avoid double-unsizing arrays in bytestring match lowering

The match lowering code, when lowering matches against bytestrings,
works by coercing both the scrutinee and the pattern to `&[u8]` and
then comparing them using `<[u8] as Eq>::eq`.

If the scrutinee is already of type `&[u8]`, then unsizing it is both
unneccessary and a trait error caught by the new and updated MIR typeck,
so this PR changes lowering to avoid doing that (match lowering tried to
avoid that before, but that attempt was quite broken).

Fixes #46920.

r? @EddyB

Update rustfmt to 0.3.6

r? @nrc

Don't include DefIndex in proc-macro registrar function symbol.

There can only ever be one registrar function per plugin or proc-macro crate, so adding the `DefIndex` to the function's symbol name does not serve a real purpose. Remove the `DefIndex` from the symbol name makes it stable across incremental compilation sessions.

This should fix issue #47292.

Compute LLVM argument indices correctly in face of padding

Closes #47278

r? @EddyB

Rollup of 6 pull requests

- Successful merges: #47250, #47313, #47398, #47468, #47471, #47520
- Failed merges:

Update Cargo and its dependencies

This'll probably have a bunch of build errors, so let's try and head those off
and find them sooner rather than later!

This'll probably have a bunch of build errors, so let's try and head those off
and find them sooner rather than later!

Use File::metadata instead of fs::metadata to choose buffer size

This replaces a `stat` syscall with `fstat` or similar, which can be faster.  Fixes #47519.

On E0283, point at method with the requirements

On required type annotation diagnostic error, point at method with the
requirements if the span is available.

CC #45453.

Do not suggest to make `mut` binding external to `Fn` closure

Re #46834.

Switch to pulldown as default markdown renderer

r? @QuietMisdreavus

rustdoc: Populate external_traits with traits only seen in impls

This means default methods can always be found and "Important traits" will include all spotlight traits.

Test rustdoc js

Add tests for the rustdoc search. It was heavily required because of all the recent breaking changes that happened while I went through improvements in doc search (add search in/for generic search for example).

Rollup of 21 pull requests

- Successful merges: #47302, #47333, #47387, #47404, #47407, #47426, #47427, #47436, #47444, #47456, #47458, #47467, #47479, #47481, #47483, #47487, #47497, #47498, #47505, #47509, #47514
- Failed merges:

whitelist x86 fxsr feature

https://github.com/rust-lang/rust/pull/47223 properly checks that only white-listed features are allowed in combination with `target_feature`, but the `fxsr` feature used by `stdsimd` was not white-listed.

r? @alexcrichton

Update rust-installer for streaming parallelism

Pull in rust-lang/rust-installer#76 to get streamed tarball generation,
rather than batching it all in memory, while still getting the benefit
of compressing in parallel.

rustc: Spawn `cmd /c` for `.bat` scripts

This fixes an accidental regression #46335 where the behavior of
`Path::ends_with` is different from `str::ends_with` (paths operate over
components, strs operate over chars).

Make non-found module name optional

No longer uses a magic string for missing or root module.

Remove incorrect `Default::default` links, add a new one

`map_or` and `map_or_else` don't use `Default::default`, but `unwrap_or_default` does.

implement "only-<platforms>" for test headers

This patch implements "only-<platforms>" for tests headers using which one can
specify just the platforms on which the test should run rather than listing all
the platforms to ignore using "ignore-<platforms>".

This fixes #33581 and fixes #47459.

