It prevents a full rebuild of stage 1 compiler when issuing "x.py test"
with rust.lto != thin-local in config.toml.

Two optimizations for the function signature search:

* Instead of using JSON arrays, like `[1,20]`, it uses VLQ
  hex with no commas, like `[aAd]`.
* This also adds backrefs: if you have more than one function
  with exactly the same signature, it'll not only store it once,
  it'll *decode* it once, and store in the typeIdMap only once.

Size change
-----------

standard library

```console
$ du -bs search-index-old.js search-index-new.js
4976370 search-index-old.js
4404391 search-index-new.js
```

((4976370-4404391)/4404391)*100% = 12.9%

Benchmarks are similarly shrunk:

```console
$ du -hs tmp/{arti,cortex-m,sqlx,stm32f4,ripgrep}/toolchain_{old,new}/doc/search-index.js
10555067        tmp/arti/toolchain_old/doc/search-index.js
8921236 tmp/arti/toolchain_new/doc/search-index.js
77018   tmp/cortex-m/toolchain_old/doc/search-index.js
66676   tmp/cortex-m/toolchain_new/doc/search-index.js
2876330 tmp/sqlx/toolchain_old/doc/search-index.js
2436812 tmp/sqlx/toolchain_new/doc/search-index.js
63632890        tmp/stm32f4/toolchain_old/doc/search-index.js
52337438        tmp/stm32f4/toolchain_new/doc/search-index.js
631150  tmp/ripgrep/toolchain_old/doc/search-index.js
541646  tmp/ripgrep/toolchain_new/doc/search-index.js
```

…ans`

This draws a clear distinction between the fields/methods that are needed by
initial span extraction and preprocessing, and those that are needed by the
main "refinement" loop.

The struct itself is already non-public, so having public fields doesn't
achieve anything.

nightly feature

(Using this attribute still requires a nightly feature, this just
enables that this feature does not need to be enabled on the child crate
as well)

`#[diagnostic::on_unimplemented]`

This commit replaces those `#[rustc_on_unimplemented]` attributes with
their equivalent `#[diagnostic::on_unimplemented]` where this is
supported (So no filter or any extended option)

the corresponding feature.

…tinem

coverage: Hoist some complex code out of the main span refinement loop

The span refinement loop in `spans.rs` takes the spans that have been extracted from MIR, and modifies them to produce more helpful output in coverage reports.

It is also one of the most complicated pieces of code in the coverage instrumentor. It has an abundance of moving pieces that make it difficult to understand, and most attempts to modify it end up accidentally changing its behaviour in unacceptable ways.

This PR nevertheless tries to make a dent in it by hoisting two pieces of special-case logic out of the main loop, and into separate preprocessing passes. Coverage tests show that the resulting mappings are *almost* identical, with all known differences being unimportant.

This should hopefully unlock further simplifications to the refinement loop, since it now has fewer edge cases to worry about.

…in_stdlib, r=compiler-errors

Use diagnostic namespace in stdlib

This required a minor fix to have the diagnostics shown in third party crates when the `diagnostic_namespace` feature is not enabled. See rust-lang@5d63f5d for details. I've opted for having a single PR for both changes as it's really not that much code. If it is required it should be easy to split up the change into several PR's.

r? `@compiler-errors`

…ulacrum

bootstrap: Move -Clto= setting from Rustc::run to rustc_cargo

It prevents a full rebuild of stage 1 compiler when issuing "x.py test" with rust.lto != thin-local in config.toml.

…errors

Handle ForeignItem as TAIT scope.

Fixes rust-lang#119295

…=GuillaumeGomez

rustdoc-search: tighter encoding for f index

Depends on rust-lang#119457

Two optimizations for the function signature search:

* Instead of using JSON arrays, like `[1,20]`, it uses VLQ
  hex with no commas, like `[aAd]`.
* This also adds backrefs: if you have more than one function
  with exactly the same signature, it'll not only store it once,
  it'll *decode* it once, and store in the typeIdMap only once.

Based partially on discussions on zulip:
https://rust-lang.zulipchat.com/#narrow/stream/266220-t-rustdoc/topic/search.20index.20size

Performance
-----------

https://notriddle.com/rustdoc-html-demo-8/compression-perf-v2/index.html

### memory/time profiler output (for more details, consult the above link)

<table>
<thead><tr><th>benchmark<th>before<th>after</tr></thead>
<tbody>
<tr><th>arti<td>

```
user: 002.789 s
sys:  000.390 s
wall: 002.096 s
child_RSS_high:     440796 KiB
group_mem_high:     414924 KiB
```

</td><td>

```
user: 002.295 s
sys:  000.278 s
wall: 001.738 s
child_RSS_high:     314588 KiB
group_mem_high:     285220 KiB
```

</td></tr><tr><th>cortex-m<td>

```
user: 000.127 s
sys:  000.030 s
wall: 000.134 s
child_RSS_high:      60264 KiB
group_mem_high:      23824 KiB
```

</td><td>

```
user: 000.136 s
sys:  000.038 s
wall: 000.137 s
child_RSS_high:      59204 KiB
group_mem_high:      22712 KiB
```

</td></tr><tr><th>sqlx<td>

```
user: 000.887 s
sys:  000.118 s
wall: 000.592 s
child_RSS_high:     190408 KiB
group_mem_high:     157804 KiB
```

</td><td>

```
user: 000.798 s
sys:  000.101 s
wall: 000.525 s
child_RSS_high:     159292 KiB
group_mem_high:     126292 KiB
```

