rustdoc only use cors when needed

The `crossorigin` attribute may cause issues when the href is not actuall across origins. Specifically, the tag causes the browser to send a preflight OPTIONS request to the href even if it is same-origin.
Some tempermental servers may reject all CORS preflect requests even if they're actually same-origin, which causes a CORS error and prevents the fonts from loading, even later on.

This commit fixes that problem by not emitting `crossorigin` if the url looks like a domain-relative url.

Author: MingweiSamuel

src/librustdoc/html/layout.rs

@@ -68,6 +68,14 @@ struct PageLayout<'a> {
     display_krate_version_extra: &'a str,
 }
 
+impl PageLayout<'_> {
+    /// Determines if [`Self::static_route_path`] is relative to the same origin.
+    fn static_root_path_same_origin(&self) -> bool {
+        (self.static_root_path.starts_with('/') && !self.static_root_path.starts_with("//"))
+            || self.static_root_path.starts_with(".")
+    }
+}
+
 pub(crate) use crate::html::render::sidebar::filters;
 
 pub(crate) fn render<T: Display, S: Display>(

src/librustdoc/html/templates/page.html

@@ -7,7 +7,7 @@
     <meta name="description" content="{{page.description}}"> {# #}
     <title>{{page.title}}</title> {# #}
     <script>if(window.location.protocol!=="file:") {# Hack to skip preloading fonts locally - see #98769 #}
-    document.head.insertAdjacentHTML("beforeend","{{files.source_serif_4_regular}},{{files.fira_sans_italic}},{{files.fira_sans_regular}},{{files.fira_sans_medium_italic}},{{files.fira_sans_medium}},{{files.source_code_pro_regular}},{{files.source_code_pro_semibold}}".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2" crossorigin href="{{static_root_path|safe}}${f}">`).join("")) {# #}
+    document.head.insertAdjacentHTML("beforeend","{{files.source_serif_4_regular}},{{files.fira_sans_italic}},{{files.fira_sans_regular}},{{files.fira_sans_medium_italic}},{{files.fira_sans_medium}},{{files.source_code_pro_regular}},{{files.source_code_pro_semibold}}".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2" {% if !static_root_path_same_origin() %} crossorigin {% endif %} href="{{static_root_path|safe}}${f}">`).join("")) {# #}
     </script> {# #}
     <link rel="stylesheet" {#+ #}
           href="{{static_root_path|safe}}{{files.normalize_css}}"> {# #}