Cleanup: remove graphviz::IntoCow

It's just `Into<Cow<...>>` and the applicable methods already exist for `Vec`/`[T]` and `String`/`str`.

Clarify docs for when binary_search has many matches.

Fixes https://github.com/rust-lang/rust/issues/51817.

Add the library search box on the 404 page

It actually has a link to search already, but it would be better to
have the search "box" as like index.md to be consistent.

<style> can be shared with index.md, but these pages currently
use https://doc.rust-lang.org/rust.css directly.

Fixes #14572.

Add doc for impl From for Error

As part of issue #51430 (cc @skade).

The impl is very simple, let me know if we need to go into any details.

Fix dead code lint for functions using impl Trait

Fixes https://github.com/rust-lang/rust/issues/54754

This is a minimal fix that doesn't add any new queries or touches unnecessary code. Please nominate for beta backport if wanted.

Stabilize `min_const_fn`

tracking issue: #53555

r? @Centril

Fixes https://github.com/rust-lang/rust/issues/51817.

Fix two UI tests with locale-dependent output

Closes https://github.com/rust-lang/rust/issues/54719

Add tests for some E-needstest issues

Fixes #28134.
Fixes #24338.
Fixes #29743.

rustc: Allow `#[no_mangle]` anywhere in a crate

This commit updates the compiler to allow the `#[no_mangle]` (and
`#[export_name]` attributes) to be located anywhere within a crate.
These attributes are unconditionally processed, causing the compiler to
always generate an exported symbol with the appropriate name.

After some discussion on #54135 it was found that not a great reason
this hasn't been allowed already, and it seems to match the behavior
that many expect! Previously the compiler would only export a
`#[no_mangle]` symbol if it were *publicly reachable*, meaning that it
itself is `pub` and it's otherwise publicly reachable from the root of
the crate. This new definition is that `#[no_mangle]` *is always
reachable*, no matter where it is in a crate or whether it has `pub` or
not.

This should make it much easier to declare an exported symbol with a
known and unique name, even when it's an internal implementation detail
of the crate itself. Note that these symbols will persist beyond LTO as
well, always making their way to the linker.

Along the way this commit removes the `private_no_mangle_functions` lint
(also for statics) as there's no longer any need to lint these
situations. Furthermore a good number of tests were updated now that
symbol visibility has been changed.

Closes #54135

NLL: temps in block tail expression diagnostic

This change adds a diagnostic that explains when temporaries in a block tail expression live longer than block local variables that they borrow, and attempts to suggest turning the tail expresion into a statement (either by adding a semicolon at the end, when its result value is clearly unused, or by introducing a `let`-binding for the result value and then returning that).

Fix #54556

This commit updates the compiler to allow the `#[no_mangle]` (and
`#[export_name]` attributes) to be located anywhere within a crate.
These attributes are unconditionally processed, causing the compiler to
always generate an exported symbol with the appropriate name.

After some discussion on #54135 it was found that not a great reason
this hasn't been allowed already, and it seems to match the behavior
that many expect! Previously the compiler would only export a
`#[no_mangle]` symbol if it were *publicly reachable*, meaning that it
itself is `pub` and it's otherwise publicly reachable from the root of
the crate. This new definition is that `#[no_mangle]` *is always
reachable*, no matter where it is in a crate or whether it has `pub` or
not.

This should make it much easier to declare an exported symbol with a
known and unique name, even when it's an internal implementation detail
of the crate itself. Note that these symbols will persist beyond LTO as
well, always making their way to the linker.

Along the way this commit removes the `private_no_mangle_functions` lint
(also for statics) as there's no longer any need to lint these
situations. Furthermore a good number of tests were updated now that
symbol visibility has been changed.

Closes #54135

Cleanup rustc/middle

- improve allocations
- use `Cow<'static, str>` where applicable
- improve some patterns
- whitespace & formatting fixes

 submodules: update clippy to 22d37b53 to fix tests.

Should fix clippy toolstate.

wasm: Explicitly export all symbols with LLD

This commit fixes an oddity on the wasm target where LTO can produce
working executables but plain old optimizations doesn't. The compiler
already knows what set of symbols it would like to export, but LLD only
discovers this list transitively through symbol visibilities. LLD may
not, however, always find all the symbols that we'd like to export.

