rustdoc: add ways of collapsing all impl blocks

[lolbinarycat]

either shift+click the Summary button,
or use the _ key.

this collapses everything,
including (inherent) impl blocks.

no need for a special "expand all impl blocks"
method, as impl blocks are expanded during regular "expand all".
doing "expand all" -> "collapse all" will always
result in only impl blocks being expaned.

not sure the best way to add a GUI test.

fixes #134429

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[rustbot]

Some changes occurred in HTML/CSS/JS.

cc @GuillaumeGomez, @jsha, @lolbinarycat

[GuillaumeGomez]

I'm neutral about this. I don't see the need but I suppose if someone opened the issue, there is one...

cc @rust-lang/rustdoc-frontend

[lolbinarycat]

It's a small improvement, but I think it is helpful, especially for internal docs. For example, if I had this, I might not have made the mistake of initially adding BufReader::peek to the wrong impl block. The feature also seems very trivial to implement and maintain.

[notriddle]

It wouldn't be hard to test the _ keyboard shortcut using the GUI test runner (it's the same way the - keyboard shortcut is tested).

Anyway, 👍 this feature.

[GuillaumeGomez]

I don't think adding a new key to handle it is a good idea. What you suggested with shift+minus sounds like a better approach.

[lolbinarycat]

doesn't shift + minus send _ on a standard US keyboard? or is there something I don't know about JS events?

[notriddle]

It does, yes. getVirtualKey uses event.key, which sends the printable representation of the text.

[GuillaumeGomez]

I don't have opinion on the feature, however I think we should definitely talk about the new key binding (_).

[lolbinarycat]

I think it's also worth asking if we should make a way of doing this on mobile, but i don't see an easy way, it seems like we would have to manually implement a double tap delay or something similar.

[GuillaumeGomez]

@rfcbot merge

[rfcbot]

Team member @GuillaumeGomez has proposed to merge this. The next step is review by the rest of the tagged team members:

• @GuillaumeGomez
• @camelid
• @jsha
• @notriddle

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