Moved details of unstable non-ascii identifiers from the Reference
Moved details of unstable non-ascii identifiers from the Reference to the Unstable book
r? @steveklabnik
Implement `and_modify` on `Entry`
## Motivation
`Entry`s are useful for allowing access to existing values in a map while also allowing default values to be inserted for absent keys. The existing API is similar to that of `Option`, where `or` and `or_with` can be used if the option variant is `None`.
The `Entry` API is, however, missing an equivalent of `Option`'s `and_then` method. If it were present it would be possible to modify an existing entry before calling `or_insert` without resorting to matching on the entry variant.
Tracking issue: https://github.com/rust-lang/rust/issues/44733.
Add ..= to the parser
Add ..= to libproc_macro
Add ..= to ICH
Highlight ..= in rustdoc
Update impl Debug for RangeInclusive to ..=
Replace `...` to `..=` in range docs
Make the dotdoteq warning point to the ...
Add warning for ... in expressions
Updated more tests to the ..= syntax
Updated even more tests to the ..= syntax
Updated the inclusive_range entry in unstable book
hide internal types/traits from std docs via new #[doc(masked)] attribute
Fixes#43701 (hopefully for good this time)
This PR introduces a new parameter to the `#[doc]` attribute that rustdoc looks for on `extern crate` statements. When it sees `#[doc(masked)]` on such a statement, it hides traits and types from that crate from appearing in either the "Trait Implementations" section of many type pages, or the "Implementors" section of trait pages. This is then applied to the `libc`/`rand`/`compiler_builtins` imports in libstd to prevent those crates from creating broken links in the std docs.
Like in #43348, this also introduces a feature gate, `doc_masked`, that controls the use of this parameter.
To view the std docs generated with this change, head to https://tonberry.quietmisdreavus.net/std-43701/std/index.html.
stabilized compiler_fences (fixes#41091)
I did not know what to proceed with "unstable-book" entry. The feature would no longer be unstable so I have deleted it. If it was the wrong call I'll revert it (unfortunately his case is not described in the CONTRIBUTING.md).
Compile fail stable
Since #30726, we never made the `compile_fail` flag nor the error code check stable. I think it's time to change this fact.
r? @alexcrichton
