Emit canonical URLs for all rustdoc pages

Previously, we did not emit canonical URLs for crates that had an
alternate documentation URL. However, this produces bad results for
those crates, with older versions being selected as canonical even
if the latest version uses docs.rs as its documentation URL.

Author: jsha

src/web/rustdoc.rs

@@ -490,25 +490,16 @@ pub fn rustdoc_html_server_handler(req: &mut Request) -> IronResult<Response> {
     let latest_path = format!("/crate/{}/latest{}{}", name, target_redirect, query_string);
 
     // Set the canonical URL for search engines to the `/latest/` page on docs.rs.
-    // For crates with a documentation URL, where that URL doesn't point at docs.rs,
-    // omit the canonical link to avoid penalizing external documentation.
     // Note: The URL this points to may not exist. For instance, if we're rendering
     // `struct Foo` in version 0.1.0 of a crate, and version 0.2.0 of that crate removes
     // `struct Foo`, this will point at a 404. That's fine: search engines will crawl
     // the target and will not canonicalize to a URL that doesn't exist.
-    let canonical_url = if krate.documentation_url.is_none()
-        || krate
-            .documentation_url
-            .as_ref()
-            .unwrap()
-            .starts_with("https://docs.rs/")
-    {
-        // Don't include index.html in the canonical URL.
-        let canonical_path = inner_path.replace("index.html", "");
-        format!("https://docs.rs/{}/latest/{}", name, canonical_path)
-    } else {
-        "".to_string()
-    };
+    // Don't include index.html in the canonical URL.
+    let canonical_url = format!(
+        "https://docs.rs/{}/latest/{}",
+        name,
+        inner_path.replace("index.html", "")
+    );
 
     metrics
         .recently_accessed_releases
@@ -2063,7 +2054,7 @@ mod test {
 
             let web = env.frontend();
 
-            assert!(!web
+            assert!(web
                 .get("/dummy-dash/0.1.0/dummy_dash/")
                 .send()?
                 .text()?

templates/rustdoc/head.html

@@ -3,8 +3,6 @@
 
         <link rel="search" href="/-/static/opensearch.xml" type="application/opensearchdescription+xml" title="Docs.rs" />
 
-        {%- if canonical_url -%}
         <link rel="canonical" href="{{canonical_url | safe}}" />
-        {%- endif -%}
 
         <script type="text/javascript">{%- include "theme.js" -%}</script>