Provides an overview on why synchronization is required,
as well a short summary of what sync primitives are available.

Because `fn main()` was added automatically, the variables
were actually local statics.

Reword the lead paragraph and turn the list items into
complete sentences.

This property was introduced by 3f92ff3, but looks it doesn't
overwrap even without the property.

Fixes rust-lang#54672.

closes rust-lang#54441

Fixes rust-lang#54065.

This reverts commit 21d2a6c.

This reverts commit 1908892.

This reverts commit 1a1a7f6.

This reverts commit 11e488b.

This reverts commit 6ce76ac.

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

…teveklabnik

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

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

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.

…nikomatsakis

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

Fixes rust-lang#54586.

r? @pnkfelix
cc @blitzerr

add suggestion for inverted function parameters

Fixes rust-lang#54065.

…pe-with-lifetime, r=nikomatsakis

Regression test for rust-lang#32382.

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 rust-lang#54441

r? @petrochenkov
cc @dtolnay

…omez

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

This property was introduced by 3f92ff3, but looks it doesn't
overwrap even without the property.

Fixes rust-lang#54672.

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

contast -> contrast

…ckler

Fix a regression in 1.30 by reverting rust-lang#53564

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

…ime-suggestion-test, r=nikomatsakis

Remove unneccessary error from test, revealing NLL error.

Part of rust-lang#52663.

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

r? @nikomatsakis