Allow `!` as the return type of proc/closure literals

Fixes #13490.
Change rustc to say `array` instead of `vector`
core: Make TwoWaySearcher reset its prefix memory when shifting by byteset

Closes #16878.
Add many comments to TwoWaySearcher.
Add some tests for closures that return `!`
Change method lookup to require invariance for mutable references

Fixes #17033.
Fixes #15965.
ignore uninitialized submodules when checking if ./configure should be re-run
fixes for Box<[T]>

The pointer in the slice must not be null, because enum representations
make that assumption. The `exchange_malloc` function returns a non-null
sentinel for the zero size case, and it must not be passed to the
`exchange_free` lang item.

Since the length is always equal to the true capacity, a branch on the
length is enough for most types. Slices of zero size types are
statically special cased to never attempt deallocation. This is the same
implementation as `Vec<T>`.

Closes #14395
Add links to forums in README.md, including discuss.rust-lang.org
Fix snapshot.py for win64
Fix naming of windows installer
Implement tuple and tuple struct indexing

This allows code to access the fields of tuples and tuple structs:

    let x = (1i, 2i);
    assert_eq!(x.1, 2);

    struct Point(int, int);
    let origin = Point(0, 0);
    assert_eq!(origin.0, 0);
    assert_eq!(origin.1, 0);
Avoid ever constructing cyclic types in the first place, rather than detecting them in resolve. This simplifies logic elsewhere in the compiler. cc #5527
Prefer lualatex, xelatex, pdflatex, in that order. #12804
Don't ICE on macros with -Z show-span

Closes #17115
Add unnecessary_import_braces lint.

The lint checks any unnecessary braces around one imported item like
`use std::num::{abs};`.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
auto merge of #17109 : brson/rust/win64snap, r=alexcrichton
auto merge of #17129 : epdtry/rust/misc/llvm-root-reconfig, r=brson

Currently `./configure --llvm-root=...` and similar flags will break incremental builds by forcing reconfiguration on every `make`.  This happens because `reconfig.mk` incorrectly treats submodules in the `-` (uninitialized) state as requiring reconfiguration, and `./configure` deliberately deinitializes unneeded submodules.  The fix is to reconfigure only when submodules are in the `+` state (wrong commit checked out).
Change ItemModifier and ItemDecorator to traits

For convenience, the traits are implemented for the respective bare
functions. Change code from this:

```rust
ItemDecorator(some_function)
// or
ItemModifier(some_other_function)
```
to
```rust
ItemDecorator(box some_function)
// or
ItemModifier(box some_other_function)
```

[breaking-change]
auto merge of #16680 : brson/rust/readme, r=steveklabnik

This adds links to SO, reddit, and discuss to the README. The main intent is to start advertising discuss.rust-lang.org more, in a location that doesn't mislead casual users to it (people who are building Rust are more likely to be the right audience than those that are just visiting the web site).