Rollup merge of rust-lang#118194 - notriddle:notriddle/tuple-unit, r=GuillaumeGomez

rustdoc: search for tuples and unit by type with `()`

This feature extends rustdoc to support the syntax that most users will naturally attempt to use to search for tuples. Part of rust-lang#60485

Function signature searches already support tuples and unit. The explicit name `primitive:tuple` and `primitive:unit` can be used to match a tuple or unit, while `()` will match either one. It also follows the direction set by the actual language for parens as a group, so `(u8,)` will only match a tuple, while `(u8)` will match a plain, unwrapped byte—thanks to loose search semantics, it will also match the tuple.

## Preview

* [`option<t>, option<u> -> (t, u)`](<https://notriddle.com/rustdoc-html-demo-5/tuple-unit/std/index.html?search=option%3Ct%3E%2C option%3Cu%3E -%3E (t%2C u)>)
* [`[t] -> (t,)`](<https://notriddle.com/rustdoc-html-demo-5/tuple-unit/std/index.html?search=[t] -%3E (t%2C)>)
* [`(ipaddr,) -> socketaddr`](<https://notriddle.com/rustdoc-html-demo-5/tuple-unit/std/index.html?search=(ipaddr%2C) -%3E socketaddr>)

## Motivation

When type-based search was first landed, it was directly [described as incomplete][a comment].

[a comment]: rust-lang#23289 (comment)

Filling out the missing functionality is going to mean adding support for more of Rust's [type expression] syntax, such as tuples (in this PR), references, raw pointers, function pointers, and closures.

[type expression]: https://doc.rust-lang.org/reference/types.html#type-expressions

There does seem to be demand for this sort of thing, such as [this Discord message](https://discord.com/channels/442252698964721669/443150878111694848/1042145740065099796) expressing regret at rustdoc not supporting tuples in search queries.

## Reference description (from the Rustdoc book)

<table>
<thead>
  <tr>
    <th>Shorthand</th>
    <th>Explicit names</th>
  </tr>
</thead>
<tbody>
  <tr><td colspan="2">Before this PR</td></tr>
  <tr>
    <td><code>[]</code></td>
    <td><code>primitive:slice</code> and/or <code>primitive:array</code></td>
  </tr>
  <tr>
    <td><code>[T]</code></td>
    <td><code>primitive:slice&lt;T&gt;</code> and/or <code>primitive:array&lt;T&gt;</code></td>
  </tr>
  <tr>
    <td><code>!</code></td>
    <td><code>primitive:never</code></td>
  </tr>
  <tr><td colspan="2">After this PR</td></tr>
  <tr>
    <td><code>()</code></td>
    <td><code>primitive:unit</code> and/or <code>primitive:tuple</code></td>
  </tr>
  <tr>
    <td><code>(T)</code></td>
    <td><code>T</code></td>
  </tr>
  <tr>
    <td><code>(T,)</code></td>
    <td><code>primitive:tuple&lt;T&gt;</code></td>
  </tr>
</tbody>
</table>

A single type expression wrapped in parens is the same as that type expression, since parens act as the grouping operator. If they're empty, though, they will match both `unit` and `tuple`, and if there's more than one type (or a trailing or leading comma) it is the same as `primitive:tuple<...>`.

However, since items can be left out of the query, `(T)` will still return results for types that match tuples, even though it also matches the type on its own. That is, `(u32)` matches `(u32,)` for the exact same reason that it also matches `Result<u32, Error>`.

## Future direction

The [type expression grammar](https://doc.rust-lang.org/reference/types.html#type-expressions) from the Reference is given below:

<pre><code>Syntax
    Type :
        TypeNoBounds
        | <a href="https://doc.rust-lang.org/reference/types/impl-trait.html">ImplTraitType</a>
        | <a href="https://doc.rust-lang.org/reference/types/trait-object.html">TraitObjectType</a>
<br>
    TypeNoBounds :
        <a href="https://doc.rust-lang.org/reference/types.html#parenthesized-types">ParenthesizedType</a>
        | <a href="https://doc.rust-lang.org/reference/types/impl-trait.html">ImplTraitTypeOneBound</a>
        | <a href="https://doc.rust-lang.org/reference/types/trait-object.html">TraitObjectTypeOneBound</a>
        | <a href="https://doc.rust-lang.org/reference/paths.html#paths-in-types">TypePath</a>
        | <a href="https://doc.rust-lang.org/reference/types/tuple.html#tuple-types">TupleType</a>
        | <a href="https://doc.rust-lang.org/reference/types/never.html">NeverType</a>
        | <a href="https://doc.rust-lang.org/reference/types/pointer.html#raw-pointers-const-and-mut">RawPointerType</a>
        | <a href="https://doc.rust-lang.org/reference/types/pointer.html#shared-references-">ReferenceType</a>
        | <a href="https://doc.rust-lang.org/reference/types/array.html">ArrayType</a>
        | <a href="https://doc.rust-lang.org/reference/types/slice.html">SliceType</a>
        | <a href="https://doc.rust-lang.org/reference/types/inferred.html">InferredType</a>
        | <a href="https://doc.rust-lang.org/reference/paths.html#qualified-paths">QualifiedPathInType</a>
        | <a href="https://doc.rust-lang.org/reference/types/function-pointer.html">BareFunctionType</a>
        | <a href="https://doc.rust-lang.org/reference/macros.html#macro-invocation">MacroInvocation</a>
</code></pre>

ImplTraitType and TraitObjectType (and ImplTraitTypeOneBound and TraitObjectTypeOneBound) are not yet implemented. They would mostly desugar to `trait:`, similarly to how `!` desugars to `primitive:never`.

ParenthesizedType and TuplePath are added in this PR.

TypePath is already implemented (except const generics, which is not planned, and function-like trait syntax, which is planned as part of closure support).

NeverType is already implemented.

RawPointerType and ReferenceType require parsing and fixes to the search index to store this information, but otherwise their behavior seems simple enough. Just like tuples and slices, `&T` would be equivalent to `primitive:reference<T>`, `&mut T` would be equivalent to `primitive:reference<keyword:mut, T>`, `*T` would be equivalent to `primitive:pointer<T>`, `*mut T` would be equivalent to `primitive:pointer<keyword:mut, T>`, and `*const T` would be equivalent to `primitive:pointer<keyword:const, T>`. Lifetime generics support is not planned, because lifetime subtyping seems too complicated.

ArrayType is subsumed by SliceType right now. Implementing const generics is not planned, because it seems like it would require a lot of implementation complexity for not much gain.

InferredType isn't really covered right now. Its semantics in a search context are not obvious.

QualifiedPathInType is not implemented, and it is not planned. I would need a use case to justify it, and act as a guide for what the exact semantics should be.

BareFunctionType is not implemented. Along with function-like trait syntax, which is formally considered a TypePath, it's the biggest missing feature to be able to do structured searches over generic APIs like `Option`.

MacroInvocation is not parsed (macro names are, but they don't mean the same thing here at all). Those are gone by the time Rustdoc sees the source code.

…-hof, r=GuillaumeGomez

rustdoc-search: search types by higher-order functions

This feature extends rustdoc with syntax and search index information for searching function pointers and closures (Higher-Order Functions, or HOF). Part of rust-lang#60485

This PR adds two syntaxes: a high-level one for finding any kind of HOF, and a direct implementation of the parenthesized path syntax that Rust itself uses.

## Preview pages

| Query | Results |
|-------|---------|
| [`option<T>, (fnonce (T) -> bool) -> option<T>`][optionfilter] | `Option::filter` |
| [`option<T>, (T -> bool) -> option<T>`][optionfilter2] | `Option::filter` |

Updated chapter of the book: https://notriddle.com/rustdoc-html-demo-9/search-hof/rustdoc/read-documentation/search.html

[optionfilter]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=option<T>%2C+(fnonce+(T)+->+bool)+->+option<T>&filter-crate=std
[optionfilter2]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=option<T>%2C+(T+->+bool)+->+option<T>&filter-crate=std

## Motivation

When type-based search was first landed, it was directly [described as incomplete][a comment].

[a comment]: rust-lang#23289 (comment)

Filling out the missing functionality is going to mean adding support for more of Rust's [type expression] syntax, such as references, raw pointers, function pointers, and closures. This PR adds function pointers and closures.

[type expression]: https://doc.rust-lang.org/reference/types.html#type-expressions

There's been demand for something "like Hoogle, but for Rust" expressed a few times [1](https://www.reddit.com/r/rust/comments/y8sbid/is_there_a_website_like_haskells_hoogle_for_rust/) [2](https://users.rust-lang.org/t/rust-equivalent-of-haskells-hoogle/102280) [3](https://internals.rust-lang.org/t/std-library-inclusion-policy/6852/2) [4](https://discord.com/channels/442252698964721669/448238009733742612/1109502307495858216). Some of them just don't realize what functionality already exists ([`Duration -> u64`](https://doc.rust-lang.org/nightly/std/?search=duration%20-%3E%20u64) already works), but a lot of them specifically want to search for higher-order functions like option combinators.

## Guide-level explanation (from the Rustdoc book)

To search for a function that accepts a function as a parameter, like `Iterator::all`, wrap the nested signature in parenthesis, as in [`Iterator<T>, (T -> bool) -> bool`][iterator-all]. You can also search for a specific closure trait, such as `Iterator<T>, (FnMut(T) -> bool) -> bool`, but you need to know which one you want.

[iterator-all]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=Iterator<T>%2C+(T+->+bool)+->+bool&filter-crate=std

## Reference-level description (also from the Rustdoc book)

### Primitives with Special Syntax

<table>
<thead>
  <tr>
    <th>Shorthand</th>
    <th>Explicit names</th>
  </tr>
</thead>
<tbody>
  <tr><td colspan="2">Before this PR</td></tr>
  <tr>
    <td><code>[]</code></td>
    <td><code>primitive:slice</code> and/or <code>primitive:array</code></td>
  </tr>
  <tr>
    <td><code>[T]</code></td>
    <td><code>primitive:slice&lt;T&gt;</code> and/or <code>primitive:array&lt;T&gt;</code></td>
  </tr>
  <tr>
    <td><code>!</code></td>
    <td><code>primitive:never</code></td>
  </tr>
  <tr>
    <td><code>()</code></td>
    <td><code>primitive:unit</code> and/or <code>primitive:tuple</code></td>
  </tr>
  <tr>
    <td><code>(T)</code></td>
    <td><code>T</code></td>
  </tr>
  <tr>
    <td><code>(T,)</code></td>
    <td><code>primitive:tuple&lt;T&gt;</code></td>
  </tr>
  <tr><td colspan="2">After this PR</td></tr>
  <tr>
    <td><code>(T, U -> V, W)</code></td>
    <td><code>fn(T, U) -> (V, W)</code>, Fn, FnMut, and FnOnce</td>
  </tr>
</tbody>
</table>

The `->` operator has lower precedence than comma. If it's not wrapped in brackets, it delimits the return value for the function being searched for. To search for functions that take functions as parameters, use parenthesis.

### Search query grammar

```ebnf
ident = *(ALPHA / DIGIT / "_")
path = ident *(DOUBLE-COLON ident) [BANG]
slice-like = OPEN-SQUARE-BRACKET [ nonempty-arg-list ] CLOSE-SQUARE-BRACKET
tuple-like = OPEN-PAREN [ nonempty-arg-list ] CLOSE-PAREN
arg = [type-filter *WS COLON *WS] (path [generics] / slice-like / tuple-like)
type-sep = COMMA/WS *(COMMA/WS)
nonempty-arg-list = *(type-sep) arg *(type-sep arg) *(type-sep) [ return-args ]
generic-arg-list = *(type-sep) arg [ EQUAL arg ] *(type-sep arg [ EQUAL arg ]) *(type-sep)
normal-generics = OPEN-ANGLE-BRACKET [ generic-arg-list ] *(type-sep)
            CLOSE-ANGLE-BRACKET
fn-like-generics = OPEN-PAREN [ nonempty-arg-list ] CLOSE-PAREN [ RETURN-ARROW arg ]
generics = normal-generics / fn-like-generics
return-args = RETURN-ARROW *(type-sep) nonempty-arg-list

exact-search = [type-filter *WS COLON] [ RETURN-ARROW ] *WS QUOTE ident QUOTE [ generics ]
type-search = [ nonempty-arg-list ]

query = *WS (exact-search / type-search) *WS

; unchanged parts of the grammar, like the full list of type filters, are omitted
```

## Future direction

### The remaining type expression grammar

As described in rust-lang#118194, this is another step in the type expression grammar: BareFunction, and the function-like mode of TypePath, are now supported.

* RawPointerType and ReferenceType actually are a priority.
* ImplTraitType and TraitObjectType (and ImplTraitTypeOneBound and TraitObjectTypeOneBound) aren't as much of a priority, since they desugar pretty easily.

### Search subtyping and traits

This is the other major factor that makes it less useful than it should be.

* `iterator<result<t>> -> result<t>` doesn't find `Result::from_iter`. You have to search [`intoiterator<result<t>> -> result<t>`](https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=intoiterator%3Cresult%3Ct%3E%3E%20-%3E%20result%3Ct%3E&filter-crate=std). Nobody's going to search for IntoIterator unless they basically already know about it and don't need the search engine anyway.

* Iterator combinators are usually structs that happen to implement Iterator, like `std::iter::Map`.

