Add lint for intra link resolution failure
This PR is almost done, just remains this note:
```
note: requested on the command line with `-W intra-link-resolution-failure`
```
I have no idea why my lint is considered as being passed through command line and wasn't able to find where it was set. If anyone has an idea, it'd be very helpful!
cc @QuietMisdreavus
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.
Introduce a TargetTriple enum to support absolute target paths
This PR replaces target triple strings with a `TargetTriple` enum, which represents either a target triple or a path to a JSON target file. The path variant is used if the `--target` argument has a `.json` extension, else the target triple variant is used.
The motivation of this PR is support for absolute target paths to avoid the need for setting the `RUST_TARGET_PATH` environment variable (see rust-lang/cargo#4905 for more information). For places where some kind of triple is needed (e.g. in the sysroot folder), we use the file name (without extension).
For compatibility, we keep the old behavior of searching for a file named `$(target_triple).json` in `RUST_TARGET_PATH` for non-official target triples.
rustdoc: don't crash when an external trait's docs needs to import another trait
Fixes https://github.com/rust-lang/rust/issues/48414
When resolving intra-paths for an item, rustdoc needs to have information about their items on hand, for proper bookkeeping. When loading a path for an external item, it needs to load these items from their host crate, since their information isn't otherwise available. This includes resolving paths for those docs. which can cause this process to recurse. Rustdoc keeps a map of external traits in a `RefCell<HashMap<DefId, Trait>>`, and it keeps a borrow of this active when importing an external trait. In the linked crash, this led to a RefCell borrow error, panic, and ICE.
This PR manually releases the borrow while importing the trait, and also keeps a list of traits being imported at the given moment. The latter keeps rustdoc from infinitely recursing as it tries to import the same trait repeatedly.
A new section is added to both both struct and trait doc pages.
On struct/enum pages, a new 'Auto Trait Implementations' section displays any
synthetic implementations for auto traits. Currently, this is only done
for Send and Sync.
On trait pages, a new 'Auto Implementors' section displays all types
which automatically implement the trait. Effectively, this is a list of
all public types in the standard library.
Synthesized impls for a particular auto trait ('synthetic impls') take
into account generic bounds. For example, a type 'struct Foo<T>(T)' will
have 'impl<T> Send for Foo<T> where T: Send' generated for it.
Manual implementations of auto traits are also taken into account. If we have
the following types:
'struct Foo<T>(T)'
'struct Wrapper<T>(Foo<T>)'
'unsafe impl<T> Send for Wrapper<T>' // pretend that Wrapper<T> makes
this sound somehow
Then Wrapper will have the following impl generated:
'impl<T> Send for Wrapper<T>'
reflecting the fact that 'T: Send' need not hold for 'Wrapper<T>: Send'
to hold
Lifetimes, HRTBS, and projections (e.g. '<T as Iterator>::Item') are
taken into account by synthetic impls
However, if a type can *never* implement a particular auto trait
(e.g. 'struct MyStruct<T>(*const T)'), then a negative impl will be
generated (in this case, 'impl<T> !Send for MyStruct<T>')
All of this means that a user should be able to copy-paste a synthetic
impl into their code, without any observable changes in behavior
(assuming the rest of the program remains unchanged).
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.
