Rename some Rust 2021 lints to better names
Based on conversation in https://github.com/rust-lang/rust/issues/85894.
Rename a bunch of Rust 2021 related lints:
Lints that are officially renamed because they are already in beta or stable:
* `disjoint_capture_migration` => `rust_2021_incompatible_closure_captures`
* `or_patterns_back_compat` => `rust_2021_incompatible_or_patterns`
* `non_fmt_panic` => `non_fmt_panics`
Lints that are renamed but don't require any back -compat work since they aren't yet in stable:
* `future_prelude_collision` => `rust_2021_prelude_collisions`
* `reserved_prefix` => `rust_2021_token_prefixes`
Lints that have been discussed but that I did not rename:
* ~`non_fmt_panic` and `bare_trait_object`: is making this plural worth the headache we might cause users?~
* `array_into_iter`: I'm unsure of a good name and whether bothering users with a name change is worth it.
r? `@nikomatsakis`
Add Integer::log variants
_This is another attempt at landing https://github.com/rust-lang/rust/pull/70835, which was approved by the libs team but failed on Android tests through Bors. The text copied here is from the original issue. The only change made so far is the addition of non-`checked_` variants of the log methods._
_Tracking issue: #70887_
---
This implements `{log,log2,log10}` methods for all integer types. The implementation was provided by `@substack` for use in the stdlib.
_Note: I'm not big on math, so this PR is a best effort written with limited knowledge. It's likely I'll be getting things wrong, but happy to learn and correct. Please bare with me._
## Motivation
Calculating the logarithm of a number is a generally useful operation. Currently the stdlib only provides implementations for floats, which means that if we want to calculate the logarithm for an integer we have to cast it to a float and then back to an int.
> would be nice if there was an integer log2 instead of having to either use the f32 version or leading_zeros() which i have to verify the results of every time to be sure
_— [`@substack,` 2020-03-08](https://twitter.com/substack/status/1236445105197727744)_
At higher numbers converting from an integer to a float we also risk overflows. This means that Rust currently only provides log operations for a limited set of integers.
The process of doing log operations by converting between floats and integers is also prone to rounding errors. In the following example we're trying to calculate `base10` for an integer. We might try and calculate the `base2` for the values, and attempt [a base swap](https://www.rapidtables.com/math/algebra/Logarithm.html#log-rules) to arrive at `base10`. However because we're performing intermediate rounding we arrive at the wrong result:
```rust
// log10(900) = ~2.95 = 2
dbg!(900f32.log10() as u64);
// log base change rule: logb(x) = logc(x) / logc(b)
// log2(900) / log2(10) = 9/3 = 3
dbg!((900f32.log2() as u64) / (10f32.log2() as u64));
```
_[playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=6bd6c68b3539e400f9ca4fdc6fc2eed0)_
This is somewhat nuanced as a lot of the time it'll work well, but in real world code this could lead to some hard to track bugs. By providing correct log implementations directly on integers we can help prevent errors around this.
## Implementation notes
I checked whether LLVM intrinsics existed before implementing this, and none exist yet. ~~Also I couldn't really find a better way to write the `ilog` function. One option would be to make it a private method on the number, but I didn't see any precedent for that. I also didn't know where to best place the tests, so I added them to the bottom of the file. Even though they might seem like quite a lot they take no time to execute.~~
## References
- [Log rules](https://www.rapidtables.com/math/algebra/Logarithm.html#log-rules)
- [Rounding error playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=6bd6c68b3539e400f9ca4fdc6fc2eed0)
- [substack's tweet asking about integer log2 in the stdlib](https://twitter.com/substack/status/1236445105197727744)
- [Integer Logarithm, A. Jaffer 2008](https://people.csail.mit.edu/jaffer/III/ilog.pdf)
Remove some doc aliases
As per the new doc alias policy in https://github.com/rust-lang/std-dev-guide/pull/25, this removes some controversial doc aliases:
- `malloc`, `alloc`, `realloc`, etc.
- `length` (alias for `len`)
- `delete` (alias for `remove` in collections and also file/directory deletion)
r? `@joshtriplett`
aborts: Clarify documentation and comments
In the docs for intrinsics::abort():
* Strengthen the recommendation by to use process::abort instead.
* Document the fact that it sometimes (ab)uses an LLVM debug trap and what the likely consequences are.
* State that the precise behaviour is unstable.
In the docs for process::abort():
* Promise that we have the same behaviour as C `abort()`.
* Document the likely consequences, including, specifically, the consequences on Unix.
In the internal comment for unix::abort_internal:
* Refer to the public docs for the public API functions.
* Correct and expand the description of libc::abort. Specifically:
* Do not claim that abort() unregisters signal handlers. It doesn't; it honours the SIGABRT handler.
* Discuss, extensively, the issue with abort() flushing stdio buffers.
* Describe the glibc behaviour in some detail.
Co-authored-by: Mark Wooding <mdw@distorted.org.uk>
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
Fixes#40230
And withdraw the allegation of "abuse".
Adapted from a suggestion by @m-ou-se.
Co-authored-by: Mara Bos <m-ou.se@m-ou.se>
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
In the docs for intrinsics::abort():
* Strengthen the recommendation by to use process::abort instead.
* Document the fact that it (ab)uses an LLVM debug trap and what the
likely consequences are.
* State that the precise behaviour is unstable.
In the docs for process::abort():
* Promise that we have the same behaviour as C `abort()`.
