Shorten even more panic temporary lifetimes
Followup to #104134. As pointed out by `@bjorn3` in https://github.com/rust-lang/rust/pull/104134#pullrequestreview-1425585948, there are other cases in the panic macros which would also benefit from dropping their non-Send temporaries as soon as possible, avoiding pointlessly holding them across an await point.
For the tests added in this PR, here are the failures you get today on master without the macro changes in this PR:
<details>
<summary>tests/ui/macros/panic-temporaries-2018.rs</summary>
```console
error: future cannot be sent between threads safely
--> tests/ui/macros/panic-temporaries-2018.rs:52:18
|
LL | require_send(panic_display());
| ^^^^^^^^^^^^^^^ future returned by `panic_display` is not `Send`
|
= help: within `impl Future<Output = ()>`, the trait `Send` is not implemented for `*const u8`
note: future is not `Send` as this value is used across an await
--> tests/ui/macros/panic-temporaries-2018.rs:35:31
|
LL | f(panic!("{}", NOT_SEND)).await;
| -------- ^^^^^- `NOT_SEND` is later dropped here
| | |
| | await occurs here, with `NOT_SEND` maybe used later
| has type `NotSend` which is not `Send`
note: required by a bound in `require_send`
--> tests/ui/macros/panic-temporaries-2018.rs:48:25
|
LL | fn require_send(_: impl Send) {}
| ^^^^ required by this bound in `require_send`
error: future cannot be sent between threads safely
--> tests/ui/macros/panic-temporaries-2018.rs:52:18
|
LL | require_send(panic_display());
| ^^^^^^^^^^^^^^^ future returned by `panic_display` is not `Send`
|
= help: within `NotSend`, the trait `Sync` is not implemented for `*const u8`
note: future is not `Send` as this value is used across an await
--> tests/ui/macros/panic-temporaries-2018.rs:35:31
|
LL | f(panic!("{}", NOT_SEND)).await;
| ---------------------- ^^^^^- the value is later dropped here
| | |
| | await occurs here, with the value maybe used later
| has type `&NotSend` which is not `Send`
note: required by a bound in `require_send`
--> tests/ui/macros/panic-temporaries-2018.rs:48:25
|
LL | fn require_send(_: impl Send) {}
| ^^^^ required by this bound in `require_send`
error: future cannot be sent between threads safely
--> tests/ui/macros/panic-temporaries-2018.rs:53:18
|
LL | require_send(panic_str());
| ^^^^^^^^^^^ future returned by `panic_str` is not `Send`
|
= help: within `impl Future<Output = ()>`, the trait `Send` is not implemented for `*const u8`
note: future is not `Send` as this value is used across an await
--> tests/ui/macros/panic-temporaries-2018.rs:40:36
|
LL | f(panic!((NOT_SEND, "...").1)).await;
| -------- ^^^^^- `NOT_SEND` is later dropped here
| | |
| | await occurs here, with `NOT_SEND` maybe used later
| has type `NotSend` which is not `Send`
note: required by a bound in `require_send`
--> tests/ui/macros/panic-temporaries-2018.rs:48:25
|
LL | fn require_send(_: impl Send) {}
| ^^^^ required by this bound in `require_send`
error: future cannot be sent between threads safely
--> tests/ui/macros/panic-temporaries-2018.rs:54:18
|
LL | require_send(unreachable_display());
| ^^^^^^^^^^^^^^^^^^^^^ future returned by `unreachable_display` is not `Send`
|
= help: within `impl Future<Output = ()>`, the trait `Send` is not implemented for `*const u8`
note: future is not `Send` as this value is used across an await
--> tests/ui/macros/panic-temporaries-2018.rs:45:31
|
LL | f(unreachable!(NOT_SEND)).await;
| -------- ^^^^^- `NOT_SEND` is later dropped here
| | |
| | await occurs here, with `NOT_SEND` maybe used later
| has type `NotSend` which is not `Send`
note: required by a bound in `require_send`
--> tests/ui/macros/panic-temporaries-2018.rs:48:25
|
LL | fn require_send(_: impl Send) {}
| ^^^^ required by this bound in `require_send`
