Introduce warning topbar menu, allow following crates to see warnings for

static/warnings.js

@@ -0,0 +1,120 @@
+(function() {
+    function load(key, def = null) {
+        const value = window.localStorage.getItem(key)
+        if (value) {
+            try {
+                return JSON.parse(value)
+            } catch (ex) {
+                console.error(`Failed loading ${key} from local storage`, ex)
+                return def
+            }
+        } else {
+            return def
+        }
+    }
+
+    function store(key, value) {
+        window.localStorage.setItem(key, JSON.stringify(value))
+    }
+
+    function create(tagName, attrs = {}, children = [], listeners = {}) {
+        const el = document.createElement(tagName)
+        for (const key of Object.keys(attrs)) {
+            if (typeof attrs[key] === 'object') {
+                for (const subkey of Object.keys(attrs[key])) {
+                    el[key].setProperty(subkey, attrs[key][subkey])
+                }
+            } else {
+                el.setAttribute(key, attrs[key])
+            }
+        }
+        el.append(...children)
+        for (const key of Object.keys(listeners)) {
+            el.addEventListener(key, listeners[key])
+        }
+        return el
+    }
+
+
+    if (!load('docs-rs-warnings-enabled', false)) {
+        return
+    }
+
+    const parentEl = document.getElementById('warnings-menu-parent')
+    parentEl.removeAttribute('hidden')
+
+    const current = JSON.parse(document.getElementById("crate-metadata")?.innerText || null)
+
+    const menuEl = document.getElementById('warnings-menu')
+
+    const followed = load('docs-rs-warnings-followed', [])
+
+    function update() {
+        const children = []
+
+        if (followed.length > 0) {
+            children.push(
+                create('div', { class: 'pure-g' }, [
+                    create('div', { class: 'pure-u-1' }, [
+                        create('ul', { class: 'pure-menu-list', style:  { width: '100%' } }, [
+                            create('li', { class: 'pure-menu-heading' }, [
+                                create('b', {}, ['Followed crates']),
+                            ]),
+                            ...followed.map(name => (
+                                create('li', { class: 'pure-menu-item followed' }, [
+                                    create('a', { class: 'pure-menu-link', href: `/${name}` }, [
+                                        name,
+                                    ]),
+                                    create('a', { class: 'pure-menu-link remove', href: '#' }, ['🗙'], {
+                                        click: (ev) => {
+                                            const index = followed.indexOf(name)
+                                            followed.splice(index, 1)
+                                            store('docs-rs-warnings-followed', followed)
+                                            update()
+                                        },
+                                    }),
+                                ])
+                            )),
+                        ]),
+                    ]),
+                ]),
+            )
+        }
+
+        if (current && !followed.includes(current.name)) {
+            children.push(
+                create('div', { class: 'pure-g' }, [
+                    create('div', { class: 'pure-u-1' }, [
+                        create('ul', { class: 'pure-menu-list', style:  { width: '100%' } }, [
+                            create('li', { class: 'pure-menu-item' }, [
+                                create('a', { class: 'pure-menu-link', href: '#' }, [
+                                    "Follow ",
+                                    create('b', {}, [current.name]),
+                                ], {
+                                    click: () => {
+                                        const index = followed.findIndex((name) => name > current.name)
+                                        if (index >= 0) {
+                                            followed.splice(index, 0, current.name)
+                                        } else {
+                                            followed.push(current.name)
+                                        }
+                                        store('docs-rs-warnings-followed', followed)
+                                        update()
+                                    }
+                                }),
+                            ]),
+                        ]),
+                    ]),
+                ]),
+            )
+        }
+
+        for (const child of children.slice(0, -1)) {
+            child.classList.add('menu-item-divided')
+        }
+
+        menuEl.replaceChildren(...children)
+    }
+
+    update()
+})()

templates/base.html

@@ -22,6 +22,7 @@
 
         <script defer type="text/javascript" nonce="{{ csp_nonce }}" src="/-/static/menu.js?{{ docsrs_version() | slugify }}"></script>
         <script defer type="text/javascript" nonce="{{ csp_nonce }}" src="/-/static/index.js?{{ docsrs_version() | slugify }}"></script>
+        <script defer type="text/javascript" nonce="{{ csp_nonce }}" src="/-/static/warnings.js?{{ docsrs_version() | slugify }}"></script>
     </head>
 
     <body class="{% block body_classes %}{% endblock body_classes %}">

templates/header/topbar_end.html

@@ -4,6 +4,8 @@
                 {# The global alert, if there is one #}
                 {% include "header/global_alert.html" -%}
 
+                {% include "header/warnings.html" -%}
+
                 <ul class="pure-menu-list">
                     {#
                     The Rust dropdown menu

templates/header/warnings.html

@@ -0,0 +1,7 @@
+<ul id="warnings-menu-parent" class="pure-menu-list" hidden>
+    <li class="pure-menu-item pure-menu-has-children">
+        <a href="#" class="pure-menu-link" aria-label="Warnings">Warnings <span id="warnings-count"></span></a>
+        <div id="warnings-menu" class="pure-menu-children">
+        </div>
+    </li>
+</ul>

templates/rustdoc/body.html

@@ -1,4 +1,5 @@
 <script async src="/-/static/menu.js?{{ docsrs_version() | slugify }}"></script>
 <script async src="/-/static/index.js?{{ docsrs_version() | slugify }}"></script>
+<script async src="/-/static/warnings.js?{{ docsrs_version() | slugify }}"></script>
 {# see comment in ../storage-change-detection.html for details #}
 <iframe src="/-/storage-change-detection.html" width="0" height="0" style="display: none"></iframe>

templates/style/_navbar.scss

@@ -362,6 +362,22 @@ div.nav-container {
             }
         }
     }
+
+    #warnings-menu {
+        .followed {
+            display: flex;
+            align-items: center;
+            :first-child {
+                flex: auto;
+            }
+        }
+        .remove {
+            padding: 0 .5em;
+            &:hover {
+                color: var(--color-error);
+            }
+        }
+    }
 }
 
 #nav-search, #nav-sort {