Replaced outdated use of the `range(start, end)` function where appropriate with `start..end`, and tweaked the examples to compile and run with the latest rust. I also fixed two periphery compile issues in reference.md which were occluding whether there were any new errors created by these changes.

This PR adds a dedicated regression test for #15881 as @cmr suggested.

This PR is an optimization of the `FromIterator` implementation of `Vec`

Benchmark: https://gist.github.com/alexcrichton/03d666159a28a80e7c70

Before:

    test macro_repeat1     ... bench:        57 ns/iter (+/- 1)
    test macro_repeat2     ... bench:        56 ns/iter (+/- 1)
    test map_clone1        ... bench:       828 ns/iter (+/- 13)
    test map_clone2        ... bench:       828 ns/iter (+/- 8)
    test repeat1           ... bench:      1104 ns/iter (+/- 10)
    test repeat2           ... bench:      1106 ns/iter (+/- 11)

After:

    test macro_repeat1     ... bench:        75 ns/iter (+/- 21)
    test macro_repeat2     ... bench:        59 ns/iter (+/- 31)
    test map_clone1        ... bench:        34 ns/iter (+/- 22)
    test map_clone2        ... bench:        52 ns/iter (+/- 21)
    test repeat1           ... bench:        34 ns/iter (+/- 11)
    test repeat2           ... bench:        33 ns/iter (+/- 12)

The idea behind this optimization is to avoid all bounds checks for space
already allocated into the vector. This may involve running the iterator twice,
but the first run of the iterator should be optimizable to a memcpy or memset if
possible.

The same treatment can in theory be applied to `Vec::extend` but the benchmarks
for that currently get *worse* if the change is applied. This appears to be some
LLVM optimizations going awry but it's seems prudent to land at least the
`collect` portion beforehand.

Names of structs, enums, traits, type aliases and type parameters (i.e. all identifiers that can be used as full paths in type position) are not allowed to match the names of primitive types.
See #20427 for more information.

This is a minor [breaking-change]

borrowck: Prevent partial reinitialization of uninitialized structures

This is a pnkfelix-swiped squash of #22079, which was a rebase and revision of #18963

Fixes #18571.

This resolves a number of bugs that trigger stack overflows or other cyclic errors.

r? @nick29581 (it is based on work that you started)
f? @jroesch (also based on your branch)

and the type appearing in the trait would (previously) trigger an
error message. The code is now accepted. No reported issue that I am
aware of.

fetch trait definitions. This allows is to be used early in the compiler
without triggering ICEs. Also make -Z verbose less horrifyingly ugly.

predicates and renaming some things.

This PR is an optimization of the `FromIterator` implementation of `Vec`

Benchmark: https://gist.github.com/alexcrichton/03d666159a28a80e7c70

Before:
    test macro_repeat1     ... bench:        57 ns/iter (+/- 1)
    test macro_repeat2     ... bench:        56 ns/iter (+/- 1)
    test map_clone1        ... bench:       828 ns/iter (+/- 13)
    test map_clone2        ... bench:       828 ns/iter (+/- 8)
    test repeat1           ... bench:      1104 ns/iter (+/- 10)
    test repeat2           ... bench:      1106 ns/iter (+/- 11)

After:
    test macro_repeat1     ... bench:        75 ns/iter (+/- 21)
    test macro_repeat2     ... bench:        59 ns/iter (+/- 31)
    test map_clone1        ... bench:        34 ns/iter (+/- 22)
    test map_clone2        ... bench:        52 ns/iter (+/- 21)
    test repeat1           ... bench:        34 ns/iter (+/- 11)
    test repeat2           ... bench:        33 ns/iter (+/- 12)

The idea behind this optimization is to avoid all bounds checks for space
already allocated into the vector. This may involve running the iterator twice,
but the first run of the iterator should be optimizable to a memcpy or memset if
possible.

The same treatment can in theory be applied to `Vec::extend` but the benchmarks
for that currently get *worse* if the change is applied. This appears to be some
LLVM optimizations going awry but it's seems prudent to land at least the
`collect` portion beforehand.

and predicates. Try to document how things work. More cleanup is
needed here but I had to draw the line somewhere gosh darn it.

Split the predicates listing out of `TraitDef` and `TypeScheme` and into a separate map, `tcx.predicates`, that is used for both traits and other kinds of items. Also use two newtypes to distinguish
instantiated predicates from the raw, unsubstituted predicates extracted from the map.

enumerations that implement the `Drop` trait.

This breaks code like:

    struct Struct {
        f: String,
        g: String,
    }

    impl Drop for Struct { ... }

    fn main() {
        let x = Struct { ... };
        drop(x);
        x.f = ...;
    }

Change this code to not create partially-initialized structures. For
example:

    struct Struct {
        f: String,
        g: String,
    }

    impl Drop for Struct { ... }

    fn main() {
        let x = Struct { ... };
        drop(x);
        x = Struct {
            f: ...,
            g: ...,
        }
    }

Closes #18571.

[breaking-change]

----

(Joint authorship by pcwalton and Ryman; thanks all!)

There are two dots at the end of a line in the documentation of std::char.

Replaced outdated use of the `range(start, end)` function where
approriate with `start..end`, and tweaked the examples to compile and run with the latest rust. I also fixed two periphery compile issues in reference.md which were occluding whether there were any new errors created by these changes, so I fixed them.

PR #22012 followup: clean up vtable::check_object_cast by reusing `fresh_ty`

(hat tip to nikomatsakis, who was the one who pointed out this simplification to the logic.)

This flag seems to have erroneously been set to `true`.

(hat tip to nikomatsakis who was the one who pointed out this
simplification to the logic.)

- DoubleEndedIterator
- ExactSizeIterator
- RandomAccessIterator

This commit is an implementation of [RFC 807][rfc] which adds a `std::net`
module for basic neworking based on top of `std::io`. This module serves as a
replacement for the `std::old_io::net` module and networking primitives in
`old_io`.

[rfc]: fillmein

The major focus of this redesign is to cut back on the level of abstraction to
the point that each of the networking types is just a bare socket. To this end
functionality such as timeouts and cloning has been removed (although cloning
can be done through `duplicate`, it may just yield an error).

With this `net` module comes a new implementation of `SocketAddr` and `IpAddr`.
This work is entirely based on #20785 and the only changes were to alter the
in-memory representation to match the `libc`-expected variants and to move from
public fields to accessors.

This commit is an implementation of [RFC 807][rfc] which adds a `std::net`
module for basic neworking based on top of `std::io`. This module serves as a
replacement for the `std::old_io::net` module and networking primitives in
`old_io`.

[rfc]: fillmein

The major focus of this redesign is to cut back on the level of abstraction to
the point that each of the networking types is just a bare socket. To this end
functionality such as timeouts and cloning has been removed (although cloning
can be done through `duplicate`, it may just yield an error).

With this `net` module comes a new implementation of `SocketAddr` and `IpAddr`.
This work is entirely based on #20785 and the only changes were to alter the
in-memory representation to match the `libc`-expected variants and to move from
public fields to accessors.

- DoubleEndedIterator
- ExactSizeIterator
- RandomAccessIterator