Rollup merge of #111892 - notriddle:notriddle/timeout-tooltip, r=me,GuillaumeGomez,Manishearth

rustdoc: add interaction delays for tooltip popovers

Preview:

* [notable traits](http://notriddle.com/rustdoc-demo-html-3/delay-tooltip/testing/struct.Vec.html#method.iter)
* [panicking code block](http://notriddle.com/rustdoc-demo-html-3/delay-tooltip/testing/struct.Vec.html#indexing)

Designing a good hover microinteraction is a matter of guessing user intent from what are, literally, vague gestures. In this case, guessing if hovering in our out of the tooltip base is intentional or not.

To figure this out, a few different techniques are used:

* When the mouse pointer enters a tooltip anchor point, its hitbox is grown on the bottom, where the popover is/will appear. This was already there before this commit: search "hover tunnel" in rustdoc.css for the implementation.

* This commit adds a delay when the mouse pointer enters the base anchor, in case the mouse pointer was just passing through and the user didn't want to open it.

* This commit also adds a delay when the mouse pointer exits the tooltip's base anchor or its popover, before hiding it.

* A fade-out animation is layered onto the pointer exit delay to immediately inform the user that they successfully dismissed the popover, while still providing a way for them to cancel it if it was a mistake and they still wanted to interact with it.

* No animation is used for revealing it, because we don't want people to try to interact with an element while it's in the middle of fading in: either they're allowed to interact with it while it's fading in, meaning it can't serve as mistake- proofing for opening the popover, or they can't, but they might try and be frustrated.

See also:

* https://www.nngroup.com/articles/timing-exposing-content/
* https://www.nngroup.com/articles/tooltip-guidelines/
* https://bjk5.com/post/44698559168/breaking-down-amazons-mega-dropdown

1 files changed, 12 insertions, 0 deletions

diff --git a/src/librustdoc/html/static/css/rustdoc.css b/src/librustdoc/html/static/css/rustdoc.css
index a7d5f497756..054cfe7597e 100644
--- a/src/librustdoc/html/static/css/rustdoc.css
+++ b/src/librustdoc/html/static/css/rustdoc.css
@@ -1179,6 +1179,10 @@ a.test-arrow:hover {
 	position: relative;
 }
 
+.code-header a.tooltip:hover {
+	color: var(--link-color);
+}
+
 /* placeholder thunk so that the mouse can easily travel from "(i)" to popover
 	the resulting "hover tunnel" is a stepped triangle, approximating
 	https://bjk5.com/post/44698559168/breaking-down-amazons-mega-dropdown */
@@ -1191,6 +1195,14 @@ a.tooltip:hover::after {
 	content: "\00a0";
 }
 
+/* This animation is layered onto the mistake-proofing delay for dismissing
+	a hovered tooltip, to ensure it feels responsive even with the delay.
+	*/
+.fade-out {
+	opacity: 0;
+	transition: opacity 0.45s cubic-bezier(0, 0, 0.1, 1.0);
+}
+
 .popover.tooltip .content {
 	margin: 0.25em 0.5em;
 }