…t types match.

I reworded it slightly to make it more clear that the function only take
two arguments - the output and the Arguments struct that can be
generated from the format_args! macro.

r? @steveklabnik

This rewords and removes the `Arguments` section from the docs for
fmt::format.

r? @steveklabnik

This had an accidental `u8 as *mut T` where it was intended to have just a
normal pointer-to-pointer cast.

Closes rust-lang#42827

Try to make clear that this isn't an API guarantee for now, as we likely
want to refine these errors in the future, e.g. `ENOSPC` "No space left
on device".

CC rust-lang#40322

…paths, r=arielb1

Note different versions of same crate when absolute paths of different types match.

The current check to address rust-lang#22750 only works when the paths of the mismatched types relative to the current crate are equal, but this does not always work if one of the types is only included through an indirect dependency. If reexports are involved, the indirectly included path can e.g. [contain private modules](rust-lang#22750 (comment)).

This PR takes care of these cases by also comparing the *absolute* path, which is equal if the type hasn't moved in the module hierarchy between versions. A more coarse check would be to compare only the crate names instead of full paths, but that might lead to too many false positives.

Additionally, I believe it would be helpful to show where the differing crates came from, i.e. the information in `rustc::middle::cstore::CrateSource`, but I'm not sure yet how to nicely display all of that, so I'm leaving it to a future PR.

Update docs for fmt::write.

rust-lang#29355

I reworded it slightly to make it more clear that the function only take
two arguments - the output and the Arguments struct that can be
generated from the format_args! macro.

r? @steveklabnik

Update docs for std::fmt::format rust-lang#29355.

This rewords and removes the `Arguments` section from the docs for
fmt::format.

r? @steveklabnik

…ches, r=alexcrichton

Improve tests and benchmarks for slice::sort and slice::sort_unstable

This PR just hardens the tests and improves benchmarks.
More specifically:

1. Benchmarks don't generate vectors in `Bencher::iter` loops, but simply clone pregenerated vectors.
2. Benchmark `*_strings` doesn't allocate Strings in `Bencher::iter` loops, but merely clones a `Vec<&str>`.
3. Benchmarks use seeded `XorShiftRng` to be more consistent.
4. Additional tests for `slice::sort` are added, which test sorting on slices with several ascending/descending runs. The implementation identifies such runs so it's a good idea to test that scenario a bit.
5. More checks are added to `run-pass/vector-sort-panic-safe.rs`. Sort algorithms copy elements around a lot (merge sort uses an auxilliary buffer and pdqsort copies the pivot onto the stack before partitioning, then writes it back into the slice). If elements that are being sorted are internally mutable and comparison function mutates them, it is important to make sure that sort algorithms always use the latest "versions" of elements. New checks verify that this is true for both `slice::sort` and `slice::sort_unstable`.

As a side note, all of those improvements were made as part of the parallel sorts PR in Rayon (nikomatsakis/rayon#379) and now I'm backporting them into libcore/libstd.

r? @alexcrichton

std: Fix implementation of `Alloc::alloc_one`

This had an accidental `u8 as *mut T` where it was intended to have just a
normal pointer-to-pointer cast.

Closes rust-lang#42827

…r=GuillaumeGomez

Document possible `io::ErrorKind`s of `fs::open`

Try to make clear that this isn't an API guarantee for now, as we likely
want to refine these errors in the future, e.g. `ENOSPC` "No space left
on device".

CC rust-lang#40322

compile-error.md: Fix link reference

Was a copy-paste mistake, I guess