For example if you depend on an rlib with a `#[no_mangle]` symbol, then
if you don't actually use anything from the rlib then the symbol won't
appear in the final artifact! It will appear, however, with LTO. This
commit attempts to rectify this situation by ensuring that all symbols
rustc would otherwise preserve through LTO are also preserved through
the linking process with LLD by default.

Rollup of 11 pull requests

Successful merges:

 - #54078 (Expand the documentation for the `std::sync` module)
 - #54717 (Cleanup rustc/ty part 1)
 - #54781 (Add examples to `TyKind::FnDef` and `TyKind::FnPtr` docs)
 - #54787 (Only warn about unused `mut` in user-written code)
 - #54804 (add suggestion for inverted function parameters)
 - #54812 (Regression test for #32382.)
 - #54833 (make `Parser::parse_foreign_item()` return a foreign item or error)
 - #54834 (rustdoc: overflow:auto doesn't work nicely on small screens)
 - #54838 (Fix typo in src/libsyntax/parse/parser.rs)
 - #54851 (Fix a regression in 1.30 by reverting #53564)
 - #54853 (Remove unneccessary error from test, revealing NLL error.)

Failed merges:

r? @ghost

Remove unneccessary error from test, revealing NLL error.

Part of #52663.

Removes unnecessary type mismatch error from test that was hiding
borrow check error from NLL stderr.

r? @nikomatsakis

Fix a regression in 1.30 by reverting #53564

Investigation on #54477 revealed https://github.com/rust-lang/rust/pull/53564 as the culprit in the regression for that crate. I've reproduced the regression with the [detailed test cases provided](https://github.com/rust-lang/rust/issues/54477#issuecomment-427398456). While we figure out how to fix the regression this commit reverts the current culprit.

Fix typo in src/libsyntax/parse/parser.rs

contast -> contrast

rustdoc: overflow:auto doesn't work nicely on small screens

This property was introduced by 3f92ff34, but looks it doesn't
overwrap even without the property.

Fixes #54672.

make `Parser::parse_foreign_item()` return a foreign item or error

Fixes `Parser::parse_foreign_item()` to follow the convention of `parse_trait_item()` and `parse_impl_item()` in that it *must* parse an item or return an error, and then the caller is responsible for detecting the closing delimiter.

This prevents it from looping endlessly on an unexpected token in `ext/expand.rs` where it was also leaking memory by continually pushing to `Parser::expected_tokens` via `Parser::check_keyword()`.

closes #54441

r? @petrochenkov
cc @dtolnay

Regression test for #32382.

add suggestion for inverted function parameters

Fixes #54065.

Only warn about unused `mut` in user-written code

Fixes https://github.com/rust-lang/rust/issues/54586.

r? @pnkfelix
cc @blitzerr

Add examples to `TyKind::FnDef` and `TyKind::FnPtr` docs

This adds two examples to the docs of `TyKind::FnDef` and `TyKind::FnPtr`.

I found these two types a bit confusing when I learned about them and I think adding these examples might help others.

Cleanup rustc/ty part 1

Part 2 will follow soon; I wouldn't want these changes to rot too quickly.

- improve stack shifting and remove related allocations
- move a faster early return up
- improve allocations
- use Cow<str> where applicable
- simplify common patterns
- whitespace fixes

Expand the documentation for the `std::sync` module

I've tried to expand the documentation for Rust's synchronization primitives. The module level documentation explains why synchronization is required when working with a multiprocessor system,
and then links to the appropiate structure in this module.

Fixes #29377, since this should be the last item on the checklist (documentation for `Atomic*` was fixed in #44854, but not ticked off the checklist).

Cleanup rustc/ty part 2

The second part of cleanups and minor improvements for rustc/ty.
- improve allocations
- calculate span after a possible early continue
- simplify some patterns
- mark a comment as FIXME
- whitespace fixes

The PR is independent from from the first part.

Removes unnecessary type mismatch error from test that was hiding
borrow check error from NLL stderr.

This reverts commit 6ce76aca.

This reverts commit 11e488b6.

This reverts commit 1a1a7f61.

This reverts commit 1908892d.