Improve uninit/zeroed lint
* Also warn when creating a raw pointer with a NULL vtable.
* Also identify `MaybeUninit::uninit().assume_init()` and `MaybeUninit::zeroed().assume_init()` as dangerous.
gate rustc_on_unimplemented under rustc_attrs
Move `rustc_on_implemented` from the `on_implemented` gate to `rustc_attrs` as it is internal.
Closes#29628
r? @varkor
caller_location: point to macro invocation sites, like file!/line!, and use in core::panic!.
The main change here is to `core::panic!`, trying to fix this remaining regression: https://github.com/rust-lang/rust/pull/65927#issuecomment-547625147
However, in order for `caller_location` to be usable from macros the same way `file!()`/`line!()` are, it needs to have the same behavior (of extracting the macro invocation site `Span` and using that).
Arguably we would've had to do this at some point anyway, if we want to use `#[track_caller]` to replace the `file!()`/`line!()` uses from macros, but I'm not sure the RFC mentions this at all.
r? @petrochenkov cc @anp @nnethercote
Improve MaybeUninit::get_{ref,mut} documentation
As mentioned in https://github.com/rust-lang/rust/issues/63568#issuecomment-544106668, `MaybeUninit`'s `get_{ref,mut}` documentation is lacking, so this PR attempts to fix that.
That being said, and as @RalfJung mentions in that thread,
> In particular, we should clarify that all the UB rules for these methods equally apply when calling the raw ptr methods and creating a reference manually.
these other docs also need to be improved, which I can do in this PR ~~(hence the `[WIP]`)~~.
Finally, since all these documentations are related to clearly establishing when dealing with uninitialized memory which patterns are known to be sound and which patterns are currently UB (that is, until, if ever, the rules around references to unintialized integers get relaxed, this documentation will treat them as UB, and advise against such patterns (_e.g._, it is not possible to use uninitialized buffers with the `Read` API)), I think that adding even more examples to the main documentation of `MaybeUninit` inherent definition wouldn't hurt either.
___
- [Rendered](http://dreamy-ritchie-99d637.netlify.com/core/mem/union.maybeuninit#method.get_ref)
doc(str): show example of chars().count() under len()
the docs are great at explaining that .len() isn't like in other
languages but stops short of explaining how to get the character length.
Improved std::iter::Chain documentation
Replaces `strings two iterators` by `links two iterators` in `std::iter::Chain` documentation.
I didn't find any meaning of `strings` which can be evaluated as `links` or `joins`.
I don't think that `std::iter:Chain` works as a stringer or plays billiards. (https://www.lexico.com/en/definition/string).
the docs are great at explaining that .len() isn't like in other
languages but stops short of explaining how to get the character length.
r? @steveklabnik
doc: introduce `once` in `iter::chain` document
I find it hard to find which one to use with `chain` when I only need to
chain one value. Also [`once`][1] talks about `chain`.
[1]: https://doc.rust-lang.org/nightly/std/iter/fn.once.html
Stabilize `Option::flatten`
- PR: https://github.com/rust-lang/rust/pull/60256
- Tracking issue: https://github.com/rust-lang/rust/issues/60258
@elahn
> I was trying to `flat_map()` and found `map().flatten()` does the trick. This has been on nightly for 4 months, can we stabilise it?
@ethanboxx
> @Centril Helped me get this merged. What is the stabilization process?
@Centril
> @ethanboxx I'd just file a PR to stabilize it and we'll ask T-libs to FCP.
So here I am.
I am was unsure what number to put in `since = "-"` so I copied what someone had done in a recent PR.
This allows us to remove `static_panic_msg` from the SSA<->LLVM
boundary, along with its fat pointer representation for &str.
Also changes the signature of PanicInfo::internal_contructor to
avoid copying.
Closes#65856.
trait-based structural match implementation
Moves from using a `#[structural_match]` attribute to using a marker trait (or pair of such traits, really) instead.
Fix#63438.
(This however does not remove the hacks that I believe were put into place to support the previous approach of injecting the attribute based on the presence of both derives... I have left that for follow-on work.)
(Or more precisely, a pair of such traits: one for `derive(PartialEq)` and one
for `derive(Eq)`.)
((The addition of the second marker trait, `StructuralEq`, is largely a hack to
work-around `fn (&T)` not implementing `PartialEq` and `Eq`; see also issue
rust-lang/rust#46989; otherwise I would just check if `Eq` is implemented.))
