This commit removes the reexports of `old_io` traits as well as `old_path` types
and traits from the prelude. This functionality is now all deprecated and needs
to be removed to make way for other functionality like `Seek` in the `std::io`
module (currently reexported as `NewSeek` in the io prelude).
Closes#23377Closes#23378
This commit is an implementation of [RFC 526][rfc] which is a change to alter
the definition of the old `fmt::FormatWriter`. The new trait, renamed to
`Writer`, now only exposes one method `write_str` in order to guarantee that all
implementations of the formatting traits can only produce valid Unicode.
[rfc]: https://github.com/rust-lang/rfcs/blob/master/text/0526-fmt-text-writer.md
One of the primary improvements of this patch is the performance of the
`.to_string()` method by avoiding an almost-always redundant UTF-8 check. This
is a breaking change due to the renaming of the trait as well as the loss of the
`write` method, but migration paths should be relatively easy:
* All usage of `write` should move to `write_str`. If truly binary data was
being written in an implementation of `Show`, then it will need to use a
different trait or an altogether different code path.
* All usage of `write!` should continue to work as-is with no modifications.
* All usage of `Show` where implementations just delegate to another should
continue to work as-is.
[breaking-change]
Closes#20352
The trait has an obvious, sensible implementation directly on vectors so
the MemWriter wrapper is unnecessary. This will halt the trend towards
providing all of the vector methods on MemWriter along with eliminating
the noise caused by conversions between the two types. It also provides
the useful default Writer methods on Vec<u8>.
After the type is removed and code has been migrated, it would make
sense to add a new implementation of MemWriter with seeking support. The
simple use cases can be covered with vectors alone, and ones with the
need for seeks can use a new MemWriter implementation.
This commit fills in the documentation holes for the FormatWriter trait which
were previously accidentally left blank. Additionally, this adds the `write_fmt`
method to the trait to allow usage of the `write!` macro with implementors of
the `FormatWriter` trait. This is not useful for consumers of the standard
library who should generally avoid the `FormatWriter` trait, but it is useful
for consumers of the core library who are not using the standard library.
1. Wherever the `buf` field of a `Formatter` was used, the `Formatter` is used
instead.
2. The usage of `write_fmt` is minimized as much as possible, the `write!` macro
is preferred wherever possible.
3. Usage of `fmt::write` is minimized, favoring the `write!` macro instead.
If you were writing to something along the lines of `self.foo` then with the new
closure rules it meant that you were borrowing `self` for the entirety of the
closure, meaning that you couldn't format other fields of `self` at the same
time as writing to a buffer contained in `self`.
By lifting the borrow outside of the closure the borrow checker can better
understand that you're only borrowing one of the fields at a time. This had to
use type ascription as well in order to preserve trait object coercions.
