Fix redirect loop with one-component path for crate without trailling slash

src/web/extractors/rustdoc.rs

@@ -723,10 +723,24 @@ fn generate_rustdoc_path_for_url(
         && !path.is_empty()
         && path != INDEX_HTML
     {
-        // ust juse the given inner to start, if:
-        // * it's not empty
-        // * it's not just "index.html"
-        path.to_string()
+        if let Some(target_name) = target_name
+            && path == target_name
+        {
+            // Sometimes people add a path that is just the target name.
+            // This matches our `rustdoc_redirector_handler` route,
+            // without trailing slash (`/{name}/{version}/{target}`).
+            //
+            // Even though the rustdoc html handler would also be capable
+            // handling this input, we want to redirect to the trailing
+            // slash version (`/{name}/{version}/{target}/`),
+            // so they are separate.
+            format!("{}/", target_name)
+        } else {
+            // just use the given inner to start, if:
+            // * it's not empty
+            // * it's not just "index.html"
+            path.to_string()
+        }
     } else if let Some(target_name) = target_name {
         // after having no usable given path, we generate one with the
         // target name, if we have one.
@@ -1600,4 +1614,48 @@ mod tests {
         assert_eq!(params.doc_target(), Some(DEFAULT_TARGET));
         assert_eq!(params.inner_path(), "dummy/struct.Dummy.html");
     }
+
+    #[test]
+    fn test_parse_something() {
+        // test for https://github.com/rust-lang/docs.rs/issues/2989
+        let params = dbg!(
+            RustdocParams::new(KRATE)
+                .with_page_kind(PageKind::Rustdoc)
+                .try_with_original_uri(format!("/{KRATE}/latest/{KRATE}"))
+                .unwrap()
+                .with_req_version(ReqVersion::Latest)
+                .with_doc_target(KRATE)
+        );
+
+        assert_eq!(params.rustdoc_url(), "/krate/latest/krate/");
+
+        let params = dbg!(
+            params
+                .with_target_name(KRATE)
+                .with_default_target(DEFAULT_TARGET)
+                .with_doc_targets(TARGETS.iter().cloned())
+        );
+
+        assert_eq!(params.rustdoc_url(), "/krate/latest/krate/");
+    }
+
+    #[test_case(Some(PageKind::Rustdoc))]
+    #[test_case(None)]
+    fn test_only_target_name_without_slash(page_kind: Option<PageKind>) {
+        // test for https://github.com/rust-lang/docs.rs/issues/2989
+        let params = RustdocParams::new(KRATE)
+            .with_maybe_page_kind(page_kind)
+            .try_with_original_uri("/dummy/latest/dummy")
+            .unwrap()
+            .with_req_version(ReqVersion::Latest)
+            .with_maybe_doc_target(None::<String>)
+            .with_inner_path(KRATE)
+            .with_default_target(DEFAULT_TARGET)
+            .with_target_name(KRATE)
+            .with_doc_targets(TARGETS.iter().cloned());
+
+        dbg!(&params);
+
+        assert_eq!(params.rustdoc_url(), "/krate/latest/krate/");
+    }
 }

src/web/rustdoc.rs

@@ -229,7 +229,7 @@ pub(crate) async fn rustdoc_redirector_handler(
             url
         };
 
-        trace!("redirect to doc");
+        trace!(%url, ?cache_policy, path_in_crate, "redirect to doc");
         Ok(axum_cached_redirect(url, cache_policy)?)
     }
 
@@ -3341,4 +3341,33 @@ mod test {
         assert_eq!(response.status(), StatusCode::NOT_FOUND);
         Ok(())
     }
+
+    #[tokio::test(flavor = "multi_thread")]
+    #[test_case("/dummy/"; "only krate")]
+    #[test_case("/dummy/latest/"; "with version")]
+    #[test_case("/dummy/latest/dummy"; "full without trailing slash")]
+    #[test_case("/dummy/latest/dummy/"; "final target")]
+    async fn test_full_latest_url_without_trailing_slash(path: &str) -> Result<()> {
+        // test for https://github.com/rust-lang/docs.rs/issues/2989
+
+        let env = TestEnvironment::new().await?;
+
+        env.fake_release()
+            .await
+            .name("dummy")
+            .version("1.0.0")
+            .create()
+            .await?;
+
+        let web = env.web_app().await;
+        const TARGET: &str = "/dummy/latest/dummy/";
+        if path == TARGET {
+            web.get(path).await?.status().is_success();
+        } else {
+            web.assert_redirect_unchecked(path, "/dummy/latest/dummy/")
+                .await?;
+        }
+
+        Ok(())
+    }
 }