We currently compiled bools to i8 values, because there was a bug in
LLVM that sometimes caused miscompilations when using i1 in, for
example, structs.

Using i8 means a lot of unnecessary zero-extend and truncate operations
though, since we have to convert the value from and to i1 when using for
example icmp or br instructions. Besides the unnecessary overhead caused
by this, it also sometimes made LLVM miss some optimizations.

First, we have to fix some bugs concerning the handling of
attributes in foreign function declarations and calls. These
are required because the i1 type needs the ZExt attribute when
used as a function parameter or return type.

Then we have to update LLVM to get a bugfix without which LLVM
sometimes generates broken code when using i1.

And then, finally, we can switch bools over to i1.

We currently compiled bools to i8 values, because there was a bug in
LLVM that sometimes caused miscompilations when using i1 in, for
example, structs.

Using i8 means a lot of unnecessary zero-extend and truncate operations
though, since we have to convert the value from and to i1 when using for
example icmp or br instructions. Besides the unnecessary overhead caused
by this, it also sometimes made LLVM miss some optimizations.

Fixes #8106.

To fix #8106, we need an LLVM version that contains r211082 aka 0dee6756
which fixes a bug that blocks that issue.

There have been some tiny API changes in LLVM, and cmpxchg changed its
return type. The i1 part of the new return type is only interesting when
using the new weak cmpxchg, which we don't do.

When calling a foreign function, some arguments and/or return value
attributes are required to conform to the foreign ABI. Currently those
attributes are only added to the declaration of foreign functions. With
direct calls, this is no problem, because LLVM can see that those
attributes apply to the call. But with an indirect call, LLVM cannot do
that and the attribute is missing.

To fix that, we have to add those attribute to the calls to foreign
functions as well.

This also allows to remove the special handling of the SRet attribute,
which is ABI-dependent and will be set via the `attr` field of the
return type's `ArgType`.

The ArgType type gives us a generic way to specify an attribute for a
type to ensure ABI conformance for foreign functions. But the code that
actually sets the argument attributes in the function declaration
only sets the attribute for the return type when the type is indirect.

Since LLVMAddAttribute() doesn't allow to set attributes on the return
type, we have to use LLVMAddFunctionAttribute() instead.

This didn't cause problems yet, because currently only some indirect
types require attributes to be set.

Using something like:

```rust
box "string"
```

yields
```shell
"`~\"string\"` has been removed; use `\"string\".to_string()` instead"
```

Should the error message maybe say `box "string"` instead?

This will break code that looks like `Box<Trait+>`. Change that code to
`Box<Trait>` instead.

Closes #14925.

[breaking-change]

r? @brson

This commit makes several changes to the stability index infrastructure:

* Stability levels are now inherited lexically, i.e., each item's
  stability level becomes the default for any nested items.

* The computed stability level for an item is stored as part of the
  metadata. When using an item from an external crate, this data is
  looked up and cached.

* The stability lint works from the computed stability level, rather
  than manual stability attribute annotations. However, the lint still
  checks only a limited set of item uses (e.g., it does not check every
  component of a path on import). This will be addressed in a later PR,
  as part of issue #8962.

* The stability lint only applies to items originating from external
  crates, since the stability index is intended as a promise to
  downstream crates.

* The "experimental" lint is now _allow_ by default. This is because
  almost all existing crates have been marked "experimental", pending
  library stabilization. With inheritance in place, this would generate
  a massive explosion of warnings for every Rust program.

  The lint should be changed back to deny-by-default after library
  stabilization is complete.

* The "deprecated" lint still warns by default.

The net result: we can begin tracking stability index for the standard
libraries as we stabilize, without impacting most clients.

Closes #13540.