To solve these cases, it needs to look at trait implementations, knowing that Iterator is a "subtype of" IntoIterator, and Map is a "subtype of" Iterator, so `iterator -> result` is a subtype of `intoiterator -> result` and `iterator<t>, (t -> u) -> iterator<u>` is a subtype of [`iterator<t>, (t -> u) -> map<t -> u>`](https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=iterator%3Ct%3E%2C%20(t%20-%3E%20u)%20-%3E%20map%3Ct%20-%3E%20u%3E&filter-crate=std).

…-hof, r=GuillaumeGomez

rustdoc-search: search types by higher-order functions

This feature extends rustdoc with syntax and search index information for searching function pointers and closures (Higher-Order Functions, or HOF). Part of rust-lang#60485

This PR adds two syntaxes: a high-level one for finding any kind of HOF, and a direct implementation of the parenthesized path syntax that Rust itself uses.

## Preview pages

| Query | Results |
|-------|---------|
| [`option<T>, (fnonce (T) -> bool) -> option<T>`][optionfilter] | `Option::filter` |
| [`option<T>, (T -> bool) -> option<T>`][optionfilter2] | `Option::filter` |

Updated chapter of the book: https://notriddle.com/rustdoc-html-demo-9/search-hof/rustdoc/read-documentation/search.html

[optionfilter]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=option<T>%2C+(fnonce+(T)+->+bool)+->+option<T>&filter-crate=std
[optionfilter2]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=option<T>%2C+(T+->+bool)+->+option<T>&filter-crate=std

## Motivation

When type-based search was first landed, it was directly [described as incomplete][a comment].

[a comment]: rust-lang#23289 (comment)

Filling out the missing functionality is going to mean adding support for more of Rust's [type expression] syntax, such as references, raw pointers, function pointers, and closures. This PR adds function pointers and closures.

[type expression]: https://doc.rust-lang.org/reference/types.html#type-expressions

There's been demand for something "like Hoogle, but for Rust" expressed a few times [1](https://www.reddit.com/r/rust/comments/y8sbid/is_there_a_website_like_haskells_hoogle_for_rust/) [2](https://users.rust-lang.org/t/rust-equivalent-of-haskells-hoogle/102280) [3](https://internals.rust-lang.org/t/std-library-inclusion-policy/6852/2) [4](https://discord.com/channels/442252698964721669/448238009733742612/1109502307495858216). Some of them just don't realize what functionality already exists ([`Duration -> u64`](https://doc.rust-lang.org/nightly/std/?search=duration%20-%3E%20u64) already works), but a lot of them specifically want to search for higher-order functions like option combinators.

## Guide-level explanation (from the Rustdoc book)

To search for a function that accepts a function as a parameter, like `Iterator::all`, wrap the nested signature in parenthesis, as in [`Iterator<T>, (T -> bool) -> bool`][iterator-all]. You can also search for a specific closure trait, such as `Iterator<T>, (FnMut(T) -> bool) -> bool`, but you need to know which one you want.

[iterator-all]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=Iterator<T>%2C+(T+->+bool)+->+bool&filter-crate=std

## Reference-level description (also from the Rustdoc book)

### Primitives with Special Syntax

<table>
<thead>
  <tr>
    <th>Shorthand</th>
    <th>Explicit names</th>
  </tr>
</thead>
<tbody>
  <tr><td colspan="2">Before this PR</td></tr>
  <tr>
    <td><code>[]</code></td>
    <td><code>primitive:slice</code> and/or <code>primitive:array</code></td>
  </tr>
  <tr>
    <td><code>[T]</code></td>
    <td><code>primitive:slice&lt;T&gt;</code> and/or <code>primitive:array&lt;T&gt;</code></td>
  </tr>
  <tr>
    <td><code>!</code></td>
    <td><code>primitive:never</code></td>
  </tr>
  <tr>
    <td><code>()</code></td>
    <td><code>primitive:unit</code> and/or <code>primitive:tuple</code></td>
  </tr>
  <tr>
    <td><code>(T)</code></td>
    <td><code>T</code></td>
  </tr>
  <tr>
    <td><code>(T,)</code></td>
    <td><code>primitive:tuple&lt;T&gt;</code></td>
  </tr>
  <tr><td colspan="2">After this PR</td></tr>
  <tr>
    <td><code>(T, U -> V, W)</code></td>
    <td><code>fn(T, U) -> (V, W)</code>, Fn, FnMut, and FnOnce</td>
  </tr>
</tbody>
</table>

The `->` operator has lower precedence than comma. If it's not wrapped in brackets, it delimits the return value for the function being searched for. To search for functions that take functions as parameters, use parenthesis.

### Search query grammar

```ebnf
ident = *(ALPHA / DIGIT / "_")
path = ident *(DOUBLE-COLON ident) [BANG]
slice-like = OPEN-SQUARE-BRACKET [ nonempty-arg-list ] CLOSE-SQUARE-BRACKET
tuple-like = OPEN-PAREN [ nonempty-arg-list ] CLOSE-PAREN
arg = [type-filter *WS COLON *WS] (path [generics] / slice-like / tuple-like)
type-sep = COMMA/WS *(COMMA/WS)
nonempty-arg-list = *(type-sep) arg *(type-sep arg) *(type-sep) [ return-args ]
generic-arg-list = *(type-sep) arg [ EQUAL arg ] *(type-sep arg [ EQUAL arg ]) *(type-sep)
normal-generics = OPEN-ANGLE-BRACKET [ generic-arg-list ] *(type-sep)
            CLOSE-ANGLE-BRACKET
fn-like-generics = OPEN-PAREN [ nonempty-arg-list ] CLOSE-PAREN [ RETURN-ARROW arg ]
generics = normal-generics / fn-like-generics
return-args = RETURN-ARROW *(type-sep) nonempty-arg-list

exact-search = [type-filter *WS COLON] [ RETURN-ARROW ] *WS QUOTE ident QUOTE [ generics ]
type-search = [ nonempty-arg-list ]

query = *WS (exact-search / type-search) *WS

; unchanged parts of the grammar, like the full list of type filters, are omitted
```

## Future direction

### The remaining type expression grammar

As described in rust-lang#118194, this is another step in the type expression grammar: BareFunction, and the function-like mode of TypePath, are now supported.

* RawPointerType and ReferenceType actually are a priority.
* ImplTraitType and TraitObjectType (and ImplTraitTypeOneBound and TraitObjectTypeOneBound) aren't as much of a priority, since they desugar pretty easily.

### Search subtyping and traits

This is the other major factor that makes it less useful than it should be.

* `iterator<result<t>> -> result<t>` doesn't find `Result::from_iter`. You have to search [`intoiterator<result<t>> -> result<t>`](https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=intoiterator%3Cresult%3Ct%3E%3E%20-%3E%20result%3Ct%3E&filter-crate=std). Nobody's going to search for IntoIterator unless they basically already know about it and don't need the search engine anyway.

* Iterator combinators are usually structs that happen to implement Iterator, like `std::iter::Map`.

To solve these cases, it needs to look at trait implementations, knowing that Iterator is a "subtype of" IntoIterator, and Map is a "subtype of" Iterator, so `iterator -> result` is a subtype of `intoiterator -> result` and `iterator<t>, (t -> u) -> iterator<u>` is a subtype of [`iterator<t>, (t -> u) -> map<t -> u>`](https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=iterator%3Ct%3E%2C%20(t%20-%3E%20u)%20-%3E%20map%3Ct%20-%3E%20u%3E&filter-crate=std).

…-hof, r=GuillaumeGomez

rustdoc-search: search types by higher-order functions

This feature extends rustdoc with syntax and search index information for searching function pointers and closures (Higher-Order Functions, or HOF). Part of rust-lang#60485

This PR adds two syntaxes: a high-level one for finding any kind of HOF, and a direct implementation of the parenthesized path syntax that Rust itself uses.

## Preview pages

| Query | Results |
|-------|---------|
| [`option<T>, (fnonce (T) -> bool) -> option<T>`][optionfilter] | `Option::filter` |
| [`option<T>, (T -> bool) -> option<T>`][optionfilter2] | `Option::filter` |

Updated chapter of the book: https://notriddle.com/rustdoc-html-demo-9/search-hof/rustdoc/read-documentation/search.html

[optionfilter]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=option<T>%2C+(fnonce+(T)+->+bool)+->+option<T>&filter-crate=std
[optionfilter2]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=option<T>%2C+(T+->+bool)+->+option<T>&filter-crate=std

## Motivation

When type-based search was first landed, it was directly [described as incomplete][a comment].

[a comment]: rust-lang#23289 (comment)

Filling out the missing functionality is going to mean adding support for more of Rust's [type expression] syntax, such as references, raw pointers, function pointers, and closures. This PR adds function pointers and closures.

[type expression]: https://doc.rust-lang.org/reference/types.html#type-expressions

There's been demand for something "like Hoogle, but for Rust" expressed a few times [1](https://www.reddit.com/r/rust/comments/y8sbid/is_there_a_website_like_haskells_hoogle_for_rust/) [2](https://users.rust-lang.org/t/rust-equivalent-of-haskells-hoogle/102280) [3](https://internals.rust-lang.org/t/std-library-inclusion-policy/6852/2) [4](https://discord.com/channels/442252698964721669/448238009733742612/1109502307495858216). Some of them just don't realize what functionality already exists ([`Duration -> u64`](https://doc.rust-lang.org/nightly/std/?search=duration%20-%3E%20u64) already works), but a lot of them specifically want to search for higher-order functions like option combinators.

## Guide-level explanation (from the Rustdoc book)

To search for a function that accepts a function as a parameter, like `Iterator::all`, wrap the nested signature in parenthesis, as in [`Iterator<T>, (T -> bool) -> bool`][iterator-all]. You can also search for a specific closure trait, such as `Iterator<T>, (FnMut(T) -> bool) -> bool`, but you need to know which one you want.

[iterator-all]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=Iterator<T>%2C+(T+->+bool)+->+bool&filter-crate=std

## Reference-level description (also from the Rustdoc book)

### Primitives with Special Syntax

<table>
<thead>
  <tr>
    <th>Shorthand</th>
    <th>Explicit names</th>
  </tr>
</thead>
<tbody>
  <tr><td colspan="2">Before this PR</td></tr>
  <tr>
    <td><code>[]</code></td>
    <td><code>primitive:slice</code> and/or <code>primitive:array</code></td>
  </tr>
  <tr>
    <td><code>[T]</code></td>
    <td><code>primitive:slice&lt;T&gt;</code> and/or <code>primitive:array&lt;T&gt;</code></td>
  </tr>
  <tr>
    <td><code>!</code></td>
    <td><code>primitive:never</code></td>
  </tr>
  <tr>
    <td><code>()</code></td>
    <td><code>primitive:unit</code> and/or <code>primitive:tuple</code></td>
  </tr>
  <tr>
    <td><code>(T)</code></td>
    <td><code>T</code></td>
  </tr>
  <tr>
    <td><code>(T,)</code></td>
    <td><code>primitive:tuple&lt;T&gt;</code></td>
  </tr>
  <tr><td colspan="2">After this PR</td></tr>
  <tr>
    <td><code>(T, U -> V, W)</code></td>
    <td><code>fn(T, U) -> (V, W)</code>, Fn, FnMut, and FnOnce</td>
  </tr>
</tbody>
</table>

The `->` operator has lower precedence than comma. If it's not wrapped in brackets, it delimits the return value for the function being searched for. To search for functions that take functions as parameters, use parenthesis.

### Search query grammar

```ebnf
ident = *(ALPHA / DIGIT / "_")
path = ident *(DOUBLE-COLON ident) [BANG]
slice-like = OPEN-SQUARE-BRACKET [ nonempty-arg-list ] CLOSE-SQUARE-BRACKET
tuple-like = OPEN-PAREN [ nonempty-arg-list ] CLOSE-PAREN
arg = [type-filter *WS COLON *WS] (path [generics] / slice-like / tuple-like)
type-sep = COMMA/WS *(COMMA/WS)
nonempty-arg-list = *(type-sep) arg *(type-sep arg) *(type-sep) [ return-args ]
generic-arg-list = *(type-sep) arg [ EQUAL arg ] *(type-sep arg [ EQUAL arg ]) *(type-sep)
normal-generics = OPEN-ANGLE-BRACKET [ generic-arg-list ] *(type-sep)
            CLOSE-ANGLE-BRACKET
fn-like-generics = OPEN-PAREN [ nonempty-arg-list ] CLOSE-PAREN [ RETURN-ARROW arg ]
generics = normal-generics / fn-like-generics
return-args = RETURN-ARROW *(type-sep) nonempty-arg-list

exact-search = [type-filter *WS COLON] [ RETURN-ARROW ] *WS QUOTE ident QUOTE [ generics ]
type-search = [ nonempty-arg-list ]

query = *WS (exact-search / type-search) *WS

; unchanged parts of the grammar, like the full list of type filters, are omitted
```

## Future direction

### The remaining type expression grammar

As described in rust-lang#118194, this is another step in the type expression grammar: BareFunction, and the function-like mode of TypePath, are now supported.

* RawPointerType and ReferenceType actually are a priority.
* ImplTraitType and TraitObjectType (and ImplTraitTypeOneBound and TraitObjectTypeOneBound) aren't as much of a priority, since they desugar pretty easily.

### Search subtyping and traits

This is the other major factor that makes it less useful than it should be.

