Try to fix a perf regression by updating log

Upgrade `log` to `0.4` in multiple crates ~and `cargo`~.
Cc: #47154.

Upgrade `log` to `0.4` in multiple crates.

rustdoc: Add missing src links for generic impls on trait pages

`implementor2item` would return `None` for generic impls so instead this clones the entire `clean::Item` into the `implementors` map which simplifies some code.

Auto merge of #47177 - michaelwoerister:erase-invalid-spans-during-metadata-encoding, r=alexcrichton

Map invalid Spans to DUMMY_SP during crate metadata encoding.

This mirrors what we do for stabilizing the incr. comp. cache and is necessary for reproducible builds. For the incr. comp. cache, we *have* to do this because the encoding there cannot represent broken Spans. Metadata encoding has to be in sync with that as not to get unexpected interactions when compiling incrementally.

This should help with fixing issue https://github.com/rust-lang/rust/issues/47066.

r? @alexcrichton

ci: use a shared script to build musl

The dist-x86_64-musl, dist-various-1 and dist-i586-gnu-i686-musl builders had different scripts to build musl. This PR creates an unified script, which makes it easier to add new musl targets and update musl and libunwind (used in the musl targets).

The libunwind is update from 3.7 to 3.9 for dist-x86_64-musl and dist-i586-gnu-i686-musl (dist-various-1 already used 3.9 version).

Support `extern` in paths

Implement the primary alternative to https://github.com/rust-lang/rust/pull/46613 + https://github.com/rust-lang/rust/pull/45771, achieving the same effect without requiring changes to other imports.
Both need to be experimentally evaluated before making further progress.

The PR also adds docs for all these related features into the unstable book.

cc https://github.com/rust-lang/rust/issues/44660
r? @nikomatsakis

Rollup of 7 pull requests

- Successful merges: #46947, #47170, #47190, #47205, #47217, #47220, #47230
- Failed merges: #47233

Debuginfo Shadowed Variable test: fix check numbering

Appears to be a simple fix to restore this test. Ref issue #47163, CC @arielb1

Use name-discarding LLVM context

This is only applicable when neither of --emit=llvm-ir or --emit=llvm-bc are not
requested.

In case either of these outputs are wanted, but the benefits of such context are
desired as well, -Zfewer_names option provides the same functionality regardless
of the outputs requested.

Should be a viable fix for https://github.com/rust-lang/rust/issues/46449

Write examples for {BTree,Hash}Set::{get,replace,take}

miri: use AllocId instead of u64.

This makes @alexreg's miri allocation -> LLVM global translation more straight-forward.

r? @oli-obk

Port libpanic_abort and libpanic_unwind to CloudABI

This change ports both the libpanic* libraries to CloudABI.

The most interesting part of this pull request, however, is that it imports the CloudABI system call API into the Rust tree through a Git submodule. These will also be used by my port of libstd to CloudABI extensively, as that library obviously needs to invoke system calls to implement its primitives.

I have taken the same approach as libc: `src/libcloudabi` + `src/rustc/cloudabi_shim`. If some other naming scheme is preferred, feel free to let me know! As `libcloudabi` is pretty small, maybe it makes sense to copy, instead of using a submodule?

rustc: use {U,I}size instead of {U,I}s shorthands.

`Us`/`Is` come from a time when `us` and `is` were the literal suffixes that are now `usize` / `isize`.

r? @nikomatsakis

doc: improve None condition doc for `checked_div` and `checked_rem`

This commit improves the condition mentioned in the docs for which `checked_div` and `checked_rem` return `None`.

For signed division, the commit changes "the operation results in overflow" to "the division results in overflow", otherwise there is room for misinterpretation for `checked_rem`: Without considering overflow, `MIN % -1` would be simply zero, allowing the misinterpretation that "the operation" does not result in overflow in this case. This ambiguity is removed using "when the division results in overflow".

For unsigned division, the condition for `None` should be simply when `rhs == 0`, as no other overflow is possible.