* Document the likely consequences, including, specifically, the
consequences on Unix.
In the internal comment for unix::abort_internal:
* Refer to the public docs for the public API functions.
* Correct and expand the description of libc::abort. Specifically:
* Do not claim that abort() unregisters signal handlers. It doesn't;
it honours the SIGABRT handler.
* Discuss, extensively, the issue with abort() flushing stdio buffers.
* Describe the glibc behaviour in some detail.
Co-authored-by: Mark Wooding <mdw@distorted.org.uk>
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
Add examples to the various methods of `core::task::Poll`
This improves the documentation of the various methods of [`core::task::Poll`](https://doc.rust-lang.org/std/task/enum.Poll.html). These currently have fairly simple docs with no examples. This PR changes these methods to be closer to `core::option::Option` and adds usage examples (and importantly: tests!) to `Poll`'s methods.
cc/ `@rust-lang/wg-async-foundations`
## Screenshots
<details>
<summary>View generated rustdoc page</summary>
<image src="https://user-images.githubusercontent.com/2467194/123286616-59ee9b00-d50e-11eb-9e02-40269070f904.png" alt="Poll in core::task"></details>
core: add unstable no_fp_fmt_parse to disable float formatting code
In some projects (e.g. kernel), floating point is forbidden. They can disable
hardware floating point support and use `+soft-float` to avoid fp instructions
from being generated, but as libcore contains the formatting code for `f32`
and `f64`, some fp intrinsics are depended. One could define stubs for these
intrinsics that just panic [1], but it means that if any formatting functions
are accidentally used, mistake can only be caught during the runtime rather
than during compile-time or link-time, and they consume a lot of space without
LTO.
This patch provides an unstable cfg `no_fp_fmt_parse` to disable these.
A panicking stub is still provided for the `Debug` implementation (unfortunately)
because there are some SIMD types that use `#[derive(Debug)]`.
[1]: https://lkml.org/lkml/2021/4/14/1028
Stabilize `str::from_utf8_unchecked` as `const`
This stabilizes `unsafe fn str::from_utf8_unchecked` as `const` pending FCP on #75196. By the time FCP finishes, the beta will have already been cut, so I've set 1.55 as the stable-since version.
(should also be +relnotes but I don't have the permission to do that)
r? `@m-ou-se`
Closes#75196
In some projects (e.g. kernel), floating point is forbidden. They can disable
hardware floating point support and use `+soft-float` to avoid fp instructions
from being generated, but as libcore contains the formatting code for `f32`
and `f64`, some fp intrinsics are depended. One could define stubs for these
intrinsics that just panic [1], but it means that if any formatting functions
are accidentally used, mistake can only be caught during the runtime rather
than during compile-time or link-time, and they consume a lot of space without
LTO.
This patch provides an unstable cfg `no_fp_fmt_parse` to disable these.
A panicking stub is still provided for the `Debug` implementation (unfortunately)
because there are some SIMD types that use `#[derive(Debug)]`.
[1]: https://lkml.org/lkml/2021/4/14/1028
Use HTTPS links where possible
While looking at #86583, I wondered how many other (insecure) HTTP links were in `rustc`. This changes most other `http` links to `https`. While most of the links are in comments or documentation, there are a few other HTTP links that are used by CI that are changed to HTTPS.
Notes:
- I didn't change any to or in licences
- Some links don't support HTTPS :(
- Some `http` links were dead, in those cases I upgraded them to their new places (all of which used HTTPS)
Use `#[non_exhaustive]` where appropriate
Due to the std/alloc split, it is not possible to make `alloc::collections::TryReserveError::AllocError` non-exhaustive without having an unstable, doc-hidden method to construct (which negates the benefits from `#[non_exhaustive]`).
`@rustbot` label +C-cleanup +T-libs +S-waiting-on-review
Due to the std/alloc split, it is not possible to make
`alloc::collections::TryReserveError::AllocError` non-exhaustive without
having an unstable, doc-hidden method to construct (which negates the
benefits from `#[non_exhaustive]`.
Document associativity of iterator folds.
Document the associativity of `Iterator::fold` and
`DoubleEndedIterator::rfold` and add examples demonstrating this.
Add links to direct users to the fold of the opposite associativity.
Better errors for Debug and Display traits
Currently, if someone tries to pass value that does not implement `Debug` or `Display` to a formatting macro, they get a very verbose and confusing error message. This PR changes the error messages for missing `Debug` and `Display` impls to be less overwhelming in this case, as suggested by #85844. I was a little less aggressive in changing the error message than that issue proposed. Still, this implementation would be enough to reduce the number of messages to be much more manageable.
After this PR, information on the cause of an error involving a `Debug` or `Display` implementation would suppressed if the requirement originated within a standard library macro. My reasoning was that errors originating from within a macro are confusing when they mention details that the programmer can't see, and this is particularly problematic for `Debug` and `Display`, which are most often used via macros. It is possible that either a broader or a narrower criterion would be better. I'm quite open to any feedback.
Fixes#85844.
Add comments around code where ordering is important due for panic-safety
Iterators contain arbitrary code which may panic. Unsafe code has to be
careful to do its state updates at the right point between calls that may panic.
As requested in https://github.com/rust-lang/rust/pull/86452#discussion_r655153948
r? `@RalfJung`
Iterators contain arbitrary code which may panic. Unsafe code has to be
careful to do its state updates at the right point between calls
that may panic.