error: future cannot be sent between threads safely
--> tests/ui/macros/panic-temporaries-2018.rs:54:18
|
LL | require_send(unreachable_display());
| ^^^^^^^^^^^^^^^^^^^^^ future returned by `unreachable_display` is not `Send`
|
= help: within `NotSend`, the trait `Sync` is not implemented for `*const u8`
note: future is not `Send` as this value is used across an await
--> tests/ui/macros/panic-temporaries-2018.rs:45:31
|
LL | f(unreachable!(NOT_SEND)).await;
| ---------------------- ^^^^^- the value is later dropped here
| | |
| | await occurs here, with the value maybe used later
| has type `&NotSend` which is not `Send`
note: required by a bound in `require_send`
--> tests/ui/macros/panic-temporaries-2018.rs:48:25
|
LL | fn require_send(_: impl Send) {}
| ^^^^ required by this bound in `require_send`
error: aborting due to 5 previous errors
```
</details>
<details>
<summary>tests/ui/macros/panic-temporaries.rs</summary>
```console
error: future cannot be sent between threads safely
--> tests/ui/macros/panic-temporaries.rs:42:18
|
LL | require_send(panic_display());
| ^^^^^^^^^^^^^^^ future returned by `panic_display` is not `Send`
|
= help: within `impl Future<Output = ()>`, the trait `Send` is not implemented for `*const u8`
note: future is not `Send` as this value is used across an await
--> tests/ui/macros/panic-temporaries.rs:35:31
|
LL | f(panic!("{}", NOT_SEND)).await;
| -------- ^^^^^- `NOT_SEND` is later dropped here
| | |
| | await occurs here, with `NOT_SEND` maybe used later
| has type `NotSend` which is not `Send`
note: required by a bound in `require_send`
--> tests/ui/macros/panic-temporaries.rs:38:25
|
LL | fn require_send(_: impl Send) {}
| ^^^^ required by this bound in `require_send`
error: future cannot be sent between threads safely
--> tests/ui/macros/panic-temporaries.rs:42:18
|
LL | require_send(panic_display());
| ^^^^^^^^^^^^^^^ future returned by `panic_display` is not `Send`
|
= help: within `NotSend`, the trait `Sync` is not implemented for `*const u8`
note: future is not `Send` as this value is used across an await
--> tests/ui/macros/panic-temporaries.rs:35:31
|
LL | f(panic!("{}", NOT_SEND)).await;
| ---------------------- ^^^^^- the value is later dropped here
| | |
| | await occurs here, with the value maybe used later
| has type `&NotSend` which is not `Send`
note: required by a bound in `require_send`
--> tests/ui/macros/panic-temporaries.rs:38:25
|
LL | fn require_send(_: impl Send) {}
| ^^^^ required by this bound in `require_send`
error: aborting due to 2 previous errors
```
</details>
r? bjorn3
* ensuring that offset_of!(Self, ...) works iff inside an impl block
* ensuring that the output type is usize and doesn't coerce. this can be
changed in the future, but if it is done, it should be a conscious descision
* improving the privacy checking test
* ensuring that generics don't let you escape the unsized check
Add a conversion from `&mut T` to `&mut UnsafeCell<T>`
Provides a safe way of downgrading an exclusive reference into an alias-able `&UnsafeCell<T>` reference.
ACP: https://github.com/rust-lang/libs-team/issues/198.
The recent LLVM 16 update changes code-gen to be not branchless anymore, in the
slice::sort implementation merge function. This improves performance by 30% for
random patterns, restoring the performance to the state with LLVM 15.
Fix some misleading and copy-pasted `Pattern` examples
These examples were listed twice and also were confusable with doing a substring match instead of a any-of-set match.
Update doc for `PhantomData` to match code example
After https://github.com/rust-lang/rust/pull/106621, there is no longer a `T: 'a` annotation in the doc example, so update the text to match the code.