Bump to 1.25.0

* Bump the release version to 1.25
* Bump the bootstrap compiler to the recent beta
* Allow using unstable rustdoc features on beta - this fix has been applied to
  the beta branch but needed to go to the master branch as well.

Add 'Span::parent()' and 'Span::source()' to proc_macro API.

As the title suggests: a couple of useful methods for `proc_macro`.

Issue 46976

ICE is due to an empty path segments, so I set the path to be the same as the in band ty params symbol. (I think this is how regular generics end up being handled?)

Pinging @cramertj, this is your code I'm editing here.

Restore working debuginfo tests by trimming comments from non-header directive lines

I noticed when adding a debuginfo test that nothing I did caused the test to fail. Tracing back this seems to have been caused by 3e6c83de which broke parsing of the command/check lines, leaving all tests passing without any checking. This commit provides a basic (although still not very robust) restoration of tests and a should-fail test which checks the parser is running

Rollup of 5 pull requests

- Successful merges: #46987, #47165, #47173, #47202, #47216
- Failed merges:

Clarify appending behavior of 'io::Read::read_to_string()'.

A simple doc clarification.

Fix search bar defocus

Fixes #47134.

r? @QuietMisdreavus

Remove some outdated LLVM-related code

Ticks two boxes on #46437

[unix] Don't clone command-line args on startup

Fixes part of #47164 and simplifies the `args` code on non-Apple Unix platforms.

Note: This could change behavior for programs that use both `std::env::args` *and* unsafe code that mutates `argv` directly.  However, these programs already behave differently on different platforms.  The new behavior on non-Apple platforms is closer to the existing behavior on Apple platforms.

Minor rewrite of env::current_exe docs; clarify symlinks.

- Update example in ‘security’ section to use hard links, like the
  linked securityvulns.com example.
- Weaken language on symbolic links – indicate behavior is
  platform-specific

Fixes https://github.com/rust-lang/rust/issues/43617.

Ideally, we should make use of CloudABI's internal proc_raise(SIGABRT)
system call. POSIX abort() requires things like flushing of stdios,
which may not be what we want under panic conditions. Invoking the raw
CloudABI system call would have prevented that.

Unfortunately, we have to make use of the "cloudabi" crate to invoke raw
CloudABI system calls. This is undesired, as discussed in the pull
request (#47190).

This showed up on the Windows bot for testing this PR, and this pr allows
`mark_incr_comp_session_as_invalid` ok if it's already invalid, hopefully
avoiding scary ICEs and instead leaving the nicely printed errors

This is only applicable when neither of --emit=llvm-ir or --emit=llvm-bc are not
requested.

In case either of these outputs are wanted, but the benefits of such context are
desired as well, -Zfewer_names option provides the same functionality regardless
of the outputs requested.

Implement TrustedRandomAccess for slice::{Chunks, ChunksMut, Windows}

As suggested by @bluss in https://github.com/rust-lang/rust/issues/47115#issuecomment-354888334

Rollup of 10 pull requests

- Successful merges: #47030, #47033, #47110, #47149, #47150, #47160, #47162, #47182, #47198, #47199
- Failed merges:

rustbuild: Don't allow stable bootstrap from dev

I forgot to update the bootstrap compiler for the 1.23.0 release so let's make
sure it doesn't happen again!

Fix an error in std::process documentation

Equivalent example for ? operator

The example with the ? operator in the documentation for try! macro was missing file.write_all.
Now all three examples are consistent.

Remove `T: Ord` bound from `BTreeSet::{is_empty, len}`

This change makes the API for `BTreeSet` more consistent with `BTreeMap`, where `BTreeMap::{is_empty, len}` don't require `T: Ord` either.

Also, it reduces the number of `impl`s for `BTreeSet`, making the generated documentation look much cleaner. Closes #47138.

cc @rust-lang/libs

This isn't in Rust 1.23

r? @alexcrichton

Return None from Span::join if in different files

Fixes #47148. r? @abonander