* `iterator<result<t>> -> result<t>` doesn't find `Result::from_iter`. You have to search [`intoiterator<result<t>> -> result<t>`](https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=intoiterator%3Cresult%3Ct%3E%3E%20-%3E%20result%3Ct%3E&filter-crate=std). Nobody's going to search for IntoIterator unless they basically already know about it and don't need the search engine anyway.

* Iterator combinators are usually structs that happen to implement Iterator, like `std::iter::Map`.

To solve these cases, it needs to look at trait implementations, knowing that Iterator is a "subtype of" IntoIterator, and Map is a "subtype of" Iterator, so `iterator -> result` is a subtype of `intoiterator -> result` and `iterator<t>, (t -> u) -> iterator<u>` is a subtype of [`iterator<t>, (t -> u) -> map<t -> u>`](https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=iterator%3Ct%3E%2C%20(t%20-%3E%20u)%20-%3E%20map%3Ct%20-%3E%20u%3E&filter-crate=std).

…-hof, r=GuillaumeGomez

rustdoc-search: search types by higher-order functions

This feature extends rustdoc with syntax and search index information for searching function pointers and closures (Higher-Order Functions, or HOF). Part of rust-lang#60485

This PR adds two syntaxes: a high-level one for finding any kind of HOF, and a direct implementation of the parenthesized path syntax that Rust itself uses.

## Preview pages

| Query | Results |
|-------|---------|
| [`option<T>, (fnonce (T) -> bool) -> option<T>`][optionfilter] | `Option::filter` |
| [`option<T>, (T -> bool) -> option<T>`][optionfilter2] | `Option::filter` |

Updated chapter of the book: https://notriddle.com/rustdoc-html-demo-9/search-hof/rustdoc/read-documentation/search.html

[optionfilter]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=option<T>%2C+(fnonce+(T)+->+bool)+->+option<T>&filter-crate=std
[optionfilter2]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=option<T>%2C+(T+->+bool)+->+option<T>&filter-crate=std

## Motivation

When type-based search was first landed, it was directly [described as incomplete][a comment].

[a comment]: rust-lang#23289 (comment)

Filling out the missing functionality is going to mean adding support for more of Rust's [type expression] syntax, such as references, raw pointers, function pointers, and closures. This PR adds function pointers and closures.

[type expression]: https://doc.rust-lang.org/reference/types.html#type-expressions

There's been demand for something "like Hoogle, but for Rust" expressed a few times [1](https://www.reddit.com/r/rust/comments/y8sbid/is_there_a_website_like_haskells_hoogle_for_rust/) [2](https://users.rust-lang.org/t/rust-equivalent-of-haskells-hoogle/102280) [3](https://internals.rust-lang.org/t/std-library-inclusion-policy/6852/2) [4](https://discord.com/channels/442252698964721669/448238009733742612/1109502307495858216). Some of them just don't realize what functionality already exists ([`Duration -> u64`](https://doc.rust-lang.org/nightly/std/?search=duration%20-%3E%20u64) already works), but a lot of them specifically want to search for higher-order functions like option combinators.

## Guide-level explanation (from the Rustdoc book)

To search for a function that accepts a function as a parameter, like `Iterator::all`, wrap the nested signature in parenthesis, as in [`Iterator<T>, (T -> bool) -> bool`][iterator-all]. You can also search for a specific closure trait, such as `Iterator<T>, (FnMut(T) -> bool) -> bool`, but you need to know which one you want.

[iterator-all]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=Iterator<T>%2C+(T+->+bool)+->+bool&filter-crate=std

## Reference-level description (also from the Rustdoc book)

### Primitives with Special Syntax

<table>
<thead>
  <tr>
    <th>Shorthand</th>
    <th>Explicit names</th>
  </tr>
</thead>
<tbody>
  <tr><td colspan="2">Before this PR</td></tr>
  <tr>
    <td><code>[]</code></td>
    <td><code>primitive:slice</code> and/or <code>primitive:array</code></td>
  </tr>
  <tr>
    <td><code>[T]</code></td>
    <td><code>primitive:slice&lt;T&gt;</code> and/or <code>primitive:array&lt;T&gt;</code></td>
  </tr>
  <tr>
    <td><code>!</code></td>
    <td><code>primitive:never</code></td>
  </tr>
  <tr>
    <td><code>()</code></td>
    <td><code>primitive:unit</code> and/or <code>primitive:tuple</code></td>
  </tr>
  <tr>
    <td><code>(T)</code></td>
    <td><code>T</code></td>
  </tr>
  <tr>
    <td><code>(T,)</code></td>
    <td><code>primitive:tuple&lt;T&gt;</code></td>
  </tr>
  <tr><td colspan="2">After this PR</td></tr>
  <tr>
    <td><code>(T, U -> V, W)</code></td>
    <td><code>fn(T, U) -> (V, W)</code>, Fn, FnMut, and FnOnce</td>
  </tr>
</tbody>
</table>

The `->` operator has lower precedence than comma. If it's not wrapped in brackets, it delimits the return value for the function being searched for. To search for functions that take functions as parameters, use parenthesis.

### Search query grammar

```ebnf
ident = *(ALPHA / DIGIT / "_")
path = ident *(DOUBLE-COLON ident) [BANG]
slice-like = OPEN-SQUARE-BRACKET [ nonempty-arg-list ] CLOSE-SQUARE-BRACKET
tuple-like = OPEN-PAREN [ nonempty-arg-list ] CLOSE-PAREN
arg = [type-filter *WS COLON *WS] (path [generics] / slice-like / tuple-like)
type-sep = COMMA/WS *(COMMA/WS)
nonempty-arg-list = *(type-sep) arg *(type-sep arg) *(type-sep) [ return-args ]
generic-arg-list = *(type-sep) arg [ EQUAL arg ] *(type-sep arg [ EQUAL arg ]) *(type-sep)
normal-generics = OPEN-ANGLE-BRACKET [ generic-arg-list ] *(type-sep)
            CLOSE-ANGLE-BRACKET
fn-like-generics = OPEN-PAREN [ nonempty-arg-list ] CLOSE-PAREN [ RETURN-ARROW arg ]
generics = normal-generics / fn-like-generics
return-args = RETURN-ARROW *(type-sep) nonempty-arg-list

exact-search = [type-filter *WS COLON] [ RETURN-ARROW ] *WS QUOTE ident QUOTE [ generics ]
type-search = [ nonempty-arg-list ]

query = *WS (exact-search / type-search) *WS

; unchanged parts of the grammar, like the full list of type filters, are omitted
```

## Future direction

### The remaining type expression grammar

As described in rust-lang#118194, this is another step in the type expression grammar: BareFunction, and the function-like mode of TypePath, are now supported.

* RawPointerType and ReferenceType actually are a priority.
* ImplTraitType and TraitObjectType (and ImplTraitTypeOneBound and TraitObjectTypeOneBound) aren't as much of a priority, since they desugar pretty easily.

### Search subtyping and traits

This is the other major factor that makes it less useful than it should be.

* `iterator<result<t>> -> result<t>` doesn't find `Result::from_iter`. You have to search [`intoiterator<result<t>> -> result<t>`](https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=intoiterator%3Cresult%3Ct%3E%3E%20-%3E%20result%3Ct%3E&filter-crate=std). Nobody's going to search for IntoIterator unless they basically already know about it and don't need the search engine anyway.

* Iterator combinators are usually structs that happen to implement Iterator, like `std::iter::Map`.

To solve these cases, it needs to look at trait implementations, knowing that Iterator is a "subtype of" IntoIterator, and Map is a "subtype of" Iterator, so `iterator -> result` is a subtype of `intoiterator -> result` and `iterator<t>, (t -> u) -> iterator<u>` is a subtype of [`iterator<t>, (t -> u) -> map<t -> u>`](https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=iterator%3Ct%3E%2C%20(t%20-%3E%20u)%20-%3E%20map%3Ct%20-%3E%20u%3E&filter-crate=std).

…-hof, r=GuillaumeGomez

rustdoc-search: search types by higher-order functions

This feature extends rustdoc with syntax and search index information for searching function pointers and closures (Higher-Order Functions, or HOF). Part of rust-lang#60485

This PR adds two syntaxes: a high-level one for finding any kind of HOF, and a direct implementation of the parenthesized path syntax that Rust itself uses.

## Preview pages

| Query | Results |
|-------|---------|
| [`option<T>, (fnonce (T) -> bool) -> option<T>`][optionfilter] | `Option::filter` |
| [`option<T>, (T -> bool) -> option<T>`][optionfilter2] | `Option::filter` |

Updated chapter of the book: https://notriddle.com/rustdoc-html-demo-9/search-hof/rustdoc/read-documentation/search.html

[optionfilter]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=option<T>%2C+(fnonce+(T)+->+bool)+->+option<T>&filter-crate=std
[optionfilter2]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=option<T>%2C+(T+->+bool)+->+option<T>&filter-crate=std

## Motivation

When type-based search was first landed, it was directly [described as incomplete][a comment].

[a comment]: rust-lang#23289 (comment)

Filling out the missing functionality is going to mean adding support for more of Rust's [type expression] syntax, such as references, raw pointers, function pointers, and closures. This PR adds function pointers and closures.

[type expression]: https://doc.rust-lang.org/reference/types.html#type-expressions

There's been demand for something "like Hoogle, but for Rust" expressed a few times [1](https://www.reddit.com/r/rust/comments/y8sbid/is_there_a_website_like_haskells_hoogle_for_rust/) [2](https://users.rust-lang.org/t/rust-equivalent-of-haskells-hoogle/102280) [3](https://internals.rust-lang.org/t/std-library-inclusion-policy/6852/2) [4](https://discord.com/channels/442252698964721669/448238009733742612/1109502307495858216). Some of them just don't realize what functionality already exists ([`Duration -> u64`](https://doc.rust-lang.org/nightly/std/?search=duration%20-%3E%20u64) already works), but a lot of them specifically want to search for higher-order functions like option combinators.

## Guide-level explanation (from the Rustdoc book)

To search for a function that accepts a function as a parameter, like `Iterator::all`, wrap the nested signature in parenthesis, as in [`Iterator<T>, (T -> bool) -> bool`][iterator-all]. You can also search for a specific closure trait, such as `Iterator<T>, (FnMut(T) -> bool) -> bool`, but you need to know which one you want.

[iterator-all]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=Iterator<T>%2C+(T+->+bool)+->+bool&filter-crate=std

## Reference-level description (also from the Rustdoc book)

### Primitives with Special Syntax

<table>
<thead>
  <tr>
    <th>Shorthand</th>
    <th>Explicit names</th>
  </tr>
</thead>
<tbody>
  <tr><td colspan="2">Before this PR</td></tr>
  <tr>
    <td><code>[]</code></td>
    <td><code>primitive:slice</code> and/or <code>primitive:array</code></td>
  </tr>
  <tr>
    <td><code>[T]</code></td>
    <td><code>primitive:slice&lt;T&gt;</code> and/or <code>primitive:array&lt;T&gt;</code></td>
  </tr>
  <tr>
    <td><code>!</code></td>
    <td><code>primitive:never</code></td>
  </tr>
  <tr>
    <td><code>()</code></td>
    <td><code>primitive:unit</code> and/or <code>primitive:tuple</code></td>
  </tr>
  <tr>
    <td><code>(T)</code></td>
    <td><code>T</code></td>
  </tr>
  <tr>
    <td><code>(T,)</code></td>
    <td><code>primitive:tuple&lt;T&gt;</code></td>
  </tr>
  <tr><td colspan="2">After this PR</td></tr>
  <tr>
    <td><code>(T, U -> V, W)</code></td>
    <td><code>fn(T, U) -> (V, W)</code>, Fn, FnMut, and FnOnce</td>
  </tr>
</tbody>
</table>

The `->` operator has lower precedence than comma. If it's not wrapped in brackets, it delimits the return value for the function being searched for. To search for functions that take functions as parameters, use parenthesis.

### Search query grammar

```ebnf
ident = *(ALPHA / DIGIT / "_")
path = ident *(DOUBLE-COLON ident) [BANG]
slice-like = OPEN-SQUARE-BRACKET [ nonempty-arg-list ] CLOSE-SQUARE-BRACKET
tuple-like = OPEN-PAREN [ nonempty-arg-list ] CLOSE-PAREN
arg = [type-filter *WS COLON *WS] (path [generics] / slice-like / tuple-like)
type-sep = COMMA/WS *(COMMA/WS)
nonempty-arg-list = *(type-sep) arg *(type-sep arg) *(type-sep) [ return-args ]
generic-arg-list = *(type-sep) arg [ EQUAL arg ] *(type-sep arg [ EQUAL arg ]) *(type-sep)
normal-generics = OPEN-ANGLE-BRACKET [ generic-arg-list ] *(type-sep)
            CLOSE-ANGLE-BRACKET
fn-like-generics = OPEN-PAREN [ nonempty-arg-list ] CLOSE-PAREN [ RETURN-ARROW arg ]
generics = normal-generics / fn-like-generics
return-args = RETURN-ARROW *(type-sep) nonempty-arg-list

exact-search = [type-filter *WS COLON] [ RETURN-ARROW ] *WS QUOTE ident QUOTE [ generics ]
type-search = [ nonempty-arg-list ]

query = *WS (exact-search / type-search) *WS

; unchanged parts of the grammar, like the full list of type filters, are omitted
```

## Future direction

### The remaining type expression grammar

As described in rust-lang#118194, this is another step in the type expression grammar: BareFunction, and the function-like mode of TypePath, are now supported.

