Rollup merge of rust-lang#94260 - GuillaumeGomez:infinite-redirection, r=notriddle

Fix rustdoc infinite redirection generation

Someone came to me about a funny bug they had when clicking on any link on [this page](https://world.pages.gitlab.gnome.org/Rust/libadwaita-rs/stable/latest/docs/libadwaita/builders/index.html): it ended one page redirecting to itself indefinitely.

I was able to make a minimum reproducible case to trigger this bug which I now use as a test.

r? ``@notriddle``

Author: matthiaskrgr

src/librustdoc/html/render/context.rs

@@ -201,19 +201,19 @@ impl<'tcx> Context<'tcx> {
         } else {
             tyname.as_str()
         };
-        let page = layout::Page {
-            css_class: tyname_s,
-            root_path: &self.root_path(),
-            static_root_path: self.shared.static_root_path.as_deref(),
-            title: &title,
-            description: &desc,
-            keywords: &keywords,
-            resource_suffix: &self.shared.resource_suffix,
-            extra_scripts: &[],
-            static_extra_scripts: &[],
-        };
 
         if !self.render_redirect_pages {
+            let page = layout::Page {
+                css_class: tyname_s,
+                root_path: &self.root_path(),
+                static_root_path: self.shared.static_root_path.as_deref(),
+                title: &title,
+                description: &desc,
+                keywords: &keywords,
+                resource_suffix: &self.shared.resource_suffix,
+                extra_scripts: &[],
+                static_extra_scripts: &[],
+            };
             layout::render(
                 &self.shared.layout,
                 &page,
@@ -223,23 +223,31 @@ impl<'tcx> Context<'tcx> {
             )
         } else {
             if let Some(&(ref names, ty)) = self.cache().paths.get(&it.def_id.expect_def_id()) {
-                let mut path = String::new();
-                for name in &names[..names.len() - 1] {
-                    path.push_str(&name.as_str());
-                    path.push('/');
-                }
-                path.push_str(&item_path(ty, &names.last().unwrap().as_str()));
-                match self.shared.redirections {
-                    Some(ref redirections) => {
-                        let mut current_path = String::new();
-                        for name in &self.current {
-                            current_path.push_str(&name.as_str());
-                            current_path.push('/');
+                if self.current.len() + 1 != names.len()
+                    || self.current.iter().zip(names.iter()).any(|(a, b)| a != b)
+                {
+                    // We checked that the redirection isn't pointing to the current file,
+                    // preventing an infinite redirection loop in the generated
+                    // documentation.
+
+                    let mut path = String::new();
+                    for name in &names[..names.len() - 1] {
+                        path.push_str(&name.as_str());
+                        path.push('/');
+                    }
+                    path.push_str(&item_path(ty, &names.last().unwrap().as_str()));
+                    match self.shared.redirections {
+                        Some(ref redirections) => {
+                            let mut current_path = String::new();
+                            for name in &self.current {
+                                current_path.push_str(&name.as_str());
+                                current_path.push('/');
+                            }
+                            current_path.push_str(&item_path(ty, &names.last().unwrap().as_str()));
+                            redirections.borrow_mut().insert(current_path, path);
                         }
-                        current_path.push_str(&item_path(ty, &names.last().unwrap().as_str()));
-                        redirections.borrow_mut().insert(current_path, path);
+                        None => return layout::redirect(&format!("{}{}", self.root_path(), path)),
                     }
-                    None => return layout::redirect(&format!("{}{}", self.root_path(), path)),
                 }
             }
             String::new()

src/test/rustdoc/infinite-redirection.rs

@@ -0,0 +1,29 @@
+#![crate_name = "foo"]
+
+// This test ensures that there is no "infinite redirection" file generated (a
+// file which redirects to itself).
+
+// We check it's not a redirection file.
+// @has 'foo/builders/struct.ActionRowBuilder.html'
+// @has - '//*[@id="synthetic-implementations"]' 'Auto Trait Implementations'
+
+// And that the link in the module is targetting it.
+// @has 'foo/builders/index.html'
+// @has - '//a[@href="struct.ActionRowBuilder.html"]' 'ActionRowBuilder'
+
+mod auto {
+    mod action_row {
+        pub struct ActionRowBuilder;
+    }
+
+    #[doc(hidden)]
+    pub mod builders {
+        pub use super::action_row::ActionRowBuilder;
+    }
+}
+
+pub use auto::*;
+
+pub mod builders {
+    pub use crate::auto::builders::*;
+}