|
rustdoc: add header map to the table of contents
## Summary
Add header sections to the sidebar TOC.
### Preview
* http://notriddle.com/rustdoc-html-demo-9/toc/rust/std/index.html
* http://notriddle.com/rustdoc-html-demo-9/toc/rust-derive-builder/derive_builder/index.html
## Motivation
Some pages are very wordy, like these.
| crate | word count |
|--|--|
| [std::option](https://doc.rust-lang.org/stable/std/option/index.html) | 2,138
| [derive_builder](https://docs.rs/derive_builder/0.13.0/derive_builder/index.html) | 2,403
| [tracing](https://docs.rs/tracing/0.1.40/tracing/index.html) | 3,912
| [regex](https://docs.rs/regex/1.10.3/regex/index.html) | 8,412
This kind of very long document is more navigable with a table of contents, like Wikipedia's or the one [GitHub recently added](https://github.blog/changelog/2021-04-13-table-of-contents-support-in-markdown-files/) for READMEs.
In fact, the use case is so compelling, that it's been requested multiple times and implemented in an extension:
* https://github.com/rust-lang/rust/issues/80858
* https://github.com/rust-lang/rust/issues/28056
* https://github.com/rust-lang/rust/issues/14475
* https://rust.extension.sh/#show-table-of-content
(Some of these issues ask for more than this, so don’t close them.)
It's also been implemented by hand in some crates, because the author really thought it was needed. Protip: for a more exhaustive list, run [`site:docs.rs table of contents`](https://duckduckgo.com/?t=ffab&q=site%3Adocs.rs+table+of+contents&ia=web), though some of them are false positives.
* https://docs.rs/figment/0.10.14/figment/index.html#table-of-contents
* https://docs.rs/csv/1.3.0/csv/tutorial/index.html#table-of-contents
* https://docs.rs/axum/0.7.4/axum/response/index.html#table-of-contents
* https://docs.rs/regex-automata/0.4.5/regex_automata/index.html#table-of-contents
Unfortunately for these hand-built ToCs, because they're just part of the docs, there's no consistent way to turn them off if the reader doesn't want them. It's also more complicated to ensure they stay in sync with the docs they're supposed to describe, and they don't stay with you when you scroll like Wikipedia's [does now](https://uxdesign.cc/design-notes-on-the-2023-wikipedia-redesign-d6573b9af28d).
## Guide-level explanation
When writing docs for a top-level item, the first and second level of headers will be shown in an outline in the sidebar. In this context, "top level" means "not associated".
This means, if you're writing very long guides or explanations, and you want it to have a table of contents in the sidebar for its headings, the ideal place to attach it is usually the *module* or *crate*, because this page has fewer other things on it (and is the ideal place to describe "cross-cutting concerns" for its child items).
If you're reading documentation, and want to get rid of the table of contents, open the  Settings panel and checkmark "Hide table of contents."
## Reference-level explanation
Top-level items have an outline generated. This works for potentially-malformed header trees by pairing a header with the nearest header with a higher level. For example:
```markdown
## A
# B
# C
## D
## E
```
A, B, and C are all siblings, and D and E are children of C.
Rustdoc only presents two layers of tree, but it tracks up to the full depth of 6 while preparing it.
That means that these two doc comment both generate the same outline:
```rust
/// # First
/// ## Second
struct One;
/// ## First
/// ### Second
struct Two;
```
## Drawbacks
The biggest drawback is adding more stuff to the sidebar.
My crawl through docs.rs shows this to, surprisingly, be less of a problem than I thought. The manually-built tables of contents, and the pages with dozens of headers, usually seem to be modules or crates, not types (where extreme scrolling would become a problem, since they already have methods to deal with).
The best example of a type with many headers is [vec::Vec](https://doc.rust-lang.org/1.75.0/std/vec/struct.Vec.html), which still only has five headers, not dozens like [axum::extract](https://docs.rs/axum/0.7.4/axum/extract/index.html).
## Rationale and alternatives
### Why in the existing sidebar?
The method links and the top-doc header links have more in common with each other than either of them do with the "In [parent module]" links, and should go together.
### Why limited to two levels?
The sidebar is pretty narrow, and I don't want too much space used by indentation. Making the sidebar wider, while it has some upsides, also takes up more space on middling-sized screens or tiled WMs.
### Why not line wrap?
That behaves strangely when resizing.
## Prior art
### Doc generators that have TOC for headers
https://hexdocs.pm/phoenix/Phoenix.Controller.html is very close, in the sense that it also has header sections directly alongside functions and types.
Another example, referenced as part of the [early sidebar discussion](https://github.com/rust-lang/rust/issues/37856) that added methods, Ruby will show a table of contents in the sidebar (for example, on the [ARGF](https://docs.ruby-lang.org/en/master/ARGF.html) class). According to their changelog, [they added it in 2013](https://github.com/ruby/rdoc/blob/06137bde8ccc48cd502bc28178bcd8f2dfe37624/History.rdoc#400--2013-02-24-).