Add "-lmsvcrt" twice to get rustc to build with the latest mingw64

After updating mingw-w64 in Msys2, I started getting this when doing `./x.py build --stage 1 src/libtest`:
```
error: linking with `gcc` failed: exit code: 1
  |
  = note: "gcc" "-Wl,--enable-long-section-names" "-fno-use-linker-plugin" "-Wl,--nxcompat" "-nostdlib" "-m64" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-sysroot\\lib\\rustlib\\x86_64-pc-windows-gnu\\lib\\crt2.o" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-sysroot\\lib\\rustlib\\x86_64-pc-windows-gnu\\lib\\rsbegin.o" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-sysroot\\lib\\rustlib\\x86_64-pc-windows-gnu\\lib" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps\\rustc-b67a4fe646fd8794.rustc0-833528dbd46ff06c3b1f5154abdef2ed.rs.rcgu.o" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps\\rustc-b67a4fe646fd8794.rustc1-833528dbd46ff06c3b1f5154abdef2ed.rs.rcgu.o" "-o" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps\\rustc-b67a4fe646fd8794.exe" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps\\rustc-b67a4fe646fd8794.crate.allocator.rcgu.o" "-Wl,--gc-sections" "-nodefaultlibs" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\release\\deps" "-L" "...\\.cargo\\registry\\src\\github.com-1ecc6299db9ec823\\dbghelp-sys-0.2.0/x86_64" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\build\\miniz-sys-98d83a845f69b3ab\\out" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\build\\rustc_binaryen-f106436b515711ff\\out/build/lib" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\build\\rustc_binaryen-f106436b515711ff\\out" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\build\\rustc_llvm-9a040fa1f1937a67\\out" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\llvm/lib" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-sysroot\\lib\\rustlib\\x86_64-pc-windows-gnu\\lib" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_driver-224d9efe142c632e" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_trans-767a58ff60ff6a03" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_resolve-bcc2d91b756552d1" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_incremental-e93e816231352cc9" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_plugin-8273bd6d564e8657" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_metadata-5537b9a8ab6e6015" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_lint-796681662b9ad8e1" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_passes-9ef6de765e132a7c" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_privacy-2289da126d06c49e" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_llvm-893cdac51017c26f" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_borrowck-ac2009fc1ce58d88" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_mir-d4ce85a1cded4423" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_const_eval-a4e766ec47afde96" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_save_analysis-66d4c41e75392976" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_typeck-4e21db5573af1446" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_platform_intrinsics-f40c4b99b60d15e9" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_allocator-86ef12c8efbcf068" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_trans_utils-8199c3d0e673bb7b" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc-8f435ca07f1a04ff" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-sysroot\\lib\\rustlib\\x86_64-pc-windows-gnu\\lib" "-l" "test-8abb197945b79a6a" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_const_math-fa724350247d1ae6" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_back-838b735c189dd798" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "graphviz-42c69c0ff2aacc5b" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "arena-454325a3f2773bc8" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "syntax_ext-7880c41067f1be05" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "proc_macro-f609718c6b927026" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "syntax-3d2aaf6e201abcfe" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_errors-2c007ffe6a847ed7" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "syntax_pos-067e758dda669d03" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_data_structures-50e5e6db2f34c196" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-sysroot\\lib\\rustlib\\x86_64-pc-windows-gnu\\lib" "-l" "term-9d9f4c10ffba6dd6" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "serialize-e55b4fb27a4d08bf" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "rustc_cratesio_shim-baed94e463835a87" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-rustc\\x86_64-pc-windows-gnu\\release\\deps" "-l" "fmt_macros-3c2cdca7d2f8dd09" "-L" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-sysroot\\lib\\rustlib\\x86_64-pc-windows-gnu\\lib" "-l" "std-b1b09a5d7798628b" "-Wl,-Bstatic" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-sysroot\\lib\\rustlib\\x86_64-pc-windows-gnu\\lib\\libcompiler_builtins-69f85297d9318c97.rlib" "-Wl,-Bdynamic" "-l" "advapi32" "-l" "ole32" "-l" "oleaut32" "-l" "psapi" "-l" "shell32" "-l" "ole32" "-l" "uuid" "-l" "stdc++" "-l" "gcc_eh" "-l" "pthread" "-l" "psapi" "-l" "dbghelp" "-l" "kernel32" "-l" "advapi32" "-l" "kernel32" "-l" "advapi32" "-l" "ws2_32" "-l" "userenv" "-l" "shell32" "-lmingwex" "-lmingw32" "-lgcc" "-lmsvcrt" "-luser32" "-lkernel32" "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0-sysroot\\lib\\rustlib\\x86_64-pc-windows-gnu\\lib\\rsend.o"
  = note: rust/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/7.2.0/../../../../x86_64-w64-mingw32/lib/../lib/libmsvcrt.a(lib64_libmsvcrt_os_a-__p__fmode.o):__p__fmode.c:(.rdata$.refptr.__imp__fmode[.refptr.__imp__fmode]+0x0): undefined reference to `__imp__fmode'
          collect2.exe: error: ld returned 1 exit status

error: aborting due to previous error

error: Could not compile `rustc-main`.

Caused by:
  process didn't exit successfully: `rust\msys64\home\...\rust\build\bootstrap/debug/rustc --crate-name rustc rustc\rustc.rs --error-format json --crate-type bin --emit=dep-info,link -C opt-level=2 --cfg feature="jemalloc" --cfg feature="llvm" --cfg feature="rustc_back" --cfg feature="rustc_driver" -C metadata=b67a4fe646fd8794 -C extra-filename=-b67a4fe646fd8794 --out-dir rust\msys64\home\...\rust\build\x86_64-pc-windows-gnu\stage0-rustc\x86_64-pc-windows-gnu\release\deps --target x86_64-pc-windows-gnu -L dependency=rust\msys64\home\...\rust\build\x86_64-pc-windows-gnu\stage0-rustc\x86_64-pc-windows-gnu\release\deps -L dependency=rust\msys64\home\...\rust\build\x86_64-pc-windows-gnu\stage0-rustc\release\deps --extern rustc_back=rust\msys64\home\...\rust\build\x86_64-pc-windows-gnu\stage0-rustc\x86_64-pc-windows-gnu\release\deps\rustc_back-838b735c189dd798.dll --extern rustc_driver=rust\msys64\home\...\rust\build\x86_64-pc-windows-gnu\stage0-rustc\x86_64-pc-windows-gnu\release\deps\rustc_driver-224d9efe142c632e.dll -L native=...\.cargo\registry\src\github.com-1ecc6299db9ec823\dbghelp-sys-0.2.0/x86_64 -L native=rust\msys64\home\...\rust\build\x86_64-pc-windows-gnu\stage0-rustc\x86_64-pc-windows-gnu\release\build\miniz-sys-98d83a845f69b3ab\out -L native=rust\msys64\home\...\rust\build\x86_64-pc-windows-gnu\stage0-rustc\x86_64-pc-windows-gnu\release\build\rustc_binaryen-f106436b515711ff\out/build/lib -L native=rust\msys64\home\...\rust\build\x86_64-pc-windows-gnu\stage0-rustc\x86_64-pc-windows-gnu\release\build\rustc_binaryen-f106436b515711ff\out -L native=rust\msys64\home\...\rust\build\x86_64-pc-windows-gnu\stage0-rustc\x86_64-pc-windows-gnu\release\build\rustc_llvm-9a040fa1f1937a67\out -L native=rust\msys64\home\...\rust\build\x86_64-pc-windows-gnu\llvm/lib` (exit code: 101)
thread 'main' panicked at 'command did not execute successfully: "rust\\msys64\\home\\...\\rust\\build\\x86_64-pc-windows-gnu\\stage0/bin\\cargo.exe" "build" "--target" "x86_64-pc-windows-gnu" "-j" "4" "--release" "--features" " jemalloc llvm" "--manifest-path" "rust/msys64/home/.../rust\\src/rustc/Cargo.toml" "--message-format" "json"
expected success, got: exit code: 101', bootstrap\compile.rs:886:9
note: Run with `RUST_BACKTRACE=1` for a backtrace.
failed to run: rust/msys64/home/.../rust/build/bootstrap/debug/bootstrap build --stage 1 src/libtest
Build completed unsuccessfully in 0:00:25
```