* RawPointerType and ReferenceType actually are a priority.
* ImplTraitType and TraitObjectType (and ImplTraitTypeOneBound and TraitObjectTypeOneBound) aren't as much of a priority, since they desugar pretty easily.

### Search subtyping and traits

This is the other major factor that makes it less useful than it should be.

* `iterator<result<t>> -> result<t>` doesn't find `Result::from_iter`. You have to search [`intoiterator<result<t>> -> result<t>`](https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=intoiterator%3Cresult%3Ct%3E%3E%20-%3E%20result%3Ct%3E&filter-crate=std). Nobody's going to search for IntoIterator unless they basically already know about it and don't need the search engine anyway.

* Iterator combinators are usually structs that happen to implement Iterator, like `std::iter::Map`.

To solve these cases, it needs to look at trait implementations, knowing that Iterator is a "subtype of" IntoIterator, and Map is a "subtype of" Iterator, so `iterator -> result` is a subtype of `intoiterator -> result` and `iterator<t>, (t -> u) -> iterator<u>` is a subtype of [`iterator<t>, (t -> u) -> map<t -> u>`](https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=iterator%3Ct%3E%2C%20(t%20-%3E%20u)%20-%3E%20map%3Ct%20-%3E%20u%3E&filter-crate=std).

…-hof, r=GuillaumeGomez

rustdoc-search: search types by higher-order functions

This feature extends rustdoc with syntax and search index information for searching function pointers and closures (Higher-Order Functions, or HOF). Part of rust-lang#60485

This PR adds two syntaxes: a high-level one for finding any kind of HOF, and a direct implementation of the parenthesized path syntax that Rust itself uses.

## Preview pages

| Query | Results |
|-------|---------|
| [`option<T>, (fnonce (T) -> bool) -> option<T>`][optionfilter] | `Option::filter` |
| [`option<T>, (T -> bool) -> option<T>`][optionfilter2] | `Option::filter` |

Updated chapter of the book: https://notriddle.com/rustdoc-html-demo-9/search-hof/rustdoc/read-documentation/search.html

[optionfilter]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=option<T>%2C+(fnonce+(T)+->+bool)+->+option<T>&filter-crate=std
[optionfilter2]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=option<T>%2C+(T+->+bool)+->+option<T>&filter-crate=std

## Motivation

When type-based search was first landed, it was directly [described as incomplete][a comment].

[a comment]: rust-lang#23289 (comment)

Filling out the missing functionality is going to mean adding support for more of Rust's [type expression] syntax, such as references, raw pointers, function pointers, and closures. This PR adds function pointers and closures.

[type expression]: https://doc.rust-lang.org/reference/types.html#type-expressions

There's been demand for something "like Hoogle, but for Rust" expressed a few times [1](https://www.reddit.com/r/rust/comments/y8sbid/is_there_a_website_like_haskells_hoogle_for_rust/) [2](https://users.rust-lang.org/t/rust-equivalent-of-haskells-hoogle/102280) [3](https://internals.rust-lang.org/t/std-library-inclusion-policy/6852/2) [4](https://discord.com/channels/442252698964721669/448238009733742612/1109502307495858216). Some of them just don't realize what functionality already exists ([`Duration -> u64`](https://doc.rust-lang.org/nightly/std/?search=duration%20-%3E%20u64) already works), but a lot of them specifically want to search for higher-order functions like option combinators.

## Guide-level explanation (from the Rustdoc book)

To search for a function that accepts a function as a parameter, like `Iterator::all`, wrap the nested signature in parenthesis, as in [`Iterator<T>, (T -> bool) -> bool`][iterator-all]. You can also search for a specific closure trait, such as `Iterator<T>, (FnMut(T) -> bool) -> bool`, but you need to know which one you want.

[iterator-all]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=Iterator<T>%2C+(T+->+bool)+->+bool&filter-crate=std

## Reference-level description (also from the Rustdoc book)

### Primitives with Special Syntax

<table>
<thead>
  <tr>
    <th>Shorthand</th>
    <th>Explicit names</th>
  </tr>
</thead>
<tbody>
  <tr><td colspan="2">Before this PR</td></tr>
  <tr>
    <td><code>[]</code></td>
    <td><code>primitive:slice</code> and/or <code>primitive:array</code></td>
  </tr>
  <tr>
    <td><code>[T]</code></td>
    <td><code>primitive:slice&lt;T&gt;</code> and/or <code>primitive:array&lt;T&gt;</code></td>
  </tr>
  <tr>
    <td><code>!</code></td>
    <td><code>primitive:never</code></td>
  </tr>
  <tr>
    <td><code>()</code></td>
    <td><code>primitive:unit</code> and/or <code>primitive:tuple</code></td>
  </tr>
  <tr>
    <td><code>(T)</code></td>
    <td><code>T</code></td>
  </tr>
  <tr>
    <td><code>(T,)</code></td>
    <td><code>primitive:tuple&lt;T&gt;</code></td>
  </tr>
  <tr><td colspan="2">After this PR</td></tr>
  <tr>
    <td><code>(T, U -> V, W)</code></td>
    <td><code>fn(T, U) -> (V, W)</code>, Fn, FnMut, and FnOnce</td>
  </tr>
</tbody>
</table>

The `->` operator has lower precedence than comma. If it's not wrapped in brackets, it delimits the return value for the function being searched for. To search for functions that take functions as parameters, use parenthesis.

### Search query grammar

```ebnf
ident = *(ALPHA / DIGIT / "_")
path = ident *(DOUBLE-COLON ident) [BANG]
slice-like = OPEN-SQUARE-BRACKET [ nonempty-arg-list ] CLOSE-SQUARE-BRACKET
tuple-like = OPEN-PAREN [ nonempty-arg-list ] CLOSE-PAREN
arg = [type-filter *WS COLON *WS] (path [generics] / slice-like / tuple-like)
type-sep = COMMA/WS *(COMMA/WS)
nonempty-arg-list = *(type-sep) arg *(type-sep arg) *(type-sep) [ return-args ]
generic-arg-list = *(type-sep) arg [ EQUAL arg ] *(type-sep arg [ EQUAL arg ]) *(type-sep)
normal-generics = OPEN-ANGLE-BRACKET [ generic-arg-list ] *(type-sep)
            CLOSE-ANGLE-BRACKET
fn-like-generics = OPEN-PAREN [ nonempty-arg-list ] CLOSE-PAREN [ RETURN-ARROW arg ]
generics = normal-generics / fn-like-generics
return-args = RETURN-ARROW *(type-sep) nonempty-arg-list

exact-search = [type-filter *WS COLON] [ RETURN-ARROW ] *WS QUOTE ident QUOTE [ generics ]
type-search = [ nonempty-arg-list ]

query = *WS (exact-search / type-search) *WS

; unchanged parts of the grammar, like the full list of type filters, are omitted
```

## Future direction

### The remaining type expression grammar

As described in rust-lang#118194, this is another step in the type expression grammar: BareFunction, and the function-like mode of TypePath, are now supported.

* RawPointerType and ReferenceType actually are a priority.
* ImplTraitType and TraitObjectType (and ImplTraitTypeOneBound and TraitObjectTypeOneBound) aren't as much of a priority, since they desugar pretty easily.

### Search subtyping and traits

This is the other major factor that makes it less useful than it should be.

* `iterator<result<t>> -> result<t>` doesn't find `Result::from_iter`. You have to search [`intoiterator<result<t>> -> result<t>`](https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=intoiterator%3Cresult%3Ct%3E%3E%20-%3E%20result%3Ct%3E&filter-crate=std). Nobody's going to search for IntoIterator unless they basically already know about it and don't need the search engine anyway.

* Iterator combinators are usually structs that happen to implement Iterator, like `std::iter::Map`.

To solve these cases, it needs to look at trait implementations, knowing that Iterator is a "subtype of" IntoIterator, and Map is a "subtype of" Iterator, so `iterator -> result` is a subtype of `intoiterator -> result` and `iterator<t>, (t -> u) -> iterator<u>` is a subtype of [`iterator<t>, (t -> u) -> map<t -> u>`](https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=iterator%3Ct%3E%2C%20(t%20-%3E%20u)%20-%3E%20map%3Ct%20-%3E%20u%3E&filter-crate=std).

Rollup merge of rust-lang#119676 - notriddle:notriddle/rustdoc-search-hof, r=GuillaumeGomez

rustdoc-search: search types by higher-order functions

This feature extends rustdoc with syntax and search index information for searching function pointers and closures (Higher-Order Functions, or HOF). Part of rust-lang#60485

This PR adds two syntaxes: a high-level one for finding any kind of HOF, and a direct implementation of the parenthesized path syntax that Rust itself uses.

## Preview pages

| Query | Results |
|-------|---------|
| [`option<T>, (fnonce (T) -> bool) -> option<T>`][optionfilter] | `Option::filter` |
| [`option<T>, (T -> bool) -> option<T>`][optionfilter2] | `Option::filter` |

Updated chapter of the book: https://notriddle.com/rustdoc-html-demo-9/search-hof/rustdoc/read-documentation/search.html

[optionfilter]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=option<T>%2C+(fnonce+(T)+->+bool)+->+option<T>&filter-crate=std
[optionfilter2]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=option<T>%2C+(T+->+bool)+->+option<T>&filter-crate=std

## Motivation

When type-based search was first landed, it was directly [described as incomplete][a comment].

[a comment]: rust-lang#23289 (comment)

Filling out the missing functionality is going to mean adding support for more of Rust's [type expression] syntax, such as references, raw pointers, function pointers, and closures. This PR adds function pointers and closures.

[type expression]: https://doc.rust-lang.org/reference/types.html#type-expressions

There's been demand for something "like Hoogle, but for Rust" expressed a few times [1](https://www.reddit.com/r/rust/comments/y8sbid/is_there_a_website_like_haskells_hoogle_for_rust/) [2](https://users.rust-lang.org/t/rust-equivalent-of-haskells-hoogle/102280) [3](https://internals.rust-lang.org/t/std-library-inclusion-policy/6852/2) [4](https://discord.com/channels/442252698964721669/448238009733742612/1109502307495858216). Some of them just don't realize what functionality already exists ([`Duration -> u64`](https://doc.rust-lang.org/nightly/std/?search=duration%20-%3E%20u64) already works), but a lot of them specifically want to search for higher-order functions like option combinators.

## Guide-level explanation (from the Rustdoc book)

To search for a function that accepts a function as a parameter, like `Iterator::all`, wrap the nested signature in parenthesis, as in [`Iterator<T>, (T -> bool) -> bool`][iterator-all]. You can also search for a specific closure trait, such as `Iterator<T>, (FnMut(T) -> bool) -> bool`, but you need to know which one you want.

[iterator-all]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=Iterator<T>%2C+(T+->+bool)+->+bool&filter-crate=std

## Reference-level description (also from the Rustdoc book)

### Primitives with Special Syntax

<table>
<thead>
  <tr>
    <th>Shorthand</th>
    <th>Explicit names</th>
  </tr>
</thead>
<tbody>
  <tr><td colspan="2">Before this PR</td></tr>
  <tr>
    <td><code>[]</code></td>
    <td><code>primitive:slice</code> and/or <code>primitive:array</code></td>
  </tr>
  <tr>
    <td><code>[T]</code></td>
    <td><code>primitive:slice&lt;T&gt;</code> and/or <code>primitive:array&lt;T&gt;</code></td>
  </tr>
  <tr>
    <td><code>!</code></td>
    <td><code>primitive:never</code></td>
  </tr>
  <tr>
    <td><code>()</code></td>
    <td><code>primitive:unit</code> and/or <code>primitive:tuple</code></td>
  </tr>
  <tr>
    <td><code>(T)</code></td>
    <td><code>T</code></td>
  </tr>
  <tr>
    <td><code>(T,)</code></td>
    <td><code>primitive:tuple&lt;T&gt;</code></td>
  </tr>
  <tr><td colspan="2">After this PR</td></tr>
  <tr>
    <td><code>(T, U -> V, W)</code></td>
    <td><code>fn(T, U) -> (V, W)</code>, Fn, FnMut, and FnOnce</td>
  </tr>
</tbody>
</table>

The `->` operator has lower precedence than comma. If it's not wrapped in brackets, it delimits the return value for the function being searched for. To search for functions that take functions as parameters, use parenthesis.

### Search query grammar

```ebnf
ident = *(ALPHA / DIGIT / "_")
path = ident *(DOUBLE-COLON ident) [BANG]
slice-like = OPEN-SQUARE-BRACKET [ nonempty-arg-list ] CLOSE-SQUARE-BRACKET
tuple-like = OPEN-PAREN [ nonempty-arg-list ] CLOSE-PAREN
arg = [type-filter *WS COLON *WS] (path [generics] / slice-like / tuple-like)
type-sep = COMMA/WS *(COMMA/WS)
nonempty-arg-list = *(type-sep) arg *(type-sep arg) *(type-sep) [ return-args ]
generic-arg-list = *(type-sep) arg [ EQUAL arg ] *(type-sep arg [ EQUAL arg ]) *(type-sep)
normal-generics = OPEN-ANGLE-BRACKET [ generic-arg-list ] *(type-sep)
            CLOSE-ANGLE-BRACKET
fn-like-generics = OPEN-PAREN [ nonempty-arg-list ] CLOSE-PAREN [ RETURN-ARROW arg ]
generics = normal-generics / fn-like-generics
return-args = RETURN-ARROW *(type-sep) nonempty-arg-list

exact-search = [type-filter *WS COLON] [ RETURN-ARROW ] *WS QUOTE ident QUOTE [ generics ]
type-search = [ nonempty-arg-list ]

query = *WS (exact-search / type-search) *WS

; unchanged parts of the grammar, like the full list of type filters, are omitted
```

## Future direction

### The remaining type expression grammar

As described in rust-lang#118194, this is another step in the type expression grammar: BareFunction, and the function-like mode of TypePath, are now supported.

