fix: offline rustdoc html missing favicon

src/bootstrap/src/core/build_steps/doc.rs

@@ -575,6 +575,31 @@ fn run(self, builder: &Builder<'_>) -> Self::Output {
             FileType::Regular,
         );
 
+        builder.copy_link(
+            &builder
+                .src
+                .join("src")
+                .join("librustdoc")
+                .join("html")
+                .join("static")
+                .join("images")
+                .join("favicon.svg"),
+            &out.join("favicon.svg"),
+            FileType::Regular,
+        );
+        builder.copy_link(
+            &builder
+                .src
+                .join("src")
+                .join("librustdoc")
+                .join("html")
+                .join("static")
+                .join("images")
+                .join("favicon-32x32.png"),
+            &out.join("favicon-32x32.png"),
+            FileType::Regular,
+        );
+
         SharedAssetsPaths { version_info }
     }
 }

src/doc/favicon.inc

@@ -1 +1,2 @@
-<link rel="icon" href="https://www.rust-lang.org/favicon.ico">
+<link rel="alternate icon" type="image/png" href="favicon-32x32.png">
+<link rel="icon" type="image/svg+xml" href="favicon.svg">

src/doc/redirect.inc

@@ -1,2 +1,3 @@
 <meta name="robots" content="noindex,follow">
-<link rel="icon" href="https://www.rust-lang.org/favicon.ico">
+<link rel="alternate icon" type="image/png" href="../favicon-32x32.png">
+<link rel="icon" type="image/svg+xml" href="../favicon.svg">