core: add Duration constructors
Add more `Duration` constructors.
Tracking issue: #120301.
These match similar convenience constructors available on both `chrono::Duration` and `time::Duration`.
What's the best ordering for these with respect to the existing constructors?
Suggest less bug-prone construction of Duration in docs
std::time::Duration has a well-known quirk: Duration::as_nanos() returns u128 [1], but Duration::from_nanos() takes u64 [2]. So these methods cannot easily roundtrip [3]. It is not possible to simply accept u128 in from_nanos [4], because it requires breaking other API [5].
It seems to me that callers have basically only two options:
1. `Duration::from_nanos(d.as_nanos() as u64)`, which is the "obvious" and buggy approach.
2. `Duration::new(d.as_secs(), d.subsecs_nanos())`, which only becomes apparent after reading and digesting the entire Duration struct documentation.
I suggest that the documentation of `from_nanos` is changed to make option 2 more easily discoverable.
There are two major usecases for this:
- "Weird math" operations that should not be supported directly by `Duration`, like squaring.
- "Disconnected roundtrips", where the u128 value is passed through various other stack frames, and perhaps reconstructed into a Duration on a different machine.
In both cases, it seems like a good idea to not tempt people into thinking "Eh, u64 is good enough, what could possibly go wrong!". That's why I want to add a note that points out the similarly-easy and *safe* way to reconstruct a Duration.
[1] https://doc.rust-lang.org/stable/std/time/struct.Duration.html#method.as_nanos
[2] https://doc.rust-lang.org/stable/std/time/struct.Duration.html#method.from_nanos
[3] https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=fa6bab2b6b72f20c14b5243610ea1dde
[4] https://github.com/rust-lang/rust/issues/103332
[5] https://github.com/rust-lang/rust/issues/51107#issuecomment-392353166
This PR will fix some typos detected by [typos].
I only picked the ones I was sure were spelling errors to fix, mostly in
the comments.
[typos]: https://github.com/crate-ci/typos
This updates the standard library's documentation to use the new syntax. The
documentation is worthwhile to update as it should be more idiomatic
(particularly for features like this, which are nice for users to get acquainted
with). The general codebase is likely more hassle than benefit to update: it'll
hurt git blame, and generally updates can be done by folks updating the code if
(and when) that makes things more readable with the new format.
A few places in the compiler and library code are updated (mostly just due to
already having been done when this commit was first authored).
Methods that were only blocked on `const_panic` have been stabilized.
The remaining methods of `duration_consts_2` are all related to floats,
and as such have been placed behind the `duration_consts_float` feature
gate.
