The as_ref method already has a Null-unchecked version section, its
example is a modification of the example in the main as_ref section.
Similarly the example in this commit is a modification of the example
in main as_mut section.
Use matches macro in libcore and libstd
This PR replaces matches like
```rust
match var {
value => true,
_ => false,
}
```
with use of `matches!` macro.
r? @Centril
`Option::{expect,unwrap}` and `Result::{expect, expect_err, unwrap, unwrap_err}` have `#[track_caller]`
The annotated functions now produce panic messages pointing to the location where they were called, rather than `core`'s internals.
Remove wrong advice about spin locks from `spin_loop_hint` docs
Using a pure spin lock for a critical section in a preemptable thread
is always wrong, however short the critical section may be. The thread
might be preempted, which will cause all other threads to hammer
busily at the core for the whole quant. Moreover, if threads have
different priorities, this might lead to a priority inversion problem
and a deadlock. More generally, a spinlock is not more efficient than
a well-written mutex, which typically does several spin iterations at
the start anyway.
The advise about UP vs SMP is also irrelevant in the context of
preemptive threads.
See also accompanying piece: https://matklad.github.io/2020/01/02/spinlocs-considered-harmful.html
And another, independent piece: https://probablydance.com/2019/12/30/measuring-mutexes-spinlocks-and-how-bad-the-linux-scheduler-really-is
EDIT: obligatory disclosure that I am not an expert in these things, and might be terribly wrong :)
no longer promote non-pattern const functions
This is trying to pack-pedal a bit on promotion feature creep, as proposed by @eddyb [here](https://github.com/rust-lang/const-eval/issues/19#issuecomment-472799062): possibly, a sane subset of `const fn` that we could promote are those that are just constructors -- the same subset that we might want to allow in pattern position at some point.
So, this removes the `rustc_promotable` attribute from the three functions they identified that do not fit this pattern. The first step is to run crater to see if there is code in the wild that relies on this being promotable.
r? @oli-obk
Rollup of 10 pull requests
Successful merges:
- #67450 (Allow for setting a ThinLTO import limit during bootstrap)
- #67595 (Suggest adding a lifetime constraint for opaque type)
- #67636 (allow rustfmt key in [build] section)
- #67736 (Less-than is asymmetric, not antisymmetric)
- #67762 (Add missing links for insecure_time)
- #67783 (Warn for bindings named same as variants when matching against a borrow)
- #67796 (Ensure that we process projections during MIR inlining)
- #67807 (Use drop instead of the toilet closure `|_| ()`)
- #67816 (Clean up err codes)
- #67825 (Minor: change take() docs grammar to match other docs)
Failed merges:
r? @ghost
Using a pure spin lock for a critical section in a preemptable thread
is always wrong, however short the critical section may be. The thread
might be preempted, which will cause all other threads to hammer
busily at the core for the whole quant. Moreover, if threads have
different priorities, this might lead to a priority inversion problem
and a deadlock. More generally, a spinlock is not more efficient than
a well-written mutex, which typically does several spin iterations at
the start anyway.
The advise about UP vs SMP is also irrelevant in the context of
preemptive threads.
Clean up const-hack PRs now that const if / match exist.
Closes#67627.
Cleans up these merged PRs tagged with `const-hack`:
- #63810
- #63786
- #61635
- #58044
reverting their contents to have the match or if expressions they originally contained.
r? @oli-obk
There's one more PR in those tagged with `const-hack` that originally wasn't merged (#65107). Reading the thread, it looks like it was originally closed because the `const-hack` for the checked arithmetic non-negligibly hurt performance, and because there was no way to manipulate the returned Option at compile time anyway (with neither const if nor const match). Would you like me to add these changes to the changes from this PR here too, now that we have the necessary features?
docs: Iterator adapters have unspecified results after a panic
Fixes#58170.
That issue also has rough consensus from 3 members of the library team for this being the behavior we would like to specify.
Remove redundant link texts
Most of these links are followed by a parenthesized expression. I think that the redundant link texts were added to prevent interpretation as an inline link. This is unnecessary since the closing square bracket and opening parenthesis are separated by whitespace.
Use NonNull in slice::Iter and slice::IterMut.
`ptr` of `slice::Iter` and `slice::IterMut` can never be null, but this
fact wasn't exploited for layout optimizations. By changing `ptr` from
`*<mutability> T` to `NonNull<T>`, the compiler can now optimize layout
of `Option<Iter<'a, T>>`.
Closes#67228