Haskell seems to mix text and functions even more freely than Elixir. For example, this [Naming conventions](https://hackage.haskell.org/package/base-4.19.0.0/docs/Control-Monad.html#g:3) is plain text, and is immediately followed by functions. And the [Pandoc top level](https://hackage.haskell.org/package/pandoc-3.1.11.1/docs/Text-Pandoc.html) has items split up by function, rather than by kind. Their TOC matches exactly with the contents of the page.
### Doc generators that don't have header TOC, but still have headers
Elm, interestingly enough, seems to have the same setup that Rust used to have: sibling navigation between modules, and no index within a single page. [They keep Haskell's habit of named sections with machine-generated type signatures](https://package.elm-lang.org/packages/elm/browser/latest/Browser-Dom), though.
[PHP](https://www.php.net/manual/en/book.datetime.php), like elm, also has a right-hand sidebar with sibling navigation. However, PHP has a single page for a single method, unlike Rust's page for an entire "class." So even though these pages have headers, it's never more than ten at most. And when they have guides, those guides are also multi-page.
## Unresolved questions
* Writing recommendations for anyone who wants to take advantage of this.
* Right now, it does not line wrap. That might be a bad idea: a lot of these are getting truncated.
* Split sidebars, which I [tried implementing](https://rust-lang.zulipchat.com/#narrow/stream/266220-t-rustdoc/topic/Table.20of.20contents), are not required. The TOC can be turned off, if it's really a problem. Implemented in https://github.com/rust-lang/rust/pull/120818, but needs more, separate, discussion.
## Future possibilities
I would like to do a better job of distinguishing global navigation from local navigation. Rustdoc has a pretty reasonable information architecture, if only we did a better job of communicating it.
This PR aims, mostly, to help doc authors help their users by writing docs that can be more effectively skimmed. But it doesn't do anything to make it easier to tell the TOC and the Module Nav apart.
|
|
GuillaumeGomez:stabilize-custom_code_classes_in_docs, r=rustdoc
Stabilize `custom_code_classes_in_docs` feature
Fixes #79483.
This feature has been around for quite some time now, I think it's fine to stabilize it now.
## Summary
## What is the feature about?
In short, this PR changes two things, both related to codeblocks in doc comments in Rust documentation:
* Allow to disable generation of `language-*` CSS classes with the `custom` attribute.
* Add your own CSS classes to a code block so that you can use other tools to highlight them.
#### The `custom` attribute
Let's start with the new `custom` attribute: it will disable the generation of the `language-*` CSS class on the generated HTML code block. For example:
```rust
/// ```custom,c
/// int main(void) {
/// return 0;
/// }
/// ```
```
The generated HTML code block will not have `class="language-c"` because the `custom` attribute has been set. The `custom` attribute becomes especially useful with the other thing added by this feature: adding your own CSS classes.
#### Adding your own CSS classes
The second part of this feature is to allow users to add CSS classes themselves so that they can then add a JS library which will do it (like `highlight.js` or `prism.js`), allowing to support highlighting for other languages than Rust without increasing burden on rustdoc. To disable the automatic `language-*` CSS class generation, you need to use the `custom` attribute as well.
This allow users to write the following:
```rust
/// Some code block with `{class=language-c}` as the language string.
///
/// ```custom,{class=language-c}
/// int main(void) {
/// return 0;
/// }
/// ```
fn main() {}
```
This will notably produce the following HTML:
```html
<pre class="language-c">
int main(void) {
return 0;
}</pre>
```
Instead of:
```html
<pre class="rust rust-example-rendered">
<span class="ident">int</span> <span class="ident">main</span>(<span class="ident">void</span>) {
<span class="kw">return</span> <span class="number">0</span>;
}
</pre>
```
To be noted, we could have written `{.language-c}` to achieve the same result. `.` and `class=` have the same effect.
One last syntax point: content between parens (`(like this)`) is now considered as comment and is not taken into account at all.
In addition to this, I added an `unknown` field into `LangString` (the parsed code block "attribute") because of cases like this:
```rust
/// ```custom,class:language-c
/// main;
/// ```
pub fn foo() {}
```
Without this `unknown` field, it would generate in the DOM: `<pre class="language-class:language-c language-c">`, which is quite bad. So instead, it now stores all unknown tags into the `unknown` field and use the first one as "language". So in this case, since there is no unknown tag, it'll simply generate `<pre class="language-c">`. I added tests to cover this.
EDIT(camelid): This description is out-of-date. Using `custom,class:language-c` will generate the output `<pre class="language-class:language-c">` as would be expected; it treats `class:language-c` as just the name of a language (similar to the langstring `c` or `js` or what have you) since it does not use the designed class syntax.
Finally, I added a parser for the codeblock attributes to make it much easier to maintain. It'll be pretty easy to extend.
As to why this syntax for adding attributes was picked: it's [Pandoc's syntax](https://pandoc.org/MANUAL.html#extension-fenced_code_attributes). Even if it seems clunkier in some cases, it's extensible, and most third-party Markdown renderers are smart enough to ignore Pandoc's brace-delimited attributes (from [this comment](https://github.com/rust-lang/rust/pull/110800#issuecomment-1522044456)).
r? `@notriddle`
|
