rustdoc: improve the summary icon

[liigo]

I changed the summary icon, from double-down-arrows to double-up-arrows, and the new icon also has a grey part that can be used to hint users 'part of docs will be hidden', or 'less docs will be shown', when clicked two arrows pointing at each other. The old icon with double-down-arrow maybe has the meaning 'show more docs' which always confused me.

old:

new:

new new:

[rustbot]

r? @GuillaumeGomez

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[rustbot]

Some changes occurred in HTML/CSS/JS.

cc @GuillaumeGomez, @jsha

[GuillaumeGomez]

cc @notriddle

[notriddle]

I guess this icon should be changed to have two arrows pointing at each other?

If I try to take a survey of similar applications, there's not a very strong consensus here:

• IntelliJ and Notepad++ have expand/collapse all buttons in their directory sidebars that look like this:

  

  This is the only icon design I found that's used by more than one app.

• VSCode has a collapse button in its sidebar that looks like this:

  

• The sidebars in Sublime Text, GitHub's file viewer, ExDoc, MDN, MSDN, and Windows Explorer don't seem to have an options to collapse everything at once at all.

• The "List" view in macOS Finder, the tree comments on Reddit, HN, and Lobsters, and the GitHub Actions log viewer don't have any ways to collapse/expand everything at once, either.

• As for code folding, none of them have a toolbar button. This is the one that truly surprises me, because the option to collapse everything seems most useful if everything is expanded by default (which code viewers do).

  When I customize the toolbar in intellij to add folding buttons to it, they're meaningless placeholders (which still provides no hint for an icon that users might already be familiar with).

  

  Most of them have an option to fold/unfold everything in the command pallet or the menu bar. But Rustdoc doesn't have or want one of those.

---

Also, a tidy nit

This definitely needs fixed

tidy error: /checkout/src/librustdoc/html/static/css/rustdoc.css:2069: line longer than 100 chars

[liigo]

r? @notriddle

the new summary icon:

[notriddle]

@rfcbot poll change the summary icon to two arrows pointing at each other

[rfcbot]

Team member @notriddle has asked teams: T-rustdoc-frontend, for consensus on:

change the summary icon to two arrows pointing at each other

[notriddle]

sorry about messing up the rfcbot

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

[camelid]

I feel like this new icon isn't really any clearer. Granted, the old one isn't so obvious either. But I'd rather not change the UI unless the new one is markedly better, since then it feels like churn.

[GuillaumeGomez]

I agree with @camelid, I don't see any benefit with the new icon.

[notriddle]

Do you think either new, proposed icon is better?

[GuillaumeGomez]

For some reason I completely skipped that it was using:

This one I think is an improvement. Sorry about that, checking my box.