Rollup merge of #74370 - Manishearth:re-spotlight, r=GuillaumeGomez

Reintroduce spotlight / "important traits" feature

(Reopened version of https://github.com/rust-lang/rust/pull/74111 because Github is broken, see discussion there)

Fixes https://github.com/rust-lang/rust/issues/73785

This PR reintroduces the "spotlight" ("important traits") feature.

A couple changes have been made:

As there were concerns about its visibility, it has been moved to be next to the return type, as opposed to being on the side.

It also no longer produces a modal, it shows the traits on hover, and it can be clicked on to pin the hover bubble.

![image](https://user-images.githubusercontent.com/1617736/86674555-a82d2600-bfad-11ea-9a4a-a1a9ffd66ae5.png)

![image](https://user-images.githubusercontent.com/1617736/86674533-a1061800-bfad-11ea-9e8a-c62ad86ed0d7.png)

It also works fine on mobile:

![image](https://user-images.githubusercontent.com/1617736/86674638-bda25000-bfad-11ea-8d8d-1798b608923e.png)

5 files changed, 87 insertions, 9 deletions

diff --git a/src/librustdoc/html/static/main.js b/src/librustdoc/html/static/main.js
index 336c691ac1c..082f9cca064 100644
--- a/src/librustdoc/html/static/main.js
+++ b/src/librustdoc/html/static/main.js
@@ -2636,6 +2636,13 @@ function defocusSearchBar() {
         });
     }());
 
+    onEachLazy(document.getElementsByClassName("important-traits"), function(e) {
+        e.onclick = function() {
+            this.getElementsByClassName('important-traits-tooltiptext')[0]
+                .classList.toggle("force-tooltip");
+        };
+    });
+
     // In the search display, allows to switch between tabs.
     function printTab(nb) {
         if (nb === 0 || nb === 1 || nb === 2) {
diff --git a/src/librustdoc/html/static/rustdoc.css b/src/librustdoc/html/static/rustdoc.css
index 15a0c76ceea..f5551446bf2 100644
--- a/src/librustdoc/html/static/rustdoc.css
+++ b/src/librustdoc/html/static/rustdoc.css
@@ -146,9 +146,12 @@ code, pre, a.test-arrow {
 	border-radius: 3px;
 	padding: 0 0.1em;
 }
-.docblock pre code, .docblock-short pre code {
+.docblock pre code, .docblock-short pre code, .docblock code.spotlight {
 	padding: 0;
 }
+.docblock code.spotlight :last-child {
+	padding-bottom: 0.6em;
+}
 pre {
 	padding: 14px;
 }
@@ -523,7 +526,7 @@ h4 > code, h3 > code, .invisible > code {
 	font-size: 0.8em;
 }
 
-.content .methods > div {
+.content .methods > div:not(.important-traits) {
 	margin-left: 40px;
 	margin-bottom: 15px;
 }
@@ -1079,10 +1082,6 @@ h3 > .collapse-toggle, h4 > .collapse-toggle {
 	font-size: 16px;
 }
 
-.tooltip:hover .tooltiptext {
-	display: inline;
-}
-
 .tooltip .tooltiptext::after {
 	content: " ";
 	position: absolute;
@@ -1098,13 +1097,52 @@ h3 > .collapse-toggle, h4 > .collapse-toggle {
 	font-size: 20px;
 }
 
-.tooltip .tooltiptext {
+.important-traits-tooltip {
+	display: inline-block;
+	cursor: pointer;
+}
+
+.important-traits:hover .important-traits-tooltiptext,
+.important-traits .important-traits-tooltiptext.force-tooltip {
+	display: inline-block;
+}
+
+.important-traits .important-traits-tooltiptext {
+	display: none;
+	padding: 5px 3px 3px 3px;
+	border-radius: 6px;
+	margin-left: 5px;
+	z-index: 10;
+	font-size: 16px;
+	cursor: default;
+	position: absolute;
 	border: 1px solid;
-	font-weight: normal;
 }
 
-pre.rust {
+.important-traits-tooltip::after {
+	/* The margin on the tooltip does not capture hover events,
+	   this extends the area of hover enough so that mouse hover is not
+	   lost when moving the mouse to the tooltip */
+    content: "\00a0\00a0\00a0";
+}
+
+.important-traits .important, .important-traits .docblock {
+	margin: 0;
+}
+
+.important-traits .docblock code.content{
+    margin: 0;
+    padding: 0;
+    font-size: 20px;
+}
+
+/* Example code has the "Run" button that
+   needs to be positioned relative to the pre */
+pre.rust.rust-example-rendered {
 	position: relative;
+}
+
+pre.rust {
 	tab-size: 4;
 	-moz-tab-size: 4;
 }
@@ -1144,6 +1182,18 @@ pre.rust {
 	font-size: 16px;
 }
 
+.important-traits {
+	cursor: pointer;
+	z-index: 2;
+	margin-left: 5px;
+}
+
+h4 > .important-traits {
+	position: absolute;
+	left: -44px;
+	top: 2px;
+}
+
 #all-types {
 	text-align: center;
 	border: 1px solid;
@@ -1370,6 +1420,12 @@ pre.rust {
 		z-index: 1;
 	}
 
+	h4 > .important-traits {
+		position: absolute;
+		left: -22px;
+		top: 24px;
+	}
+
 	#titles > div > div.count {
 		float: left;
 		width: 100%;
diff --git a/src/librustdoc/html/static/themes/ayu.css b/src/librustdoc/html/static/themes/ayu.css
index bc21c28750f..b436997da58 100644
--- a/src/librustdoc/html/static/themes/ayu.css
+++ b/src/librustdoc/html/static/themes/ayu.css
@@ -394,6 +394,11 @@ pre.ignore:hover, .information:hover + pre.ignore {
 	border-color: transparent #314559 transparent transparent;
 }
 
+.important-traits-tooltiptext {
+    background-color: #314559;
+    border-color: #5c6773;
+}
+
 #titles > div.selected {
     background-color: #141920 !important;
 	border-bottom: 1px solid #ffb44c !important;
diff --git a/src/librustdoc/html/static/themes/dark.css b/src/librustdoc/html/static/themes/dark.css
index 41dcb5c2450..f4ca67f8540 100644
--- a/src/librustdoc/html/static/themes/dark.css
+++ b/src/librustdoc/html/static/themes/dark.css
@@ -337,6 +337,11 @@ pre.ignore:hover, .information:hover + pre.ignore {
 	border-color: transparent black transparent transparent;
 }
 
+.important-traits-tooltiptext {
+	background-color: #111;
+	border-color: #777;
+}
+
 #titles > div:not(.selected) {
 	background-color: #252525;
 	border-top-color: #252525;
diff --git a/src/librustdoc/html/static/themes/light.css b/src/librustdoc/html/static/themes/light.css
index 386fe2398e6..b5a0ba4775c 100644
--- a/src/librustdoc/html/static/themes/light.css
+++ b/src/librustdoc/html/static/themes/light.css
@@ -331,6 +331,11 @@ pre.ignore:hover, .information:hover + pre.ignore {
 	border-color: transparent black transparent transparent;
 }
 
+.important-traits-tooltiptext {
+	background-color: #eee;
+	border-color: #999;
+}
+
 #titles > div:not(.selected) {
 	background-color: #e6e6e6;
 	border-top-color: #e6e6e6;