[3.12] Doc: Render version/language selector on Read the Docs (GH-116966) (#118038)

Co-authored-by: Manuel Kaufmann <humitos@gmail.com>

Doc/tools/templates/layout.html

@@ -41,4 +41,90 @@
       {{ "}" }}
     </style>
 {{ super() }}
+
+<meta name="readthedocs-addons-api-version" content="1">
+<script type="text/javascript">
+ function onSwitch(event) {
+     const option = event.target.selectedIndex;
+     const item = event.target.options[option];
+     window.location.href = item.dataset.url;
+ }
+
+ document.addEventListener("readthedocs-addons-data-ready", function(event) {
+   const config = event.detail.data()
+
+   // Add some mocked hardcoded versions pointing to the official
+   // documentation while migrating to Read the Docs.
+   // These are only for testing purposes.
+   // TODO: remove them when managing all the versions on Read the Docs,
+   // since all the "active, built and not hidden" versions will be shown automatically.
+   let versions = config.versions.active.concat([
+       {
+           slug: "dev (3.13)",
+           urls: {
+               documentation: "https://docs.python.org/3.13/",
+           }
+       },
+       {
+           slug: "3.12",
+           urls: {
+               documentation: "https://docs.python.org/3.12/",
+           }
+       },
+       {
+           slug: "3.11",
+           urls: {
+               documentation: "https://docs.python.org/3.11/",
+           }
+       },
+   ]);
+
+   const versionSelect = `
+   <select id="version_select">
+   ${ versions.map(
+       (version) => `
+       <option
+           value="${ version.slug }"
+           ${ config.versions.current.slug === version.slug ? 'selected="selected"' : '' }
+           data-url="${ version.urls.documentation }">
+           ${ version.slug }
+       </option>`
+   ).join("\n") }
+   </select>
+   `;
+
+   // Prepend the current language to the options on the selector
+   let languages = config.projects.translations.concat(config.projects.current);
+   languages = languages.sort((a, b) => a.language.name.localeCompare(b.language.name));
+
+   const languageSelect = `
+   <select id="language_select">
+   ${ languages.map(
+       (translation) => `
+       <option
+           value="${ translation.slug }"
+           ${ config.projects.current.slug === translation.slug ? 'selected="selected"' : '' }
+           data-url="${ translation.urls.documentation }">
+           ${ translation.language.name }
+       </option>`
+   ).join("\n") }
+   </select>
+   `;
+
+   // Query all the placeholders because there are different ones for Desktop/Mobile
+   const versionPlaceholders = document.querySelectorAll(".version_switcher_placeholder");
+   for (placeholder of versionPlaceholders) {
+       placeholder.innerHTML = versionSelect;
+       let selectElement = placeholder.querySelector("select");
+       selectElement.addEventListener("change", onSwitch);
+   }
+
+   const languagePlaceholders = document.querySelectorAll(".language_switcher_placeholder");
+   for (placeholder of languagePlaceholders) {
+       placeholder.innerHTML = languageSelect;
+       let selectElement = placeholder.querySelector("select");
+       selectElement.addEventListener("change", onSwitch);
+   }
+ });
+</script>
 {% endblock %}