* RawPointerType and ReferenceType actually are a priority.
* ImplTraitType and TraitObjectType (and ImplTraitTypeOneBound and TraitObjectTypeOneBound) aren't as much of a priority, since they desugar pretty easily.

### Search subtyping and traits

This is the other major factor that makes it less useful than it should be.

* `iterator<result<t>> -> result<t>` doesn't find `Result::from_iter`. You have to search [`intoiterator<result<t>> -> result<t>`](https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=intoiterator%3Cresult%3Ct%3E%3E%20-%3E%20result%3Ct%3E&filter-crate=std). Nobody's going to search for IntoIterator unless they basically already know about it and don't need the search engine anyway.

* Iterator combinators are usually structs that happen to implement Iterator, like `std::iter::Map`.

To solve these cases, it needs to look at trait implementations, knowing that Iterator is a "subtype of" IntoIterator, and Map is a "subtype of" Iterator, so `iterator -> result` is a subtype of `intoiterator -> result` and `iterator<t>, (t -> u) -> iterator<u>` is a subtype of [`iterator<t>, (t -> u) -> map<t -> u>`](https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=iterator%3Ct%3E%2C%20(t%20-%3E%20u)%20-%3E%20map%3Ct%20-%3E%20u%3E&filter-crate=std).

…uillaumeGomez

rustdoc-search: search types by higher-order functions

This feature extends rustdoc with syntax and search index information for searching function pointers and closures (Higher-Order Functions, or HOF). Part of rust-lang/rust#60485

This PR adds two syntaxes: a high-level one for finding any kind of HOF, and a direct implementation of the parenthesized path syntax that Rust itself uses.

## Preview pages

| Query | Results |
|-------|---------|
| [`option<T>, (fnonce (T) -> bool) -> option<T>`][optionfilter] | `Option::filter` |
| [`option<T>, (T -> bool) -> option<T>`][optionfilter2] | `Option::filter` |

Updated chapter of the book: https://notriddle.com/rustdoc-html-demo-9/search-hof/rustdoc/read-documentation/search.html

[optionfilter]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=option<T>%2C+(fnonce+(T)+->+bool)+->+option<T>&filter-crate=std
[optionfilter2]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=option<T>%2C+(T+->+bool)+->+option<T>&filter-crate=std

## Motivation

When type-based search was first landed, it was directly [described as incomplete][a comment].

[a comment]: rust-lang/rust#23289 (comment)

Filling out the missing functionality is going to mean adding support for more of Rust's [type expression] syntax, such as references, raw pointers, function pointers, and closures. This PR adds function pointers and closures.

[type expression]: https://doc.rust-lang.org/reference/types.html#type-expressions

There's been demand for something "like Hoogle, but for Rust" expressed a few times [1](https://www.reddit.com/r/rust/comments/y8sbid/is_there_a_website_like_haskells_hoogle_for_rust/) [2](https://users.rust-lang.org/t/rust-equivalent-of-haskells-hoogle/102280) [3](https://internals.rust-lang.org/t/std-library-inclusion-policy/6852/2) [4](https://discord.com/channels/442252698964721669/448238009733742612/1109502307495858216). Some of them just don't realize what functionality already exists ([`Duration -> u64`](https://doc.rust-lang.org/nightly/std/?search=duration%20-%3E%20u64) already works), but a lot of them specifically want to search for higher-order functions like option combinators.

## Guide-level explanation (from the Rustdoc book)

To search for a function that accepts a function as a parameter, like `Iterator::all`, wrap the nested signature in parenthesis, as in [`Iterator<T>, (T -> bool) -> bool`][iterator-all]. You can also search for a specific closure trait, such as `Iterator<T>, (FnMut(T) -> bool) -> bool`, but you need to know which one you want.

[iterator-all]: https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=Iterator<T>%2C+(T+->+bool)+->+bool&filter-crate=std

## Reference-level description (also from the Rustdoc book)

### Primitives with Special Syntax

<table>
<thead>
  <tr>
    <th>Shorthand</th>
    <th>Explicit names</th>
  </tr>
</thead>
<tbody>
  <tr><td colspan="2">Before this PR</td></tr>
  <tr>
    <td><code>[]</code></td>
    <td><code>primitive:slice</code> and/or <code>primitive:array</code></td>
  </tr>
  <tr>
    <td><code>[T]</code></td>
    <td><code>primitive:slice&lt;T&gt;</code> and/or <code>primitive:array&lt;T&gt;</code></td>
  </tr>
  <tr>
    <td><code>!</code></td>
    <td><code>primitive:never</code></td>
  </tr>
  <tr>
    <td><code>()</code></td>
    <td><code>primitive:unit</code> and/or <code>primitive:tuple</code></td>
  </tr>
  <tr>
    <td><code>(T)</code></td>
    <td><code>T</code></td>
  </tr>
  <tr>
    <td><code>(T,)</code></td>
    <td><code>primitive:tuple&lt;T&gt;</code></td>
  </tr>
  <tr><td colspan="2">After this PR</td></tr>
  <tr>
    <td><code>(T, U -> V, W)</code></td>
    <td><code>fn(T, U) -> (V, W)</code>, Fn, FnMut, and FnOnce</td>
  </tr>
</tbody>
</table>

The `->` operator has lower precedence than comma. If it's not wrapped in brackets, it delimits the return value for the function being searched for. To search for functions that take functions as parameters, use parenthesis.

### Search query grammar

```ebnf
ident = *(ALPHA / DIGIT / "_")
path = ident *(DOUBLE-COLON ident) [BANG]
slice-like = OPEN-SQUARE-BRACKET [ nonempty-arg-list ] CLOSE-SQUARE-BRACKET
tuple-like = OPEN-PAREN [ nonempty-arg-list ] CLOSE-PAREN
arg = [type-filter *WS COLON *WS] (path [generics] / slice-like / tuple-like)
type-sep = COMMA/WS *(COMMA/WS)
nonempty-arg-list = *(type-sep) arg *(type-sep arg) *(type-sep) [ return-args ]
generic-arg-list = *(type-sep) arg [ EQUAL arg ] *(type-sep arg [ EQUAL arg ]) *(type-sep)
normal-generics = OPEN-ANGLE-BRACKET [ generic-arg-list ] *(type-sep)
            CLOSE-ANGLE-BRACKET
fn-like-generics = OPEN-PAREN [ nonempty-arg-list ] CLOSE-PAREN [ RETURN-ARROW arg ]
generics = normal-generics / fn-like-generics
return-args = RETURN-ARROW *(type-sep) nonempty-arg-list

exact-search = [type-filter *WS COLON] [ RETURN-ARROW ] *WS QUOTE ident QUOTE [ generics ]
type-search = [ nonempty-arg-list ]

query = *WS (exact-search / type-search) *WS

; unchanged parts of the grammar, like the full list of type filters, are omitted
```

## Future direction

### The remaining type expression grammar

As described in rust-lang/rust#118194, this is another step in the type expression grammar: BareFunction, and the function-like mode of TypePath, are now supported.

* RawPointerType and ReferenceType actually are a priority.
* ImplTraitType and TraitObjectType (and ImplTraitTypeOneBound and TraitObjectTypeOneBound) aren't as much of a priority, since they desugar pretty easily.

### Search subtyping and traits

This is the other major factor that makes it less useful than it should be.

* `iterator<result<t>> -> result<t>` doesn't find `Result::from_iter`. You have to search [`intoiterator<result<t>> -> result<t>`](https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=intoiterator%3Cresult%3Ct%3E%3E%20-%3E%20result%3Ct%3E&filter-crate=std). Nobody's going to search for IntoIterator unless they basically already know about it and don't need the search engine anyway.

* Iterator combinators are usually structs that happen to implement Iterator, like `std::iter::Map`.

To solve these cases, it needs to look at trait implementations, knowing that Iterator is a "subtype of" IntoIterator, and Map is a "subtype of" Iterator, so `iterator -> result` is a subtype of `intoiterator -> result` and `iterator<t>, (t -> u) -> iterator<u>` is a subtype of [`iterator<t>, (t -> u) -> map<t -> u>`](https://notriddle.com/rustdoc-html-demo-9/search-hof/std/vec/struct.Vec.html?search=iterator%3Ct%3E%2C%20(t%20-%3E%20u)%20-%3E%20map%3Ct%20-%3E%20u%3E&filter-crate=std).

…uillaumeGomez

rustdoc-search: search for references

This feature extends rustdoc with syntax and search index information for searching borrow references. Part of rust-lang#60485

## Preview

- [`&mut`](https://notriddle.com/rustdoc-html-demo-11/reference/std/index.html?search=%26mut)
- [`&Option<T> -> Option<&T>`](https://notriddle.com/rustdoc-html-demo-11/reference/std/index.html?search=%26Option%3CT%3E%20-%3E%20Option%3C%26T%3E)
- [`&mut Option<T> -> Option<&mut T>`](https://notriddle.com/rustdoc-html-demo-11/reference/std/index.html?search=%26mut%20Option%3CT%3E%20-%3E%20Option%3C%26mut%20T%3E)

Updated chapter of the book: https://notriddle.com/rustdoc-html-demo-11/reference/rustdoc/read-documentation/search.html

## Motivation

See rust-lang#119676

## Guide-level explanation

You can't search by lifetimes, but other than that it's the same syntax references normally use.

## Reference-level description

<table>
<thead>
  <tr>
    <th>Shorthand</th>
    <th>Explicit names</th>
  </tr>
</thead>
<tbody>
  <tr><td colspan="2">Before this PR</td></tr>
  <tr>
    <td><code>[]</code></td>
    <td><code>primitive:slice</code> and/or <code>primitive:array</code></td>
  </tr>
  <tr>
    <td><code>[T]</code></td>
    <td><code>primitive:slice&lt;T&gt;</code> and/or <code>primitive:array&lt;T&gt;</code></td>
  </tr>
  <tr>
    <td><code>!</code></td>
    <td><code>primitive:never</code></td>
  </tr>
  <tr>
    <td><code>()</code></td>
    <td><code>primitive:unit</code> and/or <code>primitive:tuple</code></td>
  </tr>
  <tr>
    <td><code>(T)</code></td>
    <td><code>T</code></td>
  </tr>
  <tr>
    <td><code>(T,)</code></td>
    <td><code>primitive:tuple&lt;T&gt;</code></td>
  </tr>
  <tr>
    <td><code>(T, U -> V, W)</code></td>
    <td><code>fn(T, U) -> (V, W)</code>, Fn, FnMut, and FnOnce</td>
  </tr>
  <tr><td colspan="2">New additions with this PR</td></tr>
  <tr>
    <td><code>&</code></td>
    <td><code>primitive:reference</td>
  </tr>
  <tr>
    <td><code>&mut</code></td>
    <td><code>primitive:reference&lt;keyword:mut&gt;</td>
  </tr>
  <tr>
    <td><code>&T</code></td>
    <td><code>primitive:reference&lt;T&gt;</td>
  </tr>
  <tr>
    <td><code>&mut T</code></td>
    <td><code>primitive:reference&lt;keyword:mut, T&gt;</td>
  </tr>
</tbody>
</table>

### Search query grammar

<code><pre><strong>borrow-ref = AMP *WS [MUT] *WS [arg]</strong>
arg = [type-filter *WS COLON *WS] (path [generics] / slice-like / tuple-like / <strong>borrow-ref</strong>)</pre></code>

```
AMP = "&"
MUT = "mut"
```

## Future direction

As described in rust-lang#118194 and rust-lang#119676

* The remaining type expression grammar (this is another step in the type expression grammar: `ReferenceType` is now supported)
* Search subtyping and traits

Rollup merge of rust-lang#124148 - notriddle:notriddle/reference, r=GuillaumeGomez

rustdoc-search: search for references

This feature extends rustdoc with syntax and search index information for searching borrow references. Part of rust-lang#60485

## Preview

- [`&mut`](https://notriddle.com/rustdoc-html-demo-11/reference/std/index.html?search=%26mut)
- [`&Option<T> -> Option<&T>`](https://notriddle.com/rustdoc-html-demo-11/reference/std/index.html?search=%26Option%3CT%3E%20-%3E%20Option%3C%26T%3E)
- [`&mut Option<T> -> Option<&mut T>`](https://notriddle.com/rustdoc-html-demo-11/reference/std/index.html?search=%26mut%20Option%3CT%3E%20-%3E%20Option%3C%26mut%20T%3E)

Updated chapter of the book: https://notriddle.com/rustdoc-html-demo-11/reference/rustdoc/read-documentation/search.html

## Motivation

See rust-lang#119676

## Guide-level explanation

You can't search by lifetimes, but other than that it's the same syntax references normally use.

