It is not totally clear if we should just use whitespace, or if the full
unicode word-breaking algorithm is more correct. If there is demand we
can reconsider this decision (and consider the precise algorithm to use
in detail).
cc #15628.
This commit exposes the `is_sep` function and `MAIN_SEP` constant, as
well as Windows path prefixes. The path prefix enum is safely exposed on
all platforms, but it only yielded as a component for Windows.
Exposing the prefix enum as part of prefix components involved changing
the type from `OsStr` to the `Prefix` enum, which is a:
[breaking-change]
Since `tr` converts lowercase to uppercase according to system locale using `LC_CTYPE` environment variable; on some locales, rustup.sh fails to use correct variables names, thus deletes temporarily downloaded files and gives a meaningless error as shown below. This a simple fix which explictly sets `LC_CTYPE` as `C`.
This includes everything necessary for promoting borrows of constant rvalues to `'static`.
That is, `&expr` will have the type `&'static T` if `const T: &'static T = &expr;` is valid.
There is a small exception, dereferences of raw pointers, as they misbehave.
They still "work" in constants as I didn't want to break legitimate uses (are there any?).
The qualification done here can be expanded to allow simple CTFE via `const fn`.
Nonetheless, as this commit demonstrates, the previous commits was a [breaking-change].
In practice, breakage is focused on functions of this form:
```rust
fn foo(..., object: Box<FnMut()>)
````
where `FnMut()` could be any trait object type. The older scheme defaulted objects in argument
position so that they were bounded by a fresh lifetime:
```rust
fn foo<'a>(..., object: Box<FnMut()+'a>)
```
This meant that the object could contain borrowed data. The newer
scheme defaults to a lifetime bound of `'static`:
```rust
fn foo(..., object: Box<FnMut()+'static>)
```
This means that the object cannot contain borrowed data. In some cases, the best fix
is to stop using `Box`:
```rust
fn foo(..., object: &mut FnMut())
```
but another option is to write an explicit annotation for the `'a`
lifetime that used to be implicit. Both fixes are demonstrated in
this commit.
