Update books
## nomicon
1 commits in 25854752549d44d76fbd7650e17cb4f167a0b8fb..6e57e64501f61873ab80cb78a07180a22751a5d6
2020-08-19 16:41:48 -0400 to 2020-09-14 11:40:23 -0400
- Fix API change to alloc::Global::grow. (rust-lang-nursery/nomicon#236)
## reference
3 commits in 25391dba46262f882fa846beefaff54a966a8fa5..56a13c082ee90736c08d6abdcd90462517b703d3
2020-09-02 07:22:55 -0700 to 2020-09-14 23:20:16 -0700
- Update the description of staticlib (rust-lang-nursery/reference#884)
- Rust 1.46 now allows more features in const fn (rust-lang-nursery/reference#883)
- Document the enum changes in RFC 2195 (rust-lang-nursery/reference#879)
## book
1 commits in e5ed97128302d5fa45dbac0e64426bc7649a558c..cb28dee95e5e50b793e6ba9291c5d1568d3ad72e
2020-08-31 12:53:40 -0500 to 2020-09-09 10:06:00 -0500
- Fixed the error message of invalid array element access in ch03.2 (rust-lang/book#2446)
Add aarch64-unknown-linux-musl host builds
This adds aarch64-unknown-linux-musl to the hosts list and adds the build to the dist-arm-linux builder as `@Mark-Simulacrum` suggested to me in Zulip. `@jyn514` requested to be mentioned 😄
I had to update the config for crosstool-ng as it had a prompt about the glibc version.
I ran `src/ci/docker/run.sh dist-arm-linux` to test it.
```
Build completed successfully in 1:31:50
Compile requests 8180
Compile requests executed 8135
Cache hits 287
Cache misses 7848
Cache timeouts 0
Cache read errors 0
Forced recaches 0
Cache write errors 0
Compilation failures 0
Cache errors 0
Non-cacheable compilations 0
Non-cacheable calls 36
Non-compilation calls 9
Unsupported compiler calls 0
Average cache write 0.000 s
Average cache read miss 6.389 s
Average cache read hit 0.000 s
Cache location Local disk: "/sccache"
Cache size 202 MiB
Max cache size 10 GiB
== clock drift check ==
local time: Sun Sep 6 19:30:17 UTC 2020
network time: Sun, 06 Sep 2020 19:30:17 GMT
== end clock drift check ==
```
Only errors were in miri due to struct fields being private (already been reported [here](https://github.com/rust-lang/rust/issues/76337))
Edit: Maybe it is helpful if I add that it is a working compiler
```sh
/rust-nightly-aarch64-unknown-linux-musl # ash install.sh
install: creating uninstall script at /usr/local/lib/rustlib/uninstall.sh
install: installing component 'rustc'
install: installing component 'cargo'
install: installing component 'rls-preview'
install: installing component 'rust-analyzer-preview'
install: installing component 'clippy-preview'
install: installing component 'rustfmt-preview'
install: installing component 'llvm-tools-preview'
install: installing component 'rust-analysis-aarch64-unknown-linux-musl'
install: installing component 'rust-std-aarch64-unknown-linux-musl'
install: WARNING: failed to run ldconfig. this may happen when not installing as root. run with --verbose to see the error
Rust is ready to roll.
/ # cat test.rs
fn main() { println!("hello world"); }
/ # rustc test.rs
/ # ./test
hello world
# file test
test: ELF 64-bit LSB executable, ARM aarch64, version 1 (SYSV), statically linked, not stripped
```
Reword `trivial_casts` lint in rustc book to better explain what it does.
The current description of the trivial casts lint under the "allowed
by default" listing in the rustc book indicates the lint is for casts
which may be removed, which is less clear than saying it's for casts
which may be replaced by coercion (which is the wording used by the
error message included in the doc).
This commit changes the wording slightly to better describe what the
lint does.
This issue bit me in some recent code where I was attempting to
convert a `Vec<SomeType>` to a `Vec<SomeTraitObject>`, and
hit my project-wide `#![deny(trivial_casts)]` with
`map(|o| Box::new(o) as TraitObject)`. I'd read the book docs for
`trivial_casts` and was surprised by the error, as I took it to mean
the cast ought to be removed (rather than replaced by ascription
in this case). Removing the cast meant other code didn't compile,
and I then found issues like #23742 and realized my misunderstanding.
The current description of the trivial casts lint under the "allowed
by default" listing in the rustc book indicates the lint is for lints
which may be removed, which is less clear than saying it's for lints
which may be replaced by coercion (which is the wording used by the
error message included in the doc).
This commit changes the wording slightly to better describe what the
lint does.
[AVR] Replace broken 'avr-unknown-unknown' target with 'avr-unknown-gnu-atmega328' target
The `avr-unknown-unknown` target has never worked correctly, always trying to invoke
the host linker and failing. It aimed to be a mirror of AVR-GCC's
default handling of the `avr-unknown-unknown' triple (assume bare
minimum chip features, silently skip linking runtime libraries, etc).
This behaviour is broken-by-default as it will cause a miscompiled executable
when flashed.
This patch improves the AVR builtin target specifications to instead
expose only a 'avr-unknown-gnu-atmega328' target. This target system is
`gnu`, as it uses the AVR-GCC frontend along with avr-binutils. The
target triple ABI is 'atmega328'.
In the future, it should be possible to replace the dependency on
AVR-GCC and binutils by using the in-progress AVR LLD and compiler-rt support.
Perhaps at that point it would make sense to add an
'avr-unknown-unknown-atmega328' target as a better default when
implemented.
There is no current intention to add in-tree AVR target specifications for other
AVR microcontrollers - this one can serve as a reference implementation
for other devices via `rustc --print target-spec-json
avr-unknown-gnu-atmega328p`.
There should be no users of the existing 'avr-unknown-unknown' Rust
target as a custom target specification JSON has always been
recommended, and the avr-unknown-unknown target could never pass the
linking step anyway.
