no tests - sorry

this does add some complexity, but to do otherwise would require unsized
lvalues to have their own allocas, which would be ugly.

The implementation itself only requires changes to trans, but
a few additional bugs concerning the handling of fat pointers
had to be fixed.

Fixes #29578

r? @nikomatsakis

My own observations are posted inline as comments.

BinaryHeap: Simplify sift down

Sift down was doing all too much work: it can stop directly when the
current element obeys the heap property in relation to its children.

In the old code, sift down didn't compare the element to sift down at
all, so it was maximally sifted down and relied on the sift up call to
put it in the correct location.

This should speed up heapify and .pop().

Also rename Hole::removed() to Hole::element()

Sift down was doing all too much work: it can stop directly when the
current element obeys the heap property in relation to its children.

In the old code, sift down didn't compare the element to sift down at
all, so it was maximally sifted down and relied on the sift up call to
put it in the correct location.

This should speed up heapify and .pop().

Also rename Hole::removed() to Hole::element()

Just `sed s/_nopanic//g`.  Hopefully makes libsyntax a bit more
readable.

Fundamental attribute was missing a feature gate test.

sort: Fast path for already sorted data

When merging two sorted blocks `left` and `right` if the last element in
`left` is <= the first in `right`, the blocks are already in sorted order.

Add this as an additional fast path by simply copying the whole left
block into the output and advancing the left pointer. The right block is
then treated the same way by the already present logic in the merge
loop.

Can reduce runtime of .sort() to less than 50% of the previous, if the data
was already perfectly sorted. Sorted data with a few swaps are also
sorted quicker than before. The overhead of one comparison per merge
seems to be negligible.

cc @nagisa

This is my first code contribution to Rust, so I'm sure there are some issues with the changes I've made.

I've added the `quote_arg!`, `quote_block!`, `quote_path!`, and `quote_meta_item!` quasiquoting macros. From my experience trying to build AST in compiler plugins, I would like to be able to build any AST piece with a quasiquoting macro (e.g., `quote_struct_field!` or `quote_variant!`) and then use those AST pieces in other quasiquoting macros, but this pull request just adds some of the low-hanging fruit.

I'm not sure if these additions are desirable, and I'm sure these macros can be implemented in an external crate if not.

Adds `Example` sections to the rest of the integer methods.

cc @steveklabnik

For now, this pass does some easy transformations, like eliminating
empty blocks that just jump to another block, some trivial
conversion of If terminators into Gotos and removal of dead blocks.

r? @nikomatsakis

For now, this pass does some easy transformations, like eliminating
empty blocks that just jump to another block, some trivial
conversion of If terminators into Gotos and removal of dead blocks.

Did this alphabetically, so I didn't see [how `std` was doing things](https://dxr.mozilla.org/rust/source/src/libstd/lib.rs#215) till I was nearly finished. If you prefer to add crate-level-whitelists like std instead of test-level, I can rebase with that strategy.

A number of these commits can probably be dropped as the crates don't have much to test, and are deprecated. Let me know which if any to drop! (can also squash after review if desired)

r? @steveklabnik

`format_args!` doesn't support none Sized types so we should just pass it the references to `left_val` and `right_val`.

The following works:
```rust
assert!([1, 2, 3][..] == vec![1, 2, 3][..])
```
So I would expect this to as well:
```rust
assert_eq!([1, 2, 3][..], vec![1, 2, 3][..])
```
But it fails with "error: the trait `core::marker::Sized` is not implemented for the type `[_]` [E0277]"
I don't know if this change will have any nasty side effects I don't understand.

- Successful merges: #29776, #29785, #29786, #29787
- Failed merges:

Fix usage of wrong article in `Result` docs.

This is my first rust PR, if something about the process is wrong let me know.

As this is a documentation change, I believe the correct highfive line to use is the following:

r? @steveklabnik

This mostly brings them in line with existing linking convention, but
also has some minor re-wording.

The text at the top has been re-focused, by starting out with what the
prelude does, rather than starting from injecting std.

Also, it now mentions that other preludes exist.

Part of https://github.com/rust-lang/rust/issues/29369

In previous PRs, I changed the match desugaring to generate more efficient code for ints/chars and the like. But this doesn't help when you're matching strings, ranges, or other crazy complex things (leading to #29740). This commit restructures match desugaring *yet again* to handle that case better -- basically we now degenerate to an if-else-if chain in such cases.

~~Note that this builds on https://github.com/rust-lang/rust/pull/29763 which will hopefully land soon. So ignore the first few commits.~~ landed now

r? @Aatch since he's been reviewing the other commits in this series