The code that uses `__p__fmode` was added in https://github.com/mirror/mingw-w64/commit/2e64b9e4537d564478f17b873b2f655f518325ed, apparently in x86_64, it uses its own implementation of it. libmsvcrt.a is kind of a weird beast, it's both an import library for the system msvcrt.dll, but it also is a library that includes compiled code.

For some reason it fails to find the reference for the import symbol that is found in the very same archive as the function that uses it. I don't know what in the Rust code base triggers this. i.e. Create an MWE that can show why this PR is required.

This probably *shouldn't be merged* without understanding why this is necessary or not.

To successfully bootstrap rustc and show that this does make the build work (On latest mingw-w64 x86_64 on Msys2):
```sh
$ RUSTFLAGS="-C link-arg=-lmsvcrt" ./x.py build --stage 1 src/libtest
$ ./x.py build --keep-stage 1 --stage 2 src/libtest # Should work with the patch, and fail without it
```

Issue https://github.com/rust-lang/rust/issues/47265

Point at unused arguments for format string

Avoid overlapping spans by only pointing at the arguments that are not
being used in the argument string. Enable libsyntax to have diagnostics
with multiple primary spans by accepting `Into<MultiSpan>` instead of
`Span`.

Partially addresses #41850.

private no-mangle lints: only suggest `pub` if it doesn't already exist

Fixes #47383 (function or static can be `pub` but unreachable because it's in a private module; adding another `pub` is nonsensical).

r? @estebank

remove noop landing pads in cleanup shims

No-op landing pads are already removed in the normal optimization pipeline - so also removing them on the shim pipeline should slightly improve codegen performance, as these cleanup blocks are known to hurt LLVM.

This un-regresses and is therefore a fix for #47442. However, the reporter of that issue should try using `-C panic=abort` instead of carefully avoiding panics.

r? @EddyB

Allow a trailing comma in lint_array

fix #47428

Add NLL test for #45045

cc #45045
Part of #47366

r? @nikomatsakis

Don't include bang in macro replacement suggestion

When we suggest the replacement for a macro we include the "!" in the suggested replacement but the span only contains the name of the macro itself. Using that replacement would cause a duplicate "!" in the resulting code.

I originally tried to extend the span to be replaced by 1 byte in rust-lang/rust#47424. However, @zackmdavis pointed out that there can be whitespace between the macro name and the bang.

Instead, just remove the bang from the suggested replacement.

Fixes #47418

r? @estebank

Update html-diff crate => fix unicode parsing and invalid paths

r? @QuietMisdreavus

Add a Docker container for doing automated builds for CloudABI.