Stabilize const slice::split_at
This stabilizes the use of the following method in const context:
```rust
impl<T> [T] {
pub const fn split_at(&self, mid: usize) -> (&[T], &[T]);
}
```
cc tracking issue #101158
Add midpoint function for all integers and floating numbers
This pull-request adds the `midpoint` function to `{u,i}{8,16,32,64,128,size}`, `NonZeroU{8,16,32,64,size}` and `f{32,64}`.
This new function is analog to the [C++ midpoint](https://en.cppreference.com/w/cpp/numeric/midpoint) function, and basically compute `(a + b) / 2` with a rounding towards ~~`a`~~ negative infinity in the case of integers. Or simply said: `midpoint(a, b)` is `(a + b) >> 1` as if it were performed in a sufficiently-large signed integral type.
Note that unlike the C++ function this pull-request does not implement this function on pointers (`*const T` or `*mut T`). This could be implemented in a future pull-request if desire.
### Implementation
For `f32` and `f64` the implementation in based on the `libcxx` [one](18ab892ff7/libcxx/include/__numeric/midpoint.h (L65-L77)). I originally tried many different approach but all of them failed or lead me with a poor version of the `libcxx`. Note that `libstdc++` has a very similar one; Microsoft STL implementation is also basically the same as `libcxx`. It unfortunately doesn't seems like a better way exist.
For unsigned integers I created the macro `midpoint_impl!`, this macro has two branches:
- The first one take `$SelfT` and is used when there is no unsigned integer with at least the double of bits. The code simply use this formula `a + (b - a) / 2` with the arguments in the correct order and signs to have the good rounding.
- The second branch is used when a `$WideT` (at least double of bits as `$SelfT`) is provided, using a wider number means that no overflow can occur, this greatly improve the codegen (no branch and less instructions).
For signed integers the code basically forwards the signed numbers to the unsigned version of midpoint by mapping the signed numbers to their unsigned numbers (`ex: i8 [-128; 127] to [0; 255]`) and vice versa.
I originally created a version that worked directly on the signed numbers but the code was "ugly" and not understandable. Despite this mapping "overhead" the codegen is better than my most optimized version on signed integers.
~~Note that in the case of unsigned numbers I tried to be smart and used `#[cfg(target_pointer_width = "64")]` to determine if using the wide version was better or not by looking at the assembly on godbolt. This was applied to `u32`, `u64` and `usize` and doesn't change the behavior only the assembly code generated.~~
This means that `EscapeIterInner::as_str` no longer needs unsafe code, because the type system ensures the internal buffer is only ASCII, and thus valid UTF-8.
PhantomData: fix documentation wrt interaction with dropck
As far as I could find out, the `PhantomData`-dropck interaction *only* affects code using `may_dangle`. The documentation in the standard library has not been updated for 8 years and thus stems from a time when Rust still used "parametric dropck", before [RFC 1238](https://rust-lang.github.io/rfcs/1238-nonparametric-dropck.html). Back then what the docs said was correct, but with `may_dangle` dropck it stopped being entirely accurate and these days, with NLL, it is actively misleading.
Fixes https://github.com/rust-lang/rust/issues/102810
Fixes https://github.com/rust-lang/rust/issues/70841
Cc `@nikomatsakis` I hope what I am saying here is right.^^
Uplift `clippy::{drop,forget}_{ref,copy}` lints
This PR aims at uplifting the `clippy::drop_ref`, `clippy::drop_copy`, `clippy::forget_ref` and `clippy::forget_copy` lints.
Those lints are/were declared in the correctness category of clippy because they lint on useless and most probably is not what the developer wanted.
## `drop_ref` and `forget_ref`
The `drop_ref` and `forget_ref` lint checks for calls to `std::mem::drop` or `std::mem::forget` with a reference instead of an owned value.
