Linkify sidebar headings for sibling items

Also adjust CSS so this doesn't produce excess padding/margin.

src/librustdoc/html/static/css/rustdoc.css

@@ -472,6 +472,7 @@ nav.sub {
 }
 .block ul, .block li {
 	padding: 0;
+	margin: 0;
 	list-style: none;
 }
 
@@ -502,8 +503,6 @@ nav.sub {
 	font-weight: 500;
 	padding: 0;
 	margin: 0;
-	margin-top: 0.5rem;
-	margin-bottom: 0.25rem;
 }
 
 .sidebar-links,

src/librustdoc/html/static/js/main.js

@@ -559,7 +559,15 @@ function hideThemeButtonState() {
             others.appendChild(div);
         }
 
-        function block(shortty, longty) {
+        /**
+         * Append to the sidebar a "block" of links - a heading along with a list (`<ul>`) of items.
+         *
+         * @param {string} shortty - A short type name, like "primitive", "mod", or "macro"
+         * @param {string} id - The HTML id of the corresponding section on the module page.
+         * @param {string} longty - A long, capitalized, plural name, like "Primitive Types",
+         *                          "Modules", or "Macros".
+         */
+        function block(shortty, id, longty) {
             var filtered = items[shortty];
             if (!filtered) {
                 return;
@@ -568,7 +576,7 @@ function hideThemeButtonState() {
             var div = document.createElement("div");
             div.className = "block " + shortty;
             var h3 = document.createElement("h3");
-            h3.textContent = longty;
+            h3.innerHTML = `<a href="index.html#${id}">${longty}</a>`;
             div.appendChild(h3);
             var ul = document.createElement("ul");
 
@@ -607,20 +615,20 @@ function hideThemeButtonState() {
 
             var isModule = hasClass(document.body, "mod");
             if (!isModule) {
-                block("primitive", "Primitive Types");
-                block("mod", "Modules");
-                block("macro", "Macros");
-                block("struct", "Structs");
-                block("enum", "Enums");
-                block("union", "Unions");
-                block("constant", "Constants");
-                block("static", "Statics");
-                block("trait", "Traits");
-                block("fn", "Functions");
-                block("type", "Type Definitions");
-                block("foreigntype", "Foreign Types");
-                block("keyword", "Keywords");
-                block("traitalias", "Trait Aliases");
+                block("primitive", "primitives", "Primitive Types");
+                block("mod", "modules", "Modules");
+                block("macro", "macros", "Macros");
+                block("struct", "structs", "Structs");
+                block("enum", "enums", "Enums");
+                block("union", "unions", "Unions");
+                block("constant", "constants", "Constants");
+                block("static", "static", "Statics");
+                block("trait", "traits", "Traits");
+                block("fn", "functions", "Functions");
+                block("type", "types", "Type Definitions");
+                block("foreigntype", "foreign-types", "Foreign Types");
+                block("keyword", "keywords", "Keywords");
+                block("traitalias", "trait-aliases", "Trait Aliases");
             }
 
             // `crates{version}.js` should always be loaded before this script, so we can use

src/test/rustdoc-gui/sidebar-mobile.goml

@@ -39,4 +39,4 @@ assert-position: ("#method\.must_use", {"y": 45})
 // Check that the bottom-most item on the sidebar menu can be scrolled fully into view.
 click: ".sidebar-menu-toggle"
 scroll-to: ".block.keyword li:nth-child(1)"
-assert-position: (".block.keyword li:nth-child(1)", {"y": 542.96875})
+assert-position: (".block.keyword li:nth-child(1)", {"y": 542.234375})

src/test/rustdoc-gui/sidebar.goml

@@ -78,3 +78,10 @@ assert-text: ("#functions + .item-table .item-left > a", "foo")
 // Links to trait implementations in the sidebar should not wrap even if they are long.
 goto: file://|DOC_PATH|/lib2/struct.HasALongTraitWithParams.html
 assert-property: (".sidebar-links a", {"offsetHeight": 29})
+
+// Test that clicking on of the "In <module>" headings in the sidebar links to the
+// appropriate anchor in index.html.
+goto: file://|DOC_PATH|/test_docs/struct.Foo.html
+click: ".block.mod h3 a"
+// PAGE: index.html
+assert-css: ("#modules", {"background-color": "rgb(253, 255, 211)"})