doc/guide-ffi: A few minor typo/language fixes

Signed-off-by: Anton Lofgren <alofgren@op5.com>
Add example for str replace() and MaybeOwned

  - for 3 implementations of into_maybe_owned()
  - is_slice()
  - is_owned()
Guide: match
Guide: looping
Guide: Standard input
Use std::fmt::radix instead of to_str_radix.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
Add range lint for float literals, fixing #10934
Mistake in AtomicBool spinlock example

The current example of a spinlock was not correct. The lock is actually acquired
when old == result. So we only need to deschedule when this is not the case.
typeck: check casts from pointers to floats, closes #15445
Remove deprecated std::unstable module.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
std: Add some implementation of common traits

- semver::Version is now Eq, Ord, and Hash
- Path is now PartialOrd and Ord
rustc: Forbid plugin_registrar in only rlib form

If a plugin registrar is available, the library must be found in dylib form, not
just in rlib form.

Closes #15475
Document event_loop_factory usage

Add a couple of lines mentioning event_loop_factory - no clear error message is
given if you attempt to perform I/O in tasks created in this fashion.
auto merge of #14519 : hirschenberger/rust/issue-10934, r=alexcrichton

Issue #10934
More robust install.sh: do runnability test in fresh subdirectory.

Fix #15558.
rustc: Always mark #[crate_name] as used

It's just an annoying error if you use --crate-name on the command line and you
also have a #[crate_name] specified
rustc: Exclude #[repr(C)] from non camel case

C structs predominately do not use camel case identifiers, and we have a clear
indicator for what's a C struct now, so excuse all of them from this stylistic
lint.
auto merge of #15559 : fhahn/rust/issue-15445-mut-cast, r=alexcrichton

I've added an error message for casts from raw pointers to floats #15445.
io::process::Command: add fine-grained env builder

This commit changes the `io::process::Command` API to provide
fine-grained control over the environment:

* The `env` method now inserts/updates a key/value pair.
* The `env_remove` method removes a key from the environment.
* The old `env` method, which sets the entire environment in one shot,
  is renamed to `env_set_all`. It can be used in conjunction with the
  finer-grained methods. This renaming is a breaking change.

To support these new methods, the internal `env` representation for
`Command` has been changed to an optional `HashMap` holding owned
`CString`s (to support non-utf8 data). The `HashMap` is only
materialized if the environment is updated. The implementation does not
try hard to avoid allocation, since the cost of launching a process will
dwarf any allocation cost.

This patch also adds `PartialOrd`, `Eq`, and `Hash` implementations for
`CString`.

[breaking-change]
auto merge of #15353 : aturon/rust/env-hashmap, r=alexcrichton

This commit adds `env_insert` and `env_remove` methods to the `Command`
builder, easing updates to the environment variables for the child
process. The existing method, `env`, is still available for overriding
the entire environment in one shot (after which the `env_insert` and
`env_remove` methods can be used to make further adjustments).

To support these new methods, the internal `env` representation for
`Command` has been changed to an optional `HashMap` holding owned
`CString`s (to support non-utf8 data). The `HashMap` is only
materialized if the environment is updated. The implementation does not
try hard to avoid allocation, since the cost of launching a process will
dwarf any allocation cost.

This patch also adds `PartialOrd`, `Eq`, and `Hash` implementations for
`CString`.