| -------------
LL | const X: EFoo;
| ------------- constant defined here
...
LL | A::X => println!("A::X"),
| ^^^^
```
Fundamentally, we have *three* disjoint categories of functions:
1. const-stable functions
2. private/unstable functions that are meant to be callable from const-stable functions
3. functions that can make use of unstable const features
This PR implements the following system:
- `#[rustc_const_stable]` puts functions in the first category. It may only be applied to `#[stable]` functions.
- `#[rustc_const_unstable]` by default puts functions in the third category. The new attribute `#[rustc_const_stable_indirect]` can be added to such a function to move it into the second category.
- `const fn` without a const stability marker are in the second category if they are still unstable. They automatically inherit the feature gate for regular calls, it can now also be used for const-calls.
Also, several holes in recursive const stability checking are being closed.
There's still one potential hole that is hard to avoid, which is when MIR
building automatically inserts calls to a particular function in stable
functions -- which happens in the panic machinery. Those need to *not* be
`rustc_const_unstable` (or manually get a `rustc_const_stable_indirect`) to be
sure they follow recursive const stability. But that's a fairly rare and special
case so IMO it's fine.
The net effect of this is that a `#[unstable]` or unmarked function can be
constified simply by marking it as `const fn`, and it will then be
const-callable from stable `const fn` and subject to recursive const stability
requirements. If it is publicly reachable (which implies it cannot be unmarked),
it will be const-unstable under the same feature gate. Only if the function ever
becomes `#[stable]` does it need a `#[rustc_const_unstable]` or
`#[rustc_const_stable]` marker to decide if this should also imply
const-stability.
Adding `#[rustc_const_unstable]` is only needed for (a) functions that need to
use unstable const lang features (including intrinsics), or (b) `#[stable]`
functions that are not yet intended to be const-stable. Adding
`#[rustc_const_stable]` is only needed for functions that are actually meant to
be directly callable from stable const code. `#[rustc_const_stable_indirect]` is
used to mark intrinsics as const-callable and for `#[rustc_const_unstable]`
functions that are actually called from other, exposed-on-stable `const fn`. No
other attributes are required.
Some float methods are now `const fn` under the `const_float_methods` feature gate.
In order to support `min`, `max`, `abs` and `copysign`, the implementation of some intrinsics had to be moved from Miri to rustc_const_eval.
Prevent Deduplication of `LongRunningWarn`
Fixes#118612
As mention in the issue, `LongRunningWarn` is meant to be repeated multiple times.
Therefore, this PR stores a unique number in every instance of `LongRunningWarn` so that it's not hashed into the same value and omitted by the deduplication mechanism.
stabilize `const_extern_fn`
closes https://github.com/rust-lang/rust/issues/64926
tracking issue: https://github.com/rust-lang/rust/issues/64926
reference PR: https://github.com/rust-lang/reference/pull/1596
## Stabilizaton Report
### Summary
Using `const extern "Rust"` and `const extern "C"` was already stabilized (since version 1.62.0, see https://github.com/rust-lang/rust/pull/95346). This PR stabilizes the other calling conventions: it is now possible to write `const unsafe extern "calling-convention" fn` and `const extern "calling-convention" fn` for any supported calling convention:
```rust
const extern "C-unwind" fn foo1(val: u8) -> u8 { val + 1}
const extern "stdcall" fn foo2(val: u8) -> u8 { val + 1}
const unsafe extern "C-unwind" fn bar1(val: bool) -> bool { !val }
const unsafe extern "stdcall" fn bar2(val: bool) -> bool { !val }
```
This can be used to const-ify an `extern fn`, or conversely, to make a `const fn` callable from external code.
r? T-lang
cc `@RalfJung`
const-eval interning: accept interior mutable pointers in final value
…but keep rejecting mutable references
This fixes https://github.com/rust-lang/rust/issues/121610 by no longer firing the lint when there is a pointer with interior mutability in the final value of the constant. On stable, such pointers can be created with code like:
```rust
pub enum JsValue {
Undefined,
Object(Cell<bool>),
}
impl Drop for JsValue {
fn drop(&mut self) {}
}
// This does *not* get promoted since `JsValue` has a destructor.
// However, the outer scope rule applies, still giving this 'static lifetime.
const UNDEFINED: &JsValue = &JsValue::Undefined;
```
It's not great to accept such values since people *might* think that it is legal to mutate them with unsafe code. (This is related to how "infectious" `UnsafeCell` is, which is a [wide open question](https://github.com/rust-lang/unsafe-code-guidelines/issues/236).) However, we [explicitly document](https://doc.rust-lang.org/reference/behavior-considered-undefined.html) that things created by `const` are immutable. Furthermore, we also accept the following even more questionable code without any lint today:
```rust
let x: &'static Option<Cell<i32>> = &None;
```
This is even more questionable since it does *not* involve a `const`, and yet still puts the data into immutable memory. We could view this as promotion [potentially introducing UB](https://github.com/rust-lang/unsafe-code-guidelines/issues/493). However, we've accepted this since ~forever and it's [too late to reject this now](https://github.com/rust-lang/rust/pull/122789); the pattern is just too useful.
So basically, if you think that `UnsafeCell` should be tracked fully precisely, then you should want the lint we currently emit to be removed, which this PR does. If you think `UnsafeCell` should "infect" surrounding `enum`s, the big problem is really https://github.com/rust-lang/unsafe-code-guidelines/issues/493 which does not trigger the lint -- the cases the lint triggers on are actually the "harmless" ones as there is an explicit surrounding `const` explaining why things end up being immutable.
What all this goes to show is that the hard error added in https://github.com/rust-lang/rust/pull/118324 (later turned into the future-compat lint that I am now suggesting we remove) was based on some wrong assumptions, at least insofar as it concerns shared references. Furthermore, that lint does not help at all for the most problematic case here where the potential UB is completely implicit. (In fact, the lint is actively in the way of [my preferred long-term strategy](https://github.com/rust-lang/unsafe-code-guidelines/issues/493#issuecomment-2028674105) for dealing with this UB.) So I think we should go back to square one and remove that error/lint for shared references. For mutable references, it does seem to work as intended, so we can keep it. Here it serves as a safety net in case the static checks that try to contain mutable references to the inside of a const initializer are not working as intended; I therefore made the check ICE to encourage users to tell us if that safety net is triggered.
Closes https://github.com/rust-lang/rust/issues/122153 by removing the lint.
Cc `@rust-lang/opsem` `@rust-lang/lang`