## Reference-level description

<table>
<thead>
  <tr>
    <th>Shorthand</th>
    <th>Explicit names</th>
  </tr>
</thead>
<tbody>
  <tr><td colspan="2">Before this PR</td></tr>
  <tr>
    <td><code>[]</code></td>
    <td><code>primitive:slice</code> and/or <code>primitive:array</code></td>
  </tr>
  <tr>
    <td><code>[T]</code></td>
    <td><code>primitive:slice&lt;T&gt;</code> and/or <code>primitive:array&lt;T&gt;</code></td>
  </tr>
  <tr>
    <td><code>!</code></td>
    <td><code>primitive:never</code></td>
  </tr>
  <tr>
    <td><code>()</code></td>
    <td><code>primitive:unit</code> and/or <code>primitive:tuple</code></td>
  </tr>
  <tr>
    <td><code>(T)</code></td>
    <td><code>T</code></td>
  </tr>
  <tr>
    <td><code>(T,)</code></td>
    <td><code>primitive:tuple&lt;T&gt;</code></td>
  </tr>
  <tr>
    <td><code>(T, U -> V, W)</code></td>
    <td><code>fn(T, U) -> (V, W)</code>, Fn, FnMut, and FnOnce</td>
  </tr>
  <tr><td colspan="2">New additions with this PR</td></tr>
  <tr>
    <td><code>&</code></td>
    <td><code>primitive:reference</td>
  </tr>
  <tr>
    <td><code>&mut</code></td>
    <td><code>primitive:reference&lt;keyword:mut&gt;</td>
  </tr>
  <tr>
    <td><code>&T</code></td>
    <td><code>primitive:reference&lt;T&gt;</td>
  </tr>
  <tr>
    <td><code>&mut T</code></td>
    <td><code>primitive:reference&lt;keyword:mut, T&gt;</td>
  </tr>
</tbody>
</table>

### Search query grammar

<code><pre><strong>borrow-ref = AMP *WS [MUT] *WS [arg]</strong>
arg = [type-filter *WS COLON *WS] (path [generics] / slice-like / tuple-like / <strong>borrow-ref</strong>)</pre></code>

```
AMP = "&"
MUT = "mut"
```

## Future direction

As described in rust-lang#118194 and rust-lang#119676

* The remaining type expression grammar (this is another step in the type expression grammar: `ReferenceType` is now supported)
* Search subtyping and traits

…omez

rustdoc-search: search for references

This feature extends rustdoc with syntax and search index information for searching borrow references. Part of rust-lang/rust#60485

## Preview

- [`&mut`](https://notriddle.com/rustdoc-html-demo-11/reference/std/index.html?search=%26mut)
- [`&Option<T> -> Option<&T>`](https://notriddle.com/rustdoc-html-demo-11/reference/std/index.html?search=%26Option%3CT%3E%20-%3E%20Option%3C%26T%3E)
- [`&mut Option<T> -> Option<&mut T>`](https://notriddle.com/rustdoc-html-demo-11/reference/std/index.html?search=%26mut%20Option%3CT%3E%20-%3E%20Option%3C%26mut%20T%3E)

Updated chapter of the book: https://notriddle.com/rustdoc-html-demo-11/reference/rustdoc/read-documentation/search.html

## Motivation

See rust-lang/rust#119676

## Guide-level explanation

You can't search by lifetimes, but other than that it's the same syntax references normally use.

## Reference-level description

<table>
<thead>
  <tr>
    <th>Shorthand</th>
    <th>Explicit names</th>
  </tr>
</thead>
<tbody>
  <tr><td colspan="2">Before this PR</td></tr>
  <tr>
    <td><code>[]</code></td>
    <td><code>primitive:slice</code> and/or <code>primitive:array</code></td>
  </tr>
  <tr>
    <td><code>[T]</code></td>
    <td><code>primitive:slice&lt;T&gt;</code> and/or <code>primitive:array&lt;T&gt;</code></td>
  </tr>
  <tr>
    <td><code>!</code></td>
    <td><code>primitive:never</code></td>
  </tr>
  <tr>
    <td><code>()</code></td>
    <td><code>primitive:unit</code> and/or <code>primitive:tuple</code></td>
  </tr>
  <tr>
    <td><code>(T)</code></td>
    <td><code>T</code></td>
  </tr>
  <tr>
    <td><code>(T,)</code></td>
    <td><code>primitive:tuple&lt;T&gt;</code></td>
  </tr>
  <tr>
    <td><code>(T, U -> V, W)</code></td>
    <td><code>fn(T, U) -> (V, W)</code>, Fn, FnMut, and FnOnce</td>
  </tr>
  <tr><td colspan="2">New additions with this PR</td></tr>
  <tr>
    <td><code>&</code></td>
    <td><code>primitive:reference</td>
  </tr>
  <tr>
    <td><code>&mut</code></td>
    <td><code>primitive:reference&lt;keyword:mut&gt;</td>
  </tr>
  <tr>
    <td><code>&T</code></td>
    <td><code>primitive:reference&lt;T&gt;</td>
  </tr>
  <tr>
    <td><code>&mut T</code></td>
    <td><code>primitive:reference&lt;keyword:mut, T&gt;</td>
  </tr>
</tbody>
</table>

### Search query grammar

<code><pre><strong>borrow-ref = AMP *WS [MUT] *WS [arg]</strong>
arg = [type-filter *WS COLON *WS] (path [generics] / slice-like / tuple-like / <strong>borrow-ref</strong>)</pre></code>

```
AMP = "&"
MUT = "mut"
```

## Future direction

As described in rust-lang/rust#118194 and rust-lang/rust#119676

* The remaining type expression grammar (this is another step in the type expression grammar: `ReferenceType` is now supported)
* Search subtyping and traits

This is based on the pkgsrc-wip rust180 package, retaining
the main pkgsrc changes as best as I could.

Pkgsrc changes:
 * Adapt checksums and patches.
 * Make this work again on big-endian aarch64 (at least on NetBSD).
 * Make the choice of GCC = 12 work for sparc64 by testing options
   after options.mk is included (which is required...).  Makes this
   work on NetBSD/sparc64 10.0 again.

Upstream chnages:

Version 1.80.1 (2024-08-08)
===========================

- [Fix miscompilation in the jump threading MIR optimization when
  comparing floats]
  (rust-lang/rust#128271)
- [Revert changes to the `dead_code` lint from 1.80.0]
  (rust-lang/rust#128618)

Version 1.80.0 (2024-07-25)
==========================

Language
--------
- [Document maximum allocation size]
  (rust-lang/rust#116675)
- [Allow zero-byte offsets and ZST read/writes on arbitrary pointers]
  (rust-lang/rust#117329)
- [Support C23's variadics without a named parameter]
  (rust-lang/rust#124048)
- [Stabilize `exclusive_range_pattern` feature]
  (rust-lang/rust#124459)
- [Guarantee layout and ABI of `Result` in some scenarios]
  (rust-lang/rust#124870)

Compiler
--------
- [Update cc crate to v1.0.97 allowing additional spectre mitigations
  on MSVC targets]
  (rust-lang/rust#124892)
- [Allow field reordering on types marked `repr(packed(1))`]
  (rust-lang/rust#125360)
- [Add a lint against never type fallback affecting unsafe code]
  (rust-lang/rust#123939)
- [Disallow cast with trailing braced macro in let-else]
  (rust-lang/rust#125049)
- [Expand `for_loops_over_fallibles` lint to lint on fallibles
  behind references.]
  (rust-lang/rust#125156)
- [self-contained linker: retry linking without `-fuse-ld=lld` on
  CCs that don't support it]
  (rust-lang/rust#125417)
- [Do not parse CVarArgs (`...`) as a type in trait bounds]
  (rust-lang/rust#125863)
- Improvements to LLDB formatting [#124458]
  (rust-lang/rust#124458) [#124500]
  (rust-lang/rust#124500)
- [For the wasm32-wasip2 target default to PIC and do not use `-fuse-ld=lld`]
  (rust-lang/rust#124858)
- [Add x86_64-unknown-linux-none as a tier 3 target]
  (rust-lang/rust#125023)
- [Lint on `foo.into_iter()` resolving to `&Box<[T]>: IntoIterator`]
  (rust-lang/rust#124097)

Libraries
---------
- [Add `size_of` and `size_of_val` and `align_of` and `align_of_val`
  to the prelude]
  (rust-lang/rust#123168)
- [Abort a process when FD ownership is violated]
  (rust-lang/rust#124210)
- [io::Write::write_fmt: panic if the formatter fails when the
  stream does not fail]
  (rust-lang/rust#125012)
- [Panic if `PathBuf::set_extension` would add a path separator]
  (rust-lang/rust#125070)
- [Add assert_unsafe_precondition to unchecked_{add,sub,neg,mul,shl,shr}
  methods] (rust-lang/rust#121571)
- [Update `c_char` on AIX to use the correct type]
  (rust-lang/rust#122986)
- [`offset_of!` no longer returns a temporary]
  (rust-lang/rust#124484)
- [Handle sigma in `str.to_lowercase` correctly]
  (rust-lang/rust#124773)
- [Raise `DEFAULT_MIN_STACK_SIZE` to at least 64KiB]
  (rust-lang/rust#126059)

Stabilized APIs
---------------
- [`impl Default for Rc<CStr>`]
  (https://doc.rust-lang.org/beta/alloc/rc/struct.Rc.html#impl-Default-for-Rc%3CCStr%3E)
- [`impl Default for Rc<str>`]
  (https://doc.rust-lang.org/beta/alloc/rc/struct.Rc.html#impl-Default-for-Rc%3Cstr%3E)
- [`impl Default for Rc<[T]>`]
  (https://doc.rust-lang.org/beta/alloc/rc/struct.Rc.html#impl-Default-for-Rc%3C%5BT%5D%3E)
- [`impl Default for Arc<str>`]
  (https://doc.rust-lang.org/beta/alloc/sync/struct.Arc.html#impl-Default-for-Arc%3Cstr%3E)
- [`impl Default for Arc<CStr>`]
  (https://doc.rust-lang.org/beta/alloc/sync/struct.Arc.html#impl-Default-for-Arc%3CCStr%3E)
- [`impl Default for Arc<[T]>`]
  (https://doc.rust-lang.org/beta/alloc/sync/struct.Arc.html#impl-Default-for-Arc%3C%5BT%5D%3E)
- [`impl IntoIterator for Box<[T]>`]
  (https://doc.rust-lang.org/beta/alloc/boxed/struct.Box.html#impl-IntoIterator-for-Box%3C%5BI%5D,+A%3E)
- [`impl FromIterator<String> for Box<str>`]
  (https://doc.rust-lang.org/beta/alloc/boxed/struct.Box.html#impl-FromIterator%3CString%3E-for-Box%3Cstr%3E)
- [`impl FromIterator<char> for Box<str>`]
  (https://doc.rust-lang.org/beta/alloc/boxed/struct.Box.html#impl-FromIterator%3Cchar%3E-for-Box%3Cstr%3E)
- [`LazyCell`]
  (https://doc.rust-lang.org/beta/core/cell/struct.LazyCell.html)
- [`LazyLock`]
  (https://doc.rust-lang.org/beta/std/sync/struct.LazyLock.html)
- [`Duration::div_duration_f32`]
  (https://doc.rust-lang.org/beta/std/time/struct.Duration.html#method.div_duration_f32)
- [`Duration::div_duration_f64`]
  (https://doc.rust-lang.org/beta/std/time/struct.Duration.html#method.div_duration_f64)
- [`Option::take_if`]
  (https://doc.rust-lang.org/beta/std/option/enum.Option.html#method.take_if)
- [`Seek::seek_relative`]
  (https://doc.rust-lang.org/beta/std/io/trait.Seek.html#method.seek_relative)
- [`BinaryHeap::as_slice`]
  (https://doc.rust-lang.org/beta/std/collections/struct.BinaryHeap.html#method.as_slice)
- [`NonNull::offset`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.offset)
- [`NonNull::byte_offset`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.byte_offset)
- [`NonNull::add`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.add)
- [`NonNull::byte_add`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.byte_add)
- [`NonNull::sub`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.sub)
- [`NonNull::byte_sub`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.byte_sub)
- [`NonNull::offset_from`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.offset_from)
- [`NonNull::byte_offset_from`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.byte_offset_from)
- [`NonNull::read`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.read)
- [`NonNull::read_volatile`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.read_volatile)
- [`NonNull::read_unaligned`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.read_unaligned)
- [`NonNull::write`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.write)
- [`NonNull::write_volatile`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.write_volatile)
- [`NonNull::write_unaligned`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.write_unaligned)
- [`NonNull::write_bytes`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.write_bytes)
- [`NonNull::copy_to`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.copy_to)
- [`NonNull::copy_to_nonoverlapping`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.copy_to_nonoverlapping)
- [`NonNull::copy_from`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.copy_from)
- [`NonNull::copy_from_nonoverlapping`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.copy_from_nonoverlapping)
- [`NonNull::replace`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.replace)
- [`NonNull::swap`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.swap)
- [`NonNull::drop_in_place`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.drop_in_place)
- [`NonNull::align_offset`]
  (https://doc.rust-lang.org/beta/std/ptr/struct.NonNull.html#method.align_offset)
- [`<[T]>::split_at_checked`]
  (https://doc.rust-lang.org/beta/std/primitive.slice.html#method.split_at_checked)
- [`<[T]>::split_at_mut_checked`]
  (https://doc.rust-lang.org/beta/std/primitive.slice.html#method.split_at_mut_checked)
- [`str::split_at_checked`]
  (https://doc.rust-lang.org/beta/std/primitive.str.html#method.split_at_checked)
- [`str::split_at_mut_checked`]
  (https://doc.rust-lang.org/beta/std/primitive.str.html#method.split_at_mut_checked)
- [`str::trim_ascii`]
  (https://doc.rust-lang.org/beta/std/primitive.str.html#method.trim_ascii)
- [`str::trim_ascii_start`]
  (https://doc.rust-lang.org/beta/std/primitive.str.html#method.trim_ascii_start)
- [`str::trim_ascii_end`]
  (https://doc.rust-lang.org/beta/std/primitive.str.html#method.trim_ascii_end)
- [`<[u8]>::trim_ascii`]
  (https://doc.rust-lang.org/beta/core/primitive.slice.html#method.trim_ascii)
- [`<[u8]>::trim_ascii_start`]
  (https://doc.rust-lang.org/beta/core/primitive.slice.html#method.trim_ascii_start)
- [`<[u8]>::trim_ascii_end`]
  (https://doc.rust-lang.org/beta/core/primitive.slice.html#method.trim_ascii_end)
- [`Ipv4Addr::BITS`]
  (https://doc.rust-lang.org/beta/core/net/struct.Ipv4Addr.html#associatedconstant.BITS)
- [`Ipv4Addr::to_bits`]
  (https://doc.rust-lang.org/beta/core/net/struct.Ipv4Addr.html#method.to_bits)
- [`Ipv4Addr::from_bits`]
  (https://doc.rust-lang.org/beta/core/net/struct.Ipv4Addr.html#method.from_bits)
- [`Ipv6Addr::BITS`]
  (https://doc.rust-lang.org/beta/core/net/struct.Ipv6Addr.html#associatedconstant.BITS)
- [`Ipv6Addr::to_bits`]
  (https://doc.rust-lang.org/beta/core/net/struct.Ipv6Addr.html#method.to_bits)
- [`Ipv6Addr::from_bits`]
  (https://doc.rust-lang.org/beta/core/net/struct.Ipv6Addr.html#method.from_bits)
- [`Vec::<[T; N]>::into_flattened`]
  (https://doc.rust-lang.org/beta/alloc/vec/struct.Vec.html#method.into_flattened)
- [`<[[T; N]]>::as_flattened`]
  (https://doc.rust-lang.org/beta/core/primitive.slice.html#method.as_flattened)
- [`<[[T; N]]>::as_flattened_mut`]
  (https://doc.rust-lang.org/beta/core/primitive.slice.html#method.as_flattened_mut)

