patterns/theme/head.hbs

{{! Move to template code after fixing this issue:
https://github.com/google/mdbook-i18n-helpers/issues/70 }}
<script>
    (function () {
        // See these pages for details:
        // https://developers.google.com/search/docs/crawling-indexing/consolidate-duplicate-urls
        // https://developers.google.com/search/docs/crawling-indexing/javascript/javascript-seo-basics
        let base = "https://rust-unofficial.github.io/patterns";
        {{#if(eq language "en")}}
        let canonical_href = `${base}/{{ path }}`;
        {{else}}
        let canonical_href = `${base}/{{ language }}/{{ path }}`;
        {{/if}}

                // mdbook gives us a string ending in ".md", we replace it with ".html":
                canonical_href = canonical_href.slice(0, -"md".length) + "html";
                if (canonical_href.endsWith("/index.html")) {
                    canonical_href = canonical_href.slice(0, -"index.html".length);
                }

                let link = document.createElement("link");
                link.rel = "canonical";
                link.href = canonical_href;
                document.head.appendChild(link);
            }) ()
</script>