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std: Enforce Unicode in fmt::Writer

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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
This commit is contained in:
Alex Crichton 2014-12-12 10:59:41 -08:00
parent cd614164e6
commit e423fcf0e0
25 changed files with 320 additions and 359 deletions
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3
src/libsyntax/ast.rs
View file

@ -1662,6 +1662,7 @@ mod test {
use serialize;
use codemap::*;
use super::*;
use std::fmt;
// are ASTs encodable?
#[test]
@ -1687,6 +1688,6 @@ mod test {
exported_macros: Vec::new(),
};
// doesn't matter which encoder we use....
let _f = &e as &serialize::Encodable<json::Encoder, io::IoError>;
let _f = &e as &serialize::Encodable<json::Encoder, fmt::Error>;
}
}