These APIs are now stable in const contexts:

- [`<[T]>::last_chunk`]
  (https://doc.rust-lang.org/beta/core/primitive.slice.html#method.last_chunk)
- [`BinaryHeap::new`]
  (https://doc.rust-lang.org/beta/std/collections/struct.BinaryHeap.html#method.new)

Cargo
-----

- [Stabilize `-Zcheck-cfg` as always enabled]
  (rust-lang/cargo#13571)
- [Warn, rather than fail publish, if a target is excluded]
  (rust-lang/cargo#13713)
- [Add special `check-cfg` lint config for the `unexpected_cfgs` lint]
  (rust-lang/cargo#13913)
- [Stabilize `cargo update --precise <yanked>`]
  (rust-lang/cargo#13974)
- [Don't change file permissions on `Cargo.toml` when using `cargo add`]
  (rust-lang/cargo#13898)
- [Support using `cargo fix` on IPv6-only networks]
  (rust-lang/cargo#13907)

Rustdoc
-----

- [Allow searching for references]
  (rust-lang/rust#124148)
- [Stabilize `custom_code_classes_in_docs` feature]
  (rust-lang/rust#124577)
- [fix: In cross-crate scenarios show enum variants on type aliases of enums]
  (rust-lang/rust#125300)

Compatibility Notes
-------------------

- [rustfmt estimates line lengths differently when using non-ascii characters]
  (rust-lang/rustfmt#6203)
- [Type aliases are now handled correctly in orphan check]
  (rust-lang/rust#117164)
- [Allow instructing rustdoc to read from stdin via `-`]
  (rust-lang/rust#124611)
- [`std::env::{set_var, remove_var}` can no longer be converted to
  safe function pointers and no longer implement the `Fn` family of
  traits]
  (rust-lang/rust#124636)
- [Warn (or error) when `Self` constructor from outer item is
  referenced in inner nested item]
  (rust-lang/rust#124187)
- [Turn `indirect_structural_match` and `pointer_structural_match`
  lints into hard errors]
  (rust-lang/rust#124661)
- [Make `where_clause_object_safety` lint a regular object safety violation]
  (rust-lang/rust#125380)
- [Turn `proc_macro_back_compat` lint into a hard error.]
  (rust-lang/rust#125596)
- [Detect unused structs even when implementing private traits]
  (rust-lang/rust#122382)
- [`std::sync::ReentrantLockGuard<T>` is no longer `Sync` if `T: !Sync`]
  (rust-lang/rust#125527) which means
  [`std::io::StdoutLock` and `std::io::StderrLock` are no longer
  Sync] (rust-lang/rust#127340)

Internal Changes
----------------

These changes do not affect any public interfaces of Rust, but they represent
significant improvements to the performance or internals of rustc and related
tools.

- Misc improvements to size of generated html by rustdoc e.g. [#124738]
  (rust-lang/rust#124738) and [#123734]
  (rust-lang/rust#123734)
- [MSVC targets no longer depend on libc]
  (rust-lang/rust#124050)


Version 1.79.0 (2024-06-13)
==========================

Language
--------
- [Stabilize inline `const {}` expressions.]
  (rust-lang/rust#104087)
- [Prevent opaque types being instantiated twice with different
  regions within the same function.]
  (rust-lang/rust#116935)
- [Stabilize WebAssembly target features that are in phase 4 and 5.]
  (rust-lang/rust#117457)
- [Add the `redundant_lifetimes` lint to detect lifetimes which
  are semantically redundant.]
  (rust-lang/rust#118391)
- [Stabilize the `unnameable_types` lint for public types that can't be named.]
  (rust-lang/rust#120144)
- [Enable debuginfo in macros, and stabilize `-C collapse-macro-debuginfo`
  and `#[collapse_debuginfo]`.]
  (rust-lang/rust#120845)
- [Propagate temporary lifetime extension into `if` and `match` expressions.]
  (rust-lang/rust#121346)
- [Restrict promotion of `const fn` calls.]
  (rust-lang/rust#121557)
- [Warn against refining impls of crate-private traits with
  `refining_impl_trait` lint.]
  (rust-lang/rust#121720)
- [Stabilize associated type bounds (RFC 2289).]
  (rust-lang/rust#122055)
- [Stabilize importing `main` from other modules or crates.]
  (rust-lang/rust#122060)
- [Check return types of function types for well-formedness]
  (rust-lang/rust#115538)
- [Rework `impl Trait` lifetime inference]
  (rust-lang/rust#116891)
- [Change inductive trait solver cycles to be ambiguous]
  (rust-lang/rust#122791)

Compiler
--------
- [Define `-C strip` to only affect binaries, not artifacts like `.pdb`.]
  (rust-lang/rust#115120)
- [Stabilize `-Crelro-level` for controlling runtime link hardening.]
  (rust-lang/rust#121694)
- [Stabilize checking of `cfg` names and values at compile-time
  with `--check-cfg`.]
  (rust-lang/rust#123501)
  *Note that this only stabilizes the compiler part, the Cargo part
  is still unstable in this release.*
- [Add `aarch64-apple-visionos` and `aarch64-apple-visionos-sim`
  tier 3 targets.]
  (rust-lang/rust#121419)
- [Add `riscv32ima-unknown-none-elf` tier 3 target.]
  (rust-lang/rust#122696)
- [Promote several Windows targets to tier 2]
  (rust-lang/rust#121712):
  `aarch64-pc-windows-gnullvm`, `i686-pc-windows-gnullvm`, and
  `x86_64-pc-windows-gnullvm`.

Refer to Rust's [platform support page][platform-support-doc]
for more information on Rust's tiered platform support.

Libraries
---------

- [Implement `FromIterator` for `(impl Default + Extend, impl
  Default + Extend)`.]
  (rust-lang/rust#107462)
- [Implement `{Div,Rem}Assign<NonZero<X>>` on `X`.]
  (rust-lang/rust#121952)
- [Document overrides of `clone_from()` in core/std.]
  (rust-lang/rust#122201)
- [Link MSVC default lib in core.]
  (rust-lang/rust#122268)
- [Caution against using `transmute` between pointers and integers.]
  (rust-lang/rust#122379)
- [Enable frame pointers for the standard library.]
  (rust-lang/rust#122646)

Stabilized APIs
---------------

- [`{integer}::unchecked_add`]
  (https://doc.rust-lang.org/stable/core/primitive.i32.html#method.unchecked_add)
- [`{integer}::unchecked_mul`]
  (https://doc.rust-lang.org/stable/core/primitive.i32.html#method.unchecked_mul)
- [`{integer}::unchecked_sub`]
  (https://doc.rust-lang.org/stable/core/primitive.i32.html#method.unchecked_sub)
- [`<[T]>::split_at_unchecked`]
  (https://doc.rust-lang.org/stable/core/primitive.slice.html#method.split_at_unchecked)
- [`<[T]>::split_at_mut_unchecked`]
  (https://doc.rust-lang.org/stable/core/primitive.slice.html#method.split_at_mut_unchecked)
- [`<[u8]>::utf8_chunks`]
  (https://doc.rust-lang.org/stable/core/primitive.slice.html#method.utf8_chunks)
- [`str::Utf8Chunks`]
  (https://doc.rust-lang.org/stable/core/str/struct.Utf8Chunks.html)
- [`str::Utf8Chunk`]
  (https://doc.rust-lang.org/stable/core/str/struct.Utf8Chunk.html)
- [`<*const T>::is_aligned`]
  (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.is_aligned)
- [`<*mut T>::is_aligned`]
  (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.is_aligned-1)
- [`NonNull::is_aligned`]
  (https://doc.rust-lang.org/stable/core/ptr/struct.NonNull.html#method.is_aligned)
- [`<*const [T]>::len`]
  (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.len)
- [`<*mut [T]>::len`]
  (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.len-1)
- [`<*const [T]>::is_empty`]
  (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.is_empty)
- [`<*mut [T]>::is_empty`]
  (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.is_empty-1)
- [`NonNull::<[T]>::is_empty`]
  (https://doc.rust-lang.org/stable/core/ptr/struct.NonNull.html#method.is_empty)
- [`CStr::count_bytes`]
  (https://doc.rust-lang.org/stable/core/ffi/c_str/struct.CStr.html#method.count_bytes)
- [`io::Error::downcast`]
  (https://doc.rust-lang.org/stable/std/io/struct.Error.html#method.downcast)
- [`num::NonZero<T>`]
  (https://doc.rust-lang.org/stable/core/num/struct.NonZero.html)
- [`path::absolute`]
  (https://doc.rust-lang.org/stable/std/path/fn.absolute.html)
- [`proc_macro::Literal::byte_character`]
  (https://doc.rust-lang.org/stable/proc_macro/struct.Literal.html#method.byte_character)
- [`proc_macro::Literal::c_string`]
  (https://doc.rust-lang.org/stable/proc_macro/struct.Literal.html#method.c_string)

These APIs are now stable in const contexts:

- [`Atomic*::into_inner`]
  (https://doc.rust-lang.org/stable/core/sync/atomic/struct.AtomicUsize.html#method.into_inner)
- [`io::Cursor::new`]
  (https://doc.rust-lang.org/stable/std/io/struct.Cursor.html#method.new)
- [`io::Cursor::get_ref`]
  (https://doc.rust-lang.org/stable/std/io/struct.Cursor.html#method.get_ref)
- [`io::Cursor::position`]
  (https://doc.rust-lang.org/stable/std/io/struct.Cursor.html#method.position)
- [`io::empty`]
  (https://doc.rust-lang.org/stable/std/io/fn.empty.html)
- [`io::repeat`]
  (https://doc.rust-lang.org/stable/std/io/fn.repeat.html)
- [`io::sink`]
  (https://doc.rust-lang.org/stable/std/io/fn.sink.html)
- [`panic::Location::caller`]
  (https://doc.rust-lang.org/stable/std/panic/struct.Location.html#method.caller)
- [`panic::Location::file`]
  (https://doc.rust-lang.org/stable/std/panic/struct.Location.html#method.file)
- [`panic::Location::line`]
  (https://doc.rust-lang.org/stable/std/panic/struct.Location.html#method.line)
- [`panic::Location::column`]
  (https://doc.rust-lang.org/stable/std/panic/struct.Location.html#method.column)

Cargo
-----

- [Prevent dashes in `lib.name`, always normalizing to `_`.]
  (rust-lang/cargo#12783)
- [Stabilize MSRV-aware version requirement selection in `cargo add`.]
  (rust-lang/cargo#13608)
- [Switch to using `gitoxide` by default for listing files.]
  (rust-lang/cargo#13696)

Rustdoc
-----

- [Always display stability version even if it's the same as the
  containing item.]
  (rust-lang/rust#118441)
- [Show a single search result for items with multiple paths.]
  (rust-lang/rust#119912)
- [Support typing `/` in docs to begin a search.]
  (rust-lang/rust#123355)

Misc
----

Compatibility Notes
-------------------

- [Update the minimum external LLVM to 17.]
  (rust-lang/rust#122649)
- [`RustcEncodable` and `RustcDecodable` are soft-destabilized, to
  be removed from the prelude in next edition.]
  (rust-lang/rust#116016)
- [The `wasm_c_abi` future-incompatibility lint will warn about use of the
  non-spec-compliant C ABI.]
  (rust-lang/rust#117918)
  Use `wasm-bindgen v0.2.88` to generate forward-compatible bindings.
- [Check return types of function types for well-formedness]
  (rust-lang/rust#115538)