Note: this does not use trait fulfillment error-reporting machinery; it just
uses the trait system to determine if the ADT was tagged or not. (Nonetheless, I
have kept an `on_unimplemented` message on the new trait for structural_match
check, even though it is currently not used.)
Note also: this does *not* resolve the ICE from rust-lang/rust#65466, as noted
in a comment added in this commit. Further work is necessary to resolve that and
other problems with the structural match checking, especially to do so without
breaking stable code (adapted from test fn-ptr-is-structurally-matchable.rs):
```rust
fn r_sm_to(_: &SM) {}
fn main() {
const CFN6: Wrap<fn(&SM)> = Wrap(r_sm_to);
let input: Wrap<fn(&SM)> = Wrap(r_sm_to);
match Wrap(input) {
Wrap(CFN6) => {}
Wrap(_) => {}
};
}
```
where we would hit a problem with the strategy of unconditionally checking for
`PartialEq` because the type `for <'a> fn(&'a SM)` does not currently even
*implement* `PartialEq`.
----
added review feedback:
* use an or-pattern
* eschew `return` when tail position will do.
* don't need fresh_expansion; just add `structural_match` to appropriate `allow_internal_unstable` attributes.
also fixed example in doc comment so that it actually compiles.
The iterator is implemented using const generics. It implements the
traits `Iterator`, `DoubleEndedIterator`, `ExactSizeIterator`,
`FusedIterator` and `TrustedLen`. It also contains a public method
`new` to create it from an array.
`IntoIterator` was not implemented for arrays yet, as there are still
some open questions regarding backwards compatibility. This commit
only adds the iterator impl and does not yet offer a convenient way
to obtain that iterator.
Add the `matches!( $expr, $pat ) -> bool` macro
# Motivation
This macro is:
* General-purpose (not domain-specific)
* Simple (the implementation is short)
* Very popular [on crates.io](https://crates.io/crates/matches) (currently 37th in all-time downloads)
* The two previous points combined make it number one in [left-pad index](https://twitter.com/bascule/status/1184523027888988160) score
As such, I feel it is a good candidate for inclusion in the standard library.
In fact I already felt that way five years ago: https://github.com/rust-lang/rust/pull/14685 (Although the proof of popularity was not as strong at the time.)
# API
<details>
<del>
Back then, the main concern was that this macro may not be quite universally-enough useful to belong in the prelude.
Therefore, this PR adds the macro such that using it requires one of:
```rust
use core::macros::matches;
use std::macros::matches;
```
</del>
</details>
Like arms of a `match` expression, the macro supports multiple patterns separated by `|` and optionally followed by `if` and a guard expression:
```rust
let foo = 'f';
assert!(matches!(foo, 'A'..='Z' | 'a'..='z'));
let bar = Some(4);
assert!(matches!(bar, Some(x) if x > 2));
```
<details>
<del>
# Implementation constraints
A combination of reasons make it tricky for a standard library macro not to be in the prelude.
Currently, all public `macro_rules` macros in the standard library macros end up “in the prelude” of every crate not through `use std::prelude::v1::*;` like for other kinds of items, but through `#[macro_use]` on `extern crate std;`. (Both are injected by `src/libsyntax_ext/standard_library_imports.rs`.)
`#[macro_use]` seems to import every macro that is available at the top-level of a crate, even if through a `pub use` re-export.
Therefore, for `matches!` not to be in the prelude, we need it to be inside of a module rather than at the root of `core` or `std`.
However, the only way to make a `macro_rules` macro public outside of the crate where it is defined appears to be `#[macro_export]`. This exports the macro at the root of the crate regardless of which module defines it. See [macro scoping](https://doc.rust-lang.org/reference/macros-by-example.html#scoping-exporting-and-importing) in the reference.
Therefore, the macro needs to be defined in a crate that is not `core` or `std`.
# Implementation
This PR adds a new `matches_macro` crate as a private implementation detail of the standard library. This crate is `#![no_core]` so that libcore can depend on it. It contains a `macro_rules` definition with `#[macro_export]`.
libcore and libstd each have a new public `macros` module that contains a `pub use` re-export of the macro. Both the module and the macro are unstable, for now.
The existing private `macros` modules are renamed `prelude_macros`, though their respective source remains in `macros.rs` files.
</del>
</details>
