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rustdoc-search: search types by higher-order functions #119676

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merged 4 commits into from
Mar 14, 2024

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notriddle
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@notriddle notriddle commented Jan 7, 2024

This feature extends rustdoc with syntax and search index information for searching function pointers and closures (Higher-Order Functions, or HOF). Part of #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> Option::filter
option<T>, (T -> bool) -> option<T> Option::filter

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

Motivation

When type-based search was first landed, it was directly described as incomplete.

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.

There's been demand for something "like Hoogle, but for Rust" expressed a few times 1 2 3 4. Some of them just don't realize what functionality already exists (Duration -> u64 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. 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.

Reference-level description (also from the Rustdoc book)

Primitives with Special Syntax

Shorthand Explicit names
Before this PR
[] primitive:slice and/or primitive:array
[T] primitive:slice<T> and/or primitive:array<T>
! primitive:never
() primitive:unit and/or primitive:tuple
(T) T
(T,) primitive:tuple<T>
After this PR
(T, U -> V, W) fn(T, U) -> (V, W), Fn, FnMut, and FnOnce

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

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 #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>. 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>.

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rustbot commented Jan 7, 2024

Some changes occurred in HTML/CSS/JS.

cc @GuillaumeGomez, @jsha

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-rustdoc Relevant to the rustdoc team, which will review and decide on the PR/issue. labels Jan 7, 2024
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The syntax complexity for the search is to be considered here. I'm personally in favour, but I wonder if we should keep pushing more advanced search features or not. I'll add it to the rustdoc team meeting agenda so it can be discussed.

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The syntax complexity for the search is to be considered here. I'm personally in favour, but I wonder if we should keep pushing more advanced search features or not. I'll add it to the rustdoc team meeting agenda so it can be discussed.

That doesn't seem avoidable if I want these two things:

  • Everyone wants the function-signature-search pages to show the signature.
  • I want the visible signature to act as a search tutorial, which means you should be able to copy and paste a type signature from a result and search for it.

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It was discussed in today's rustdoc meeting and approved by the team, so let's move forward with this. Thanks!

@bors r+ rollup

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bors commented Mar 11, 2024

📌 Commit 84d7a2c has been approved by GuillaumeGomez

It is now in the queue for this repository.

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Mar 11, 2024
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Mar 11, 2024
…-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).
workingjubilee added a commit to workingjubilee/rustc that referenced this pull request Mar 11, 2024
…-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).
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Broke in #122350. Please rebase and fix things for tidy's preferences about file length.

@bors r-

@bors bors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Mar 11, 2024
Option::map, for example, looks like this:

    option<t>, (t -> u) -> option<u>

This syntax searches all of the HOFs in Rust: traits Fn, FnOnce,
and FnMut, and bare fn primitives.
It's going to be a no-op on the empty list anyway
(we have plenty of test cases that return nothing)
so why send extra code?
Initialize them before the search index is loaded.
This is implemented, in addition to the ML-style one,
because Rust does it. If we don't, we'll never hear the end of it.

This commit also refactors some duplicate parts of the parser
into a dedicated function.
@notriddle notriddle force-pushed the notriddle/rustdoc-search-hof branch from 84d7a2c to 7b92655 Compare March 12, 2024 05:27
@notriddle notriddle added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Mar 12, 2024
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@bors r=GuillaumeGomez

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bors commented Mar 13, 2024

📌 Commit 7b92655 has been approved by GuillaumeGomez

It is now in the queue for this repository.

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Mar 13, 2024
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Mar 14, 2024
…-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).
bors added a commit to rust-lang-ci/rust that referenced this pull request Mar 14, 2024
…iaskrgr

Rollup of 11 pull requests

Successful merges:

 - rust-lang#104353 (Add CStr::bytes iterator)
 - rust-lang#114038 (unix time module now return result)
 - rust-lang#119676 (rustdoc-search: search types by higher-order functions)
 - rust-lang#120699 (Document `TRACK_DIAGNOSTIC` calls.)
 - rust-lang#121899 (Document how removing a type's field can be bad and what to do instead)
 - rust-lang#121940 (Mention Register Size in `#[warn(asm_sub_register)]`)
 - rust-lang#122397 (Various cleanups around the const eval query providers)
 - rust-lang#122405 (Add methods to create StableMIR constant)
 - rust-lang#122416 (Various style improvements to `rustc_lint::levels`)
 - rust-lang#122440 (const-eval: organize and extend tests for required-consts)
 - rust-lang#122461 (fix unsoundness in Step::forward_unchecked for signed integers)

r? `@ghost`
`@rustbot` modify labels: rollup
jhpratt added a commit to jhpratt/rust that referenced this pull request Mar 14, 2024
…-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).
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Mar 14, 2024
…-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).
bors added a commit to rust-lang-ci/rust that referenced this pull request Mar 14, 2024
…iaskrgr

Rollup of 9 pull requests

Successful merges:

 - rust-lang#104353 (Add CStr::bytes iterator)
 - rust-lang#119676 (rustdoc-search: search types by higher-order functions)
 - rust-lang#120699 (Document `TRACK_DIAGNOSTIC` calls.)
 - rust-lang#121899 (Document how removing a type's field can be bad and what to do instead)
 - rust-lang#122405 (Add methods to create StableMIR constant)
 - rust-lang#122416 (Various style improvements to `rustc_lint::levels`)
 - rust-lang#122421 (Improve `Step` docs)
 - rust-lang#122440 (const-eval: organize and extend tests for required-consts)
 - rust-lang#122461 (fix unsoundness in Step::forward_unchecked for signed integers)

Failed merges:

 - rust-lang#122397 (Various cleanups around the const eval query providers)

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 6694918 into rust-lang:master Mar 14, 2024
11 checks passed
@rustbot rustbot added this to the 1.78.0 milestone Mar 14, 2024
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request Mar 14, 2024
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).
@notriddle notriddle deleted the notriddle/rustdoc-search-hof branch March 14, 2024 14:51
GuillaumeGomez added a commit to GuillaumeGomez/rust that referenced this pull request May 5, 2024
…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
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request May 5, 2024
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
flip1995 pushed a commit to flip1995/rust-clippy that referenced this pull request May 24, 2024
…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
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