</td></tr><tr><th>stm32f4<td>

```
user: 013.884 s
sys:  005.399 s
wall: 013.149 s
child_RSS_high:    1942244 KiB
group_mem_high:    1954916 KiB
```

</td><td>

```
user: 006.128 s
sys:  003.297 s
wall: 007.994 s
child_RSS_high:    1038108 KiB
group_mem_high:    1023900 KiB
```

</td></tr><tr><th>ripgrep<td>

```
user: 000.441 s
sys:  000.063 s
wall: 000.264 s
child_RSS_high:     109180 KiB
group_mem_high:      74272 KiB
```

</td><td>

```
user: 000.408 s
sys:  000.044 s
wall: 000.238 s
child_RSS_high:     101488 KiB
group_mem_high:      66000 KiB
```

</td></tr></tbody></table>

Size change
-----------

standard library without gzip:

```console
$ du -bs search-index-old.js search-index-new.js
4976370 search-index-old.js
4404391 search-index-new.js
```

((4976370-4404391)/4404391)*100% = 12.9%

with gzip:

```console
$ du -hs search-index-old.js.gz search-index-new.js.gz
520K    search-index-old.js.gz
504K    search-index-new.js.gz

$ du -bs search-index-old.js.gz search-index-new.js.gz
522092  search-index-old.js.gz
507654  search-index-new.js.gz
```

((522092-507654)/507654)*100% = 2.8%

Benchmarks are similarly shrunk.

Without gzip:

```console
$ du -hs tmp/{arti,cortex-m,sqlx,stm32f4,ripgrep}/toolchain_{old,new}/doc/search-index.js
10555067        tmp/arti/toolchain_old/doc/search-index.js
8921236 tmp/arti/toolchain_new/doc/search-index.js
77018   tmp/cortex-m/toolchain_old/doc/search-index.js
66676   tmp/cortex-m/toolchain_new/doc/search-index.js
2876330 tmp/sqlx/toolchain_old/doc/search-index.js
2436812 tmp/sqlx/toolchain_new/doc/search-index.js
63632890        tmp/stm32f4/toolchain_old/doc/search-index.js
52337438        tmp/stm32f4/toolchain_new/doc/search-index.js
631150  tmp/ripgrep/toolchain_old/doc/search-index.js
541646  tmp/ripgrep/toolchain_new/doc/search-index.js
```

With gzip:

```console
$ du -bs tmp/{arti,cortex-m,sqlx,stm32f4,ripgrep}/toolchain_{old,new}/doc/search-index.js.gz
1618852 tmp/arti/toolchain_old/doc/search-index.js.gz
1582007 tmp/arti/toolchain_new/doc/search-index.js.gz
16109   tmp/cortex-m/toolchain_old/doc/search-index.js.gz
15831   tmp/cortex-m/toolchain_new/doc/search-index.js.gz
422257  tmp/sqlx/toolchain_old/doc/search-index.js.gz
411507  tmp/sqlx/toolchain_new/doc/search-index.js.gz
4454761 tmp/stm32f4/toolchain_old/doc/search-index.js.gz
4334924 tmp/stm32f4/toolchain_new/doc/search-index.js.gz
98312   tmp/ripgrep/toolchain_old/doc/search-index.js.gz
96864   tmp/ripgrep/toolchain_new/doc/search-index.js.gz

$ du -hs tmp/{arti,cortex-m,sqlx,stm32f4,ripgrep}/toolchain_{old,new}/doc/search-index.j
s.gz
1.6M    tmp/arti/toolchain_old/doc/search-index.js.gz
1.6M    tmp/arti/toolchain_new/doc/search-index.js.gz
24K     tmp/cortex-m/toolchain_old/doc/search-index.js.gz
24K     tmp/cortex-m/toolchain_new/doc/search-index.js.gz
424K    tmp/sqlx/toolchain_old/doc/search-index.js.gz
412K    tmp/sqlx/toolchain_new/doc/search-index.js.gz
4.3M    tmp/stm32f4/toolchain_old/doc/search-index.js.gz
4.2M    tmp/stm32f4/toolchain_new/doc/search-index.js.gz
108K    tmp/ripgrep/toolchain_old/doc/search-index.js.gz
104K    tmp/ripgrep/toolchain_new/doc/search-index.js.gz
```

…r-errors

remove duplicate test

This was added in rust-lang@ace6fc3 where overflowing-rsh-6 differed from overflowing-rsh-5 in a feature gate, but the feature has since been stabilized, making the tests 100% identical.

Most of these tests in numbers-arithmetic could be put into one file rather than having so many files that all test the same lint... but it doesn't seem worth the effort. After rust-lang#119432 we might be able to remove most of them entirely as they will be covered by the new tests added there.

…le-error, r=cjgillot

fix cyle error when suggesting to use associated function instead of constructor

Fixes rust-lang#119625.

The first commit fixes the infinite recursion and makes the cycle error actually show up. We do this by making the `Display` for `ty::Instance` impl  respect `with_no_queries` so that it can be used in query descriptions.

The second commit fixes the cycle error `resolver_for_lowering` -> `normalize` -> `resolve_instance` (for evaluating const) -> `lang_items` (for `drop_in_place`) -> `resolver_for_lowering` (for collecting lang items). We do this by simply skipping the suggestion when encountering an unnormalized type.

…ulacrum

library: Fix warnings in rtstartup

Not sure why global `deny(warnings)` in bootstrap doesn't apply to this code, it did in the past.

…nton

library: Fix a symlink test failing on Windows