Add canonical URL for rustdoc pages

Omit the link for crates that specify their own documentation URL.

Author: jsha

src/web/crate_details.rs

@@ -38,7 +38,7 @@ pub struct CrateDetails {
     pub(crate) metadata: MetaData,
     is_library: bool,
     license: Option<String>,
-    documentation_url: Option<String>,
+    pub(crate) documentation_url: Option<String>,
     total_items: Option<f32>,
     documented_items: Option<f32>,
     total_items_needing_examples: Option<f32>,

src/web/rustdoc.rs

@@ -195,6 +195,7 @@ pub fn rustdoc_redirector_handler(req: &mut Request) -> IronResult<Response> {
 #[derive(Debug, Clone, PartialEq, Serialize)]
 struct RustdocPage {
     latest_path: String,
+    canonical_url: String,
     permalink_path: String,
     latest_version: String,
     target: String,
@@ -483,6 +484,22 @@ pub fn rustdoc_html_server_handler(req: &mut Request) -> IronResult<Response> {
 
     let latest_path = format!("/crate/{}/latest{}{}", name, target_redirect, query_string);
 
+    let canonical_url = if krate.documentation_url.is_none()
+        || krate
+            .documentation_url
+            .as_ref()
+            .unwrap()
+            .starts_with("https://docs.rs/")
+    {
+        format!(
+            "https://docs.rs/{}/latest/{}",
+            name,
+            inner_path
+        )
+    } else {
+        "".to_string()
+    };
+
     metrics
         .recently_accessed_releases
         .record(krate.crate_id, krate.release_id, target);
@@ -496,6 +513,7 @@ pub fn rustdoc_html_server_handler(req: &mut Request) -> IronResult<Response> {
     rendering_time.step("rewrite html");
     RustdocPage {
         latest_path,
+        canonical_url,
         permalink_path,
         latest_version,
         target,

templates/rustdoc/head.html

@@ -3,4 +3,8 @@
 
         <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>