This is not a compelling change in isolation, but it is a necessary
step.

Suggest call fn ctor passed as arg to fn with type param bounds

_Reviewer note: the relevant changes are in the second commit, the first is simple and mechanical, but verbose._

When forgetting to call a fn in an argument position to an fn that has a generic bound:

```rust
async fn foo() {}

fn bar(f: impl Future<Output=()>) {}

fn main() {
    bar(foo); // <- should be `bar(foo());`
}
```

suggest calling it:

```
error[E0277]: the trait bound `fn() -> impl std::future::Future {foo}: std::future::Future` is not satisfied
  --> $DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:9:5
   |
LL | fn bar(f: impl Future<Output=()>) {}
   | --------------------------------- required by `bar`
...
LL |     bar(foo);
   |     ^^^ the trait `std::future::Future` is not implemented for `fn() -> impl std::future::Future {foo}`
   |
   = help: it looks like you forgot to use parentheses to call the function: `foo()`
```

Fix #63100. Follow up to #63833 and #63337.

Rollup of 5 pull requests

Successful merges:

 - #63410 (Update BufWriter example to include call to flush())
 - #64029 (Account for rounding errors when deciding the diagnostic boundaries)
 - #64032 (rustdoc use -Ccodegen-units=1 by default for test compile)
 - #64039 (Update sync condvar doc style)
 - #64042 (Fix word repetition in str documentation)

Failed merges:

r? @ghost

Fix word repetition in str documentation

Fixes a few repetitions of "like like" in the `trim*` methods documentation of `str`.

Update sync condvar doc style

rustdoc use -Ccodegen-units=1 by default for test compile

as the test is small we do not want split up in multiple codegen units
and also as there is multiple test running at the same time this
will reduce the number of concurrent threads

tested the test time with `./x.py test src/libcore --doc`
for my 16 core 32 thread cpu i get about 6% faster execution
and my 2 core 4 thread cpu I get about 10% faster execution

cc #63638
 r? @Mark-Simulacrum

Account for rounding errors when deciding the diagnostic boundaries

Fix Miri by fixing the bug raised in https://github.com/rust-lang/rust/pull/63402#discussion_r319485328.

Fixes https://github.com/rust-lang/rust/issues/64020

Update BufWriter example to include call to flush()

I was playing with a writing a Huffman encoder/decoder and was getting weird corruptions and truncations.  I finally realized it was was because `BufWriter` was swallowing write errors 😬.  I've found Rust to generally be explicit and err on the safe side, so I definitely found this unintuitive and not "rustic".

https://twitter.com/johnterickson/status/1159514988123312128

Kill borrows from assignments after generating new borrows

Closes #63719

rustdoc: warn on empty doc test

Closes #60319.

A doc test that only contains whitespace should result in a warning.

This PR adds detection of empty doc tests to `check-code-block-syntax`, as having an invalid doc test is mutually exclusive with an empty doc test.

Fixes a few repetitions of "like like" in the `trim*` methods documentation of `str`.

remove directory libstd/sys/vxworks/backtrace which is not used any more

r? @alexcrichton
cc @n-salim

`improper_ctypes`: guard against accidental change to `Unique<T>`

r? @EddyB

Properly account for left margin when setting terminal width through
CLI flag and don't trim code by default if we can't get the terminal's
dimensions.

Update rustfmt to 1.4.6

This PR updates rustfmt to 1.4.6. [CHANGELOG](https://github.com/rust-lang/rustfmt/blob/v1.4.6/CHANGELOG.md#146-2019-08-28).

Rollup of 7 pull requests

Successful merges:

 - #62957 (Match the loop examples)
 - #63600 (Merge oli-obk mail addresses)
 - #63684 (Constify LinkedList new function)
 - #63847 ([rustdoc] Fix system theme detection)
 - #63999 (Add missing links on AsRef trait)
 - #64014 ( miri: detect too large dynamically sized objects )
 - #64015 (some const-eval test tweaks)

Failed merges:

r? @ghost

some const-eval test tweaks

Best reviewed commit-by-commit.

r? @oli-obk

 miri: detect too large dynamically sized objects

Needed to make https://github.com/rust-lang/miri/pull/929 pass.

r? @oli-obk

Add missing links on AsRef trait

cc @rust-lang/docs

[rustdoc] Fix system theme detection

Fixes #63830

The problem is that it returns the property "entirely" (so with the quotes in our case). Removing them fixes the issue.

cc @fenhl

r? @kinnison

Constify LinkedList new function

Change the `LinkedList::new()` function to become a const fn, allowing the use in constant context.

Merge oli-obk mail addresses