Setting up a cross compilation toolchain for CloudABI is relatively
easy. It's just a matter of installing a somewhat recent version of
Clang (5.0 preferred) and installing the corresponding
`${target}-cxx-runtime` package, containing a set of core C/C++ libraries
(libc, libc++, libunwind, etc).

Eventually it would be nice if we could also run `x.py test`. That,
however still requires some more work. Both libtest and compiletest
would need to be adjusted to deal with CloudABI's requirement of having
all of an application's dependencies injected. Let's settle for just
doing `x.py dist` for now.

Add a default directory for -Zmir-dump-dir

The current behaviour of dumping in the current directory is rarely
desirable: a sensible default directory for dumping is much more
convenient. This makes sets the default value for `-Zmir-dump-dir`
to `mir_dump/`.

r? @EddyB

fix mispositioned span

This fixes #47377

The output now looks like this
```
error[E0369]: binary operation `+` cannot be applied to type `&str`
 --> h.rs:3:11
  |
3 |     let _a = b + ", World!";
  |              ^^^^^^^^^^^^^^ `+` can't be used to concatenate two `&str` strings
help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
  |
3 |     let _a = b.to_owned() + ", World!";
  |              ^^^^^^^^^

error: aborting due to previous error
```
For the case when emojis are involved,  it gives the new output for proper indentation.
But for an indentation as follows,
```
fn main() {
let b = "hello";
    let _a = b + ", World!";
}
```
it still mispositions the span
```
3 |     println!("🦀🦀🦀🦀🦀"); let _a = b + ", World!";
  |                                           ^^^^^^^^^^^^^^ `+` can't be used to concatenate two `&str` strings
  |
3 |     println!("🦀🦀🦀🦀🦀"); let _a = b.to_owned() + ", World!";
  |                                           ^^^^^^^
error: aborting due to previous erro
```

cc @estebank  @est31

Standardize on "re-export" rather than "reexport"

While working on the book with our editors, it was brought to our attention that we're not consistent with when we use "re-export" versus "reexport". For the book, we've decided (with our editors) to go with "re-export"; in prose, I think that looks better. In code, I'm fine with "reexport".

However, the rustdoc generated section is currently "Reexports", so when we have a screenshot of generated documentation with the prose where we use "re-export", it's inconsistent.

It's too late to fix this for the book because we're using 1.21.0 for the output in the book, and it's really only one spot so it's not a huge deal, but I'd like to advocate for changing the documentation header so that a future edition of the book can be consistent.

The first commit here only changes the documentation section heading text and rustdoc documentation that references it. This is the commit that's most important to me.

The second commit changes error messages and associated tests to also be consistent with the use of re-export. This is the next most important commit to me, but I could be argued out of this one because then it won't match code like the `macro_reexports` feature name, which ostensibly should change to `macro_re_exports` to be most consistent but I didn't want to change code.

The last commit changes re-export anywhere else in prose: either in documentation comments or regular comments. This is least important as most of them aren't user-visible. Instances like these will likely sneak back in over time. I'm totally fine dropping this commit if anyone wants, but [the hobgoblins made me do it](http://www.bartleby.com/100/420.47.html) and it sets a good example.

r? @steveklabnik

Report errors instead of panic!() when linkcheck encounters absolute paths

The RBE contained some absolute links that failed the link check in #46196. Diagnosing these issues was needlessly complicated, thanks to the linkchecker just panicing instead of reporting proper errors.

This PR replaces the panic with a proper `*errors = true` + error message handling.

The linkchecker itself doesn't have any tests so I intentionally didn't touch anything else than the code that previously did the `panic!()`. A small code quality improvement might be made by binding the `Path::new(base).join(url)` into a variable before the for-loop and using this resolved url in both the for loop and the error message.

r? @steveklabnik

(If not for any other reason than having r on the #46196.)

Optimize slice.{r}position result bounds check

Second attempt of https://github.com/rust-lang/rust/pull/45501
Fixes https://github.com/rust-lang/rust/issues/45964

Demo: https://godbolt.org/g/N4mBHp

fix faulty comment

after #43506 there is no fixed number of request sent.

This replaces a `stat` syscall with `fstat` or similar, which can be
faster.  Fixes #47519.

Remove dep-info files as targets in themselves

If you ask `rustc` to `--emit dep-info`, the resulting dependency file contains a rule for producing the dependency file itself. This differs from the output of `gcc -MD` or `clang -MD`, which only includes dependency rules for the object files produced.

Tools like Ninja often consume and delete dependency files as soon as they’re produced for performance reasons, particularly on Windows. In the case of `rustc` output, though, the recently-deleted dependency file is cached by Ninja as a target, and therefore triggers a rebuild every time.

This very small patch removes the dep-info file from the list of output filenames, so it matches the behavior of gcc and clang.