- Rename `broken_intra_doc_links` to `rustdoc::broken_intra_doc_links`
- Ensure that the old lint names still work and give deprecation errors
- Register lints even when running doctests

  Otherwise, all `rustdoc::` lints would be ignored.

- Register all existing lints as removed

  This unfortunately doesn't work with `register_renamed` because tool
  lints have not yet been registered when rustc is running. For similar
  reasons, `check_backwards_compat` doesn't work either. Call
  `register_removed` directly instead.

- Fix fallout

  + Rustdoc lints for compiler/
  + Rustdoc lints for library/

Note that this does *not* suggest `rustdoc::broken_intra_doc_links` for
`rustdoc::intra_doc_link_resolution_failure`, since there was no time
when the latter was valid.

- Use `register_renamed` when rustdoc is running so the lint will still
  be active and use a structured suggestion
- Test the behavior for rustc, not just for rustdoc (because it differs)

- Move MISSING_CRATE_LEVEL_DOCS to rustdoc directly
- Update documentation

This also takes the opportunity to make the `no-crate-level-doc-lint`
test more specific.

Note that the FIXME was removed because this can't be fixed,
`register_renamed` calls LintId::of and there's no LintId for rustdoc
lints when rustc is running.

Instead of being loaded on every page, the JS search index is now
loaded when either (a) there is a `?search=` param, or (b) the search
input is focused.

This saves both CPU and bandwidth. As of Feb 2021,
https://doc.rust-lang.org/search-index1.50.0.js is 273,838 bytes
gzipped or 2,544,939 bytes uncompressed. Evaluating it takes 445 ms
of CPU time in Chrome 88 on a i7-10710U CPU (out of a total ~2,100
ms page reload).

Generate separate JS file with crate names.

This is much smaller than the full search index, and is used in the "hot
path" to draw the page. In particular it's used to crate the dropdown
for the search bar, and to append a list of crates to the sidebar (on
some pages).

Skip early search that can bypass 500ms timeout.

This was occurring when someone had typed some text during the load of
search-index.js. Their query was usually not ready to execute, and the
search itself is fairly expensive, delaying the overall load, which
delayed the input / keyup events, which delayed eventually executing the
query.

Add font-display: swap. Per https://web.dev/font-display/, this prevents
"flash of invisible text" during load by using a system font until the
custom font is available. I've noticed this flash of invisible text
occasionally when reading Rust docs.

Add an explicit height to icons (which already had an explicit width)
to allow browsers to lay out the page more accurately before the icons
have been loaded. https://web.dev/optimize-cls/.

Add min-width: 115px to the crate search dropdown. When the HTML first
loads, this dropdown includes only the text "All crates." Later, JS
loads the items underneath it, some of which are wider. That causes
the dropdown to get wider, causing a distracting reflow. This sets a
min-width based on the size that the dropdown eventually becomes based
on the crates on doc.rust-lang.org, reducing page movement during load.

Fix rust-lang#70152.

On most platforms and browsers, `sans-serif` is equivalent to Arial.
However, on Firefox on Ubuntu (and possibly other Linuxes), `sans-serif`
is DejaVu Sans, a much wider font. This creates a larger shift in text
when the custom fonts finally load. Arial is a web-safe font, and
specifying it explicitly gives us more cross-platform consistency, as
well as reducing the layout shift that happens when fonts load.

Co-authored-by: Ralf Jung <post@ralfj.de>

On reflection on the issue in rust-lang#79540 (comment),  I think the bug was actually using the `compiler/` filter, not using `--author=bors`. rust-lang@9a1d617 has no CI artifacts because it was merged as part of a rollup:
```
$ curl -I https://ci-artifacts.rust-lang.org/rustc-builds/96e843ce6ae42e0aa519ba45e148269de347fd84/rust-std-nightly-x86_64-unknown-linux-gnu.tar.xz
HTTP/2 404
```
So 9a1d617 is the correct commit to download, and that's what `--author=bors` does:

$ git log --author=bors 4aec8a5
commit 9a1d617

Ideally it would look for "the most recent bors commit not followed by a change to `compiler/`", which would exclude things like documentation changes and avoid redownloading more than necessary, but
- Redownloading isn't the end of the world,
- That metric is hard to implement, and
- Documentation-only or library-only changes are very rare anyway since they're usually rolled up with changes to the compiler.

It's more idiomatic to pass a small Copy type by value and `CrateNum` is
half the size of `&CrateNum` on 64-bit systems. The memory use change is
almost certainly insignificant, but why not!

