This commit tweaks a few stable APIs in the `beta` branch before they hit
stable. The `str::is_whitespace` and `str::is_alphanumeric` functions were
deleted (added in #49381, issue at #49657). The `and_modify` APIs added
in #44734 were altered to take a `FnOnce` closure rather than a `FnMut` closure.
Closes#49581Closes#49657
rustdoc: add an --edition flag to compile docs/doctests with a certain edition
To correspond with the 2018 edition, this adds a (currently unstable) `--edition` flag to rustdoc that makes it compile crates and doctests with the given edition. Once this lands, Cargo should be updated to pass this flag when the edition configuration option is given.
rustdoc: move manual "extern crate" statements outside automatic "fn main"s in doctests
Gated on https://github.com/rust-lang/rust/pull/48095 - I based the branch atop that so i could show off the change in one of its tests, the actual change in this PR is just the last commit
There are a handful of unfortunate assumptions in the way rustdoc processes `extern crate` statements in doctests:
1. In the absence of an `extern crate` statement in the test, if the test also uses the local crate name, it will automatically insert an `extern crate cratename;` statement into the test.
2. If the doctest *does* include an `extern crate` statement, rustdoc will not automatically insert one, on the assumption that doing so would introduce a duplicate import.
3. If a doctest does not have the substring `fn main` outside a comment, rustdoc will wrap the whole doctest in a generated `fn main` so it can be compiled.
In short, whenever you write a doctest like this...
```rust
//! extern crate my_crate;
//! my_crate::some_cool_thing();
```
...rustdoc will turn it into (something like) this:
```rust
fn main() {
extern crate my_crate;
my_crate::some_cool_thing();
}
```
This creates issues when compiled, because now `my_crate` isn't even properly in scope! This forces people who want to have multiple crates in their doctests (or an explicit `extern crate` statement) to also manually include their own `fn main`, so rustdoc doesn't put their imports in the wrong place.
This PR just taps into another processing step rustdoc does to doctests: Whenever you add an `#![inner_attribute]` to the beginning of a doctest, rustdoc will actually splice those out and put it before the generated `fn main`. Now, we can just do the same with `extern crate`s at the beginning, too, and get a much nicer experience.
Now, the above example will be converted into this:
```rust
extern crate my_crate;
fn main() {
my_crate::some_cool_thing();
}
```
Is it really time? Have our months, no, *years* of suffering come to an end? Are we finally able to cast off the pall of Hoedown? The weight which has dragged us down for so long?
-----
So, timeline for those who need to catch up:
* Way back in December 2016, [we decided we wanted to switch out the markdown renderer](https://github.com/rust-lang/rust/issues/38400). However, this was put on hold because the build system at the time made it difficult to pull in dependencies from crates.io.
* A few months later, in March 2017, [the first PR was done, to switch out the renderers entirely](https://github.com/rust-lang/rust/pull/40338). The PR itself was fraught with CI and build system issues, but eventually landed.
* However, not all was well in the Rustdoc world. During the PR and shortly after, we noticed [some differences in the way the two parsers handled some things](https://github.com/rust-lang/rust/issues/40912), and some of these differences were major enough to break the docs for some crates.
* A couple weeks afterward, [Hoedown was put back in](https://github.com/rust-lang/rust/pull/41290), at this point just to catch tests that Pulldown was "spuriously" running. This would at least provide some warning about spurious tests, rather than just breaking spontaneously.
* However, the problems had created enough noise by this point that just a few days after that, [Hoedown was switched back to the default](https://github.com/rust-lang/rust/pull/41431) while we came up with a solution for properly warning about the differences.
* That solution came a few weeks later, [as a series of warnings when the HTML emitted by the two parsers was semantically different](https://github.com/rust-lang/rust/pull/41991). But that came at a cost, as now rustdoc needed proc-macro support (the new crate needed some custom derives farther down its dependency tree), and the build system was not equipped to handle it at the time. It was worked on for three months as the issue stumped more and more people.
* In that time, [bootstrap was completely reworked](https://github.com/rust-lang/rust/pull/43059) to change how it ordered compilation, and [the method by which it built rustdoc would change](https://github.com/rust-lang/rust/pull/43482), as well. This allowed it to only be built after stage1, when proc-macros would be available, allowing the "rendering differences" PR to finally land.
* The warnings were not perfect, and revealed a few [spurious](https://github.com/rust-lang/rust/pull/44368) [differences](https://github.com/rust-lang/rust/pull/45421) between how we handled the renderers.
* Once these were handled, [we flipped the switch to turn on the "rendering difference" warnings all the time](https://github.com/rust-lang/rust/pull/45324), in October 2017. This began the "warning cycle" for this change, and landed in stable in 1.23, on 2018-01-04.
* Once those warnings hit stable, and after a couple weeks of seeing whether we would get any more reports than what we got from sitting on nightly/beta, [we switched the renderers](https://github.com/rust-lang/rust/pull/47398), making Pulldown the default but still offering the option to use Hoedown.
And that brings us to the present. We haven't received more new issues from this in the meantime, and the "switch by default" is now on beta. Our reasoning is that, at this point, anyone who would have been affected by this has run into it already.
Building on the work of # 45684 this commit updates the compiler to
unconditionally load the `rustc_trans` crate at runtime instead of linking to it
at compile time. The end goal of this work is to implement # 46819 where rustc
will have multiple backends available to it to load.
This commit starts off by removing the `extern crate rustc_trans` from the
driver. This involved moving some miscellaneous functionality into the
`TransCrate` trait and also required an implementation of how to locate and load
the trans backend. This ended up being a little tricky because the sysroot isn't
always the right location (for example `--sysroot` arguments) so some extra code
was added as well to probe a directory relative to the current dll (the
rustc_driver dll).
Rustbuild has been updated accordingly as well to have a separate compilation
invocation for the `rustc_trans` crate and assembly it accordingly into the
sysroot. Finally, the distribution logic for the `rustc` package was also
updated to slurp up the trans backends folder.
A number of assorted fallout changes were included here as well to ensure tests
pass and such, and they should all be commented inline.