### Example
```rust
let mut lock_guard = mutex.lock();
std::mem::drop(&lock_guard) // Should have been drop(lock_guard), mutex
// still locked
operation_that_requires_mutex_to_be_unlocked();
```
### Explanation
Calling `drop` or `forget` on a reference will only drop the reference itself, which is a no-op. It will not call the `drop` or `forget` method on the underlying referenced value, which is likely what was intended.
## `drop_copy` and `forget_copy`
The `drop_copy` and `forget_copy` lint checks for calls to `std::mem::forget` or `std::mem::drop` with a value that derives the Copy trait.
### Example
```rust
let x: i32 = 42; // i32 implements Copy
std::mem::forget(x) // A copy of x is passed to the function, leaving the
// original unaffected
```
### Explanation
Calling `std::mem::forget` [does nothing for types that implement Copy](https://doc.rust-lang.org/std/mem/fn.drop.html) since the value will be copied and moved into the function on invocation.
-----
Followed the instructions for uplift a clippy describe here: https://github.com/rust-lang/rust/pull/99696#pullrequestreview-1134072751
cc `@m-ou-se` (as T-libs-api leader because the uplifting was discussed in a recent meeting)
Simplify the implementation of iterators over slices of ZSTs
Currently, slice iterators over ZSTs store `end = start.wrapping_byte_add(len)`.
That's slightly convenient for `is_empty`, but kinda annoying for pretty much everything else -- see bugs like #42789, for example.
This PR instead changes it to just `end = ptr::invalid(len)` instead.
That's easier to think about (IMHO, at least) as well as easier to represent.
`next` is still to big to get inlined into the mir-opt/pre-codegen/ tests, but if I bump the inline threshold to force it to show the whole thing, this implementation is also less MIR:
```
> git diff --numstat
241 370 tests/mir-opt/pre-codegen/slice_iter.forward_loop.PreCodegen.after.mir
255 329 tests/mir-opt/pre-codegen/slice_iter.reverse_loop.PreCodegen.after.mir
184 216 tests/mir-opt/pre-codegen/slice_iter.slice_iter_mut_next_back.PreCodegen.after.mir
182 254 tests/mir-opt/pre-codegen/slice_iter.slice_iter_next.PreCodegen.after.mir
```
(That's ≈70 lines less for `Iter::next`, for example.)
r? `@ghost`
~~Built atop #111282, so draft until that lands.~~
Currently, slice iterators over ZSTs store `end = start.wrapping_byte_add(len)`.
That's slightly convenient for `is_empty`, but kinda annoying for pretty much everything else -- see bugs like 42789, for example.
This PR instead changes it to just `end = ptr::invalid(len)` instead.
That's easier to think about (IMHO, at least) as well as easier to represent.
Fix incorrect implication of transmuting slices
transmute<&[u8]> would be useful and as a beginner it is confusing to see documents casually confuse the types of &[u8] and [u8; SZ]
Remove some `assume`s from slice iterators that don't do anything
Because the start pointer is iterators is already a `NonNull`, we emit the appropriate `!nonnull` metadata when loading the pointer to tell LLVM that it's non-null.
Probably the best way to see that it's the metadata that's important (and not the `assume`) is to observe that LLVM actually *removes* the `assume` from the optimized IR: <https://rust.godbolt.org/z/KhE6G963n>.
(I also checked that, yes, the if-not-ZST `assume` on `end` is still doing something: it's how there's a `!nonnull` metadata on its load, even though it's an ordinary raw pointer. The codegen test added in this PR fails if the other `assume` is removed.)
Revert "Populate effective visibilities in `rustc_privacy`"
This reverts commit cff85f22f5, cc #110907. It needs to be fixed, but there are too many issues being reported that I wanted to put up a revert until a proper fix can be committed.
Fixes a ton of issues where private but still reachable impls were missing during codegen:
Fixes#111320Fixes#111321Fixes#111334Fixes#111357Fixes#111368Fixes#111373Fixes#111377Fixes#111386Fixes#111387
`@bors` p=1
r? `@petrochenkov`
