Use impl restrictions in std, core

[jhpratt]

This should all be quite self-explanatory. I've used the tightest module permitted by current implementation, which is overwhelmingly self as I had expected.

r? @Urgau

[fmease]

Don't we want to block this PR on rustdoc support?

IsTerminal is stable and AFAICT the docs don't mention anywhere that the trait is sealed, so if we were to merge your PR now, users would no longer know that the trait is sealed just by looking at the docs. That feels unfortunate.

View changes since the review

[jhpratt]

I'm not opposed to blocking it on such. I deliberately left any "this trait is sealed" comments for that reason. Once there's rustdoc support, all of those can be removed as well.

[jhpratt]

CI will certainly fail again. x c core, x c std, and x c rustfmt all pass, but x t tidy fails at the rustfmt step. This is presumably due to the keyword order changing, but a bootstrap has taken place since that happened. What am I missing here?

[rust-log-analyzer]

The job tidy failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

fmt check
error: expected type, found keyword `unsafe`
##[error]  --> /checkout/library/core/src/num/nonzero.rs:34:16
   |
34 | pub impl(self) unsafe trait ZeroablePrimitive: Sized + Copy {
   |                ^^^^^^ expected type

error: expected one of `for`, `where`, or `{`, found keyword `const`
##[error] --> /checkout/library/core/src/num/traits.rs:7:16
  |
7 | pub impl(self) const trait TruncateTarget<Target> {
  |                ^^^^^ expected one of `for`, `where`, or `{`

error: expected type, found keyword `unsafe`
##[error]    --> /checkout/library/core/src/slice/mod.rs:5750:16
     |
5750 | pub impl(self) unsafe trait GetDisjointMutIndex: Clone {
     |                ^^^^^^ expected type

error: expected one of `for`, `where`, or `{`, found keyword `const`
##[error]   --> /checkout/library/core/src/slice/index.rs:123:17
    |
123 | pub impl(crate) const unsafe trait SliceIndex<T: ?Sized> {
    |                 ^^^^^ expected one of `for`, `where`, or `{`

error: expected type, found keyword `unsafe`
##[error]   --> /checkout/library/core/src/sync/atomic.rs:292:16
    |
292 | pub impl(self) unsafe trait AtomicPrimitive: Sized + Copy {
    |                ^^^^^^ expected type

error: expected type, found keyword `unsafe`
##[error]   --> /checkout/library/core/src/ffi/va_list.rs:316:16
    |
316 | pub impl(self) unsafe trait VaArgSafe: Copy {}
    |                ^^^^^^ expected type

fmt: checked 6874 files
Bootstrap failed while executing `test src/tools/tidy tidyselftest --extra-checks=py,cpp,js,spellcheck`
Build completed unsuccessfully in 0:00:46

[rust-bors]

☔ The latest upstream changes (presumably #157174) made this pull request unmergeable. Please resolve the merge conflicts.