Version 1.78.0 (2024-05-02)
===========================

Language
--------
- [Stabilize `#[cfg(target_abi = ...)]`]
  (rust-lang/rust#119590)
- [Stabilize the `#[diagnostic]` namespace and
  `#[diagnostic::on_unimplemented]` attribute]
  (rust-lang/rust#119888)
- [Make async-fn-in-trait implementable with concrete signatures]
  (rust-lang/rust#120103)
- [Make matching on NaN a hard error, and remove the rest of
  `illegal_floating_point_literal_pattern`]
  (rust-lang/rust#116284)
- [static mut: allow mutable reference to arbitrary types, not just
  slices and arrays]
  (rust-lang/rust#117614)
- [Extend `invalid_reference_casting` to include references casting
  to bigger memory layout]
  (rust-lang/rust#118983)
- [Add `non_contiguous_range_endpoints` lint for singleton gaps
  after exclusive ranges]
  (rust-lang/rust#118879)
- [Add `wasm_c_abi` lint for use of older wasm-bindgen versions]
  (rust-lang/rust#117918)
  This lint currently only works when using Cargo.
- [Update `indirect_structural_match` and `pointer_structural_match`
  lints to match RFC]
  (rust-lang/rust#120423)
- [Make non-`PartialEq`-typed consts as patterns a hard error]
  (rust-lang/rust#120805)
- [Split `refining_impl_trait` lint into `_reachable`, `_internal` variants]
  (rust-lang/rust#121720)
- [Remove unnecessary type inference when using associated types
  inside of higher ranked `where`-bounds]
  (rust-lang/rust#119849)
- [Weaken eager detection of cyclic types during type inference]
  (rust-lang/rust#119989)
- [`trait Trait: Auto {}`: allow upcasting from `dyn Trait` to `dyn Auto`]
  (rust-lang/rust#119338)

Compiler
--------

- [Made `INVALID_DOC_ATTRIBUTES` lint deny by default]
  (rust-lang/rust#111505)
- [Increase accuracy of redundant `use` checking]
  (rust-lang/rust#117772)
- [Suggest moving definition if non-found macro_rules! is defined later]
  (rust-lang/rust#121130)
- [Lower transmutes from int to pointer type as gep on null]
  (rust-lang/rust#121282)

Target changes:

- [Windows tier 1 targets now require at least Windows 10]
  (rust-lang/rust#115141)
 - [Enable CMPXCHG16B, SSE3, SAHF/LAHF and 128-bit Atomics in tier 1 Windows]
  (rust-lang/rust#120820)
- [Add `wasm32-wasip1` tier 2 (without host tools) target]
  (rust-lang/rust#120468)
- [Add `wasm32-wasip2` tier 3 target]
  (rust-lang/rust#119616)
- [Rename `wasm32-wasi-preview1-threads` to `wasm32-wasip1-threads`]
  (rust-lang/rust#122170)
- [Add `arm64ec-pc-windows-msvc` tier 3 target]
  (rust-lang/rust#119199)
- [Add `armv8r-none-eabihf` tier 3 target for the Cortex-R52]
  (rust-lang/rust#110482)
- [Add `loongarch64-unknown-linux-musl` tier 3 target]
  (rust-lang/rust#121832)

Refer to Rust's [platform support page][platform-support-doc]
for more information on Rust's tiered platform support.

Libraries
---------

- [Bump Unicode to version 15.1.0, regenerate tables]
  (rust-lang/rust#120777)
- [Make align_offset, align_to well-behaved in all cases]
  (rust-lang/rust#121201)
- [PartialEq, PartialOrd: document expectations for transitive chains]
  (rust-lang/rust#115386)
- [Optimize away poison guards when std is built with panic=abort]
  (rust-lang/rust#100603)
- [Replace pthread `RwLock` with custom implementation]
  (rust-lang/rust#110211)
- [Implement unwind safety for Condvar on all platforms]
  (rust-lang/rust#121768)
- [Add ASCII fast-path for `char::is_grapheme_extended`]
  (rust-lang/rust#121138)

Stabilized APIs
---------------

- [`impl Read for &Stdin`]
  (https://doc.rust-lang.org/stable/std/io/struct.Stdin.html#impl-Read-for-%26Stdin)
- [Accept non `'static` lifetimes for several `std::error::Error`
  related implementations] (rust-lang/rust#113833)
- [Make `impl<Fd: AsFd>` impl take `?Sized`]
  (rust-lang/rust#114655)
- [`impl From<TryReserveError> for io::Error`]
  (https://doc.rust-lang.org/stable/std/io/struct.Error.html#impl-From%3CTryReserveError%3E-for-Error)

These APIs are now stable in const contexts:

- [`Barrier::new()`]
  (https://doc.rust-lang.org/stable/std/sync/struct.Barrier.html#method.new)

Cargo
-----

- [Stabilize lockfile v4](rust-lang/cargo#12852)
- [Respect `rust-version` when generating lockfile]
  (rust-lang/cargo#12861)
- [Control `--charset` via auto-detecting config value]
  (rust-lang/cargo#13337)
- [Support `target.<triple>.rustdocflags` officially]
  (rust-lang/cargo#13197)
- [Stabilize global cache data tracking]
  (rust-lang/cargo#13492)

Misc
----

- [rustdoc: add `--test-builder-wrapper` arg to support wrappers
  such as RUSTC_WRAPPER when building doctests]
  (rust-lang/rust#114651)

Compatibility Notes
-------------------

- [Many unsafe precondition checks now run for user code with debug
  assertions enabled] (rust-lang/rust#120594)
  This change helps users catch undefined behavior in their code,
  though the details of how much is checked are generally not
  stable.
- [riscv only supports split_debuginfo=off for now]
  (rust-lang/rust#120518)
- [Consistently check bounds on hidden types of `impl Trait`]
  (rust-lang/rust#121679)
- [Change equality of higher ranked types to not rely on subtyping]
  (rust-lang/rust#118247)
- [When called, additionally check bounds on normalized function return type]
  (rust-lang/rust#118882)
- [Expand coverage for `arithmetic_overflow` lint]
  (rust-lang/rust#119432)

Internal Changes
----------------

These changes do not affect any public interfaces of Rust, but they represent
significant improvements to the performance or internals of rustc and related
tools.

- [Update to LLVM 18](rust-lang/rust#120055)
- [Build `rustc` with 1CGU on `x86_64-pc-windows-msvc`]
  (rust-lang/rust#112267)
- [Build `rustc` with 1CGU on `x86_64-apple-darwin`]
  (rust-lang/rust#112268)
- [Introduce `run-make` V2 infrastructure, a `run_make_support`
  library and port over 2 tests as example]
  (rust-lang/rust#113026)
- [Windows: Implement condvar, mutex and rwlock using futex]
  (rust-lang/rust#121956)


Version 1.77.0 (2024-03-21)
==========================

- [Reveal opaque types within the defining body for exhaustiveness checking.]
  (rust-lang/rust#116821)
- [Stabilize C-string literals.]
  (rust-lang/rust#117472)
- [Stabilize THIR unsafeck.]
  (rust-lang/rust#117673)
- [Add lint `static_mut_refs` to warn on references to mutable statics.]
  (rust-lang/rust#117556)
- [Support async recursive calls (as long as they have indirection).]
  (rust-lang/rust#117703)
- [Undeprecate lint `unstable_features` and make use of it in the compiler.]
  (rust-lang/rust#118639)
- [Make inductive cycles in coherence ambiguous always.]
  (rust-lang/rust#118649)
- [Get rid of type-driven traversal in const-eval interning]
  (rust-lang/rust#119044),
  only as a [future compatiblity lint]
  (rust-lang/rust#122204) for now.
- [Deny braced macro invocations in let-else.]
  (rust-lang/rust#119062)

Compiler
--------

- [Include lint `soft_unstable` in future breakage reports.]
  (rust-lang/rust#116274)
- [Make `i128` and `u128` 16-byte aligned on x86-based targets.]
  (rust-lang/rust#116672)
- [Use `--verbose` in diagnostic output.]
  (rust-lang/rust#119129)
- [Improve spacing between printed tokens.]
  (rust-lang/rust#120227)
- [Merge the `unused_tuple_struct_fields` lint into `dead_code`.]
  (rust-lang/rust#118297)
- [Error on incorrect implied bounds in well-formedness check]
  (rust-lang/rust#118553),
  with a temporary exception for Bevy.
- [Fix coverage instrumentation/reports for non-ASCII source code.]
  (rust-lang/rust#119033)
- [Fix `fn`/`const` items implied bounds and well-formedness check.]
  (rust-lang/rust#120019)
- [Promote `riscv32{im|imafc}-unknown-none-elf` targets to tier 2.]
  (rust-lang/rust#118704)
- Add several new tier 3 targets:
  - [`aarch64-unknown-illumos`]
    (rust-lang/rust#112936)
  - [`hexagon-unknown-none-elf`]
    (rust-lang/rust#117601)
  - [`riscv32imafc-esp-espidf`]
    (rust-lang/rust#119738)
  - [`riscv32im-risc0-zkvm-elf`]
    (rust-lang/rust#117958)

Refer to Rust's [platform support page][platform-support-doc]
for more information on Rust's tiered platform support.

Libraries
---------

- [Implement `From<&[T; N]>` for `Cow<[T]>`.]
  (rust-lang/rust#113489)
- [Remove special-case handling of `vec.split_off
  (0)`.](rust-lang/rust#119917)

Stabilized APIs
---------------

- [`array::each_ref`]
  (https://doc.rust-lang.org/stable/std/primitive.array.html#method.each_ref)
- [`array::each_mut`]
  (https://doc.rust-lang.org/stable/std/primitive.array.html#method.each_mut)
- [`core::net`]
  (https://doc.rust-lang.org/stable/core/net/index.html)
- [`f32::round_ties_even`]
  (https://doc.rust-lang.org/stable/std/primitive.f32.html#method.round_ties_even)
- [`f64::round_ties_even`]
  (https://doc.rust-lang.org/stable/std/primitive.f64.html#method.round_ties_even)
- [`mem::offset_of!`]
  (https://doc.rust-lang.org/stable/std/mem/macro.offset_of.html)
- [`slice::first_chunk`]
  (https://doc.rust-lang.org/stable/std/primitive.slice.html#method.first_chunk)
- [`slice::first_chunk_mut`]
  (https://doc.rust-lang.org/stable/std/primitive.slice.html#method.first_chunk_mut)
- [`slice::split_first_chunk`]
  (https://doc.rust-lang.org/stable/std/primitive.slice.html#method.split_first_chunk)
- [`slice::split_first_chunk_mut`]
  (https://doc.rust-lang.org/stable/std/primitive.slice.html#method.split_first_chunk_mut)
- [`slice::last_chunk`]
  (https://doc.rust-lang.org/stable/std/primitive.slice.html#method.last_chunk)
- [`slice::last_chunk_mut`]
  (https://doc.rust-lang.org/stable/std/primitive.slice.html#method.last_chunk_mut)
- [`slice::split_last_chunk`]
  (https://doc.rust-lang.org/stable/std/primitive.slice.html#method.split_last_chunk)
- [`slice::split_last_chunk_mut`]
  (https://doc.rust-lang.org/stable/std/primitive.slice.html#method.split_last_chunk_mut)
- [`slice::chunk_by`]
  (https://doc.rust-lang.org/stable/std/primitive.slice.html#method.chunk_by)
- [`slice::chunk_by_mut`]
  (https://doc.rust-lang.org/stable/std/primitive.slice.html#method.chunk_by_mut)
- [`Bound::map`]
  (https://doc.rust-lang.org/stable/std/ops/enum.Bound.html#method.map)
- [`File::create_new`]
  (https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.create_new)
- [`Mutex::clear_poison`]
  (https://doc.rust-lang.org/stable/std/sync/struct.Mutex.html#method.clear_poison)
- [`RwLock::clear_poison`]
  (https://doc.rust-lang.org/stable/std/sync/struct.RwLock.html#method.clear_poison)

Cargo
-----

- [Extend the build directive syntax with `cargo::`.]
  (rust-lang/cargo#12201)
- [Stabilize metadata `id` format as `PackageIDSpec`.]
  (rust-lang/cargo#12914)
- [Pull out as `cargo-util-schemas` as a crate.]
  (rust-lang/cargo#13178)
- [Strip all debuginfo when debuginfo is not requested.]
  (rust-lang/cargo#13257)
- [Inherit jobserver from env for all kinds of runners.]
  (rust-lang/cargo#12776)
- [Deprecate rustc plugin support in cargo.]
  (rust-lang/cargo#13248)

Rustdoc
-----

- [Allows links in markdown headings.]
  (rust-lang/rust#117662)
- [Search for tuples and unit by type with `()`.]
  (rust-lang/rust#118194)
- [Clean up the source sidebar's hide button.]
  (rust-lang/rust#119066)
- [Prevent JS injection from `localStorage`.]
  (rust-lang/rust#120250)

Misc
----

- [Recommend version-sorting for all sorting in style guide.]
  (rust-lang/rust#115046)

Internal Changes
----------------

These changes do not affect any public interfaces of Rust, but they represent
significant improvements to the performance or internals of rustc and related
tools.

- [Add more weirdness to `weird-exprs.rs`.]
  (rust-lang/rust#119028)