Make rustdoc lints a tool lint instead of built-in

- Rename `broken_intra_doc_links` to `rustdoc::broken_intra_doc_links` (and similar for other rustdoc lints; I don't expect any others to be used frequently, though).
- Ensure that the old lint names still work and give deprecation errors
- Register lints even when running doctests
- Move lint machinery into a separate file
- Add `declare_rustdoc_lint!` macro

Unblocks rust-lang#80300, rust-lang#79816, rust-lang#80965. Makes the strangeness in rust-lang#77364 more apparent to the end user (note that `missing_docs` is *not* moved to rustdoc in this PR). Closes rust-lang#78786.

## Current status

This is blocked on rust-lang#82620 (see rust-lang#80527 (comment))

…laumeGomez

Load rustdoc's JS search index on-demand.

Instead of being loaded on every page, the JS search index is now loaded when either (a) there is a `?search=` param, or (b) the search input is focused.

This saves both CPU and bandwidth. As of Feb 2021, https://doc.rust-lang.org/search-index1.50.0.js is 273,838 bytes gzipped or 2,544,939 bytes uncompressed. Evaluating it takes 445 ms of CPU time in Chrome 88 on a i7-10710U CPU (out of a total ~2,100 ms page reload).

Tested on Firefox and Chrome.

New:
https://jacob.hoffman-andrews.com/rust/search-on-demand/std/primitive.slice.html
https://jacob.hoffman-andrews.com/rust/search-on-demand/std/primitive.slice.html?search=fn

Old:
https://jacob.hoffman-andrews.com/rust/search-on-load/std/primitive.slice.html
https://jacob.hoffman-andrews.com/rust/search-on-load/std/primitive.slice.html?search=fn

…Gomez

Improve page load performance in rustdoc

Add an explicit height to icons (which already had an explicit width) to allow browsers to lay out the page more accurately before the icons have been loaded. https://web.dev/optimize-cls/.

Add min-width: 115px to the crate search dropdown. When the HTML first loads, this dropdown includes only the text "All crates." Later, JS loads the items underneath it, some of which are wider. That causes the dropdown to get wider, causing a distracting reflow. This sets a min-width based on the size that the dropdown eventually becomes based on the crates on doc.rust-lang.org, reducing page movement during load.

Add font-display: swap. Per https://web.dev/font-display/, this prevents "flash of invisible text" during load by using a system font until the custom font is available. I've noticed this flash of invisible text occasionally when reading Rust docs. Note that users without cached fonts will see text, and then see it reflow. For `docs.rust-lang.org`, [setting caching headers will help a lot](rust-lang/simpleinfra#62).

Generated output at https://jacob.hoffman-andrews.com/rust/flow-improvements/std/string/struct.String.html.

…lfJung

Revert `Vec::spare_capacity_mut` impl to prevent pointers invalidation

The implementation was changed in rust-lang#79015.

Later it was [pointed out](rust-lang#81944 (comment)) that the implementation invalidates pointers to the buffer (initialized elements) by creating a unique reference to the buffer. This PR reverts the implementation.

r? ```@RalfJung```

Fix stabilization version of move_ref_pattern

Both the [changelog](https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1490-2020-12-31) and the milestone of the [stabilization PR](rust-lang#76119) say 1.49.0, but the source says 1.48.0. I think the former is correct.

Account for macros when suggesting adding lifetime

Fix rust-lang#70152.

…acrum

Fix commit detected when using `download-rustc`

On reflection on the issue in rust-lang#79540 (comment), I think the bug was actually using the `compiler/` filter, not using `--author=bors`. rust-lang@9a1d617 has no CI artifacts because it was merged as part of a rollup:
```
$ curl -I https://ci-artifacts.rust-lang.org/rustc-builds/96e843ce6ae42e0aa519ba45e148269de347fd84/rust-std-nightly-x86_64-unknown-linux-gnu.tar.xz
HTTP/2 404
```
So 9a1d617 is the correct commit to download, and that's what `--author=bors` does:

$ git log --author=bors 4aec8a5
commit 9a1d617

Ideally it would look for "the most recent bors commit not followed by a change to `compiler/`", which would exclude things like documentation changes and avoid redownloading more than necessary, but
- Redownloading isn't the end of the world,
- That metric is hard to implement, and
- Documentation-only or library-only changes are very rare anyway since they're usually rolled up with changes to the compiler.

Helps with rust-lang#81930.

r? `@Mark-Simulacrum`

…Gomez

Pass `CrateNum` by value instead of by reference

It's more idiomatic to pass a small Copy type by value and `CrateNum` is
half the size of `&CrateNum` on 64-bit systems. The memory use change is
almost certainly insignificant, but why not!