This PR is changing the error messages for non-exhaustive pattern matching to include a more accurate witness, i.e. a pattern that is not covered by any of the ones provided by the user. Example:

```rust
fn main() {
	match (true, (Some("foo"), [true, true]), Some(42u)) {
		(false, _, _) => (),
		(true, (None, [true, _]), None) => (),
		(true, (None, [false, _]), Some(1u)) => ()
	}
}
```

```sh
/tmp/witness.rs:2:2: 6:3 error: non-exhaustive patterns: (true, (core::option::Some(_), _), _) not covered
/tmp/witness.rs:2 	match (true, (Some("foo"), [true, true]), Some(42u)) {
/tmp/witness.rs:3 		(false, _, _) => (),
/tmp/witness.rs:4 		(true, (None, [true, _]), None) => (),
/tmp/witness.rs:5 		(true, (None, [false, _]), Some(1u)) => ()
/tmp/witness.rs:6 	}
```

As part of that, I refactored some of the relevant code and carried over the changes to fixed vectors from the previous PR.

I'm putting it out there for now but the tests will be red.

This will break code that looks like `Box<Trait+>`. Change that code to
`Box<Trait>` instead.

Closes #14925.

[breaking-change]

Closes #8142.

This is not the semantics we want long-term. You can continue to use
`#[unsafe_destructor]`, but you'll need to add
`#![feature(unsafe_destructor)]` to the crate attributes.

[breaking-change]

r? @alexcrichton

Closes #8142.

This is not the semantics we want long-term. You can continue to use
`#[unsafe_destructor]`, but you'll need to add
`#![feature(unsafe_destructor)]` to the crate attributes.

[breaking-change]

The parser already has special logic for parsing `>` tokens from `>>`, and this
commit extends the logic to the acquiring a `>` from the `>=` and `>>=` tokens
as well.

Closes #15043

The parser already has special logic for parsing `>` tokens from `>>`, and this
commit extends the logic to the acquiring a `>` from the `>=` and `>>=` tokens
as well.

Closes #15043

String patterns should have a single constructor of arity 0.

Fixed #13482

Fixes #7784

Fixed #4321

There is no space between the TOC and the succeeding para.

See http://doc.rust-lang.org/guide-pointers.html for example.

This corrects some misinformation.

This was erroneously disabled as part of 065e121f and it hasn't been turned on
since. This was a 3x perf improvement in a test of mine.

TaskPool is the only item in the std::sync doc that doesn't have a summary. This fixes that problem.

The struct and module doc comments are reformulated. The `execute`
method's documentation are put up to date, and failure information
is added. A test is also added to address the possible failure.

Splits 'extern resources' into 'external documentation and 'community',
adds rustforrubyists.com, rustbyexample.com, stackoverflow.com.

    ```test_harness
    #[test]
    fn foo() {}
    ```

will now compile and run the tests, rather than just ignoring & stripping them (i.e. it is as if `--test` was passed).

Also, the specific example in https://github.com/rust-lang/rust/issues/12242 was fixed (but that issue is broader than that example).

This corrects some misinformation.

There is no space between the TOC and the succeeding para.

rustdoc now supports compiling things with `--test` so the examples in
this guide can be compiled & tested properly (revealing a few issues &
out-dated behaviours).

Also, reword an example to be clearer, cc #12242.

This was erroneously disabled as part of 065e121f and it hasn't been turned on
since. This was a 3x perf improvement in a test of mine.

Continuing from #15012, this makes four changes to the `rustdoc` static files.

- Change the placeholder text of the search bar to `Click or press 'S' to search, '?' for more options...` to make keyboard hotkeys more apparent (capitalizing the `S` to match the help text).
- Change the `main.js` file to use browser-normalized key codes (`e.which`, from `jQuery`), instead of `e.keyCode`.
- Change the key code for `?` to be the correct `191` instead of `188`, so that the hotkey works to bring up search information.
- Change the search information to display `tab` and `shift+tab` instead of `up` and `down`, as those do not yet work outside of Firefox (see #15011). Also, adjust the height so it does not cut off the help text.

<s>I've also opened up #15038 about the non-functional `up` and `down` functionality, although this does nothing to fix it.</s>

Splits 'extern resources' into 'external documentation and 'community',
adds rustforrubyists.com and rustbyexample.com, stackoverflow.com.